On the origin of whistler mode radiation in the plasmasphere

Abstract

[1] The origin of whistler mode radiation in the plasmasphere is examined from 3 years of plasma wave observations from the Dynamics Explorer and the Imager for Magnetopauseto-Aurora Global Exploration spacecraft. These data are used to construct plasma wave intensity maps of whistler mode radiation in the plasmasphere. The highest average intensities of the radiation in the wave maps show source locations and/or sites of wave amplification. Each type of wave is classified on the basis of its magnetic latitude and longitude rather than any spectral feature. Equatorial electromagnetic (EM) emissions ($30-330 Hz), plasmaspheric hiss ($330 Hz to 3.3 kHz), chorus ($2-6 kHz), and VLF transmitters ($10-50 kHz) are the main types of waves that are clearly delineated in the plasma wave maps. Observations of the equatorial EM emissions show that the most intense region is on or near the magnetic equator in the afternoon sector and that during times of negative B z (interplanetary magnetic field) the maximum intensity moves from L values of 3 to <2. These observations are consistent with the origin of this emission being particle-wave interactions in or near the magnetic equator. Plasmaspheric hiss shows high intensity at high latitudes and low altitudes (L shells from 2 to 4) and in the magnetic equator with L values from 2 to 3 in the early afternoon sector. The longitudinal distribution of the hiss intensity (excluding the enhancement at the equator) is similar to the distribution of lightning: stronger over continents than over the ocean, stronger in the summer than in the winter, and stronger on the dayside than on the nightside. These observations strongly support lightning as the dominant source for plasmaspheric hiss, which, through particle-wave interactions, maintains the slot region in the radiation belts. The enhancement of hiss at the magnetic equator is consistent with particle-wave interactions. The chorus emissions are most intense on the morningside as previously reported. At frequencies from $10 to $50 kHz, VLF transmitters dominate the spectrum. The maximum intensity of the VLF transmitters is in the late evening or early morning with enhancements all along L shells from 1.8 to 3.

Slot region electron loss timescales due to plasmaspheric hiss and lightning‐generated whistlers

“…Meredith et al [2006b] subsequently analyzed the longitudinal distribution of the wave intensities over the frequency range 0.1 < f < 5.0 kHz using data from the CRRES satellite. They found that the waves at higher frequencies (2.0 < f < 5.0 kHz) are most likely related to lightning-generated whistlers, consistent with the Green et al [2005] results at 3 kHz. However, in sharp contrast to the higher-frequency waves, they found that the waves at lower frequencies (0.1 < f < 2.0 kHz) are independent of lightning activity, are stronger on the dayside, and increase with geomagnetic activity.…”

“…The slot region at $MeV energies is caused by resonant wave particle interactions with plasmaspheric hiss. Since plasmaspheric hiss is produced by wave turbulence in space, the slot region is caused by wave turbulence in space and not lightning (as suggested by Green et al [2005]). …”

“…[6] Green et al [2005] recently analyzed data from DE1 and IMAGE and showed that the distribution of the wave emissions at 3 kHz is similar to the distribution of lightning in geographic longitude, namely that the emissions are stronger over the continents than the ocean. They stated that the correspondence between the enhanced intensities and the continents occurs over the frequency range 0.5 < f < 3.0 kHz and concluded that lightning is the dominant source of plasmaspheric hiss.…”

Analytical approximation of transit time scattering due to magnetosonic waves

“…Fast magnetosonic (MS) waves are a class of right-hand elliptically polarized, electromagnetic emissions that are found in the Earth's inner magnetosphere at L shells that straddle the plasmapause, L ∼2-8 [Gurnett, 1976;Perraut et al, 1982;Laakso et al, 1990] and magnetic local time regions that favor the postnoon or dusk sectors [Green et al, 2005;Pokhotelov et al, 2008]. Typical observations show that MS waves occur as a series of narrow tones, spaced at multiples of the proton gyrofrequency (f ci ), in the range between f ci and the lower hybrid resonance frequency (f LHR ), that are spatially localized near the geomagnetic equator within ∼ 2-3…”

Enhancement of electric and magnetic wave fields at density gradients

“…They are more electromagnetic and propagate presumably at a smaller angle to B 0 . Since this emission seems rather unaffected by the local plasma properties, it may be suspected that the signal originates from a ground transmitter, such as the Omega stations transmitting at 10.2 kHz (Green et al, 2005;Kimura et al, 2001). However, a closer examination reveals that the peak frequency varies between 9.5 and 11.5 kHz, and no amplitude variations corresponding to the ∼ 1-s pulses in the Omega signals can be discerned.…”