The formation of a transient current system near the inner edge of the magnetospheric tail current

The structure of the magnetic field near the inner edge of the magnetospheric tail during the preliminary phase of the magnetic storm on Feb. 14, 2009 was studied based on the data of THEMIS satellites. The magnetic field of the currents that were flowing in the magnetospheric tail was obtained by subtracting the effect of the geomagnetic dipole and the magnetic field of magnetospheric currents other than the tail currents (mainly magnetopause currents) from the magnetic field measured on board the satellites. The parabo loid model of the magnetosphere (A2000) was used for calculating the magnetic field of magnetospheric currents. The comparison of calculations and measurements at five satellites in geomagnetically quiet periods allows one to obtain typical radial profiles of magneticfield components along the magnetospheric tail. It was demonstrated that the nonstandard structure of the magnetic field near the inner edge of the tailcurrent sheet before the onset of the magnetic storm on February 14, 2009 is connected with the formation of the transient current system in the magnetosphere. A circular current in the equatorial plane was formed before the onset of the storm in the course of adiabatic compression of the magnetosphere by the solar wind to maintain the magnetic flux through the tail lobes. The spatial position and intensity of the current were determined.