March 31, 2001 geomagnetic storm

Aurora QSOs & the interplanetary magnetic field

by Volker Grassmann, DF5AI, January 16, 2003


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Correlation between the direction of the interplanetary magnetic field and Aurora QSO activity

The magnetic fieldlines from Earth connect directly into the solar wind if the interplanetary magnetic field (IMF) points south ("southward Bz component"). In this case, energy may be injected into the Earth's magnetosphere which may cause widespread Auroras and other type of phenomena, see the storm history section of this web site. The north-south component of the IMF is displayed in the upper panel of fig. 1 based on solar wind measurements of the ACE spacecraft about 1.5 million kilometers from Earth. We may estimate the near-Earth IMF by considering a time delay of about 30 to 40 minutes corresponding to the travel time of the solar wind from the ACE spacecraft to the Earth's magnetosphere. In the lower panel of fig. 1, the meridional distribution of Aurora QSOs is displayed versus Universal Time. Note, that each QSO contributes two dot marks, i.e. a dark and a light green marker indicating the station in the east and in the west of the corresponding propagation path, respectively.

A southward IMF was available when the solar wind shock front impacted the dayside magnetosphere on 0053 UT (corresponding to 0023 UT in the upper panel of fig. 1). Very soon, the IMF however turned sharply to the north and, in consequence, Auroral backscattering did not develop except the activity at -90 degree longitude between 0115 UT and 0145 UT. On the other hand, long periods of Auroral backscattering clearly correlate to a persistent southward IMF, see 04-09 UT and 15-18 UT in the lower panel. Unfortunately, no IMF data is available after 18 UT. The correlation between Aurora data from radio amateurs and the IMF is no surprising result but this project

Figure 1. ACE measurements of the Interplanetary Magnetic Field (Bz component), adopted from [13], and the meridional distribution of Aurora QSOs versus Universal Time. The IMF curve is shifted by about 35 minutes considering the travel time of the solar wind from the ACE position in space to the Earth's magnetosphere.


Copyright (C) of Volker Grassmann. All rights reserved. The material, or parts thereof, may not be reproduced in any form without prior written permission of the author.