Tail configuration during storms Original Research Article

The configuration of the Earthʹs magnetotail is controlled by the amount of energy obtained from the solar wind and the amount of energy that exits from the tail into interplanetary space or into the dissipative ionosphere. During storm time the tail structure can significantly deviate from its average pattern because of the extreme condition of the solar wind and the interplanetary magnetic field. We study the changes in the tail structure such as orientation, size, and shape of the tail during storms by reviewing Geotail observations in the distant tail. Geotail encountered the magnetosheath during all storms including those when the satellite was located near the nominal tail axis. Changes in the average orientation of the tail were consistent with that expected from the solar wind fluctuations causing geomagnetic storms, e.g., fluctuations related to a corotating interaction region. In addition to enhanced magnetic pressure due to solar wind compression, enhanced flux in the distant tail was detected during the main phase. By averaging thirteen weak-to-moderate storm cases it is found that ∼ 5 × 1015 J is stored also in the distant tail during the storm main phase. There are evidences from Geotail and previous ISEE 3 observations that the flaring ceased earthward of X ∼ −100RE during the main phase, whereas the location of the distant neutral line, where the flaring terminates, could be located tailward of X ∼ −200RE region during the recovery phase of a storm.