Alfvén Ion Cyclotron Waves in Sheath Regions Driven by Interplanetary Coronal Mass Ejections

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http://hdl.handle.net/10138/305158

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Ala-Lahti , M , Kilpua , E K J , Soucek , J , Pulkkinen , T & Dimmock , A P 2019 , ' Alfvén Ion Cyclotron Waves in Sheath Regions Driven by Interplanetary Coronal Mass Ejections ' , Journal of geophysical research. Space physics , vol. 124 , no. 6 , pp. 3893-3909 . https://doi.org/10.1029/2019JA026579

Title: Alfvén Ion Cyclotron Waves in Sheath Regions Driven by Interplanetary Coronal Mass Ejections
Author: Ala-Lahti, Matti; Kilpua, Emilia K. J.; Soucek, Jan; Pulkkinen, Tuija; Dimmock, Andrew P.
Contributor: University of Helsinki, Particle Physics and Astrophysics
University of Helsinki, Space Physics Research Group
Date: 2019-06
Language: eng
Number of pages: 17
Belongs to series: Journal of geophysical research. Space physics
ISSN: 2169-9380
URI: http://hdl.handle.net/10138/305158
Abstract: We report on a statistical analysis of the occurrence and properties of Alfven ion cyclotron (AIC) waves in sheath regions driven by interplanetary coronal mass ejections (ICMEs). We have developed an automated algorithm to identify AIC wave events from magnetic field data and apply it to investigate 91 ICME sheath regions recorded by the Wind spacecraft. Our analysis focuses on waves generated by the ion cyclotron instability. AIC waves are observed to be frequent structures in ICME-driven sheaths, and their occurrence is the highest in the vicinity of the shock. Together with previous studies, our results imply that the shock compression has a crucial role in generating wave activity in ICME sheaths. AIC waves tend to have their frequency below the ion cyclotron frequency, and, in general, occur in plasma that is stable with respect to the ion cyclotron instability and has lower ion beta(parallel to) than mirror modes. The results suggest that the ion beta anisotropy beta(perpendicular to)/beta(parallel to) > 1 appearing in ICME sheaths is regulated by both ion cyclotron and mirror instabilities.
Subject: LOW-FREQUENCY WAVES
TEMPERATURE ANISOTROPY
EARTHS MAGNETOSHEATH
MIRROR INSTABILITY
MAGNETIC CLOUDS
FLUX-ROPE
ORIGIN
SHOCKS
CMES
FLUCTUATIONS
115 Astronomy, Space science
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