Magnetopause Reconnection and Indents Induced by Foreshock Turbulence

Abstract

Magnetopause reconnection plays a critical role in controlling energy input from the solar wind to the magnetosphere. The possibility that magnetic fluctuations generated in the foreshock may lead to magnetopause reconnection has been considered based on observations indicating that magnetosheath fields are not a simple compression of the interplanetary magnetic field (IMF) (Russell et al., 1997;Zhang et al., 1997). On account of the fact that the statistical magnetopause locations for cone angles (between the IMF and the Sun-Earth line) greater and less than 45° do not differ appreciably, the study by Zhang et al. (1997) concludes that the raised possibility is not confirmed. Recent measurements from the Magnetospheric Multiscale mission show Earth-radius-scale foreshock magnetic and density fluctuations approximately one order of magnitude larger than the respective upstream values under quasi-radial IMF (cone angles <30°) conditions (Chen et al., 2021). These intense fluctuations often contain strong B z (in Geocentric Solar magnetic (GSM) coordinates) and B y components. If these fluctuations can reach the magnetopause, they can create conditions conducive to reconnection. In this paper, based on global hybrid simulation results, we predict that foreshock fluctuations in the form of strong B z and density fluctuations can reach the magnetopause and lead to reconnection as well as Earth-sized indents.To single out the effects of foreshock fluctuations, we design our simulation to have a quasi-radial IMF with a weak northward (B z > 0) and zero dawn-dusk (B y = 0) components. When the IMF is quasi-radial, foreshock waves excited due to reflected ions interacting with the incoming solar wind are the strongest, permeate the largest volume of the subsolar region, and can most strongly influence the inner magnetosphere (e.g., Russell et al.,1983; Takahashi et al., 2021, and references therein). In the aspect of reconnection, extensive statistical studies show that magnetopause reconnection occurs for shear angles (angle between the magnetosheath and magnetosphere magnetic fields across the magnetopause) as low as ∼30° but not lower than that (e.g.,

On the Occurrence of Magnetic Reconnection Along the Terrestrial Magnetopause, Using Magnetospheric Multiscale (MMS) Observations in Proximity to the Reconnection Site

“…The first part of this study investigated the occurrence of these magnetopause intervals downstream of either the quasi‐parallel or quasi‐perpendicular bow shock, in comparison to the general distribution of IMF orientations. While there was a statistically significant enhancement in the number of intervals observed downstream of the quasi‐parallel bow shock in comparison to the number downstream of the quasi‐perpendicular bow shock, it has not been determined that this is a result of enhanced reconnection caused by increased magnetosheath fluctuations (as has been suggested by the results of a recent hybrid simulation under nearly radial IMF with a small northward component (Chen et al., 2021)). Rather, the increased magnetosheath fluctuations downstream of the quasi‐parallel bow shock are believed to cause large scale oscillations of the magnetopause surface.…”

Bursty magnetic reconnection at the Earth's magnetopause triggered by high-speed jets

“…In the simulation there are additional effects that may contribute to the transient magne- as demonstrated in 3D hybrid simulations with quasi-radial northward IMF 48 . However, for the events discussed earlier, the high-speed jets are clearly important for triggering the events.…”

Unsteady Magnetopause Reconnection Under Quasi‐Steady Solar Wind Driving

“…Chen et al. ( 2021 ) demonstrated that foreshock turbulence can penetrate through the magnetosheath, grow into structures of enhanced density and magnetic field, and induce reconnection. Such reconnection is localized and bursty in nature.…”

“…Similarly, Pfau-Kempf et al (2020) showed that perturbations arising from kinetic instabilities in the magnetosheath can modulate the reconnection. Chen et al (2021) demonstrated that foreshock turbulence can penetrate through the magnetosheath, grow into structures of enhanced density and magnetic field, and induce reconnection. Such reconnection is localized and bursty in nature.…”