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We report on Cassini Imaging Science Subsystem (ISS) data correlated with Radio and Plasma Wave Science (RPWS) observations, which indicate lightning on Saturn. A rare bright cloud erupt at ∼35° South planetocentric latitude when radio emissions (Saturn Electrostatic Discharges, or SEDs) occur. The cloud consisting of few consecutive eruptions typically lasts for several weeks, and then both the cloud and the SEDs disappear. They may reappear again after several months or may stay inactive for a year. Possibly, all the clouds are produced by the same atmospheric disturbance which drifts West at 0.45 °/day. As of March 2007, four such correlated visible and radio storms have been observed since Cassini Saturn Orbit Insertion (July 2004). In all four cases the SEDs are periodic with roughly Saturn's rotation rate (h^(10)m^(39)), and show correlated phase relative to the times when the clouds are seen on the spacecraft-facing side of the planet, as had been shown for the 2004 storms in [Porco, C.C., and 34 colleagues, 2005. Science 307, 1243–1247]. The 2000-km-scale storm clouds erupt to unusually high altitudes and then slowly fade at high altitudes and spread at low altitudes. The onset time of individual eruptions is less than a day during which time the SEDs reach their maximum rates. This suggests vigorous atmospheric updrafts accompanied by strong precipitation and lightning. Unlike lightning on Earth and Jupiter, where considerable lightning activity is known to exist, only one latitude on Saturn has produced lightning strong enough to be detected during the two and a half years of Cassini observations. This may partly be a detection issue.

The Altus Cumulus Electrification Study (ACES) was conducted during the month of August, 2002 in an area near Key West, Florida. One of the goals of this uninhabited aerial vehicle (UAV) study was to collect time resolved optical pulse data from thunderstorms. During the month long campaign, we acquired 5294 lightning generated optical pulses. Most of these observations were made while close to the top of the storms. We divided our data into two amplitude groups based on prior NASA U2 aircraft optical data and our pulse characteristics. The group of large pulses with radiance greater than 2.1 mW /sq m sr had mean and median 10 - 10% optical pulse widths of 765 and 735 microns respectively, the 50-50% pulse widths of 396 and 355 microns respectively, and 10-90% rise times of 290 and 260 microns. These values are very similar to the previous U2 based optical results The other group of pulses consisting of slightly more than a quarter of the total pulses observed had radiances less than the minimum values detected in the U2 study. The small pulses were narrower than the large pulses with 5040% mean and median values of 198 and 160 ps respectively. Only 12 % of the flashes contained only small pulses, minimizing the impact of this data on the estimates of detection efficiencies of the orbital instruments, the Lightning Imaging Sensor and Optical Transient Detector.

Saturn is a source of intense kilometre-wavelength radio emissions that are believed to be associated with its polar aurorae, and which provide an important remote diagnostic of its magnetospheric activity. Previous observations implied that the radio emission originated in the polar regions, and indicated a strong correlation with solar wind dynamic pressure. The radio source also appeared to be fixed near local noon and at the latitude of the ultraviolet aurora. There have, however, been no observations relating the radio emissions to detailed auroral structures. Here we report measurements of the radio emissions, which, along with high-resolution images of Saturn's ultraviolet auroral emissions, suggest that although there are differences in the global morphology of the aurorae, Saturn's radio emissions exhibit an Earth-like correspondence between bright auroral features and the radio emissions. This demonstrates the universality of the mechanism that results in emissions near the electron cyclotron frequency narrowly beamed at large angles to the magnetic field.

By virtue of their planetary-scale magnetic fields, the Earth and all of the gas giants in our solar system possess solar-wind deformed magnetospheres. The magnetic polar regions of these “magnetic planets” produce intense, aurora-related radio emission from solar-wind powered electron currents. Simple scaling laws suggest that Jovian-mass planets close to their host stars should produce radio emission; detecting such emission would be the first direct detection of many of these planets. We describe searches using the Very Large Array (VLA) for radio emission from the planets orbiting HD 114762, 70 Vir, and τ Boo. Our limits are just above those predicted for the planetary emissions. We discuss the possibilities for more stringent limits and the implications that the existing observations have for the planets' radio emissions, and hence on the planetary magnetic fields and stellar wind environments.

The May, 1999 low density (< 1 cm -3 ) solar wind interval is one of a series of intervals of low density solar wind which have been detected since in-situ, near-Earth observations began. Examining the NSSDC OMNI database since 1965, covering solar Cycles 20-23, we show that such intervals, which are also periods of unusually low mass flux and low dynamic pressure, occur most frequently around sunspot maximum and are rarer at solar minimum. The occurrence rate of low-density plasma may be higher in weaker sunspot cycles (Cycle 20 and the current Cycle 23). Around two-thirds of periods with densities < 1 cm -3 are associated with transient solar wind structures, in particular with ejecta and post-shock flows. The majority of other events are associated with corotating streams. The May 1999 event is unusual because it is not associated with an ejecta or stream. A similar period was observed in July-August 1979.

The recent occurrence of an interval (May 9th to May 12th, 1999) of abnormally low density solar wind has drawn attention to such events. The SWE instrument on the Wind spacecraft observed nine similar events between launch (November 1994) and August 1999: one in 1997, three in 1998, and five in January-August 1999. No such events were observed in 1996, the year of solar minimum. This already suggests a strong dependence upon solar activity. In this paper we discuss observations of the electron strahl, a strong anisotropy in the solar wind electrons above 60 eV directed along the magnetic field and observed continuously during the periods of low density in 1998 and 1999. When the solar wind density was less than 2/cc, the angular width of the strahl was below 3.5 degrees and the temperature deduced from the slope of the electron strahl phase density (as a function of energy in the energy range 200 to 800 eV) was 100 to 150 eV, equivalent to a typical coronal electron temperature. Three examples of this phenomenon, observed on Feb. 20- 22, April 26-27 and May 9-12, 1999, are discussed to show their similarity to one another. These electron observations are interpreted to show that the strahl occurs as a result of the conservation of the first adiabatic invariant, combined with the lack of coulomb collisions as suggested by Fairfield and Scudder, 1985.

We present observational evidence that the long-term behavior of Jovian bKOM and nKOM radio emissions observed during the Ulysses-Jupiter encounter was controlled by the sector structure of the solar wind. Specifically, we found brightenings in the Jovian bKOM emission, followed by a sudden cessation of the bKOM emission and an onset of an nKOM “event” that lasted for some 120 hours. This sequence of events was observed to recur every ∼12 or 25 days from October, 1991 to mid-January, 1992 when Ulysses was inbound toward Jupiter and at Jovian latitudes

The frequency range below a few tens of MHz is unexplored with high angular resolution due to the opacity of Earth's ionosphere. An interferometer array in space providing arcminute angular resolution images at frequencies of a few MHz would allow a wide range of problems in solar, planetary, galactic, and extragalactic astronomy to be attacked. These include the evolution of solar radio emissions associated with shocks driven by coronal mass ejections and searches for coherent radio emission from supernova remnants and relativistic jets. In addition, it is likely that unexpected objects or emission processes will be discovered by such an instrument, as has always happened when high resolution astronomical observations first become possible in a new region of the electromagnetic spectrum. The Astronomical Low Frequency Array (ALFA) mission will consist of 16 identical small satellites forming an aperture synthesis array. The satellites will cover the surface of a spherical region ≈ 100 km in diameter, thus providing good aperture plane coverage in all directions simultaneously. The array will operate in two medes: 1) “snapshot” imaging of strong, rapidly changing sources such as solar radio bursts and 2) long-term aperture synthesis observations for maximum sensitivity, high dynamic range imaging. In both cases a large number of array elements is needed.

Given the known physical attributes of Martian dust storms, we derive their electromagnetic signatures as they would be perceived both remotely and in situ. We also describe a radiowave and optical experiment (REDD), suitable for deployment on the Mars Surveyor 2001 Lander, whose primary scientific objective is to establish the electrical nature of dust storms in the Martian atmosphere. This experiment would be capable of the remote tracking of dust storms across the Martian surface while estimating electrical properties of dust, dust densities, and surface conductivities. The experiment sensors consist of two orthogonal magnetic search coil antennas, an electric field antenna, and a horizon-looking photodetector. The sensors drive a waveform capture system and a set of multichannel analyzers that span the radio spectrum from 1 kHz to 100 MHz. The data sampling strategy incorporates a low-resolution survey mode and a high time-resolution direction-finding mode. Intelligent use of an event-trigger system, circular buffer storage, and data compression minimize the instrument data rate and the impact on spacecraft resources.

In an effort to understand the newly discovered phenomenon of cometary X-ray emission, we have obtained observations of the short period (3.3 years), well-studied comet 2P/Encke (Encke) during its July 1997 close approach to Earth. Extended, variable emission on the sunward side of the nucleus was found in the Rontgen X-ray satellite High Resolution Imager (HRI) at 0.090–0.75 keV and in the Extreme Ultraviolet Explorer (EUVE) scanner telescopes' Lexan B 0.090- to 0.28-keV and Al/Ti/C 0.050- to 0.16-keV bandpasses; useful upper limits were found in the Ti/Sb/Al 0.020- to 0.040-eV bandpass. Similar to our results for C/Hyakutake, the emission morphology was roughly symmetric with respect to a vector from the comet's nucleus toward the Sun, with a light curve consisting of a slowly varying baseline emission and a large impulsive event on 7 July 1997 with a time scale of ∼3 h and an amplitude of ∼3 times the baseline. A count rate of ∼0.17 counts s−1 in the HRI was measured for the slowly varying emission, corresponding to a total luminosity Lx of 4×1014 erg s−1. Unlike Hyakutake, however, the bulk of the emission clearly originates outside the comet's bowshock, arguing against the magnetic reconnection and plasma dust emission models. The comet's lightcurve does not correlate with the solar X-ray lightcurve, ruling out scattering of solar X-rays as the emission mechanism. The multiwavelength HRI/EUVE photometry is inconsistent with the Haberli et al. (1997, Science 276, 939–942) charge transfer, plasma dust, and attogram dust models of cometary X-ray emission and is consistent with the Wegmann et al. (1988, Planet. Space Sci. 46, 603–612) charge exchange, 0.15- to 0.45-keV thermal bremsstrahlung, and photon index 1.6–2.0 power law models. While the impulsive event correlates very well with the passage of a solar magnetic field boundary at the Earth and an increase in the solar wind particle flux, it is not coincident, according to current models of the solar wind magnetic current sheet, with the passage of the sector boundary by the comet, suggesting that new models of the current sheet are necessary.

We report on the first experiment using two high power, high frequency transmitting facilities in a bistatic, interferometer mode. The HAARP and HIPAS facilities in Alaska radiated at 4525 kHz with total combined power of about 700 kW, in the direction of the WIND spacecraft. The WAVES experiment aboard WIND received the transmissions at a distance of about 25 earth radii. The experimental setup thus resembled Young's two-slit experiment. The expected interference pattern was observed; at the distance of WIND, the fringe size was about 30 km peak to peak.

We present a model addressing the possible electrification of Martian dust storms based on the effective electrical charging of an individual dust grain. An upper charge bound on a grain can be determined based on the grain capacitance in the low-pressure Martian atmosphere. It is assumed that treiboelectric and inductive processes, like that presumed operating in terrestrial dust storms, can electrify the grain to significant levels. A collection of such grains charged in a dust cloud of many tens of kilometers in size can yield a substantial electric field moment. Given various grain charge and dust storm sizes, the electric moment will be determined along with estimates of electrical discharge and emitted radio power based upon known models. We also suggest the possibility that remote detection of discharge-related VLF emission propagating in the surface/ionosphere waveguide can be used to determine subsurface conductivity.

Under certain circumstances, ELF radiation from power lines is able to very mildly heat the electrons in the upper atmosphere via ELF wave/electron interaction. The electron temperature increase for O-mode heating is

Results from the first science experiment with the new HF Active Auroral Research Program (HAARP) in Alaska are reported. The objective was to study the effects of space plasmas on high power radiowave transmission to high altitudes in the magnetosphere. Reception was done by the NASA/WIND satellite. The data suggest that structured space plasmas along the propagation path impose a power law spectrum of fluctuations on the transmitted waves, resembling scintillations. Because the transmitted waves are near ionospheric plasma frequencies, other types of wave-plasma interactions may occur. Such measurements can provide a new diagnostic tool.

The WIND spacecraft, part of the ISTP program, was launched by NASA on 1 November 1994, to study the interplanetary medium and the effects of changes and disturbances in it upon the magnetosphere. Initially placed in a double-lunar-swingby orbit, which presently has a perigee of ∼1.5 and an apogee of ∼250 earth radii, the spacecraft may be inserted in 1997 into a halo orbit about the foreward libration point, L1 where it will remain for at least a year. WIND carries modern instrumentation to measure the magnetic field, solar wind and hot plasma, energetic particles and low energy cosmic rays, plasma and radio waves and plasma composition, in addition to two Gamma-ray burst detectors. One of the Gamma-ray instruments is the first Russian instrument to fly on a US spacecraft. This paper describes the spacecraft and some new results in various disciplines.

Using WIND spacecraft data from the WAVES, SWE, and MFI experiments for the period from January through July, 1995, we show that the occurrence of the terrestrial low frequency (LF) radio bursts is controlled primarily by the solar wind speed. A possible secondary factor in determining the occurrence of the bursts is the direction of the IMF in the x-y plane, with the ‘toward’ direction (By< 0) favored. The correlation with bulk speed suggests, on a gross scale, a viscous-like coupling mechanism between the solar wind and the magnetosphere. In terms of the nature of the solar wind correlation, terrestrial LF bursts strongly resemble the Earth's AKR and Jovian quasi-periodic bursts.

We report on a constituent of Earth's radio spectrum that shows remarkable similarities to Jovian “type III” or quasi-periodic bursts. These terrestrial bursts lie in the radio LF band, down to the in situ plasma frequency and are made of two spectral components. The lower frequency component exhibits relatively rapid negative frequency drifts, similar to type III solar bursts but on a much shorter time scale. It appears to emanate from a large source region and its characteristics are the same as those of isotropic terrestrial kilometric radiation described by other authors. The higher frequency component does not drift much in frequency, only lasts about 1 to 5 minutes and sometimes extends up to 500 kHz. It appears to emanate from a discrete source. This high frequency component was never reported before because it is often hidden by AKR events. It might be produced by a mechanism which differs from AKR. These LF bursts may belong to a more common class of radio bursts representing a previously unappreciated segment of Earth's radio spectrum.

The WAVES radio and plasma wave instrument on the Wind spacecraft, launched on November 1, 1994, has detected copious shortwave radio transmissions from broadcast stations on Earth. WAVES can easily detect signals consisting of only a few kW of transmitted power, suggesting that useful ionospheric propagation research can be accomplished with very modest equipment. We also conclude that the terrestrial radio spectrum is quite “non natural” so that any extraterrestrial radio astronomer should easily deduce that Earth is populated with a civilization with technical capabilities.

Continuous radio observations below 1 MHz of Jupiter from the Ulysses spacecraft are used to establish an upper limit to the radiated power at low frequencies associated with the traversal through the magnetosphere and impact of Comet SL-9 with the planet. Although Jovian emissions were observed throughout the impact interval, no systematic intensity changes were observed before, during, or after the fragment impact times as a whole. Examined individually, a large intensity increase, probably associated with a solar wind compression at Jupiter, was observed at the time of the P impact. Intense solar type III bursts, which can sometimes be confused with Jovian emissions, occurred often, which serves as a caution to other (groundbased) radio observers. We derive an upper limit for the interfragment dust density of 10−3/m3 in the context of a dust-magnetosphere interaction model proposed earlier.

We report a new component of Jovian radio emission observed by the Ulysses spacecraft when Ulysses was at high Jovigraphic latitudes (greater than or approximately = 30 deg north or south of the Jovian magnetic equator). This bursty high-latitude emission is elliptically polarized in the right-hand sense when observed from northern latitudes and in the left-hand sense when observed from southern latitudes, consistent with extraordinary mode. The orientation of the polarization ellipse is observed to systematically vary with time relative to the observer. It is argued that the elliptically-polarized nature of the emission is intrinsic to the source region.

We suggest that prior to its impact with Jupiter, comet Shoemaker-Levy 9 will behave as an electrical generator in the Jovian magnetosphere, converting planetary rotational energy to electrical energy via a dust/plasma interaction. This electrical energy will then be deposited in the dayside auroral region where it may drive various auroral phenomena including cyclotron radio emission. Such emission could be detected by spacecraft like Ulysses and Galileo many hours prior to the actual comet impact with the upper atmosphere. We apply the theory originally developed to explain the spokes in Saturn's rings. This theory allows us to quantify the driving potential associated with the comet and, consequently, to determine the radio power created in the auroral region. We conclude that if enough fine dust is present in the cometary system, comet-induced auroral radio emissions will reach detectable levels. This emission should be observable in the dayside hemisphere about 12-24 hours prior to each fragment impact.

Particle acceleration processes are important in understanding many of the Jovian radio and plasma wave emissions. However, except for the high-energy electrons that generate synchrotron emission following inward diffusion from the outer magnetosphere, acceleration processes in Jupiter’s magnetosphere and between Jupiter and Io are poorly understood. We discuss very recent observations from the Ulysses spacecraft of two new Jovian radio and plasma wave emissions in which particle acceleration processes are important and have been addressed directly by complementary investigations. First, radio bursts known as quasi-periodic bursts have been observed in close association with a population of highly energetic electrons. Second, a population of much lower energy (keV range) electrons on auroral field lines can be shown to be responsible for the first observation of a Jovian plasma wave emission known as auroral hiss.Subject headings: acceleration of particles — planets and satellites: individual (Jupiter) — radio continuum: solar system

Radio emissions from Jupiter provided the first evidence that this giant planet has a strong magnetic field and a large magnetosphere. Jupiter also has polar aurorae, which are similar in many respects to Earth's aurorae. The radio emissions are believed to be generated along the high-latitude magnetic field lines by the same electrons that produce the aurorae, and both the radio emission in the hectometric frequency range and the aurorae vary considerably. The origin of the variability, however, has been poorly understood. Here we report simultaneous observations using the Cassini and Galileo spacecraft of hectometric radio emissions and extreme ultraviolet auroral emissions from Jupiter. Our results show that both of these emissions are triggered by interplanetary shocks propagating outward from the Sun. When such a shock arrives at Jupiter, it seems to cause a major compression and reconfiguration of the magnetosphere, which produces strong electric fields and therefore electron acceleration along the auroral field lines, similar to the processes that occur during geomagnetic storms at the Earth.

The two main, low frequency radio components discovered at Neptune by the Planetary Radio Astronomy experiment carried aboard Voyager 2 have a well defined periodicity at about 16.1 hour. By analyzing all the available data, i.e. about 60 days around the closest approach for the 'Burst' component and 15 days for the 'Smooth' component, we determine, for each component, the best estimate of the radio period. We conclude that the two estimates are not statistically different. While the two kinds of radio emissions have very different characteristics (in particular their frequency ranges and beaming properties), and probably correspond to different emission processes, their modulation is very likely due to the rotation of the planetary magnetic field tied to the core of the planet, as it has already been assumed for the other giant planets. The deduced estimate of the sidereal rotation period of Neptune is 16.108 +/- 0.006 (or 16h06.5m +/- 0.04 m).

The Ulysses Unified Radio and Plasma (URAP) experiment has detected a new component of Jupiter's radio spectrum in the frequency range from about 10 to 30 kHz. This component is emitted in the magnetoionic ordinary mode from a localized corotating source in the northern polar region. The source is centered at system III longitude 208°, near the meridian containing the North magnetic dipole axis, at a distance of nearly 4RJ from the planet and near the last closed field line. The emission frequency is somewhat above the electron plasma frequency in the source region, but well below the electron gyrofrequency. Accompanying this O-mode emission at lower frequencies is intense Z-mode emission, which is likely to play a significant role in the generation of the O-mode.

The Ulysses flyby of Jupiter has permitted the detection of a variety of quasiperiodic magnetospheric phenomena. In this paper, Unified Radio and Plasma Wave Experiment (URAP) observations of quasiperiodic radio bursts are presented. There appear to be two preferred periods of short-term variability in the Jovian magnetosphere, as indicated by two classes of bursts, one with ∼ 40 min periodicity, the other with ∼ 15 min periodicity. The URAP radio direction determination capability provides clear evidence that the 40 min bursts originate near the southern Jovian magnetic pole, whereas the source location of the 15 min bursts remains uncertain. These bursts may be the signatures of quasiperiodic electron acceleration in the Jovian magnetosphere; however, only the 40 min bursts occur in association with observed electron bursts of similar periodicity. Both classes of bursts show some evidence of solar wind control. In particular, the onset of enhanced 40 min burst activity is well correlated with the arrival of high-velocity solar wind streams at Jupiter, thereby providing a remote monitor of solar wind conditions at Jupiter.

Ulysses URAP observations of escaping Jovian continuum radiation show a persistent 10 h variation in amplitude which can best be explained by a clock like model. The continuum shows a moderately strong preference to reach maximum intensity when the 0°–90° System III longitude sector faces the Sun.

During the Ulysses flyby of Jupiter, a whistler-mode emission was periodically detected by the unified Radio and Plasma wave (URAP) experiment during intervals when the spacecraft extended to high magnetic latitudes. The signal was detected between the local electron plasma frequency and lower hybrid resonance and appears as a funnel-shaped structure on frequency-versus-time spectrograms; these characteristics are very reminiscent of whistler-mode auroral hiss observed at high latitudes at Earth. Ray tracing of the emission occurrences suggests the emission source is on magnetic field lines extending out to at least 65 R(sub J). This location associates the emission with the boundary between open and closed field lines -- not the Io torus. The emission radiates about 10(exp 7) W of power. Consequently, the auroral input power derived from the solar wind to drive the emission is believed to be 10(exp 10-12) W (or about 1% of the energy associated with Io torus electrical processes).

The requirements for the Ulysses trajectory to attain high ecliptic latitudes using a Jovian gravitational assist resulted in a fortuitous passage through the Io torus region. Specifically, the spacecraft spent many hours at latitudes just above the torus. During this time the low-frequency cutoff of an ordinary mode (O mode) emission allowed a determination of the local electron plasma frequency (i.e., electron density) along the northern flank of the torus. Also, near a Jovian System III longitude of 100 deg, the spacecraft flew past a set of active field lines that have been previously identified to be associated with the hectometric generation region. During the passage, Ulysses observed a newly discovered O mode component and a whistler mode emission similar to that observed by Voyager 1 13 years previously. All of the broadband VLF emissions imply the presence of a particular population of electrons. We suggest that broadband VLF emissions can be used as a `particle detector' to qualitatively measure the electron plasma conditions in the torus region and identify active regions.

The Unified Radio and Plasma Wave (URAP) experiment has produced new observations of the Jupiter environment, owing to the unique capabilities of the instrument and the traversal of high Jovian latitudes. Broad-band continuum radio emission from Jupiter and in situ plasma waves have proved valuable in delineating the magnetospheric boundaries. Simultaneous measurements of electric and magnetic wave fields have yielded new evidence of whistler-mode radiation within the magnetosphere. Observations of aurorallike hiss provided evidence of a Jovian cusp. The source direction and polarization capabilities of URAP have demonstrated that the outer region of the lo plasma torus supported at least five separate radio sources that reoccurred during successive rotations with a measurable corotation lag. Thermal noise measurements of the lo torus densities yielded values in the densest portion that are similar to models suggested on the basis of Voyager observations of 13 years ago. The URAP measurements also suggest complex beaming and polarization characteristics of Jovian radio components. In addition, a new class of kilometer-wavelength striated Jovian bursts has been observed.

During the Ulysses inbound cruise to Jupiter the Unified Radio and Plasma Wave (URAP) experiment observed a variety of the planet's radio components in the frequency range below 1 MHz. Most of these emissions were already detected by the Voyager Radio Astronomy and Plasma Wave experiments, however, with much less sensitivity and different spectral coverage. These different radio components within the URAP dynamic spectra are identified, and their appearance with the previous Voyager observations are compared.

Recent observations of rare cloud-to-stratospheric lightning discharges suggest the events are inherently 'slow-rising', with the emitted energy reaching peak values in about 10 milliseconds. Applying a dipole radiation model, it is demonstrated that the emitted radio wave energy from such slow-rising events is strongest below about 50 Hz, and possesses a significant rolloff at higher frequencies. In the analysis, various current distributions are considered in order to determine the effect on the radio spectrum. Near 10 kHz, the emission from cloud-to-stratospheric lightning is significantly reduced as compared to the typical cloud-to-ground return stroke, with amplitudes as much as 50 dB lower. This result may explain the lack of detection of VLF signals from recently observed long-lasting discharge events.

The Ulysses URAP experiment has detected Jovian radio emissions in the VLF range at distances from Jupiter in excess of 1.5 AU. The URAP observations represent the first synoptic observations of Jupiter in the VLF band, from 3 to 30 kHz. In this band lie the low-frequency extent of the bKOM emission, the escaping continuum emission, and the Jovian type IIIs. Initial results indicate that the continuum varies in frequency with the solar wind ram pressure at Jupiter, whereas, the Jovian type IIIs appear to be controlled to some extent by the planetary rotation, often appearing when system III longitude 100 deg faces the spacecraft.

A sideband noise event was detected at ground level from the Andoya Rocket Range in Norway in January 1989. The signals were observed on four commercial communication receivers (tuned to 159, 515, 905, and 1200 kHz), an ionosonde (200-kHz to 3.5-MHz interference-free observations) and a riometer (32.5 MHz). The event, which occurred during a period of magnetic disturbance near magnetic midnight, was the only one observed during nearly 3 weeks of operations. This low frequency-of-occurrence is attributed partly to high local noise levels. The ease with which this event was identified on the ionograms produced by the local ionosonde suggests that routine ionosonde recordings should be inspected in search for such events. Such an effort would enhance existing research directed toward developing techniques for identifying quiet communication channels and help to identify the origin and frequency-of-occurrence of high-latitude wideband noise events.

The Voyager planetary radio astronomy experiment detected a bursty, narrow-band radio emission originating in Neptune's magnetosphere. The time of occurrence of nearly all of the episodes of this bursty radio emission can be explained on the basis of a radio source located just above and to the east of the south magnetic offset tilted dipole (OTD) tip (Farrell et al., 1990). However, several episodes of bursty emission do not occur at the usual frequency and planetaray rotation phase for emissions of this type. The occurrences of these rarely seen anomalous episodes are shifted systematically in planetary longitude so as to be consistent with a source of emission to the southwest of the southern magnetic OTD pole. Owing to the proximity of these sources to the magnetic polar region, they are associated with an active auroral region. Therefore, at least from the standpoint of the radio emission, the picture that emerges is of an auroral zone with two emission hot spots approximately diametrically east and west of the south magnetic pole. The possibility of a complete radio-active auroral oval is discussed.

While Voyager 2 was inbound to Uranus, radio bursts of narrow bandwidth (less than 5 kHz) were detected between 17-116 kHz. These R-X mode bursts, designated n-bursts, were of short duration, tended to occur when the north magnetic pole tipped toward the spacecraft, and increased in occurrence with increasing solar wind density. An explicit determination of the burst source location is presented, based upon fitting the region of detection at high and low frequencies to field-aligned, symmetric cones. The region of good fits was located between the north magnetic pole and the rotational pole, corresponding approximately to the northern polar cusp.

Previous studies on the periodicities of the Saturnian kilometric radiation (SKR) suggested a considerable solar wind influence on the occurrence of SKR, so it was obvious to investigate the relationship between parameters of the solar wind/interplanetary medium and this Saturnian radio component. Voyager 2 data from the Plasma Science experiment, the Magnetometer experiment and the Planetary Radio Astronomy experiment were used to analyze the external control of SKR. Out of the examined quantities known to be important in controlling magnetospheric processes this investigation yielded a dominance of the solar wind momentum, ram pressure and kinetic energy flux, in stimulating SKR and controlling its activity and emitted energy, and confirmed the results of the Voyager 1 analysis.

[1] It has been demonstrated that terrestrial dust devils emit ULF magnetic radiation. On Mars, dust devils may also generate such magnetic emissions, which might be used as a hazard alert for manned missions. Specifically, grains in dust devils become charged via contact electrification, and it has been proposed that the cyclonic motion of these charged grains in the vortex wind fields accounts for the magnetic emission. To test this hypothesis in general and the possible Mars application, a computer simulation of the contact electrification/wind blowing phenomena was created, with the charge distribution and resulting magnetic fields monitored as a function of time. The results indicate that indeed a fluctuating charge distribution in a vortex wind can account for the ULF magnetic fields measured from a dust devil. The contact electrification process is a function of composition, and we demonstrate that the various compositions will give rise to different magnetic field responses from the dust devil. We also demonstrate that this system of swirling charged grains develops vertical currents and associated electric fields, as suggested in preceding works.

[1] During Cassini's orbit insertion at Saturn, the trajectory took the spacecraft overtop the planet's famed ring system. At this time, the Cassini Radio and Plasma Wave Science (RPWS) instrument obtained unprecedented observations of electron density in the vicinity of the rings. Using this information and a model of photoemission anticipated from the rings, we demonstrate that the ring surface potential undergoes a seasonal change in electrical configuration, being primarily unipolar (of one charge polarity/potential) during the Voyager era and now bipolar (two separate polarities/potentials) during the Cassini era. We calculate the approximate ring/sun opening angle required for the transition from unipolar to bipolar configuration. Using electron density profiles, we explicitly examine the conditions for current balance on the B ring and show which regions are most likely to charge to positive potentials and those that may remain negative as a function of ring opening angle relative to the sun. Finally, we demonstrate that the current body of observations of Saturn ring spokes is consistent with their formation only on negatively-charged surfaces, and suggest future times and locations to look for spoke activity based upon the model.

International audience; During 2004 the Cassini/RPWS (Radio and Plasma Wave Science) instrument recorded about 5400 SEDs (Saturn Electrostatic Discharges), which were organized in 4 storm systems and 95 episodes. A computer algorithm with different intensity thresholds was applied to extract the SEDs from the RPWS data, and a statistical analysis on the main characteristics of these SEDs is performed. Compared to the SEDs recorded by the Voyagers in the early 1980s, some characteristics like SED rate, intensity, signal duration, or power spectrum are similar, but there are also remarkable differences with regard to time occurrence and frequency range: The first appearance of SEDs (storm 0) was recorded by RPWS from a distance of more than 300 Saturn radii at the end of May 2004, followed by storm A in mid-July, storm B at the beginning of August, and the most prominent storm C throughout most of September. There were also significant intervals of time with no detectable SED activity, e.g., SEDs were practically absent from October 2004 until June 2005. No clear indication for SEDs below a frequency of 1.3 MHz could be found. We suggest that the SED storms A, B, C, and possibly also storm 0 originate from the same storm system residing at a latitude of 35° South, which lasted for several months, waxed and waned in strength, and rotated with the Voyager radio period of Saturn. The SED source might be located in the updrafting water clouds beneath the visible cloud features detected in the Cassini images.

[1] During Cassini's orbit insertion about Saturn, the spacecraft passed within 1.4 Rs of the planet passing from dayside into the nightside region. During this nightside passage, the onboard Radio and Plasma Wave (RPWS) instrument surprisingly detected Saturn kilometric radiation (SKR). Prior to this encounter, it was believed that SKR originated from a high-latitude dayside source, and radio beams from such a source would not be viewable in this nearplanet night-side location. Subsequent analysis presented here reveals that this SKR did indeed originate from the near-midnight region on field lines near L ∼ 10–15. Such a radio source suggests the presence of an active region in the night-side inner magnetosphere; this source possibly being near the outer edge of the icy-moon created plasma torus surrounding the planet. The implication is that some of the SKR is driven by an internal energy source that may also account for recent UV aurora observations.

Observations of Jupiter carried out by the Chandra Advanced CCD Imaging Spectrometer (ACIS-S) instrument over 24-26 February 2003 show that the auroral X-ray spectrum consists of line emission consistent with high-charge states of precipitating ions, and not a continuum as might be expected from bremsstrahlung. The part of the spectrum due to oxygen peaks around 650 eV, which indicates a high fraction of fully stripped oxygen in the precipitating ion flux. A combination of the OVIII emission lines at 653 eV and 774 eV, as well as the OVII emission lines at 561 eV and 666 eV, are evident in the measure auroral spectrum. There is also line emission at lower energies in the spectral region extending from 250 to 350 eV, which could be from sulfur and/or carbon. The Jovian auroral X-ray spectra are significantly different from the X-ray spectra of comets. The charge state distribution of the oxygen ions implied by the measured auroral X-ray spectra strongly suggests that independent of the source of the energetic ions, magnetospheric or solar wind, the ions have undergone additional acceleration. This spectral evidence for ion acceleration is also consistent with the relatively high intensities of the X rays compared with the available phase space density of the (unaccelerated) source populations of solar wind or magnetospheric ions at Jupiter, which are orders of magnitude too small to explain the observed emissions. The Chandra X-ray observations were executed simultaneously with observations at ultraviolet wavelengths by the Hubble Space Telescope and at radio wavelengths by the Ulysses spacecraft. These additional data sets suggest that the source of the X rays is magnetospheric in origin and that the precipitating particles are accelerated by strong field-aligned electric fields, which simultaneously create both the several-MeV energetic ion population and the relativistic electrons observed in situ by Ulysses that are correlated with approx.40 min quasi-periodic radio outbursts.

[1] During Cassini's close approach to Saturn, on 1 July 2004, a set of narrow bandwidth plasma emissions were detected by the Radio and Plasma Wave Science (RPWS) instrument in the inner magnetosphere. These discrete tones were detected between 3 and 70 kHz, with individual tone bandwidths as low as a few hundred Hertz. The tones persisted for long times (∼1 hour) as Cassini flew in planetocentric radial distances of less than 2.5 Rs. During this time at lower radial distances, the spacecraft passed inside the inner edge of a clear and distinct plasma torus; this torus is located between 2.2 and ∼10 Rs. We describe the emissions, and demonstrate that the mode of propagation is the Z-mode. The emissions are found to originate at locations where electron plasma oscillations along the plasma torus edge are relatively intense. We describe a mechanism for fp electrostatic-to-electromagnetic wave conversion to explain the origin of the narrowband Z-mode tones. The tones allow remote-sensing of the plasma torus and indicate that the torus is dynamic, with changes in density in the tens of percent over the course of an hour.

International audience; We present new results from the inner magnetosphere of Saturn obtained by the Radio and Plasma Wave Science (RPWS) investigation onboard Cassini around the period of the Saturn orbit injection (July 1, 2004). Plasma wave electric field emissions, voltage sweeps by the Langmuir probe (LP) and radio sounder data were used to infer the cold plasma (

[1] We demonstrate that energy from energetic electrons upstream of interplanetary (IP) shocks are able to couple directly to the o-mode radio branch via the relativistic cyclotron harmonic resonance interaction, thereby creating the Type II radiation observed from IP shocks. The conditions required for the electron/wave resonance are that the wave frequency, f, lies near the local plasma frequency, fp, and near (but not exactly at) the cyclotron harmonics, mfc, where m is the cyclotron harmonic number. We compare the details of this relativistic electron cyclotron harmonic theory with observations in a Type II source region, with good agreement in many areas including the prediction of “Zeeman” splitting of the Type II emission. Based on the character of the high-resolution emission spectrum, we can narrow the Type II source location to the IP shock foot region and place some general conditions on shock topology required for Type II emission.

The Cassini radio and plasma wave investigation is designed to study radio emissions, plasma waves, thermal plasma, and dust in the vicinity of Saturn. Three nearly orthogonal electric field antennas are used to detect electric fields over a frequency range from 1 Hz to 16 MHz, and three orthogonal search coil magnetic antennas are used to detect magnetic fields over a frequency range from 1 Hz to 12 kHz. A Langmuir probe is used to measure the electron density and temperature. Signals from the electric and magnetic antennas are processed by five receiver systems: a high frequency receiver that covers the frequency range from 3.5 kHz to 16 MHz, a medium frequency receiver that covers the frequency range from 24 Hz to 12 kHz, a low frequency receiver that covers the frequency range from 1 Hz to 26 Hz, a five-channel waveform receiver that covers the frequency range from 1 Hz to 2.5 kHz in two bands, 1 Hz to 26 Hz and 3 Hz to 2.5 kHz, and a wideband receiver that has two frequency bands, 60 Hz to 10.5 kHz and 800 Hz to 75 kHz. In addition, a sounder transmitter can be used to stimulate plasma resonances over a frequency range from 3.6 kHz to 115.2 kHz. Fluxes of micron-sized dust particles can be counted and approximate masses of the dust particles can be determined using the same techniques as Voyager. Compared to Voyagers 1 and 2, which are the only spacecraft that have made radio and plasma wave measurements in the vicinity of Saturn, the Cassini radio and plasma wave instrument has several new capabilities. These include (1) greatly improved sensitivity and dynamic range, (2) the ability to perform direction-finding measurements of remotely generated radio emissions and wave normal measurements of plasma waves, (3) both active and passive measurements of plasma resonances in order to give precise measurements of the local electron density, and (4) Langmuir probe measurements of the local electron density and temperature. With these new capabilities, it will be possible to perform a broad range of studies of radio emissions, wave-particle interactions, thermal plasmas and dust in the vicinity of Saturn.

International audience; The Low Frequency Array (LOFAR) will come on line with unprecedented radio sensitivity and resolution between 10 and 240 MHz. Such a system will provide a factor of 10-30 improvement in sensitivity in the pursuit of the weak radio emission from extrasolar planets. To date, previous examinations of extrasolar planetary systems with the most advanced radio telescopes have yielded a negative result. However, the improvement in sensitivity by LOFAR over current systems will increase the likelihood of extrasolar planet detection in the radio. We apply radiometric models derived previously from the study of planets in our solar system to the known extrasolar planets, and demonstrate that approximately 3-5 of them should emit in the proper frequency range and with enough power to possibly become detectable at Earth with LOFAR.

[1] The gravity-assist flyby by Cassini of Jupiter on 30 December 2000 and the extended Galileo orbital mission provided a unique opportunity to obtain simultaneous measurements with two spacecraft of many Jovian plasma wave and radio emissions. One of these emissions is Jovian type III radio emissions, also known as Jovian quasi-periodic (QP) emissions. The simultaneous observations of the QP emissions show very similar characteristics, even when the two spacecraft are separated by large distances and located at very different local times (LT). These similarities suggest that this emission is beamed in a strobe light like manner (over a large angular range) and not like a search light rotating with Jupiter's magnetic field, as many other Jovian radio emissions are. The initial source of the QP bursts is likely located near Jupiter. As the emissions propagate through the magnetosphere, the QP bursts appear as enhancements of the trapped continuum. At the magnetosheath the higher density plasma disperses the lower frequency component of the bursts, producing the characteristic “type III like” spectral shape.

[1] Dust devils are significant meteorological phenomena on Mars: They are ubiquitous, continually gardening the Martian surface, and may be the primary atmospheric dustloading mechanism in nonstorm seasons. Further, dust grains in the swirling dust devils may become electrically charged via triboelectric effects. Electrical effects associated with terrestrial dust devils have been reported previously, but these were isolated measurements (electric fields only) with no corroborating measurements. To study the fluid and electrical forces associated with dust devils, NASA’s Human Exploration and Development of Space (HEDS) enterprise sponsored a set of desert field tests with a suite of mutually compatible and complementary instruments in order to determine the relationship between electric, magnetic, and fluid forces. The project (originally a selected flight project) was entitled ‘‘Martian ATmosphere And Dust in the Optical and Radio’’ (MATADOR). In this work, we present a number of interesting examples of the electromagnetic nature of the dust devil. We also describe potential hazards of the dust devil and how similar devil- and storm-related forces on Mars might affect any human occupation. INDEX TERMS: 6225 Planetology: Solar System Objects: Mars; 3304 Meteorology and Atmospheric Dynamics: Atmospheric electricity; 3379 Meteorology and Atmospheric Dynamics: Turbulence; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); KEYWORDS: triboelectricity, electric fields, dust devils, magnetic fields, atmospheric electricity