Toward adapted time-dependent magnetospheric models: A simple approach based on tuning the standard model

Abstract

[1] We suggest and test a simple procedure to adapt a magnetic field model by fitting it to observations made simultaneously by several spacecraft. This is done by varying input parameters of a standard model (T96) to find the best fit to the observed field at each time step. As a result we obtain a time-dependent model, which, can be used for evaluating the quality of the standard model and of the mapping at any particular time, to navigate in the magnetosphere and reproduce its variable configuration during large-scale dynamical events. This procedure was tested using observations made by five Time History of Events and Macroscale Interactions during Substorms (THEMIS) and other complementary (e.g., GOES) spacecraft during the tail season of THEMIS mission (January-March 2008), for which a simplest version of the adapted model was routinely calculated and has been made publicly available. We also use the proton isotropic boundaries observed by low-altitude NOAA spacecraft for independent evaluation of the obtained field models. We found that in quiet conditions deviations of ionospheric footprints between standard and adapted models are generally small (within 1° of latitude), whereas during substorms they may be as large as several, degrees, because of stretching and depolarizations of magnetospheric configuration. We found that the variable tilt of the tail current sheet, partly caused by variations of nonradial component of the solar wind flow, is an additional important factor influencing the modeling result and the mapping quality. By analyzing the adapted models constructed at the time of auroral breakup onset, we conclude that this simple approach, is not yet sufficiently accurate to evaluate the source distance in the magnetotail. Copyright 2009 by the American Geophysical Union.