Multi-satellite simultaneous observations of magnetopause and atmospheric losses of radiation belt electrons during an intense solar wind dynamic pressure pulse

Zheng Xiang,Shenyi Zhang,Zhengyang Zou,Xianguo Zhang,Zhengyu Zhao,Harlan Spence,Geoffrey Reeves,Pingbing Zuo,Xudong Gu,Binbin Ni,Chen Zhou,Xinlin Li,Xiaoxin Zhang

doi:10.5194/angeo-34-493-2016

Abstract

Abstract. Radiation belt electron flux dropouts are a kind of drastic variation in the Earth's magnetosphere, understanding of which is of both scientific and societal importance. Using electron flux data from a group of 14 satellites, we report multi-satellite simultaneous observations of magnetopause and atmospheric losses of radiation belt electrons during an event of intense solar wind dynamic pressure pulse. When the pulse occurred, magnetopause and atmospheric loss could take effect concurrently contributing to the electron flux dropout. Losses through the magnetopause were observed to be efficient and significant at L ≳ 5, owing to the magnetopause intrusion into L ∼ 6 and outward radial diffusion associated with sharp negative gradient in electron phase space density. Losses to the atmosphere were directly identified from the precipitating electron flux observations, for which pitch angle scattering by plasma waves could be mainly responsible. While the convection and substorm injections strongly enhanced the energetic electron fluxes up to hundreds of keV, they could delay other than avoid the occurrence of electron flux dropout at these energies. It is demonstrated that the pulse-time radiation belt electron flux dropout depends strongly on the specific interplanetary and magnetospheric conditions and that losses through the magnetopause and to the atmosphere and enhancements of substorm injection play an essential role in combination, which should be incorporated as a whole into future simulations for comprehending the nature of radiation belt electron flux dropouts.

Highlights

A subsequent study of Ni et al (2013a) used the measurements from six satellites and the Kalman filtering technique to investigate the radiation belt responses to solar wind dynamic pressure variations in 2002. They found that 68 % of identified solar wind dynamic pressure pulses correspond to electron phase space density dropout events and that 81 % of identified dropout events are associated with solar wind dynamic pressure sudden jumps or a modest increase, which suggests that losses to the magnetopause alone cannot fully explain radiation belt electron dropouts under evolving solar wind conditions
While a number of mechanisms are able to result in the atmospheric loss of magnetospheric electrons via transport of previously trapped electrons into the bounce or drift loss cones, we think that pitch angle scattering by plasma waves can be a viable candidate to be mainly responsible for the observed precipitating electron losses for the dynamic pressure pulse event
The present study is dedicated to a detailed investigation of the behaviors of the radiation belt electron flux dropout in response to two intense solar wind dynamic pressure enhancements on 2 October 2013

Summary

Introduction

The Earth’s electron radiation belts consist of two zones: the inner belt (1.2 < L < 2) remains stable with a long-term slow change with respect to the phases of a solar cycle, and the outer belt (3 < L < 7) is characteristically featured by highly dynamic variations on timescales ranging from minutes to years (e.g., Friedel et al, 2002; Reeves et al, 2003; Baker et al, 2014). The focus of the present study is to investigate the magnetopause and atmospheric losses of radiation belt electrons observed by multiple satellites during a radiation belt dropout event corresponding to a solar wind dynamic pressure pulse on 2 October 2013. The dual-spacecraft Van Allen Probes mission, launched in August 2012 and flying in nearly the same highly elliptical (1.1 × 5.8RE), low inclination orbits (Mauk et al, 2012), has provided a new window for looking into the dynamic variations of radiation belt electrons from ∼ 10 s of keV to 10 s of MeV Both particle and wave measurements from the twin Van Allen Probes are utilized. FengYun 3B and 3C were launched in November 2011 and September 2013, respectively, into the solar synchronization orbit at an altitude of about 800 km with an inclination of 98◦ Both satellites contain the detector to provide the electron fluxes for five energy channels between 0.15 and 5.7 MeV.

Identification of a flux dropout event

Observations of losses through the magnetopause

Observations of losses to the atmosphere

Findings

Conclusions