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Magnetic Field Orientation Effects on the Standoff Distance of Earth's Bow ShockThree-dimensional, global MHD simulations of solar wind flow onto a prescribed magnetopause obstacle are used to show that a bow shock's nose location a(sub s), and the relative subsolar magnetosheath thickness Delta(sub ms)/a(sub mp) are strong functions of the IMF cone angle theta (between v(sub sw) and B(sub sw)) and the Alfven Mach number M(sub A). For a given M(sub A) the shock is more distant for higher theta (restricted to the interval 0-90deg by symmetries), while a(sub s)/a(sub mp) and Delta(sub ms/a(sub mp) increase with decreasing M(sub A) for theta greater than or approximately 20deg but decrease with decreasing M(sub A) for theta approximately Odeg. Large differences in Delta(sub ms/a(sub mp) are predicted between theta = Odeg and 90deg at low M(sub A), with smaller differences remaining even at M(sub A) approximately 10. The theta = Odeg results confirm and extend the previous work of Spreiter and Rizzi [1974]. The simulations show that successful models for the subsolar shock location cannot subsume the dependences on M(sub A) and theta into a sole dependence on M(ms). Instead, they confirm a recent prediction [Cairns and Grabbe, 1994] that a(sub s)/a(sub mp) and Delta(sub ms)/a(sub mp) should depend strongly on theta and M(sub A) for M(sub A) less than or approximately 10 (as well as on other MHD variables). Detailed comparisons between theory and data remain to be done. However, preliminary comparisons show good agreement, with distant shock locations found for low M(sub A) and large theta greater than or approximately 45deg and closer locations found for theta less than or approximately 20deg even at M/A approximately 8.
Document ID
19990009290
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Cairns, Iver H. (Iowa Univ. Iowa City, IA United States)
Lyon, J. G. (Dartmouth Coll. Hanover, NH United States)
Date Acquired
August 19, 2013
Publication Date
October 15, 1996
Publication Information
Publication: Geophysical Research Letters
Volume: 23
Issue: 21
ISSN: 0094-8534
Subject Category
Geophysics
Report/Patent Number
Paper 96GL02755
Funding Number(s)
CONTRACT_GRANT: NAGw-4540
CONTRACT_GRANT: NAG5-1101
CONTRACT_GRANT: NAGw-2040
Distribution Limits
Public
Copyright
Other