Whistler mode waves upstream of Saturn

Ali H Sulaiman; Donald A Gurnett; Jasper S Halekas; Japheth N Yates; William S Kurth; Michele K Dougherty

doi:10.1002/2016JA023501

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Whistler mode waves upstream of Saturn

Ali H Sulaiman, Donald A Gurnett, Jasper S Halekas, Japheth N Yates, William S Kurth and Michele K Dougherty

Journal of geophysical research. Space physics, Vol.122(1), pp.227-234

03/10/2017

DOI: 10.1002/2016JA023501

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Abstract

Journal of Geophysical Research: Space Physics, Volume 122, Issue 1, January 2017, Pages 227-234 Whistler-mode waves are generated within and can propagate upstream of collisionless shocks. They are known to play a role in electron thermodynamics/acceleration and, under certain conditions, are markedly observed as wave trains preceding the shock ramp. In this paper, we take advantage of Cassini's presence at ~10 AU to explore the importance of whistler-mode waves in a parameter regime typically characterized by higher Mach number (median of ~14) shocks, as well as a significantly different IMF structure, compared to near Earth. We identify electromagnetic precursors preceding a small subset of bow shock crossings with properties which are consistent with whistler-mode waves. We find these monochromatic, low-frequency, circularly-polarized waves to have a typical frequency range of 0.2 - 0.4 Hz in the spacecraft frame. This is due to the lower ion and electron cyclotron frequencies near Saturn, between which whistler waves can develop. The waves are also observed as predominantly right-handed in the spacecraft frame, the opposite sense to what is typically observed near Earth. This is attributed to the weaker Doppler shift, owing to the large angle between the solar wind velocity and magnetic field vectors at 10 AU. Our results on the low occurrence of whistler waves upstream of Saturn also underpins the predominantly supercritical bow shock of Saturn.

Physics - Space Physics

Details

Title: Subtitle: Whistler mode waves upstream of Saturn
Creators: Ali H Sulaiman - University of Iowa
Donald A Gurnett - University of Iowa
Jasper S Halekas - University of Iowa
Japheth N Yates - Imperial College London
William S Kurth - University of Iowa
Michele K Dougherty - Imperial College London
Resource Type: Journal article
Publication Details: Journal of geophysical research. Space physics, Vol.122(1), pp.227-234
DOI: 10.1002/2016JA023501
ISSN: 2169-9380
eISSN: 2169-9402
Grant note: DOI: 10.13039/100000104, name: National Aeronautics and Space Administration, award: 1415150
Language: English
Date published: 03/10/2017
Academic Unit: Physics and Astronomy
Record Identifier: 9984199742702771

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