Prompt Disappearance and Emergence of Radiation Belt Magnetosonic Waves Induced by Solar Wind Dynamic Pressure Variations

Abstract

Magnetosonic waves are highly oblique whistler mode emissions transferring energy from the ring current protons to the radiation belt electrons in the inner magnetosphere. Here we present the first report of prompt disappearance and emergence of magnetosonic waves induced by the solar wind dynamic pressure variations. The solar wind dynamic pressure reduction caused the magnetosphere expansion, adiabatically decelerated the ring current protons for the Bernstein mode instability, and produced the prompt disappearance of magnetosonic waves. On the contrary, because of the adiabatic acceleration of the ring current protons by the solar wind dynamic pressure enhancement, magnetosonic waves emerged suddenly. In the absence of impulsive injections of hot protons, magnetosonic waves were observable even only during the time period with the enhanced solar wind dynamic pressure. Our results demonstrate that the solar wind dynamic pressure is an essential parameter for modeling of magnetosonic waves and their effect on the radiation belt electrons.

Quenching of Equatorial Magnetosonic Waves by Substorm Proton Injections

“…Note that there was no clear plasmapause structure with a sharp density gradient and the observed densities ( Figure S1 in the supporting information) were always beyond the typical values in the plasmatrough (Carpenter & Anderson, 1992;Sheeley et al, 2001). At 21:44 UT (Figures 1d, 2a, 2c, 2e, and S2), the sudden decrease in the solar wind dynamic pressure caused the expansion of the magnetosphere, the adiabatic deceleration of hot protons, and then the slightly weakening of magnetosonic waves (Liu et al, 2018b). The follow-up magnetosonic waves closely tracking f lhr were most likely destabilized by the hot proton rings around 10 keV.…”

“…With the measurements mentioned above, we analyze the wave instability using our previously developed code (Liu et al, 2018b;Su et al, 2018) in the framework of the quasi-linear theory (Chen et al, 2010;Kennel, 1966). The wave convective growth rate is written as…”

“…For the former, the enhanced hot proton pressure distorted the background magnetic field configuration and the cold plasma density distribution. For the latter (Liu et al, 2018b), the relaxed dayside geomagnetic field caused the adiabatic deceleration of hot protons and then suppressed the local proton instability. The wave quenching region could be interpreted as a zone where waves lacked sufficient gain or even became damped.…”

“…The arrows inFigures 2a, 2c, and 2e denote the solar wind dynamic pressure reduction causing the magnetosoinc weakening and the hiss disappearance(Liu et al, , 2018b. The vertical dashed lines mark the injection fronts detected by the Van Allen Probes.…”

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

“…The spacecraft potential measurement by the EFW instrument allows an alternative estimation of the cold electron density. 2017; Liu et al, 2018b;Su, Zhu, Xiao, Zong, et al, 2015;Rae et al, 2012). We use the TS04 package (Tsyganenko & Sitnov, 2005) to model the ratio of the local magnetic field to the equatorial field.…”