Open AccessAnalyzing the hemispheric asymmetry in the thermospheric density response to geomagnetic storms
Author(s) -
A Ercha,
Ridley Aaron J.,
Zhang Donghe,
Xiao Zuo
Publication year - 2012
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011ja017259
Subject(s) - equinox , solstice , northern hemisphere , southern hemisphere , atmospheric sciences , earth's magnetic field , geomagnetic storm , climatology , storm , thermosphere , geology , environmental science , ionosphere , physics , geodesy , geophysics , latitude , magnetic field , oceanography , quantum mechanics
The thermospheric densities derived by CHAMP/STAR accelerometer within the time period from 01 May 2001 to 31 December 2007 are utilized to investigate the hemispheric asymmetry in response to strong storm driving conditions. The geomagnetic storms of 03–07 April 2004 are first studied since the storms occurred close to the vernal equinox, allowing the seasonal asymmetry to be eliminated to the greatest extent. The averaged density enhancements in the southern polar region were much larger than that in the northern polar region. The comparisons of density versus Dst and Ap index indicate a strong linear dependence with the slopes of the fitted lines in the southern hemisphere being 50% greater than that in the northern hemisphere. This effect can possibly be attributed to the non‐symmetric geomagnetic field. 102 storm events are used to conduct a statistical analysis. For each storm, a linear fit is made between the averaged mass density and the Dst and Ap indices independently in each hemisphere. The seasonal variation of the intercepts and the slopes of the fitted lines are further explored. The baseline is strongly dependent on season, with the hemisphere receiving the larger amount of sunlight having larger density. The slopes showed considerable hemispheric differences around the vernal equinox yet no statistical differences around other seasons. It is speculated that competing mechanisms cancel each other during the solstices, while during the equinoxes, the lower magnetic field in the southern hemisphere may allow stronger ion flows, thereby causing more Joule heating. It is uncertain why the vernal equinox would be favored in this explanation though.