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

摘要

[1] We suggest and test a simple procedure to adapt a magnetic field model by fitting it toobservations made simultaneously by several spacecraft. This is done by varying inputparameters of a standard model (T96) to find the best fit to the observed field at each timestep. As a result we obtain a time-dependent model which can be used for evaluating thequality of the standard model and of the mapping at any particular time, to navigate in themagnetosphere and reproduce its variable configuration during large-scale dynamicalevents. This procedure was tested using observations made by five Time History of Eventsand Macroscale Interactions during Substorms (THEMIS) and other complementary (e.g.,GOES) spacecraft during the tail season of THEMIS mission (January–March 2008), forwhich a simplest version of the adapted model was routinely calculated and has been madepublicly available. We also use the proton isotropic boundaries observed by low-altitudeNOAA spacecraft for independent evaluation of the obtained field models. We found thatin quiet conditions deviations of ionospheric footprints between standard and adaptedmodels are generally small (within 1° of latitude), whereas during substorms they may beas large as several degrees, because of stretching and dipolarizations of magnetosphericconfiguration. We found that the variable tilt of the tail current sheet, partly caused byvariations of nonradial component of the solar wind flow, is an additional important factorinfluencing the modeling result and the mapping quality. By analyzing the adapted modelsconstructed at the time of auroral breakup onset, we conclude that this simple approach isnot yet sufficiently accurate to evaluate the source distance in the magnetotail.