LASP Magnetosphere Seminars

Abstract

One of the key questions for understanding the drivers of space weather is what is the magnetospheric activity mode following from the (changes in the) solar wind driving. This presentation addresses substorms, storms, and sawtooth events with the aim to assess whether they form independent peaks in the distribution driven by distinct magnetospheric processes.

We address the driver and its triggers by superposed epoch analyses of substorms and sawtooth events. Using three epoch times at substorm onset, peak and end (as measured by the auroral electrojet index SML) reveals that both substorm onset and peak times show distinct changes in the solar wind driver. In the magnetotail, the substorm peak time is associated with a maximum in the dipolarizing field in the inner transition region (10-15 Re). Further, we compare the substorm and sawtooth results to assess the three proposed scenarios for sawtooth formation, and their similarities and differences from substorms.

Global MHD simulations of magnetic storms can successfully reproduce the geomagnetic indices and magnetospheric storm-time variations. Statistical simulation results re-enforce the association of the SYM-H with both ring and tail currents, and quantify the role of the ionospheric conductance on the solar wind – magnetosphere coupling as measured by the AL and cross-polar cap potential. In an event study, we trace the energy flow through the magnetopause as well as within the magnetosphere. We demonstrate that the internal energy circulation between the nightside and dayside is at times as large as the exchange across the magnetopause. We discuss the possibility that the relative roles of the internal and external energy circulation may contribute to the magnetospheric evolution and hence the activity mode.