Dayside Magnetopause Reconnection: Its Dependence on Solar Wind and Magnetosheath Conditions

Abstract

Magnetic reconnection permits topological rearrangements of the interplanetary and magnetospheric magnetic fields and the entry of solar wind mass, energy, and momentum into the magnetosphere. Thus, magnetic reconnection is a key issue to understand space weather. However, it has not been fully understood yet under which interplanetary/magnetosheath conditions magnetic reconnection takes place more effectively at the dayside magnetopause. In the present study 25 dayside magnetopause reconnection events are investigated using the "Time History of Events and Macroscale Interactions during Substorms" (THEMIS) satellite observations in order to find its dependence on solar wind and magnetosheath conditions. It is found that the reconnection electric field is proportional to the interplanetary electric field and inversely proportional to the solar wind-Alfvén Mach number and that the reconnection outflow speed is proportional to the solar wind Alfvén speed and inversely proportional to the magnetosheath plasma beta. It is also shown that the range of magnetic shear angles for which magnetic reconnection should occur is restricted to large shears as the magnetosheath flow direction becomes more perpendicular to the direction of the local magnetopause normal vector. Since these results refer to fairly typical solar wind-Alfvén Mach number condition, they may not necessarily apply to more extreme cases.

Modulation of Magnetospheric Substorm Frequency: Dipole Tilt and IMF By Effects

“…(2014), the plasma β is typically larger in the prenoon magnetosheath plasma. These dawn‐dusk asymmetries in the shocked solar wind plasma may affect the conditions for reconnection, which is thought to be more effective in low‐ β regions (Cassak & Shay, 2007; Koga et al., 2019; Paschmann et al., 1986; review by Paschmann et al., 2013). The quasiparallel shock region (dawn) is also more prone than the quasiperpendicular region (dusk) to the development of Kelvin‐Helmholtz‐Instabilities (KHI) (Dimmock et al., 2016; Nosé et al., 1995; Nykyri et al., 2017).…”

“…10.1029/2020JA028856 9 of 17 which is thought to be more effective in low-β regions (Cassak & Shay, 2007;Koga et al, 2019;Paschmann et al, 1986;review by Paschmann et al, 2013). The quasiparallel shock region (dawn) is also more prone than the quasiperpendicular region (dusk) to the development of Kelvin-Helmholtz-Instabilities (KHI) (Dimmock et al, 2016;Nosé et al, 1995;Nykyri et al, 2017).…”

Modulation of magnetospheric substorm frequency: Dipole tilt and IMF By effects

“…As shown by, for example, Walsh et al (2014), the plasma β is typically larger in the prenoon magnetosheath plasma. These dawn-dusk asymmetries in the shocked solar wind plasma may affect the conditions for reconnection, which is thought to be more effective in low-β regions (Cassak & Shay, 2007;Koga et al, 2019;Paschmann et al, 1986;review by Paschmann et al, 2013). The quasiparallel shock region (dawn) is also more prone than the quasiperpendicular region (dusk) to the development of Kelvin-Helmholtz-Instabilities (KHI) (Dimmock et al, 2016;Nosé et al, 1995;Nykyri et al, 2017).…”

Particles and Photons as Drivers for Particle Release from the Surfaces of the Moon and Mercury

“…The underlying reason for this well-known "half-wave rectifier effect" in the response of Earth's magnetosphere to IMF clock angle is attributed to the relatively high plasma beta, the ratio of kinetic to magnetic pressure, in the magnetosheath. Under these conditions the magnetic field just inside the magnetopause is much larger than that in the magnetosheath and the reconnection rate is reduced relative to situations where the magnetic fields on the inside and outside of the magnetopause are similar (Sonnerup 1974;Koga et al 2019). The low Alfvenic Mach numbers in the inner heliosphere reduce plasma beta in Mercury's magnetosheath relative to conditions at Earth (Gershman et al 2013).…”