Planetary Radio Emissions VII

Sponsors: Europlanet Research Infrastructure, IWF: Space Research Institute, Austrian Academy of Sciences, University Graz, bm vit: Bundesministerium für Verkehr, Innovation und Technologie, Stadt Graz, FFG: Die Österreichische Forschungsförderungsgesellschaft

Schlagworte:

With the arrival of the Cassini spacecraft at Saturn in July 2004, there have been quasi-continuous observations of Saturn Kilometric Radiation (SKR) emissions. In this paper we review the response of these emissions to dynamics in Saturn’s magnetosphere, driven by factors internal and external to the system. We begin by reviewing solar wind data upstream of Saturn and discuss the link between solar wind compressions and dynamics in Saturn’s magnetosphere, evidenced by intensifications and occasional phase changes in the SKR emission. We then review the link between magnetotail reconnection and planetary radio emissions. We begin in the well-sampled magnetotail of Earth and then move to Saturn where exploration of the nightside magnetosphere has revealed evidence of plasmoid-like magnetic structures and other phenomena indicative of the kronian equivalent of terrestrial substorms. In general, there is a good correlation between the timing of reconnection events and enhancements in the SKR emission, coupled with extension of the emission to lower frequencies. We interpret this as growth of the radio source region to higher altitudes along the field lines, stimulated by increased precipitation of energetic electrons into the auroral zones following reconnection. We also comment on the observation that the majority of reconnection events occur at SKR phases where the SKR power would be expected to be rising with time, indicating that reconnection is most likely to occur at a preferred phase. We conclude with a summary of the current knowledge of the link between Saturn’s magnetospheric dynamics and SKR emissions, and list a number of open questions to be addressed in the future.

Schlagworte:

The Saturnian Kilometric Radio emission (SKR), discovered and briefly observed by Voyager spacecraft in 1980-81, is now studied in depth by Cassini, which is still in orbit around Saturn, since mid 2004. Aboard Cassini, the main radio astronomy system (the HFR part of the RPWS instrument) is based on digital, real time, spectral correlation of several pass band filters, analyzing multiple wire antennas. This system allows, in principle, the full second order statistics of the analyzed signal to be retrieved, thus providing, compared to a simple antenna system, some extra information on the received radio waves: mainly about the spatial brightness distribution (leading to direction finding (DF) for a point source model) and the intrinsic polarisation of the measured radio source. While there is no doubt that SKR, like terrestrial and Jovian radio emissions, is powered via a cyclotron maser (CMI) originating from accelerated auroral particles, the exact scenario remains, at the moment, far from being understood: the complex modulation of the SKR at the planetary spin rate is perplexing; the fact that the apparent SKR polarization changes with observer’s latitude and contains a substantial amount of linear polarisation when observed from mid to high latitudes, is quite unexpected and likely the indication of a complex source structure and/or unusual propagation regime in Saturn’s high latitude regions.

Schlagworte:

The discovery of Saturn kilometric radiation (SKR) was made by the Voyager spacecraft over three decades ago. The Voyager observations showed that SKR had a well-defined clock-like amplitude modulation with a period of 10 hr 39 min 24±7 sec. Since then much has changed. In 2000 radio observations by the Ulysses spacecraft showed that the SKR modulation period varied by as much as several minutes on time scales of years. This long-term variability was subsequently confirmed by radio measurements from the Cassini spacecraft, which was put in orbit around Saturn on 1 July 2004. We now know that there are three basic types of Saturnian radio emissions: SKR at frequencies from about 50 to 1,200 kHz; narrowband (NB) emissions in two frequency ranges, near 5 kHz and near 20 kHz; and whistler-mode auroral hiss at frequencies from a few Hz to several kHz. All of these radio emissions display long-term variations in their modulation periods of up to one percent or more on time scales of years, with smaller variations on shorter time scales. For several years prior to Saturn’s recent equinox (August 2009) these radio emissions displayed two dominant periods of about 10.6 and 10.8 hours. The 10.6-hour period has been shown to be associated with SKR and auroral hiss originating from the northern auroral zone; and the 10.8-hour period has been associated with SKR and auroral hiss originating from the southern auroral zone. The narrowband emissions observed during this period have the same two periods as the SKR and auroral hiss, but do not have the corresponding north-south symmetry. As equinox approached the two periods converged and now appear to have crossed several months after equinox. A similar crossing of the two components may have occurred in the Ulysses measurements of SKR during the Saturn’s equinox fourteen years ago. Possible models for explaining these complex long term variations will be discussed.

Schlagworte:

Among the persistent questions raised by the existence of a rotational modulation of the Saturn Kilometric Radiation (SKR), the origin of the variability of the 10.8 hours SKR period at a 1% level over weeks to years remains intriguing. While its short-term fluctuations (20-30 days) have been related to the variations of the solar wind speed, its long-term fluctuations (months to years) were proposed to be triggered by Enceladus mass-loading and/or seasonal variations. This situation has become even more complicated since the recent identification of two separated periods at 10.8h and 10.6h, each varying with time, corresponding to SKR sources located in the southern (S) and the northern (N) hemispheres, respectively. Here, six years of Cassini continuous radio measurements are investigated, from 2004 (preequinox) to the end of 2010 (post-equinox). From S and N SKR, radio periods and phase systems are derived separately for each hemisphere and fluctuations of radio periods are investigated at time scales of years to a few months. Then, the S phase is used to demonstrate that the S SKR rotational modulation is consistent with an intrinsically rotating phenomenon, in contrast with the early Voyager picture.

Schlagworte:

Saturn has been known for over thirty years to emit an intense radio emission at kilometer wavelengths called Saturn Kilometric Radiation (SKR) that is modulated by the rotation of the planet. Although the period of this modulation was initially thought to represent the rotation period of the planet, it is now known that the radiation has two distinctly different rotational modulation periods that vary by on the order of one percent on times scales of years. One component originates primarily from the northern auroral region, and the other originates primarily from the southern auroral region. The differences in the modulation periods are believed to be due to latitudinal variations in the slippage of the magnetosphere relative to the interior of planet, apparently controlled by the seasonal variation in the tilt of Saturn’s rotational axis. Since other magnetospheric phenomena display similar complicated rotational modulation effects, there is a need to define north and south longitude systems based on the variable SKR modulation periods in the two hemispheres. Because the SKR signal received by the spacecraft often includes both components it is sometimes difficult to separate the phases of the two components. In this paper we describe a method of determining the two phases based on a tracking filter approach that can separately track the modulation waveforms of the two components. The phases of the two waveforms can then be used to define a new longitude system for the northern and southern components that we call the SLS4 longitude system. This is an extension of the previous SLS2 and SLS3 longitude systems, which only described phase variations of the southern component.

Schlagworte:

Recent observations performed by the radio and plasma wave science (RPWS) experiment on board the Cassini spacecraft have revealed the presence of two distinct and variable spin modulation periods (10.6 hours and 10.8 hours) in Saturn’s radio emissions emanating from the northern and southern hemispheres respectively. The main time modulation of planetary radio emissions has always been attributed to the effect on the inner magnetosphere of the internal magnetic field which rigidly rotates with the deep interior of the planet. The magnetospheric plasma is supposed to be frozen in this magnetic field so that a north/south asymmetry in the radio modulation period should never be observed. However Saturn’s magnetic field is very particular since its dipolar moment is nearly aligned with the rotation axis of the planet. Such an alignment could bring out some phenomena in the internal structure which are masked in the case of other magnetized planets the magnetic dipole of which is significantly tilted. The existence of two separated and slowly varying periods in the saturnian magnetic field could be the signature of a dynamo the dynamics of which is governed by a Rikitake system.

Schlagworte:

Long-periodic (LP) modulations of intensity of Saturnian Kilometric Radiation (SKR) recorded by RPWS instrument onboard Cassini spacecraft were studied by means of a combined data analysis algorithm based on a ”sliding window” Fourier (SWF) procedure and the nonlinearWigner-Ville (WV) method. The analyzed SKR data record covers the years 2004-2005. It has been found that SKR has well pronounced impulsive modulation, with quasi-periodic pulses appeared approximately each 10.74 hours and having duration of about 5 hours. The period of pulses, in spite of the overall stability, has sometimes the disturbances within the interval of 10.74 - 10.76 hours. By this, the whole impulsive modulation of SKR appeared in 2004-2005 in a form of quasi-regularly repeated modulation activity storms. Time interval between the adjacent modulation activity storms most often was within 8-13 days. Altogether, 55 impulsive modulation activity storms were registered during 2004-2005. Besides of the storms of 10.7 h pulses, the intensity of SKR has several more long periodic modulations. In particular, ~6-7 days, ~8-9 days, ~12-13 days and ~25-27 days components were detected. These are connected probably with the quasi-regular character of the storms of 10.74 h pulses. While the origin of 10.74 hour pulses can be associated with the rotation of Saturn, the long periodic modulation features are very likely connected with the detected similar variations of the solar wind parameters. The last in their turn may be caused by the varying solar surface magnetic activity and rotating streams of high speed solar wind. Besides of that, the performed analysis shows that some Saturnian moons may also have influence on the intensity of SKR. In particular, specific modulations with periods corresponding to orbital motions of close moons (Enceladus, Tethys) as well as Titan, Hyperion and Dione were detected.

Schlagworte:

Earth-orbiting satellites have routinely traversed the source regions of auroral kilometric radiation. This radio emission is generated via the cyclotron maser instability very close to the electron cyclotron frequency. While Cassini’s orbit has crossed auroral field lines, the radial distance at auroral latitudes is typically too high for the analogous Saturn kilometric radiation source. However, on Oct. 17, 2008, the Radio and Plasma Wave Science instrument detected the kilometric radiation at and just below the electron cyclotron frequency. At this time the spacecraft was at a distance of 5 Saturn radii, at 0.9 hours local time, and on L-shells in the range of 25 to above 30. Here the magnetic field suggests the corresponding current was directed upward, away from the planet. Low energy electron observations by the Cassini Plasma Spectrometer instrument suggest that growth of the SKR is likely due to an unstable shell-like distribution.

Schlagworte:

The Cassini spacecraft flew very near a source region of Saturn kilometric radiation (SKR) on day 073 of 2008. This is the second known encounter with a source region at high latitude. The radio and plasma wave instrument, RPWS, observed intense SKR in the extraordinary (X) mode. The electron low-energy spectrometer (ELS) obtained a phase space distribution of sufficient energy and pitch angle resolution to allow growth rate calculations for the observed wave emissions. There is evidence of a shell or horseshoe electron plasma distribution that is unstable to the growth of SKR via the cyclotron maser instability. We present results of these calculations for comparison with a previously reported source region encounter.

Schlagworte:

On 17 October 2008, the Cassini spacecraft crossed the southern sources of Saturn kilometric radiation (SKR), while flying along high-latitude nightside magnetic field lines. In situ measurements allowed us to characterize for the first time the source region of an extra-terrestrial auroral radio emission. Using radio, magnetic field and particle observations, we characterize the plasma environment surrounding the SKR sources. Magnetic field lines supporting local as well as distant radio sources (detected on both extraordinary and ordinary modes) map a continuous, high-latitude and spiral-shaped unusual auroral oval observed on the dawnside, consistent with enhanced auroral activity. While investigating the Cyclotron Maser Instability (CMI) as a mechanism responsible for SKR generation, we find that observed cutoff frequencies are consistent with radio waves amplified perpendicular to the magnetic field by hot (6 to 9 keV) resonant electrons, measured locally. Finally, we confirm and quantify previous observations of the SKR elliptical polarization, found to evolve toward circular polarization with the distance to the source.

Schlagworte:

Saturn narrowband (NB) radio emissions are detected between 3 and 70 kHz, with occurrence probability and wave intensity peaking around 5 kHz and 20 kHz. The emissions usually occur periodically for several days after intensification of Saturn kilometric radiation (SKR). Originally detected by the Voyagers, the extended duration of the Cassini mission and the improved capabilities of the Radio and Plasma Wave Science (RPWS) instrument have significantly advanced our knowledge about them. For example, RPWS measurements of the magnetic component have validated the electromagnetic nature of Saturn NB emissions. Evidences show that the 20 kHz NB emissions are generated by mode conversion of electrostatic upper hybrid waves on the boundary of the plasma torus, whereas direction–finding results point to a source in the auroral zone for the 5 kHz component. Similar to SKR, the 5 kHz NB emissions have a clock–like modulation and display two distinct modulation periods identical to the northern and southern hemisphere periods of SKR. Polarization measurements confirm that most NB emissions are propagating in the L–O mode, with the exception of second harmonic NB emissions. At high latitudes closer to the planet, RPWS detected right hand polarized Z–mode NB emissions below the local electron cyclotron frequency (fce), which are believed to be the source of the L–O mode NB emissions detected above the local fce. Although the energy source for the generation of the Z–mode waves is still unclear, linear growth rate calculations indicate that the observed plasma distributions are unstable to the growth of electrostatic cyclotron harmonic emission. Alternatively, electromagnetic Z–mode might be directly generated by the cyclotron maser instability. The source Z–mode waves, upon reflection, propagate to the opposite hemisphere before escaping through mode conversion, which could explain the fact that both rotational modulation periods of NB emissions are observable in each hemisphere.

Schlagworte:

After Cassini&#x2019;s arrival at planet Saturn, its Radio and Plasma Wave Science (RPWS) experiment has performed numerous observations of a new type of planetary radio emissions in the lower kHz frequency range (< 50kHz). These bursty emissions have time scales of a few to 15 minutes and occur as slowly drifting events in the time-frequency spectrogram. They have neither been detected by the Voyager spacecraft nor by Ulysses. As a first approach to this new phenomenon, results of a statistical study with regard to the observer&#x2019;s position, i.e. Cassini&#x2019;s orbital position, will be presented. Furthermore, aspects of polarization will be highlighted as far as appropriate goniopolarimetric (3-antenna) observations are available.

Schlagworte:

Intense saturnian radio emission has been observed since June 2004, and until today, by the Radio and Plasma Waves Experiment (RPWS) on board Cassini spacecraft. During this long period of about six years the spacecraft was orbiting principally in the planetary equatorial plane. However in 2007 and 2008 orbits reach latitudes higher than 50? which lead us to investigate sub-auroral saturnian radio emissions. In this study we examine the spectral distinctions between the saturnian radio emissions observed in the equatorial plane and those in latitudes close to the southern and northern auroral regions. We consider the three components reported by Galopeau et al. [2007, J. Geophys. Res., 112, A11213] principally dominated by the so-called saturnian kilometric radiation (80 kHz - 900 kHz). We analyze the occurrence probability of these components taking into consideration different geometric configurations between the spacecraft, the planet and the Sun. We discuss the spectral alteration and change, from the equatorial plane to the high latitudes, of Saturnian radio emissions. Also we examine the spectral distinction between the radio emissions emitted from the northern and southern hemispheres, in particular in the case of the saturnian kilometric radiation (SKR). Our results are discussed and compared with those already reported in the literature dealing with the Voyager and the Cassini missions.

Schlagworte:

The Cassini Radio and Plasma Wave instrument has detected whistler-mode chorus during many of its one hundred thirty-five orbits of Saturn. Similar to observations of chorus in Earth&#x2019;s magnetosphere, the chorus at Saturn is found to always be propagating away from Saturn&#x2019;s magnetic equator, suggesting a source near the magnetic equator. Unlike chorus at Earth, the chorus at Saturn is only observed below half the electron cyclotron frequency unless it is detected in association with a local plasma injection event. This work will expand our earlier survey of chorus observations from the first forty-five orbits of Cassini and discuss the similarities and differences of the two types of chorus detected at Saturn to observations of chorus at Earth and Jupiter.

Schlagworte:

Electron density measurements from the Cassini RPWS Langmuir Probe instrument have identified a sharply-defined region of low plasma densities in Saturn&#x2019;s magnetosphere outside a dipole L-shell of ~15. Gradients in the density profiles define a boundary identified as the plasmapause [Gurnett et al., 2010] that separates the region of higher plasma density from the region of very low plasma density. During seven consecutive high-latitude passes in the northern hemisphere from September through December 2006, Cassini followed a series of trajectories that skimmed along high-latitude magnetic field lines for several days. The orientation of these trajectories made it possible for the RPWS to detect modulations in the high-latitude auroral hiss emissions at a 10.6 hour rotational modulation rate [Gurnett et al., 2009] and for the RPWS Langmuir Probe instrument to detect modulations in the electron density profiles that were anti-correlated with the hiss emissions [Gurnett et al., 2010]. The strong and periodic modulations in the density profiles indicate that Cassini is passing in and out of a plasma region of higher densities. One example during this seven-orbit time interval is shown in Figure 1. The periodic modulations in the density profile are shown in the bottom panel and are clearly anti-correlated with the periodic occurrence of intense auroral hiss emissions shown in the upper panel. The highest densities in this high-latitude region are 0.1 cm-3, two orders of magnitude greater than the lowest densities in this part of Saturn&#x2019;s magnetosphere but well below the densities seen inside Saturn&#x2019;s plasma disk [Morooka et al., 2009;Persoon et al., 2009].

Schlagworte:

We study the large scale structures of the electron core in the inner magnetosphere of Saturn (from the G-ring to Rhea orbit - i.e. 2.8 to 9 Rs). This study is deduced from the power spectra measurements acquired with the Cassini/RPWS electric dipole around the local plasma frequency (quasi-thermal noise spectroscopy), from July 2004 (SOI) to February 2010. We have especially investigated the radial diffusion and latitudinal confinement of the plasma torus towards Enceladus and Dione. We also discuss the longitudinal variations of the electron parameters using the recent SLS3 system. We will finally touch about the dust detection by using the RF power spectra measured on the monopole antenna and the possible effect of the dust on the observed electron parameters.

Schlagworte:

The lightning activity in Saturn&#x2019;s atmosphere has been monitored by Cassini for more than six years. The continuous observations of the radio signatures called SEDs (Saturn Electrostatic Discharges) combine favorably with imaging observations of related cloud features as well as direct observations of flash&#x2013;illuminated cloud tops. The Cassini RPWS (Radio and Plasma Wave Science) instrument and ISS (Imaging Science Subsystem) in orbit around Saturn also received ground&#x2013;based support: The intense SED radio waves were also detected by the giant UTR&#x2013;2 radio telescope, and committed amateurs observed SED&#x2013;related white spots with their backyard optical telescopes. Furthermore, the Cassini VIMS (Visual and Infrared Mapping Spectrometer) and CIRS (Composite Infrared Spectrometer) instruments have provided some information on chemical constituents possibly created by the lightning discharges and transported upward to Saturn&#x2019;s upper atmosphere by vertical convection. In this paper we summarize the main results on Saturn lightning provided by this multi&#x2013;instrumental approach and compare Saturn lightning to lightning on Jupiter and Earth.

Schlagworte:

Radio signatures of lightning discharges on Saturn have first been discovered by the Voyager spacecraft in 1980/81. After the Voyager flybys, the next sets of measurements only became available in 2004, when the Cassini spacecraft approached Saturn. Since then, Cassini provides continuous monitoring of Saturn&#x2019;s lightning activity. In 2006, ground-based observations became available as a complementary source of information. Using a new broadband receiver at the UTR-2 radio telescope (Ukraine), Saturn lightning was observed over the whole spectral range of the instrument (10-30 MHz). This allows study of the temporal fine structure of the emission with a much finer temporal resolution than that of the routine satellite observations. More recently, Saturn lightning was also observed by two further ground-based radiotelescopes, namely WSRT (the Netherlands) and LOFAR (Europe). We present first results of recent ground-based observations of Saturn lightning performed with the radiotelescopes UTR-2, WSRT and LOFAR, and we describe the aims of future observations using these instruments.

Schlagworte:

During the first 35 close Titan flybys the Radio and Plasma Wave Science instrument (RPWS) aboard the CASSINI orbiter did not observe radio signals possibly associated with lightning in the atmosphere of Titan [Fischer et al., 2007, Geophys. Res. Lett., 34, L22104). The electric field sensors of the HUYGENS PWA instrument (permittivity, waves and altimetry) observed smooth variations as well as impulsive events varying with altitude during the descent of the probe in the atmosphere of Titan. While a part of the low frequency signals was explained as externally driven Schumann resonances, there is still a debate on the origin of the impulsive events. In order to differentiate natural atmospheric discharges from sources on the parachute or the probe the HUYGENS electric field data have been re-evaluated und combined with probe attitude and velocity. The correlation results indicate that atmospheric electricity phemonena are present in the atmosphere of Titan.

Schlagworte:

Analyzing the data acquired by STEREO/WAVES,Wind/WAVES and Cassini/ RPWS instruments during the time interval between the years 2002-2010 we have revealed unusual periodic radio bursts of the non-Io controlled component of the Jovian decametric radiation (non-Io DAM). These non-Io bursts are typically observed in a frequency range from ~ 5 MHz up to ~ 10&#x2013;16 MHz and recur during several Jovian days with a surprisingly new period of ~ 10.07 hours. This period is 1.5% longer than the rotation period of the inner Jovian magnetosphere (System III, 9.925 hour). The occurrence probability of these periodic bursts has been found to be significantly higher in the sector of Jovian Central Meridian Longitude between 300? and 60? (via 360?), corresponding to the region of non-Io-C sources. Stereoscopic observations performed by STEREO/WAVES as well as Wind/WAVES and Cassini/RPWS suggest that the sources of the periodic bursts sub-corotate with Jupiter. The relations between the occurrence of the periodic bursts and solar wind activity have been analyzed.

Schlagworte:

The relationship between Jupiter&#x2019;s decametric (DAM) and hectometric (HOM) radio emissions is important to help understand the emission mechanism that both of them have in common, but it has remained an elusive enigma. We have investigated Jovian DAM and HOM emissions observed by the Cassini, Voyager 1 and Voyager 2 spacecraft. We made a statistical comparison of Cassini and combined Voyager 1 and 2 data for occurrence probability histograms in Central Meridian Longitude (CML) and in Io phase from 2 to 16 MHz, and a statistical analysis of Jovian HOM polarization plotted as a function of Jovian magnetic latitude and frequency below 3 MHz based on only the Cassini data. We found that (1) the position of Source B shows shifts in longitude from 10 to 16 MHz as seen in both Cassini and combined Voyager 1 and 2 data, (2) the effect of Io can be seen down to 4 MHz, (3) the occurrence probability of HOM emissions are separated into right- and lefthand polarization senses, and (4) attenuation bands make a large contribution to intensify the HOM emissions around the attenuated regions.

Schlagworte:

Radio emissions from the Io-Jupiter electrodynamic circuit are structured in discrete bursts, quasi-periodic (5-10 Hz), and with drifting frequency versus time (df/dt<0). High temporal and spectral radio spectrometry, associated to numerical simulations (PIC=Particle-In-Cell) allowed us to study in details the acceleration processes of the electrons responsible for the emissions. We computed the acceleration of ambient electrons within the Io Flux Tube (IFT) by an Alfv´en wave excited by Io crossing Jupiter&#x2019;s magnetic field lines. Then we computed the Cyclotron-Maser radio emission generated by the resulting electron populations. The time-frequency structure of these emissions is very similar to those observed. The detailed analysis of the bursts shape in the time-frequency plane (df/dt) allowed us to discover the existence of electric potential drops (= double-layers, ~1 kV) aligned with the IFT magnetic field. Such acceleration structures, observed in-situ above the Earth&#x2019;s auroral regions, were unknown at Jupiter. Furthermore, high resolution radio spectroscopy allowed us to study these structures on the long-term (minutes to hours), and we showed that they are moving upwards at the local sound speed. Finally, taking into account these acceleration structures in addition to Alfv´en waves in our numerical simulations, we succeeded in reproducing in details the complex timefrequency morphology observed for many ra- dio bursts. We present recent studies on large-scale solar coronal waves (so-called &#x201D;EIT waves&#x201D;) obtained with the EUVI instruments onboard the twin STEREO spacecraft. EUVI has several advantages for coronal wave studies: a) high cadence full-disk imaging, which allows us to catch the wave evolution and kinematics, b) a large field-of-view, which allows simultaneous observations of the erupting CME, and c) observations from two vantage points, which enable us to get insight into the three-dimensional structure of the wave. The present understanding is basically split into different groups of &#x201D;wave&#x201D; versus &#x201D;nonwave&#x201D; interpretations of the physical process behind the phenomenon, as well as &#x201D;flare&#x201D; versus &#x201D;CME&#x201D; for the driving agent. We will present the first observations of the full three-dimensional wave dome in the event of January 17, 2010. The study of the perturbation characteristics and the associated high-frequency radio type II bursts provide evidence for a weakly shocked fast-mode wave as the underlying physical process.

Schlagworte:

It has long been recognized that there is a marked long-term periodic variation in Jupiter&#x2019;s integrated radio occurrence probability. The period of the variation is on the order of a decade. Carr et al. [1970] showed that such variations are closely correlated with Jovicentric declination of the Earth (DE). The range of the smoothed variation of DE is from approximately +3.3 to -3.3 degrees. This DE effect was extensively studied and confirmed by Garcia [1996]. It shows that the occurrence probability of the non-Io-A source is clearly controlled by DE at 18, 20, and 22 MHz during the 1957-1994 apparitions. We propose a new model to explain the DE effect. This new model shows that the beam structure of Jupiter radio emissions, which has been thought of like a hollow-cone, has a narrow beam like a searchlight, which can be explained by assuming that the three dimensional shape of the radio source expands along the line of the magnetic field. If we consider the sizes of the radio coherent region are 1000 m along Jupiter&#x2019;s magnetic field line and 200 m along the latitudinal direction, the equivalent beam pattern is 1 degree wide along Jupiter&#x2019;s magnetic field line and 5 degrees in latitude. As the searchlight beam is fixed with Jupiter&#x2019;s magnetic field, the pure geometrical effect of DE can be explained by this searchlight beam model.

Schlagworte:

We compare a large database of Jovian DAM &#x2018;great arcs&#x201D; events with the most recent compilation of Io footprint (IFP) properties obtained from HST images of Jupiter UV auroras. The radio data was built from the last 16 years of Jupiter radio monitoring by the Wind/WAVES space experiment and by the Decameter array in Nan¸cay, and contents more than 3500 individual events. The analysis of this huge statistics lead to the following conclusions: &#x201D;Great arcs&#x201D; can be found on spectrograms of both Io and non-Io controlled emissions (in nearly equal proportion), showing that the arc phenomenon is not specific to the particular Io-Jupiter interaction scenario. In the case of Io-controlled events, the observed arc curvatures and senses of circular polarisation, show that most of the observed events originate from one or several of the four possible high latitude limbs (corresponding to the well known A,B,C and D &#x2018;regions&#x201D; in CML-Io phase diagram). In each region, a close relationship exists, at a given frequency, between observer&#x2019;s direction and Io&#x2019;s orbital position at the time of the event; already reported as &#x201C;DE effect&#x201D;, it means a surprisingly tight beaming constraint. By using reference IFP ovals (Bonfond et al., JGR 114, 2009) and magnetic field model (VIP4), the emission angle can be estimated for each individual events. When counting from magnetic field direction at the source location, the distribution of emission angles is broadly centred on ~ 70?, as previously determined by many authors. The distribution gets narrowed when the magnetic field gradient is rather used, suggesting that the observed emission angle depends primarily on propagation conditions near the source. Because of the limited accuracy of available magnetic field models, it is unclear whether our estimate of a ~ 10? &#x201C;lead angle&#x201D; between the active radio field line footprint and the auroral IFP, can be considered as statistically significant or not.

Schlagworte:

A model involving an additional contribution to Io&#x2019;s ultraviolet (UV) aurora is presented. A mechanism for heating of electrons of Io&#x2019;s ionospheric plasma up to sufficient energies for the excitation of Io&#x2019;s atmospheric oxygen and emitting of observed UV emission is proposed. The mechanism operates by the effect of the different magnetization of the electrons and ions in Io&#x2019;s ionosphere which in the course of Io&#x2019;s motion through the Jovian magnetic field causes the creation of a charge-separation electric field in the upstream part of the ionosphere. This field has a component parallel to the magnetic and shifts the electron distribution function relative to the ion distribution function by a value exceeding the thermal velocity of electrons. In this case, a Bunemann instability with a very large growth rate develops. This results in the excitation of turbulent pulsations at frequency close to the ion-sound frequency and the occurrence of anomalous resistance to the electric current. The latter causes heating of Io&#x2019;s ionospheric electrons up to a temperature of about 25 eV. Atmospheric oxygen molecules excited by collisions with the heated electrons of Io&#x2019;s ionosphere, whose density is about 6 × 104 cm-3, can contribute to the observed UV brightness. The proposed model permits one to explain the correlation of UV brightness with Io&#x2019;s magnetic longitude and the discrepancy between the anti-Jovian equatorial UV spots and sub-Jovian spots as well.

Schlagworte:

The occurrence probability of the Jovian decameter radio emissions depends on two essential parameters: the central meridian longitude (CML) and the orbital phase of the satellite Io. Four main zones of enhanced occurrence probability emerge from the CML-Io phase diagram: the so-called Io-controlled sources Io-A, Io-B, Io-C and Io-D. We study the compatibility of the location of these sources with the existence of a specific active longitude range, anchored in Jupiter&#x2019;s magnetic field, and favoring the radio emissions. A theoretical model, based on the cyclotron maser instability (CMI), was proposed a few years ago in order to explain the existence of such active longitudes, assuming that the radiation was emitted at the local gyrofrequency in a hollow cone of constant angle, along a magnetic field line carried away by Io through its revolution around Jupiter. Unfortunately this model was not able to justify the dimension in longitude of all the Io-controlled sources, in particular those located in the Jovian southern hemisphere (Io-C and Io-D). We show that the azimuthal distribution of the four occurrence regions (Io-A, Io-B, Io-C and Io-D) around the gradient of the local magnetic field is not constant so that the emission cone (in each Jovian hemisphere) presents a significant flattening in the direction of the magnetic field vector. Introducing a beaming cone with an elliptical section makes the location and extension in longitude of the sources (in the CML-Io phase diagram) compatible with the existence of an active longitude. A theory of the CMI, acting in an inhomogeneous medium in which the magnetic field vector and the gradient of its modulus are not aligned, shall be required in order to justify the flattening of the emission cone.

Schlagworte:

S-component of the sporadic radio emission of Jupiter decameter emission (DAM) is an extraordinary astrophysical phenomenon which is formed as the result of a unique interaction between the Jupiter and its Io satellite and this phenomenon is characterized by an unusual complexity of the frequency-temporal structure on the dynamic spectra. The Jovian S-burst emission appears during the decameter radio storms which can be predicted on the basis of the analysis of the geometric configuration between the Earth, the Jupiter and Io. Monitoring of the Io-dependent DAM emission revealed the characteristic Jupiter emission zones known as Io-A, Io-B, Io- C, and Io-D. It should be noted that despite of more than 50 years of extensive exploration of the Jovian DAM radiation the physical nature of this phenomenon remains insufficiently clear. On the other hand, many problems in the theory of the Jovian decameter emission have been successfully investigated and solved [Litvinenko et al., 2004; Zaitsev et al., 2006; Ladreiter et al., 1995; Shaposhnikov et al., 1997, 2011]. Nevertheless, there is reason to believe that not all issues concerning the physical nature of this unique phenomenon have been definitively resolved. One of the perspective approaches for finding new results is experimental investigation at a higher quality and quantity level followed by a detailed data analysis using both well known and modern mathematical methods. Development of the receiving equipment (improvement of the following characteristics: the temporal-frequency resolution, sensitivity, signal-to-noise ratio, etc.) allows to analyze the specific Sburst features from the microscopic to macroscopic scale [Litvinenko et al., 2009]. With this aim several observational campaigns were performed in November 2009 using the UTR-2 radio telescope (Kharkov, Ukraine) and effective registration systems possessing high frequency and temporal resolutions (antenna effective area is close to 100,000 m2, the frequency resolution is 4 kHz, the temporal resolution is 0.25 ms, the dynamic range is 70 dB) [Konovalenko et al., 2001]. The main goal of these campaigns was an experimental investigation of the Jovian decameter radio emission with an attempt to find out and analyse the phenomena which can be detected using the above mentioned equipment.

Schlagworte:

The new mechanism for the formation of a fine structure in the dynamic spectra of the Jovian decametric radio emission is proposed. The main attention is paid to the formation of narrow-band (NB) emission and quasiperiodic trains of S-bursts. Our model is based on the effects of occurrence of the amplitude-frequency modulation and extension of the frequency spectrum of a signal during propagation of the radiation in a medium with time-varied parameters. It is shown that non-stationary disturbances of the planetary magnetic field and strong frequency dispersion of the plasma at frequencies close to the cutoff frequency of the extraordinary wave in the Jovian ionosphere can play a crucial role in the formation of NB emission and quasiperiodic trains of S-bursts. As a result of the numerical experiments, it was concluded that the amplitude-frequency characteristics of an initially continuous signal can drastically vary as functions of the form of the magnetic-field disturbance in the Jovian ionosphere. Structures similar to those observed in the real experiments, ranging from NB emission and quasiperiodic trains of S-bursts to more complex structures, arise in the dynamic spectrum.

Schlagworte:

Narrow-band (NB) events in dynamic spectra and their relation with short (S-) bursts are an unresolved enigma of the Jovian decametric emission. This paper is focused on the S/NB-structure with timescales between 0.03 s and 0.3 s. We show that the main S/NB-phenomenology can be reduced to three main ingredients which are: the dispersion delay of the radio emission, the motion of emitting electrons in the parallel electric field of the standing Alfv´en wave, and the shadow effect.

Schlagworte:

Dynamic spectra of planetary radio emissions depend on physical and geometrical conditions: emission process; energy of emitting electrons; angle between the source magnetic field and the wave direction, which varies with frequency; location of the observer... Their modeling is an intrinsically 3-dimensional problem for which a code has been developed: SERPE / ExPRES (Simulateur d&#x2019;´Emissions Radio Plan´etaires et Exoplan´etaires / Exoplanetary and Planetary Radio Emissions Simulator). This tool has been successfully applied to the modeling of arc-shaped radio emissions generated by the Io-Jupiter electro-dynamic interaction, as well as of Saturn&#x2019;s Kilometric Radiation dynamic spectra. It allowed us to determine the energy of the emitting electrons, to identify the important of the oblique mode in the rarefied auroral plasmas of Jupiter and Saturn and to clarify the link between the Io-Jupiter radio emissions and of the UV spot at the magnetic footprint of Io. In light of these results, we will briefly review the characteristics of radio emissions related to Jupiter&#x2019;s aurorae and to satellite-Jupiter interactions. The EJSM (Europa Jupiter System Mission) mission is a unique opportunity to study the Jovian magnetosphere (from the close environment of Galilean satellites and their coupling with the Jovian magnetic field, to the auroral regions of Jupiter). It should carry the first goniopolarimetric radio receiver in Jovian orbit. We will illustrate with Cassini results the scientific enhancement of radio astronomy science brought by such capabilities that will not be available to any other mission around Jupiter. We will show how our present knowledge of Jupiter&#x2019;s decameter radio emissions may allow us to optimize the scheduling of low-frequency radar observations. Finally, we will discuss the unique opportunities that would be offered by multi-spacecraft magnetospheric observations in the Jovian system.

Schlagworte:

Juno is the next mission to Jupiter. Juno&#x2019;s overarching scientific goal is to understand the origin and evolution of Jupiter. As the archetype of giant planets, Jupiter holds the key to understanding the origin of our own solar system and the origin of the extra-solar planetary systems now being discovered around other stars. Juno&#x2019;s investigation of Jupiter focuses on four themes: Origin, Interior Structure, Atmospheric Composition and Dynamics, and the Polar Magnetosphere. Juno&#x2019;s scientific measurements include global maps of the gravity and magnetic fields, microwave radiometry of Jupiter&#x2019;s deep atmosphere and a full suite of fields and particles measurements of Jupiter&#x2019;s polar magnetosphere. Juno&#x2019;s 32 polar orbits extensively sample Jupiter&#x2019;s full range of latitudes and longitudes. High sensitivity radiometric measurements yields information on Jupiter&#x2019;s deep atmosphere (down to ~1000 bars) which will be used to infer the global abundance of water, and to investigate the complex meteorology of Jupiter&#x2019;s atmosphere. Determining the Jovian water abundance and whether a solid core exists within Jupiter permits discrimination between various scenarios of the formation of Jupiter. The gravity data constrain the planet&#x2019;s interior rotation, core size and interior structure. The magnetic field measurements investigate how the interior dynamo works and examine the depth of generation of Jupiter&#x2019;s powerful magnetic field. Fields and particles measurements as well as UV and IR polar images investigate Jupiter&#x2019;s auroral physics to determine what drives Jupiter&#x2019;s remarkable northern and southern lights. An overview of the mission and science objectives will be presented with an emphasis on Juno&#x2019;s investigation of Jupiter&#x2019;s polar magnetosphere and radio emission.

Schlagworte:

In the present paper, radio observations made at the wavelength of 6 cm with the VLA in 2009 are analyzed. Reconstructed images of the brightness distribution show significant intensity variations of the equatorial peak emissions on both sides of the planet. The fluctuations are characterized by asymmetrical changes in the brightness distributions. The contribution of a comet-like impact to the observed variations is discussed. During the third week of July, ground-based measurements at different radio bands confirmed that a large projectile had struck Jupiter&#x2019;s atmosphere. The examination of the 2009 VLA data sets shows that the steep enhancement of the emission radiated by Jupiter&#x2019;s electron belt occurred during the same period. The increase in the synchrotron radiation was observed to go on for a couple of weeks before gradually fading in August. Two-dimensional reconstructions of the equatorial brightness distribution demonstrate that the time variability of the radio emission during the middle of 2009 was driven by the longitudinal expansion of an impact-related synchrotron &#x201C;hot spot&#x201D; originally located at the Jupiter System III longitude of 305 degrees.

Schlagworte:

Recent Cluster WBD observations in the Earth&#x2019;s auroral acceleration region have detected trapped Z mode auroral kilometric radiation while the spacecraft were entering a deep density cavity. The Z mode has a clear cutoff at the local upper hybrid resonance frequency, while RX mode radiation is detected above the RX mode cutoff frequency. The small gap between the upper hybrid resonance and the RX mode cutoff frequencies is proportional to the local electron density as expected from cold plasma theory. The width of the observed gap provides a new sensitive measure of the ambient electron density. In addition, the relative intensities of RX and Z mode radiation provide a sensitive probe of the plasma ß = ?pe/Oce at the source since the growth rates, although identical in form, have different ranges of allowed resonant radii which depend on ß. In particular, the RX mode growth is favored for low ß, while the Z mode is favored at higher ß. The observed mode intensities and ß&#x2019;s appear to be consistent with this model, and favor generation of Z mode at the source over models in which Z mode is generated by mode-conversion at cavity boundaries. These are the first multi-point direct measurements of mode-specific AKR propagation in the auroral acceleration region of any planet.

Schlagworte:

The Auroral Kilometric Radiation (AKR) was investigated on measurements in the POLRAD experiment on the INTERBALL-2 satellite. It was revealed &#x201D;lowfrequency&#x201D; radiation with specific features in a spectrum on a polar edge of the auroral region. We have obtained that a series of narrow-band splashes are observed at frequencies between 35 and 70 kHz with the period modulation some tens seconds and bow-shaped envelope. Possible interpretation of emission generation with a specific spectrum is discussed. We suppose that increase of intensity at small frequencies is interpreted as crossing by the satellite of the source region and observation of waveguide modes within it.

Schlagworte:

Interball-2 (Auroral Probe) Polrad triaxial spectropolarimeter was used to determine positions of AKR source footprints on the auroral oval. Our findings are consistent with AKR beams narrowly confined to a plane tangent to the source magnetic latitude circle and containing the local magnetic field vector, in agreement with Mutel et al. [2008]. Our approach is based on dynamic spectra data analysis on much longer time scale of two-minute moving averages, as compared to AKR microbursts tens of milliseconds long analyzed by Mutel et al. We show detailed AKR visibility maps for a given position of the spacecraft - that allow determination of both the azimuth and elevation of the AKR beam in question for every measured AKR source position. For long data runs of the order of one hour we see apparent motion of the AKR sources as measured by Polrad, following spacecraft motion along the orbit in such a way, that the spacecraft remains within the radiation beam obeying geometric constraints reported by Mutel et al.

Schlagworte:

The emissions with extremely high intensity around electron cyclotron frequency have been sometimes registered by satellite Magion 4 - companion of Interball 1. These waves correlate with strong fluxes of high energetic electrons often observed within the polar cusp by Interball 1 and Magion 4 as well as by Polar satellites. Multipoint measurements done by Cluster satellites give new insight of these emissions. Taking into account the plasma and magnetic field parameters in the polar cusp as well as geometry of the waves propagation, one has found that one type of these emissions can be generated by so called &#x201D;fan instability&#x201D; (FI) , but as a source of the emissions around electron cyclotron frequency the &#x2019;horse shoe&#x2019; instability has been also discussed. Beam instability and interaction of Langmuir waves with energetic electrons give the broad band emissions around plasma frequency, which can be discussed as Langmuir turbulence (LT). Kilometric radiation (KR) typical for auroral zone is observed in the vicinity of the cusp&#x2019;s boundary and is associated with fluxes of electrons with energy up to 100keV. The wave measurements done by DEMETER satellite in the polar cusp at the ionospheric level shown similar effects to registered by Interball and Cluster in the outer cusp. The presence of the energetic electrons during the bursts of the plasma waves can suggest another mechanism - relativistic maser instability. The discussion of the possibility of this mechanism in relation to the presented observation will be given in our paper.

Schlagworte:

Auroral Medium Frequency Burst (MFB) is the least understood of three types of terrestrial auroral emissions detectable at ground level. MFB consists of broadband (500-2000 kHz) left-polarized impulsive emissions typically occurring for a few minutes at the onset of polar substorms, one of the most energetic phenomena in the terrestrial magnetosphere. Recent observations of the source location and fine structure of MFB provide the best opportunity yet to test theoretical models of the generation mechanism. Proposed mechanisms include mode conversion of Langmuir or electron cyclotron sound waves excited via resonant interactions with auroral electrons; the former has been shown under certain conditions to predict the frequency-time characteristics of MFB fine structure.

Schlagworte:

During the flyby of the Earth by Cassini in 1999, the Radio and Plasma Wave Science (RPWS) instrument recorded one month of quasi-continuous observations of Auroral Kilometric Radiation (AKR). Analyzing the Stokes parameters of incoming radio waves, we found AKR to be 100% circular left-handed (LH) or right-handed (RHW). We analyzed separately the northern - RH - emission, from the southern - LH - one with respect to the magnetic equator. AKR power variations reveal (i) a log-normal distribution at time scales of minutes, (ii) bursts of emission at time scales of a few hours, and (iii) a clear modulation at 24 hours, with a weaker modulation at 12 hours (especially visible for LH emissions). The prominent 24 h modulation is found to modulate LH and RH AKR in phase opposition. This is interpreted as being due to visibility effects related to the precession of the terrestrial magnetic dipole, making Cassini oscillate relative to the average AKR beaming pattern from each hemisphere. We accordingly quantified the AKR beaming vs explored latitudes. On time scales shorter than a few hours, LH and RH emissions are found to be correlated. This is attributed to the actual conjugacy of the corresponding sources, simultaneously turned on by substorm occurrence. The geometrical anti-correlation (at 24 h) dominates close to Earth, while the short term correlation (substorms) dominates far from Earth, where the detection threshold makes the visibility less important than the occurrence of substorms. Finally, the 12 h modulation is detected when it is not masked by strong visibility effects, i.e. for the LH emission which is observed mostly near the magnetic equator along the path of Cassini. A 12 h modulation being also observed in some geomagnetic indices, we suggest that a physical process (e.g. semi-diurnal variable efficiency of the reconnection between interplanetary and geomagnetic fields, or magnetotail oscillations) may be responsible of the observed AKR 12 h modulation.

Schlagworte:

The Earth&#x2019;s aurorae radiate away up to 1% of their energy in the form of radio waves, called Auroral Kilometric Radiation (AKR). The mechanism responsible for the emission, the electron cyclotron maser (ECM), produces similar emissions at other planets, in the solar atmosphere, and in astrophysical systems. AKR was not unambiguously identified until the 1970&#x2019;s because its detection requires a suitably instrumented satellite. The ECM theory predicts radiation beamed outward that cannot penetrate the increasing magnetic field and electron density near the Earth. Nevertheless, there have been observations over the years of AKR-like radio signals detected by ground-based, rocket-borne, and low-earth orbiting satellite-borne instruments, raising the question of whether a mechanism exists by which AKR can penetrate to low altitudes. Here we show the first unambiguous evidence that AKR indeed penetrates to low altitudes on occasions. We identified three examples of AKR-like emissions detected with a ground-based radio receiver at South Pole Station, Antarctica, during a 9-day interval in July, 2004, when the Geotail satellite, monitoring AKR, had a field of view including the auroral field lines above the station. The AKR-like emissions detected at ground-level have the same frequenc&#x2013;time structure as simultaneous AKR emissions detected on Geotail 115,000-190,000 km away from the Earth. Slight differences in the frequency extent of the emissions at the two locations can be explained by, for example, plasmaspheric screening of the emissions detected by Geotail. These observations represent the first coincident detections of AKR in space and on the ground. They require the existence of an as-yet unidentified mechanism to produce the ground-level emissions which are not predicted by ECM theory, they suggest that previous AKR-like emissions observed at low altitudes may indeed be AKR, and they require revision of the widely-held view that AKR is only detectable from space.

Schlagworte:

A chronological review of this relatively recent subject is presented, from the discovery of the first exoplanet &#x2013; orbiting a pulsar &#x2013; to theoretical predictions and ongoing searches conducted with most large low-frequency radiotelescopes. The specific interest of radio observations is emphasized.

Schlagworte:

The discovery of more than 500 exoplanets during the past 15 years has enabled us to characterize the upper atmosphere structure of some exosolar gas giants and to compare observational and modelling results to the known planets in the Solar System. It is of great interest to understand if these exosolar &#x201C;Hot Jupiters&#x201D; share similar physical processes compared to the giant planets (Jupiter and Saturn) in the Solar System with regard to their magnetic dynamos and the corresponding expected magnetic field strengths. In this work we discuss how observations of stellar Lyman-a absorption by so-called Energetic Neutral Atoms (ENAs) around transiting exoplanets together with theoretical modelling efforts can be used as a tool for estimating magnetic obstacle sizes and the corresponding magnetic field strength. For demonstrating this method we model the production of stellar wind related planetary hydrogen and ENA populations around the exosolar gas giant HD 209458b and show how a detailed analysis of attenuation spectra obtained during transits can be used for the estimation of the planet&#x2019;s magnetic obstacle size and hence its dynamo field strength. Our study indicates that the magnetic field strength of HD 209458b which is able to balance the stellar wind plasma flow by a magnetic obstacle around the planet which can explain the observed Lyman-a line profiles observed before and during the transits by HST corresponds to a magnetic dipole moment which is ~40 % of Jupiters value.

Schlagworte:

Massive extrasolar planets are expected to emit, in analogy with Jupiter and Saturn, detectable radio emission at low frequencies. We have carried out a series of observations of known extrasolar planetary systems at 150 MHz with the Giant Meterwave Radio Telescope (GMRT) in both interferometric and phased array modes. As low frequency observations are plagued with RFI, we have focused on observing strategies and analysis techniques to minimize, identify and remove RFI effects from dynamic spectra. Pulsar data obtained during each observing campaign have been used to validate novel detection algorithms for non-thermal events. In this report we will summarize our observing campaigns and present our detection algorithms and results. We will also briefly discuss prospects for similar searches with instruments that are now coming online as well as prospects with future instruments such as the SKA.

Schlagworte:

A planet orbiting around a pulsar would be immersed in an ultra-relativistic under-dense plasma flow. It would behave as a unipolar inductor, with a significant potential drop along the planet. As for Io in Jupiter&#x2019;s magnetosphere, there would be two stationary Alfv´en waves, the Alfv´en wings (AW), attached to the planet. The AW would be supported by strong electric currents, in some circumstances comparable to those of a pulsar. It would be a cause of powerful radio waves emitted all along the AW, and highly collimated through relativistic aberration. There would be a chance to detect these radio-emissions from Earth. The emission would be pulses as for ordinary pulsars; their occurrence would depend on the planet-star-observer angle. These results are still preliminary, further work needs to be done.

Schlagworte:

Three types of low-frequency nonthermal radio bursts are associated with coronal mass ejections (CMEs): Type III bursts due to accelerated electrons propagating along open magnetic field lines, type II bursts due to electrons accelerated in shocks, and type IV bursts due to electrons trapped in post-eruption arcades behind CMEs. This paper presents a summary of results obtained during solar cycle 23 primarily using the white-light coronagraphic observations from the Solar Heliospheric Observatory (SOHO) and the WAVES experiment on board Wind.

Schlagworte:

We present an overview of the recent results in solar observations obtained at decameter radio waves using the radio telescope UTR-2. Due to up-to-date recording facilities some newly discovered phenomena in the frequency range 10 - 30 MHz are given: fast type III bursts, fine time structures in normal type III bursts, solar S-bursts, type IV bursts with zebra-like fine structures, third harmonic in type II bursts and bursts in absorption of different time scale. Newly discovered properties of well known bursts such as type III bursts, type IIIb bursts, type II bursts and drift pairs were obtained too.

Schlagworte:

In this paper properties of decameter spikes observed in July - August, 2002 by radio telescope UTR-2 are discussed. These bursts have short duration (about 1s) and narrow frequency bandwidth (50 - 70 kHz). They are situated chaotically on the dynamic spectrum at the decameter wavelengths. These bursts are weak, their fluxes are not higher than 200 - 300 s.f.u. One of the interesting features of decameter spikes is linear dependence of frequency bandwidth on frequency. Such dependence can be explained in the frame of plasma mechanism of radio emission if to take into account that Langmuir waves are generated into the angle about 20 deg along the direction of electron beam propagation. In the paper the cause of small duration of spikes and generation of plasma waves in limited spatial regions are discussed.

Schlagworte:

It is currently accepted that the dependences of frequency drift rate and instant duration of type III bursts on frequency follow a monotonic function. The observations carried out during summer months of 2002-2006 by the world largest decameter wavelength radio telescope UTR-2 in frequency band 10-30 MHz show that sometimes these dependences may have a jump at some frequency, when the steepness of the dependence changes step-wise. In this paper the results of observations of such unusual type III bursts are given. Since the dynamic spectrum of such bursts resembles a dog&#x2019;s leg we call them &#x201C;dog-leg&#x201D; type III bursts. More than a hundred of these &#x201C;dog-leg&#x201D; bursts were observed during 5 years. The parameters of the 41 bursts observed in 2002 were defined and statistically analyzed. The fact that &#x201C;dog-leg&#x201D; type III bursts are observed on the background of standard type III bursts allows to exclude any instrumental component of the observed phenomena.

Schlagworte:

We report on the observation of powerful (fluxes are larger than 10-19 W/m2Hz) solar type III bursts at frequencies of 10-30 MHz using the radio telescope UTR - 2. The properties of powerful type III bursts observed in July 2002 (163 bursts) and August 2002 (231 bursts) were analysed. It was determined that the majority of these bursts were observed on days when an active region was located near the central meridian or at longitudes of 400 - 600 to the east or west of the central meridian. All of these bursts drift from high frequency to low with frequency drift rates of 1-2.5 MHz/s in most cases. We note that the frequency drift rate of these bursts increases linearly with frequency for all days of observation. This indicates that the solar corona above active regions shows an exponential density decrease with distance. The typical duration of the powerful type III bursts changes from 6 to 12 s. The instantaneous frequency widths of these bursts do not depend on the day of observation. There is a linear dependence between the average frequency width and frequency. The implication of these observations are discussed in the frame of the plasma model for the type III bursts generation.

Schlagworte:

During solar flares a large amount of electrons with energies greater than 20 keV is generated with a production rate of typically 1036 s-1. A part of them is able to propagate along open magnetic field lines through the corona into interplanetary space. During their travel they emit radio radiation which is observed as type III radio bursts in the frequency range from 100 MHz down to 10 kHz by the WAVES radio spectrometer aboard the spacecraft WIND, for instance. From the drift rates of these bursts in dynamic radio spectra the radial propagation velocity Vr of the type III burst exciting electrons is derived by employing a newly developed density model of the heliosphere. Calculations show that the radio radiation is emitted by electrons with different Vr and therefore by different electrons of the initially produced electron distribution.

Schlagworte:

We report on solar radio bursts observed by the RPWS experiment on board the Cassini spacecraft in the period from 1st January 2004 to 31st March 2010. In this time intervals of about six years a limited number of strong solar type III bursts, less than 300, has been recorded. This is mainly due to the solar activity which reaches its minimum in 2008&#x2013;2009. In this study we consider type III solar bursts observed at frequencies lower than 1.2 MHz generated in the interplanetary medium. We analyse the solar bursts with the aim to estimate the Cassini local time (LT) occurrence rate, where the Kronian day has been divided into eight LT sectors. Our results are combined with the Cassini orbits where the LT and the distance to the planet are taken into consideration. We show that the type III burst occurrence rates depend on the solar activity, however the day side sector (midday to early afternoon) exhibits the lowest rate of occurrence.

Schlagworte:

Solar Orbiter is an M-class mission in the ESA Science Programme Cosmic Vision 2015 &#x2013; 2025 having an orbit with perihelion as low as 0.28 AU. The Radio Plasma Waves (RPW) Analyzer on board will provide new insights into the microscale phenomenon, the propagation modes of the radio waves and the localization of their source regions. The three electric antennas (each 5 meters long) are designed to be mounted on booms in a perpendicular plane to the spacecraft-Sun axis. Effective antenna lengths and directions are different from the physical ones due to their coupling with the spacecraft body. These parameters have been investigated considering various antenna placements on the spacecraft body [Rucker et al., this issue]. Results indicate that all effective antenna directions will be slightly tilted towards the Sun. This paper discusses a possible accuracy of the Direction Finding (DF) with respect to this tilt angle and uncertainties of the effective antenna parameters.

Schlagworte:

Recently solar Type III bursts with fine time structure have been observed by radio telescope UTR-2 at frequencies 10 - 30 MHz. For the first time Type III-like bursts with high frequency drift rates were observed at these frequencies too. All this became possible due to both high sensitivity and high time resolution of UTR- 2. The properties of decameter Type III bursts can be understood if we take into account the spatial dependence of the electromagnetic wave group velocity as well as the fine spatial structure of the cloud of fast electrons responsible for Type III bursts. These effects are considered numerically in this paper. The fine time structure of Type III bursts is shown to be observed in the days when the associated active region is situated near the central meridian. In other days such structures disappeared. The Type III-like bursts with frequency drift rates of 10 - 20 MHz/s should also be observed, when the associated active region is near the central meridian. These peculiarities are confirmed by observations.

Schlagworte:

Observed spatial- and frequency-domain signatures of the most intense solar wind Langmuir waves can be described as localized, discrete-frequency eigenmodes trapped in a parabolic density fluctuation. Electric field waveforms from spacecraft in the solar wind are compared with one- and three-dimensional solutions and, in many cases, can be represented by 1-3 of the lowest order eigenmodes. The spatial scale of eigenmode wave packets is on the order of tens of Langmuir wavelengths, allowing them to draw energy directly from the unstable electron distributions associated with a solar type III radio bursts and implying that Langmuir waves can grow in a strongly inhomogeneous medium. The currents generated by localized Langmuir eigenmodes emit coherent electromagnetic radiation as antennas at the fundamental and at twice the local plasma frequency. STEREO observations demonstrate that the currents required for eigenmode antenna radiation are present and have strengths within an order of magnitude of theoretical predictions. The eigenmode antenna radiation mechanism implies that, of all the Langmuir waves excited by an electron beam, relatively few localized antenna radiators may account for a majority of observed emission from an extended radio source. Finally, the possibility that turbulence may ultimately play a strong role in the generation of Langmuir waves and the radio emissions associated with solar type II and type III radio bursts is investigated.

Schlagworte:

Several complex uncommon zebra patterns in meter/ decimeter and microwave range are shown. It is difficult to interpret them as the regular harmonics within the framework of known models, e.g. based on the double plasma resonance (DPR) mechanism. Specifically, for this reason, only in the last 5 years about 10 works devoted to an improvement of the DPR mechanism were published, and 5 new models were proposed. We propose a new advanced model of ZP based on the explosive instability in the system of the weakly-relativistic mono-velocity beam of protons - the strongly nonisothermic plasma.

Schlagworte:

One of the science goals of the Solar Orbiter mission is to study the connectivitybetween the solar corona and the inner Heliosphere as close as from 0.3 AU. Withthis respect the study of Solar radio emissions produced energetic electrons eitherflare or shock accelerated will be of prime importance. I will first review some recentfindings obtained with the help of Ulysses, WIND and Stereo observations. I willthen present the expected capabilities of the Solar Orbiter instrumentation relevantto the discussed topic.

Schlagworte:

The global distribution of solar surface activity (active regions) is connected with processes in the convection zone. To extract the information on large-scale motions in the convection zone, we study the solar synoptic charts (Mount Wilson 1998-2004, Fe I, 525.02 nm). The clear indication of large-scale (= 18°) turbulence is found. This may be a manifestations of the deep convection because there is no such global turbulent eddies in the solar photosphere. The preferred scales of longitudinal variations in surface solar activity are revealed. These correspond to ~ 15° to 51° (gigantic convection cells), 90°, 180° and 360°. Similar scales (e.g., 40° and 90°) are found in the millimeter radio-images (Mets¨ahovi Radio Observatory 1994-1998, 37 and 87 GHz). Hence, the millimeter radio astronomy could prove useful for remote sensing of the solar convection zone.

Schlagworte:

Unusual spectra with a significant decrease in circularly polarised emissions (Stokes parameter V ) in the middle part of the microwave range (6 - 12 GHz), sometimes with a change of the polarization sign, were revealed by observations with the radio telescope RATAN-600 in the microwave range 2 - 16 GHz. Such features can be explained by the presence of a hot region in the solar corona. The magnetic field strength of the hot region and the product of the relative gradient of the magnetic field on its thickness are defined.

Schlagworte:

The paper deals with interpretation of long-periodic (minutes, e.g. < 0.01 Hz) modulations, detected in the microwave records during flaring events on the Sun, as the signatures of large scale transverse oscillations of coronal loops, observed at the same time by TRACE. In the case of transverse large scale oscillatory motions of a loop a properly located observer, besides of the modulation caused by motion of the emission diagram pattern at the main oscillation frequency, may see also a modulation at double frequency of the loop oscillation, resulted by a varying magnetic field during each inclination of the loop, as well as weaker higher harmonics. Identification of such &#x201D;modulation pairs&#x201D; in the dynamic spectra of solar microwave emission and their association with the observed oscillating coronal loops form the major result of the undertaken investigation. Three different events with the detected by TRACE post-flare oscillating loops were considered in that study (Mar.23,2000; Sep.15,2001; Sep.07,2001).

Schlagworte:

When studying microwave emission of active regions on the Sun, an effect of parametric resonance between 5-min velocity oscillations in the solar photosphere and sound oscillations of coronal magnetic loops modulating the microwave emission has been discovered for the first time. The effect shows itself as simultaneous excitation in coronal magnetic loop oscillations with periods 5, 10, and 3 min, which correspond to the pumping frequency, subharmonic, and the first upper frequency of parametric resonance. The parametric resonance can serve as an effective channel of transporting the energy of photospheric oscillations into the upper layers of the solar atmosphere. The energy of acoustic waves excited in a coronal magnetic loop, rate of dissipation of acoustic waves, and rate of heating of the coronal plasma are determined. The maximum temperature predicted for the apex of the loop is calculated as a function of velocity of photospheric oscillations, length of the loop, and electric current in the loop. It is shown that the mechanism proposed can explain the origin of quasi-stationary X-ray loops with temperatures of 3-6 MK. The lengths of these loops are resonant for acoustic waves excited by the 5-min photospheric oscillations. The use of the proposed mechanism to explain heating of the X-ray loops expected to be on stars of late spectral types is discussed.

Schlagworte:

We analyzed the structure of the magnetic field in active regions at coronal altitudes, determined using multiwavelength observations of polarized radio emission in the microwave range at the radiotelescope RATAN-600. The observations were compared with the current-free magnetic field extrapolation of the photospheric field. It is shown that the measured magnetic field is always larger than the reconstructed field at the same height. The slopes of the tubes obtained by this method corresponds to the slopes obtained for the reconstructed field, although the degree of the slope differ significantly. The measured magnetic field structure is probably more complicated than the structure obtained by the reconstruction. Comparison of our measurements with previous measurements of radio astronomical heights at fixed frequencies showed good match.

Schlagworte:

Magnetohydrodynamic shocks are believed to play a significant role in the dynamics of lower solar atmosphere. Here we review the recent theoretical developments in shock wave induced phenomena and first observational evidence of slow sausage soliton in the solar chromosphere.

Schlagworte:

We present recent studies on large-scale solar coronal waves (so-called &#x201D;EIT waves&#x201D;) obtained with the EUVI instruments onboard the twin STEREO spacecraft. EUVI has several advantages for coronal wave studies: a) high cadence full-disk imaging, which allows us to catch the wave evolution and kinematics, b) a large field-of-view, which allows simultaneous observations of the erupting CME, and c) observations from two vantage points, which enable us to get insight into the threedimensional structure of the wave. The present understanding is basically split into different groups of &#x201D;wave&#x201D; versus &#x201D;non-wave&#x201D; interpretations of the physical process behind the phenomenon, as well as &#x201D;flare&#x201D; versus &#x201D;CME&#x201D; for the driving agent. We will present the first observations of the full three-dimensional wave dome in the event of January 17, 2010. The study of the perturbation characteristics and the associated high-frequency radio type II bursts provide evidence for a weakly shocked fast-mode wave as the underlying physical process.

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We analyze evolution and kinematics of the fast, globally propagating Moreton wave of 2003 October 28 associated with the extreme X17.2 solar flare/CME event. This Moreton wave is distinct due to its azimuthal span of ~ 360 deg. Thus its characteristics are studied in different propagation directions, and compared with the associated phenomena: EIT wave, coronal dimmings, radio type II burst, fast halo CME, and flare. The sectoral analysis give mean velocity values in the range of v ~ 900 - 1000 kms-1; two sectors show wave deceleration. Analyzing the perturbation profiles indicates an amplitude growth followed by amplitude weakening and broadening, which is consistent with a disturbance first driven and then evolving into a freely propagating wave. We find two &#x201D;radiant points&#x201D; for the Moreton wave fronts on opposite east-west edges of the source region, roughly co-spatial with the bipolar coronal dimming. Type II bursts are known as remote signatures of shocks propagating through solar atmosphere. Thus, the co-spatiality of the associated radio type II burst source and the first Moreton wave fronts indicate that the wave is an initially shocked fast-mode wave launched from an extended region. These findings indicate that the wave is initiated by the CME expanding flanks.

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Currents on the conducting surfaces of the spacecraft hull, induced by electric fields of radio waves, strongly influence the reception properties of spacecraft antenna systems. This influence is visualized by the so-called &#x201D;effective antenna length&#x201D; (heff ), representing the electric antenna, which differs from the physical antenna rod. Knowledge on these effective antenna vectors can be yielded by several different methods: (1) Experimental rheometry, (2) Numerical computer simulations, (3) In-flight calibration, and (4) Experimental anechoic chamber measurements. The paper addresses these methods and shows in the case of preliminary design studies of Solar Orbiter spacecraft the possibilities of numerical computer simulations, in particular the change of heff by design variations. The combined use of the above mentioned methods enables the determination of heff over a wide frequency range, the correct information on wave polarisation, and in specific cases helps to improve the performance of direction finding. So the calibration results may also be used to re-evaluate structure and position of antennas (and even positions of instruments) on board a spacecraft.

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The high-frequency electric sensors onboard Solar Orbiter are part of the radio and plasma wave experiment (RPW). The sensors consist of cylindrical antennas (ANT) mounted on three booms extruded from the central body of the spacecraft. Due to the parasitic effects of the conducting spacecraft body and solar panels the true antenna properties (effective axes and length, capacitances) do not coincide with their physical representations. The numerical analysis of the reception properties of these antennas is presented. In order to analyze the antenna system we applied a numerical method. The current distribution on the spacecraft body and the effective length vector was calculated, by solving the underlying field equations using electromagnetic code. In the applied method the spacecraft is modeled as a mesh-grid.

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The Nançay radio astronomy observatory and associated laboratories are developing the concept of a &#x201C;Super Station&#x201D; for extending the LOFAR station now installed and operational in Nan¸cay. The LOFAR Super Station (LSS) will increase the number of high sensitivity long baselines, provide short baselines and an alternate core, and be a large standalone instrument. It will operate in the low frequency band of LOFAR (30&#x2013;80 MHz) and extend this range to lower frequencies. Three key developments for the LSS are described here: (i) the design of a specific antenna, and the distribution of such antennas (ii) at small-scale (analog-phased mini array) and (iii) at large-scale (the whole LSS).

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The european radio telescope LOFAR is in its commissioning phase. It is a huge interferometer operating at low frequencies (30 to 240 MHz), composed of ~50 phased arrays (or stations) which are themselves gathering 864 to 1632 antennas. ~40 stations are located in the Netherlands along with the central correlator, and the other stations are spread over surrounding countries.In France, one of these arrays (1632 elements and their 96 associated receptors) has been built at the Nançay radioastronomy observatory. LOFAR will operate as an interferometer (for spectro-imagery) and as a global coherent phased array (for dynamic spectrometry).Its planetary objectives, that will be addressed by the Planets Working Group of LOFAR&#x2019;s &#x201D;Transients&#x201D; Key Science Project, include the fast imaging of the Jovian magnetosphere through its auroral radio emissions, and the detection and study of lightning on every planet of our solar system. Jupiter is the most intense low-frequency point source in the sky (> 106Jy), allowing extensive commissioning tests, which will be briefly described (including early interferometric observations between Nan¸cay and the Netherlands). In the case of Saturn&#x2019;s lightning, the large instantaneous bandwidth (up to 48 MHz) and the high time resolution of LOFAR (down to 5 µs per spectrum) allow us to measure the discharge spectrum and energy(see Grießmeier et al., this issue, 145-154). Moreover, one of the major objectives of LOFAR is the detection and study of exoplanetary radio emissions, which will be an unique source of information about the magnetic field, rotation and inclination of these objects, and about planet-star plasma interactions in general. In our solar system, each planetary magnetosphere has common as well as singular characteristics, which make it differ from the others. Radio detection of exoplanetary magnetospheres with allow us to explore parameter space of magnetospheric physics and enhance comparative studies (see Zarka, this issue, 287-301).

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The LOw Frequency ARray (LOFAR) is a novel radio telescope that consists of 20 core stations near Exloo in the Netherlands, 18 Dutch remote stations, and 8 international stations all distributed over central Europe. One of them was built in Potsdam. LOFAR is a radio interferometer for the frequency range of 30-240 MHz and will exceed the sensitivity and resolution of existing instruments by more than one order of magnitude. &#x201D;Solar Physics and Space Weather with LOFAR&#x201D; is one of LOFAR&#x2019;s Key Science Projects. Since LOFAR is working in the frequency range of 30-240 MHz, it is able to deliver radio images of the Sun. The solar radio radiation in this frequency range is emitted from the outer corona. Since radio waves are strongly scattered in the corona, the angular resolution of LOFAR&#x2019;s radio maps will be limited to a few 10 arcseconds. The necessary baselines include the core and the nearest remote stations.

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A procedure to combine radio data from the Low Frequency Array (LOFAR) [ASTRON, 2010] and the Giant Ukrainian Radio Telescope (GURT) [Konovalenko, et al., 2009] is described. LOFAR is being deployed with 36 stations in the Netherlands and 8 international stations in the neighbouring countries where the central 18 stations close to Exloo in the Netherlands form a core. Data from the Low Band Antennas in the frequency range 10&#x2013;80 MHz (10&#x2013;30 MHz with reduced sensitivity) of the LOFAR station in Bornim close to Potsdam, Germany, 1,500 km from GURT will be used. GURT is being built at the site of the UTR-2 radio telescope close to Charkov, Ukraine. It covers the range 10&#x2013;70 MHz and the final effective area of GURT will be comparable to the LOFAR core. The GURT data will be converted into narrow bands of the same bandwidth and the same centre frequencies as the LOFAR data. Comparisons of the dynamic spectra from the two stations will be made and the data from the stations can be combined to make use of the long baseline. Scientific focus will be on solar physics within the LOFAR Solar physics and space weather key science project, but the long baseline also allows for investigations of radio sources which require a higher angular resolution than the sun.

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According to the special Program of the National Academy of Sciences of Ukraine, creation of the new giant Ukrainian radio telescope (GURT) was started a few years ago on the UTR-2 radio telescope observatory. The main goal is to reach maximum band at the lowest frequencies (10-70 MHz), effective area (step-by-step up to 100,000 sq.m), and high interference immunity for resolving many astrophysical tasks when the sensitivity is less limited by the confusion effects. These tasks include stellar radio astronomy (the Sun, solar wind, flare stars, pulsars, transients) and planetary one (Jupiter, planetary lightnings, Earth ionosphere, the Moon, exoplanets). This array should be complementary to the LOFAR, E-LOFAR systems. The first stages of the GURT (6 x 25 cross-dipole active elements) and broad-band digital registration of the impulsive and sporadic events were tested in comparison with the existing largest decameter array UTR-2.

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In this paper, test results from a 25-element active antenna prototype array operating in the frequency range of 10&#x2013;70 MHz are presented. Observations of radio emission from different sources: solar sporadic radio emission and powerful cosmic radio sources including their ionosphere scintillation, demonstrate the high effectiveness of the system due to the Galactic background limited sensitivity and high dynamic range of the antenna amplifier (noise immunity). This demonstrates the capability of this 25-element active antenna array to engage in a wide range of unique wide band radio astronomical observations of solar system objects that do not require high sensitivity and angular resolution.

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Locating low frequency radio observatories on the lunar surface has a number of advantages, including fixed locations for the antennas and no terrestrial inteference on the far side of the moon. Here, we describe the Radio Observatory on the Lunar Surface for Solar studies (ROLSS), a concept for a near-side, low frequency, interferometric radio imaging array designed to study particle acceleration in the corona and inner heliosphere. ROLSS would be deployed during an early lunar sortie or by a robotic rover as part of an unmanned landing. The prime science mission is to image intense type II and type III solar radio bursts with the aim of determining the sites at and mechanisms by which the radiating particles are accelerated. Secondary science goals include constraining the density of the lunar ionosphere by searching for a low radio frequency cutoff of the solar radio emissions and detecting the low energy electron population in astrophysical sources. Furthermore, ROLSS serves as a pathfinder for larger, far-side lunar radio arrays, designed for faint sources.

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Studies of flare stars at radio waves are an important task of modern radio astronomy. They are connected with investigations of the physics of the stellar wind and stellar-planetary interrelations including habitable zones. One special interest is the search for radio emission bursts at extremely low frequencies (decameter wavelength). According to the analogy with the solar bursts the low frequency stellar bursts radio emission are arising in the outer stellar wind. Simultaneous observations at low frequencies and higher frequencies (from centimeter to meter wavelengths) are important also for the improvement of the detection reliability as well as for the phenomenology studies. We demonstrate the possibility to observe flare star bursts in the decametric radio band with the 70-meter dish radio telescope RT-70 (Evpatoria, Ukraine).

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Electromagnetic radiation from stars and planets appeared at the different wavebands. Radiation is provided by accelerated particles originated from plasma electromagnetic structures which are named the particle sources. Structures are selfconsistent with inductive e.m. fields and collisionless hot plasma electrodynamics including plasma part formed by accelerated particles. Here quasifree acceleration by inductive eddy e.m. field takes place. The sources are related with the diffusion regions (DR) of plasma where we get weak particle magnetization and where plasma kinetic process of magnetic reconnection takes place. In the DR electric current can be parted on the diamagnetic and on the resistive components. Current components in DR source are in ratio G and the components are related with non accelerated (diamagnetic) particles and accelerated (resistive) particles. Parameter G is calculated via momentum and energy anisotropy parameters depending on shape of the particle velocity distribution function (VDF). Parameter G can be positive and negative; G defines resistive, diamagnetic and quasi-current free dynamics of the DR as a source of accelerated particles. The G is the e.m. analog of the acoustic Mach number M. Plasma DR structures are described by anomalous skin-scale and diamagnetic skin scale. We introduced criteria on value of plasma beta and on value of anisotropy parameters to get the DR plasma structures realization.

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Dust kinetic Alfv´en waves (DKAW) instability with ?-distributed ions streaming effects have been examined rigorously in a uniform dusty magnetoplasma. A dispersion relation of low-frequency DKAW instability on the dust acoustic velocity branch is obtained in a low-ß Lorentzian plasma. It is found that nonthermality is more effective for dust kinetic Alfv´en waves in the perpendicular component having finite larmor radius effects. Lorentzian type charging currents are obtained with the aid of Vlasov theory. Effect of different dust parameters on the growth rates of instability are considered. Damping/instability due to dust charge fluctuation is found to be insensitive to the form of the distribution function for DKAW. Possible applications to dusty space plasmas are pointed out.

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The use of angular momentum and other EM degrees of freedom provide newways to improve the diagnostic of radio sources. We show how these methodscan be used to extract more information from planetary, solar and heliosphericradio emissions. Examples include imaging of plasma vorticity and sub-Rayleighresolution by up to one order of magnitude.

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Whistlers are electromagnetic waves generated by lightning discharges traveling through the ionosphere where the dispersion relations show that the higher frequency emissions travel faster than the low frequency emissions. Satellite analog wave receivers allowed the Very Low Frequency (VLF) (less than 30 kHz) waves to be transmitted to the ground by modulating a Very High Frequency carrier. Spectrograms of some whistlers showed emissions with rising components beginning below the ion cyclotron frequencies and later referred to as proton, helium, or oxygen ion whistlers. Analyses of the crossover frequency, the asymptotic frequency, and the dampening rate yielded relative mass density, magnetic field magnitude, and electron temperature. The INJUN V satellite instrumentation was able to determine the propagation direction up or down the geomagnetic field line. Whistlers verified the calibrations. VLF saucers centered on regions of intense energetic electron precipitation were shown to be upgoing from the auroral region. The upper frequency limits of the filter banks on these satellites were 35 kHz and 100 kHz. Subsequent satellite receivers progressively increased the upper frequency limits of both the digital filter banks and analog wideband receivers. The dominant auroral emission was auroral kilometric radiation (AKR) whose intensity peaks around 250 kHz. AKR observations from the UC Berkeley FAST spacecraft show that it is primarily generated slightly above the local relativistic electron cyclotron frequency. AKR frequency limits extend from below 15 kHz to at least 800 kHz showing that it is generated over a large spatial range of several Earth radii. High resolution wave forms show tones and emissions embedded in the AKR data indicating significant ion influences. Observations of Type II and Type III solar radio bursts produced by coronal mass emissions and solar flares provide details of the interplanetary medium density structure.

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