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The dawn‐dusk length of the X line in the near‐Earth magnetotail: Geotail survey in 1994–2014
Author(s) -
Nagai Tsugunobu,
Shinohara Iku,
Zenitani Seiji
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021606
Subject(s) - dusk , magnetic reconnection , physics , substorm , line (geometry) , plasma sheet , geophysics , astrophysics , ionosphere , magnetic field , earth's magnetic field , magnetosphere , astronomy , geometry , mathematics , quantum mechanics
The dawn‐dusk length of the X line is investigated for magnetic reconnection in association with substorms in the near‐Earth magnetotail on the basis of the 21 year Geotail plasma sheet observations. The X line is identified as a simultaneous plasma flow V x and magnetic field B z reversal inside the ion‐electron decoupling region of magnetic reconnection. Forty‐four X lines can be found at X GSM = −20 to −31 R E in the magnetotail. The X line length is estimated on the basis of occurrence of magnetic reconnection. Characteristics of flows and fields are investigated for magnetic reconnection and tailward flow events to verify the obtained X line length. The dawn‐dusk length of the X line is most likely 6 R E with its center in the premidnight sector for moderate substorms. Hence, the magnetic reconnection site is mapped to approximately 1 h local time sector in the auroral ionosphere. The dawn‐dusk length of the X line is extended mainly dawnward for larger substorms.