Plasmaspheric hiss properties: Observations from Polar

Abstract

In the region between L = 2 to 7 at all Magnetic Local Time (MLTs) plasmaspheric hiss was detected 32% of the time. In the limited region of L = 3 to 6 and 15 to 21 MLT (dusk sector), the wave percentage detection was the highest (51%). The latter plasmaspheric hiss is most likely due to energetic~10-100 keV electrons drifting into the dusk plasmaspheric bulge region. On average, plasmaspheric hiss intensities are an order of magnitude larger on the dayside than on the nightside. Plasmaspheric hiss intensities are considerably more intense and coherent during high-solar wind ram pressure intervals. A hypothesis for this is generation of dayside chorus by adiabatic compression of preexisting 10-100 keV outer magnetospheric electrons in minimum B pockets plus chorus propagation into the plasmasphere. In large solar wind pressure events, it is hypothesized that plasmaspheric hiss can also be generated inside the plasmasphere. These new generation mechanism possibilities are in addition to the well-established mechanism of plasmaspheric hiss generation during substorms and storms. Plasmaspheric hiss under ordinary conditions is of low coherency, with small pockets of several cycles of coherent waves. During high-solar wind ram pressure intervals (positive SYM-H intervals), plasmaspheric hiss and large L hiss can have higher intensities and be coherent. Plasmaspheric hiss in these cases is typically found to be propagating obliquely to the ambient magnetic field with θ kB0~3 0°to 40°. Hiss detected at large L has large amplitudes (~0.2 nT) and propagates obliquely to the ambient magnetic field (θ kB0~7 0°) with 2:1 ellipticity ratios. A series of schematics for plasmaspheric hiss generation is presented.

Global-scale coherence modulation of radiation-belt electron loss from plasmaspheric hiss

“…Many models assume featureless, broadband hiss, which does not accurately describe pitchangle scattering of electrons due to coherent, dispersive hiss waves. Coherent hiss waveforms are most prevalent during times when the plasmasphere is driven by solar wind or magnetosheath ULF pressure fluctuations 19 , similar to what produces the large-scale coherence for the 6 January conjunction.…”

The distribution of plasmaspheric hiss wave power with respect to plasmapause location

“…Therefore, it is reasonable to expect the location of the plasmapause and density structure of the plasmasphere to strongly influence hiss wave power spatial distribution, and authors have recognized this for many years [e.g., Thorne et al, 1973]. Instead, they sorted hiss wave power using a combination magnetic local time (MLT), magnetic latitude (MLAT), geomagnetic activity (Kp, Dst, AE, or AE*), and L parameter (MacIlwain L, dipole L, or L*) [e.g., Meredith et al, 2004Meredith et al, , 2007Glauert et al, 2014;Orlova et al, 2014;Tsurutani et al, 2015]. Instead, they sorted hiss wave power using a combination magnetic local time (MLT), magnetic latitude (MLAT), geomagnetic activity (Kp, Dst, AE, or AE*), and L parameter (MacIlwain L, dipole L, or L*) [e.g., Meredith et al, 2004Meredith et al, , 2007Glauert et al, 2014;Orlova et al, 2014;Tsurutani et al, 2015].…”

“…For reviews of hiss observations, see Hayakawa and Sazhin [1992], Bortnik et al [2009], and the introduction to Tsurutani et al [2015]. These waves are characteristically broadband, spanning several kHz.…”

Magnetospheric Chorus, Exohiss, and Magnetosonic Emissions Simultaneously Modulated by Fundamental Toroidal Standing Alfvén Waves Following Solar Wind Dynamic Pressure Fluctuations

“…The background magnetic field strength and the cold electron density determine the wave dispersion relation, and the resonant particles contribute to growth or decay of the whistler-mode emissions. Li et al, 2015;Tsurutani et al, 2015), leak from the dayside high-latitude plasmapause, and finally become the exohiss emissions (Gao et al, 2018;Zhu et al, 2015). A plausible scenario is that the chorus emissions at larger radial distances propagate into the plasmasphere, evolve into the plasmaspheric hiss emissions (Bortnik et al, 2008;Falkowski et al, 2017;W.…”