Abstract
Coupling between the solar wind and magnetosphere can be expressed in terms of energy transfer through the separating boundary known as the magnetopause. Geospace simulation is performed using the Space Weather Modeling Framework (SWMF) of a multi-ICME impact event on February 18–20, 2014 in order to study the energy transfer through the magnetopause during storm conditions. The magnetopause boundary is identified using a modified plasma β and fully closed field line criteria to a downstream distance of −20Re. Observations from Geotail, Themis, and Cluster are used as well as the Shue 1998 model to verify the simulation field data results and magnetopause boundary location. Once the boundary is identified, energy transfer is calculated in terms of total energy flux K, Poynting flux S, and hydrodynamic flux H. Surface motion effects are considered and the regional distribution of energy transfer on the magnetopause surface is explored in terms of dayside X>0, flank X<0, and tail cross section X=Xmin regions. It is found that total integrated energy flux over the boundary is nearly balanced between injection and escape, and flank contributions dominate the Poynting flux injection. Poynting flux dominates net energy input, while hydrodynamic flux dominates energy output. Surface fluctuations contribute significantly to net energy transfer and comparison with the Shue model reveals varying levels of cylindrical asymmetry in the magnetopause flank throughout the event. Finally existing energy coupling proxies such as the Akasofu ϵ parameter and Newell coupling function are compared with the energy transfer results.
Highlights
The past decades have greatly advanced our understanding of the dynamics in the space environment
Our results show that most of the energy enters as Poynting flux, while the escape is dominated by the hydrodynamic energy flux (Figure 9)
The main conclusions can be summarized as: 1) We have developed a robust method to assess the energy entry through the magnetopause into the magnetosphere
Summary
The past decades have greatly advanced our understanding of the dynamics in the space environment. The bow shock reduces the kinetic energy density by a factor of about 4 and increases the magnetic energy density by about a factor of 16, so they become comparable It is the orientation of the IMF that controls the magnetic reconnection process, which allows for energy and plasma transfer from one magnetic topology to another (Akasofu, 1981). Nykyri et al (2019) present an interesting case suggesting that a small-scale magnetosheath jet nudging the flank magnetopause can trigger a tail reconnection event leading to a substorm onset. Such sequences demonstrate the power of local disturbances to drive the magnetosphere through a large-scale reconfiguration process (Baker et al, 1999).
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