Wave‐driven gradual loss of energetic electrons in the slot region

Geophysical Research Letters

Zheng

et al. 2018

121

Whistler‐mode extremely low frequency hiss emissions commonly exist in the plasmasphere and the plasmaspheric plume and contribute to the precipitation loss of the radiation belt electrons. How these hiss waves are generated remains a critical unanswered question. Here we report the large‐amplitude (up to 1.5 nT) hiss waves in the plasmaspheric plumes, nearly an order of magnitude stronger than previous observations. These waves are found to propagate toward higher latitudes, and the corresponding frequency dependence of wave power can be qualitatively (but not quantitatively) explained by the modeled linear instability of hot electrons near the equator. At the high‐frequency end of hiss spectra, the discrete rising tones are shown to emerge, similar to the situation of whistler‐mode chorus in the plasmatrough. These data and modeling suggest that these large‐amplitude hiss waves were generated within the plasmaspheric plume probably through a combination of linear and nonlinear instabilities of hot electrons.

Section: Introductionmentioning

confidence: 99%

Large‐Amplitude Extremely Low Frequency Hiss Waves in Plasmaspheric Plumes

Geophysical Research Letters

Zheng

et al. 2018

121

“…Whistler mode emission plays an important role in the acceleration [e.g., Summers et al, 2002;Horne et al, 2005;Reeves et al, 2013;Thorne et al, 2013a;Su et al, 2014aSu et al, , 2014bYang et al, 2016] and loss [e.g., Lyons and Thorne, 1973;Abel and Thorne, 1998;Albert, 1994;Su et al, 2011aSu et al, , 2016Thorne et al, 2013b;Ni et al, 2014;Baker et al, 2014;Breneman et al, 2015;Zhu et al, 2015;He et al, 2016] of radiation belt electrons through cyclotron resonant interaction [Kennel and Engelmann, 1966;Horne and Thorne, 1998;Summers et al, 1998]. Whistler mode hiss is often observed as a structureless and incoherent band with the frequency ranging from ∼0.1 kHz to several kilohertz [Russell et al, 1969;Thorne et al, 1973;Hayakawa and Sazhin, 1992;Summers et al, 2008].…”

Section: Introductionmentioning

confidence: 99%

Simultaneous disappearances of plasmaspheric hiss, exohiss, and chorus waves triggered by a sudden decrease in solar wind dynamic pressure

Geophysical Research Letters

Gao

et al. 2017

Magnetospheric whistler mode waves are of great importance in the radiation belt electron dynamics. Here on the basis of the analysis of a rare event with the simultaneous disappearances of whistler mode plasmaspheric hiss, exohiss, and chorus triggered by a sudden decrease in the solar wind dynamic pressure, we provide evidences for the following physical scenarios: (1) nonlinear generation of chorus controlled by the geomagnetic field inhomogeneity, (2) origination of plasmaspheric hiss from chorus, and (3) leakage of plasmaspheric hiss into exohiss. Following the reduction of the solar wind dynamic pressure, the dayside geomagnetic field configuration with the enhanced inhomogeneity became unfavorable for the generation of chorus, and the quenching of chorus directly caused the disappearances of plasmaspheric hiss and then exohiss.

“…Plasmaspheric hiss can cause the radiation belt electron losses over a wide energy range from ∼0.1 MeV to several MeV through cyclotron resonant pitch angle scattering (Horne & Thorne, 1998;Summers et al, 1998). This physical process is specifically responsible for the formation of the slot region separating the inner and outer radiation belts during quiet times (e.g., Abel and Thorne, 1998;Albert, 1994;He et al, 2016;Lyons and Thorne, 1973;Meredith et al, 2007;Thorne et al, 2013) and the precipitation loss of outer radiation belt electrons during geomagnetically active times (e.g., Li et al, 2007;Mourenas and Ripoll, 2012;Ni et al, 2014;Shprits et al, 2009;Su et al, 2011Su et al, , 2016Thorne et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Shock‐Induced Disappearance and Subsequent Recovery of Plasmaspheric Hiss: Coordinated Observations of RBSP, THEMIS, and POES Satellites

Gao

et al. 2017

JGR Space Physics

Plasmaspheric hiss is an extremely low frequency whistler‐mode emission contributing significantly to the loss of radiation belt electrons. There are two main competing mechanisms for the generation of plasmaspheric hiss: excitation by local instability in the outer plasmasphere and origination from chorus outside the plasmasphere. Here on the basis of the analysis of an event of shock‐induced disappearance and subsequent recovery of plasmaspheric hiss observed by RBSP, THEMIS, and POES missions, we attempt to identify its dominant generation mechanism. In the preshock plasmasphere, the local electron instability was relatively weak and the hiss waves with bidirectional Poynting fluxes mainly originated from the dayside chorus waves. On arrival of the shock, the removal of preexisting dayside chorus and the insignificant variation of low‐frequency wave instability caused the prompt disappearance of hiss waves. In the next few hours, the local instability in the plasmasphere was greatly enhanced due to the substorm injection of hot electrons. The enhancement of local instability likely played a dominant role in the temporary recovery of hiss with unidirectional Poynting fluxes. These temporarily recovered hiss waves were generated near the equator and then propagated toward higher latitudes. In contrast, both the enhancement of local instability and the recurrence of prenoon chorus contributed to the substantial recovery of hiss with bidirectional Poynting fluxes.