Variations of the magnetic flux content in the inner magnetosphere during an intense storm

During the intense storm in December 2015, triggered by a coronal mass ejection (CME), we benefited from an exceptional configuration of several spacecraft and constellations in the inner magnetosphere from the dayside magnetopause to 13 Earth’s radii in the geomagnetic tail (Magnetospheric MultiScale mission (MMS), THEMIS, Van Allen probes and GOES 15). The simple Tsyganenko model T96 is found to reproduce satisfactory all their magnetic field observations. We used it to compute the pattern of closed drift shells of equatorial energetic particles. Relative to the quiet phase before the storm, this pattern shows a strong compression during the Storm Sudden Commencement (SSC) and the main phase and then a gradual expansion during several recovery days. We have computed the magnetic flux content in the region of closed drift shells between an inner shell at 1.5 Earth’s radii and the last closed drift shell. During the SSC, caused by the arrival of the CME, we have found a global increase, in the range 100-400 MWb, above the value during the quiet phase, with a dominant contribution from the whole diurnal magnetosphere including the inner distances close to Earth. All other phases show a decrease relative to the value during the quiet phase. The minimum is reached during the main phase and first day of the recovery phase, with values in the range -600 to -800 MWb, which could be caused by the effects of cross-tail currents observed to be particularly enhanced at larger distances in the nightside plasma sheet.