Whistler mode waves upstream of Saturn
File(s)
Author(s)
Type
Journal Article
Abstract
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 interplanetary magnetic field 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, and 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 underpin the predominantly supercritical bow shock of Saturn.
Date Issued
2017-01-13
Date Acceptance
2016-12-29
Citation
Journal of Geophysical Research: Space Physics, 2017, 122 (1), pp.227-234
ISSN
2169-9380
Publisher
American Geophysical Union
Start Page
227
End Page
234
Journal / Book Title
Journal of Geophysical Research: Space Physics
Volume
122
Issue
1
Copyright Statement
©2016. American Geophysical Union. All Rights Reserved. This is the pre-peer reviewed version of the following article, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/2016JA023501/abstract
Sponsor
The Royal Society
Science and Technology Facilities Council
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000395655800019&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Grant Number
RP140004
ST/N002776/1
Subjects
Science & Technology
Physical Sciences
Astronomy & Astrophysics
whistlers
Saturn
collisionless shocks
MAGNETIC-FIELD OBSERVATIONS
QUASI-PERPENDICULAR SHOCKS
BOW SHOCK
COLLISIONLESS SHOCK
Publication Status
Published