Interaction of solar wind pressure pulses with the magnetosphere: IMF modulation and cavity mode

Abstract

Energy transfer through the magnetopause involves an interplay of two processes. On one hand, microphysics of reconnection determines how easily the magnetopause can be opened. On the other hand, the global state of the solar wind and magnetosphere determines how much energy is available for transfer and whether there exist "resonant" interactions whereby the transfer is particularly efficient. In the case of solar wind pressure pulses, empirical evidence has suggested that the solar wind-magnetosphere interaction can become unusually intense, leading to large-scale global auroral response and occasionally geomagnetic storms. In this study, for the first time, magnetic reconnection and global magnetospheric oscillation known as the cavity mode are integrated to give a comprehensive description of energy transfer through the dayside magnetopause. Using a heuristic model in which the inflow into the magnetopause is proportional to the magnitude of pressure pulse and an IMF proxy, we derive the fractions of energy converted to reconnection and field-line resonance per unit incident compressional energy in a pressure pulse. It is found that the magnitude of energy transfer is modulated by the IMF proxy, whereas the frequency spectrum of the transfer is modulated by the cavity mode. Under extreme conditions, reconnection can transfer almost 100% of incident compressional energy at the maximum absorption bands. Even under the typical value reconnection rate (∼0.1), approximately 30% of the incident energy can be absorbed in these bands. The frequency response of reconnection transfer has pulse-like peaks in the >3 mHz range and rather insensitive to the solar wind and wave parameters. In contrast, the frequency response of the shear-Alfvénic transfer centers in the 1-4 mHz range and has a more broadband shape that is significantly influenced by the solar wind density. © 2012. American Geophysical Union. All Rights Reserved.