The role of compressional Pc5 pulsations in modulating precipitation of energetic electrons

Abstract

Pc5 (1.67-6.67 mHz) magnetic pulsations and the modulation of energetic electron precipitation are often observed simultaneously in the morning auroral-latitude data. Here we have investigated a conjunction event of Cluster spacecraft and Canadian auroral-latitude ground stations to identify the role of compressional Pc5 pulsations in modulating precipitation of energetic electrons observed by ground-based riometers. On 7 December 2002 as the spacecraft moved between L = 4.0 and 6.5 in the dawn sector (0600-0700 magnetic local time (MLT)), we found a monochromatic Pc5 magnetic pulsation at ∼4.0 mHz simultaneously in space and on the ground. Both Cluster and ground magnetometer data confirmed that the resonant oscillation at 4.0 mHz occurred around L = ∼6.0. Simultaneously, the four Cluster spacecraft identified the compressional Pc5, which was accompanied by similar temporal variations of the fluxes of medium energy (tens to hundreds of keV) electrons and of the intensity of whistler mode chorus waves. While the compressional Pc5 was present in the magnetosphere, the riometers near the spacecraft footprint observed the coincident modulation of electron precipitation at ∼4.0 mHz. Our coordinated observations indicate a convincing relationship between compressional Pc5 magnetic pulsations in the magnetosphere and the modulation of electron precipitation in the ionosphere, mediated by chorus waves modulated in the magnetosphere, as predicted by the theory of Coroniti and Kennell []. Around the resonant shell, however, some additional contributions to the modulation of electron precipitation might also come from the effects of the resonant Pc5 oscillation. Key Points Coordinated space-ground observations of Pc5 Compressional Pc5 in space related to the modulation of electron precipitation Provide a convincing relationship among Pc5, CNA, and whistler mode chorus ©2013. American Geophysical Union. All Rights Reserved.