Bidirectional electron conic observations for photoelectrons in the Martian ionosphere

作者：YuTian Cao,Jun Cui,BinBin Ni,XiaoShu Wu,Qiong Luo,ZhaoGuo He

摘要：Electron pitch angle distributions similar to bidirectional electron conics(BECs)have been reported at Mars in previous studies based on analyses of Mars Global Surveyor measurements.BEC distribution,also termed“butterfly”distribution,presents a local minimum flux at 90°and a maximum flux before reaching the local loss cone.Previous studies have focused on 115 eV electrons that were produced mainly via solar wind electron impact ionization.Here using Solar Wind Electron Analyzer measurements made onboard the Mars Atmosphere and Volatile Evolution spacecraft,we identify 513 BEC events for 19-55 eV photoelectrons that were generated via photoionization only.Therefore,we are investigating electrons observed in regions well away from their source regions,to be distinguished from 115 eV electrons observed and produced in the same regions.We investigate the spatial distribution of the 19-55 eV BECs,revealing that they are more likely observed on the nightside as well as near strong crustal magnetic anomalies.We propose that the 19-55 eV photoelectron BECs are formed due to day-to-night transport and the magnetic mirror effect of photoelectrons moving along cross-terminator closed magnetic field lines.

发文机构：Key Laboratory of Lunar and Deep Space Exploration School of Astronomy and Space Sciences School of Atmospheric Sciences Center for Excellence in Comparative Planetology Department of Space Physics

关键词：MartianionospherePHOTOELECTRONpitchangledistribution

分类号： O18[理学—基础数学]