Alfvénic Poynting Flux Characterized by a Substorm‐SMC Cycle and Ionospheric Influence

Abstract

Geomagnetic substorms are fundamental processes of explosive geospace energy release within the Earth's magnetotail, which are usually divided into three phases: the growth phase, the expansion phase, and the recovery phase. Large‐scale electromagnetic energy transport during a geomagnetic substorm is in the form of Alfvén waves, transmitting energy from the distant magnetotail to the low‐altitude ionosphere‐thermosphere system. This explosive Alfvénic energy release process plays an important role in space weather events. However, such important process has not been investigated quantitatively in global geospace models for space weather forecasting. In this study, we use coupled global simulations to investigate the dynamic evolution of Alfvénic Poynting flux during an idealized substorm‐steady magnetospheric convection (SMC) cycle. Results show that during the expansion phase, the hemispheric Alfvénic Poynting flux is enhanced by approximately 200%, and the dawn‐dusk asymmetry of the Alfvénic oval is diminished significantly. During the recovery phase and in the SMC state, the spatial distribution of downward low‐altitude Alfvénic Poynting flux exhibits a significant dawn‐dusk asymmetry. The explosive behavior of the simulated Alfvénic power is consistent with the observed enhancement in Alfvénic power and broadband power during substorms, suggesting that the global geospace model is not only capable of reproducing the time scale of the Alfvénic variation but also the magnitude of the power enhancement during substorm‐SMC cycles.