Magnetic flux in the magnetotail and polar cap during sawteeth, isolated substorms, and steady magnetospheric convection events

Abstract

Different magnetospheric dynamic processes, such as sawtooth events, isolated substorms, and steady magnetospheric convection (SMC), can occur, depending on the solar wind condition. The purpose of this study is to calculate the magnetic flux in the magnetotail and in the polar cap during these magnetospheric modes and to establish a quantitative relation between the magnetic flux and the solar wind parameters. We use the Imager for Magnetopause‐to‐Aurora Global Exploration Far Ultraviolet Imager and Polar Ultraviolet Imager measurements to derive the magnetic flux in the polar cap and the Geotail measurements to derive the magnetic flux in the magnetotail. The average value of the magnetic flux at the sawtooth onset is ∼1 GWb in the polar cap and magnetotail, and the relative decrease of the magnetic flux from the maximum value at the sawtooth onset to the minimum value after the onset is 24–26.5%. The average magnetic flux in the polar cap at the onset of isolated substorms is 0.68 GWb and decreases by 26.5% after the expansion phase. The magnetic flux in the polar cap during SMC events varies between 0.3 and 0.8 GWb. The magnetic flux at the isolated substorm onset is at the upper limit of the magnetic flux of SMC events for the same merging electric field, and the magnetic flux at the sawtooth onset is always higher than that during isolated substorms and during SMC events. The magnetic flux in the magnetotail and polar cap during sawtooth events and isolated substorms increases gradually before the onset and then decreases rapidly after the onset, which is consistent with the traditional energy loading‐unloading scenario. However, the maximum magnetic flux at the sawtooth or isolated substorm onset is not a constant but increases with the merging electric field and with the corrected Dst index. The results also provide reasonable explanation of the relatively constant period of sawtooth events.