Geoeffectiveness of Interplanetary Alfven waves: Unsteady Magnetopause Reconnection and Directly-Driven Substorms

Using solar-wind-magnetosphere-ionosphere conjunction observations, we investigate the geomagnetic responses to fluctuating IMF Bz from interplanetary Alfven waves. Interplanetary Alfven waves transmit intensified IMF Bz to the magnetosheath, leading to intervals of large magnetic shear angles across the magnetopause and magnetopause reconnection. Such intervals are promptly followed by hundreds of nT increases in AE/AU index within 10-20 min. These observations are confirmed in multiple events in corotating interaction region (CIR)-driven geomagnetic storms. To put the observations into context, we propose a phenomenological model of strongly-driven magnetosphere convection/substorm (Dai et al.,2023). The substorm electrojet is linked to the enhanced magnetopause reconnection in the short timescale of re-establishing the ionosphere electric field and the two-cell convection. The substorm expansion may reslut from magnetosphere convection driven by dayside reconnection (Dai et al.,2024). Implications for the upcoming SMILE mission will be discussed.