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Unusual locations of Earth's bow shock on September 24 - 25, 1987: Mach number effectsInternational Sun Earth Explorer 1 (ISEE 1) and Interplanetary Monitoring Platform 8 (IMP 8) data are used to identify 19 crossings of Earth's bow shock during a 30-hour period following 0000 UT on September 24, 1987. Apparent standoff distances for the shock are calculated for each crossing using two methods and the spacecraft location; one method assumes the average shock shape, while the other assumes a ram pressure-dependent shock shape. The shock's apparent standoff distance, normally approximately 14 R(sub E), is shown to increase from near 10 R(sub E) initially to near 19 R(sub E) during an 8-hour period, followed by an excursion to near 35 R(sub E) (where two IMP 8 shock crossings occur) and an eventual return to values smaller than 19 R(sub E). The Alfven M(sub A) and fast magnetosonic M(sub ms). Mach numbers remain above 2 and the number density above 4/cu cm for almost the entire period. Ram pressure effects produce the initial near-Earth shock location, whereas expansions and contractions of the bow shock due to low Mach number effects account, qualitatively and semiquantitatively, for the timing and existence of almost all the remaining ISEE crossings and both IMP 8 crossings. Significant quantitative differences exist between the apparent standoff distances for the shock crossings and those predicted using the observed plasma parameters and the standard model based on Spreiter et al.'s (1966) gasdynamic equation. These differences can be explained in terms of either a different dependence of the standoff distance on Mach number at low M(sub A) and M(sub ms), or variations in shock shape with M(sub A) and M(sub ms) (becoming increasingly "puffed up" with decreasing M(sub A) and M(sub ms), as expected theoretically), or by a combination of both effects.
Document ID
19950053469
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Cairns, Iver H.
(Univ. of Iowa, Iowa City, IA United States)
Fairfield, Donald H.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Anderson, Oger R.
(Univ. of Iowa, Iowa City, IA United States)
Carlton, Victoria E. H.
(Center for Space Research, Cambridge, MA United States)
Paularena, Karolen I.
(Center for Space Research, Cambridge, MA United States)
Lazarus, Alan J.
(Center for Space Research, Cambridge, MA United States)
Date Acquired
August 16, 2013
Publication Date
January 1, 1995
Publication Information
Publication: Journal of Geophysical Research
Volume: 100
Issue: A1
ISSN: 0148-0227
Subject Category
Plasma Physics
Accession Number
95A85068
Funding Number(s)
CONTRACT_GRANT: NAG5-584
CONTRACT_GRANT: NAG5-1093
CONTRACT_GRANT: NAGW-2040
Distribution Limits
Public
Copyright
Other

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