Possible Source of the Difference between a Model Prediction and Observations of Bow Shock Crossings

Abstract

The new data set of 1901 bow shock crossings by Geotail and Wind satellites in period 1999-2000 is selected for a wide range of distances and solar wind conditions observed by Wind and ACE upstream monitors. The data set is applied for verification of the semi-empirical bow shock model developed in the last solar minimum (1995-1997), using Geotail Crossings of the bow shock and Wind upstream solar wind data. In general, the model accuracy is reasonably good in the dayside and flank regions of the bow shock. But, the model extrapolation in the tail region has much less accuracy due to restriction of the bow shock crossing distances used in the model development. Some difference between the data of ACE and Wind upstream solar wind monitors leads also to the model discrepancies. Analysis of long time variations of the bow shock parameters during last three solar cycles shows noticeable difference in the heliospheric conditions controlling the bow shock size and shape in the solar minimum and maximum. In the solar maximum, the variations of the interplanetary conditions are much higher than in the solar minimum. This difference produces additional disagreement in prediction of the bow shock crossings in the current solar maximum by the model developed using a data set obtained in the solar minimum.

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