Occurrence frequency and location of magnetic islands at the dayside magnetopause

Abstract

Simulations of magnetic reconnection often predict the formation of magnetic islands forming and propagating out through the reconnection exhaust region. However, to date, only a few observations of magnetic islands at the Earth's magnetopause have been identified and analyzed. Crossings near reconnection sites at the dayside magnetopause by Cluster from 2001 to 2009 are examined in a systematic effort to determine the frequency and location of magnetic islands. Using the maximum magnetic shear model as a guide for the distance to the reconnection site, 47 magnetopause crossings within 3 RE of the predicted reconnection site are examined. The occurrence of island structures in the reconnection exhaust is investigated in the context of how the type of reconnection, antiparallel or component, affects the frequency of formation of the islands. For Cluster magnetopause crossings confirmed to be near reconnection sites, island signatures, primarily bidirectional streaming electrons in the magnetosheath boundary layer, are seen for approximately 85% of the crossings and are common features for both antiparallel and component reconnection.

The Transition Between Antiparallel and Component Magnetic Reconnection at Earth's Dayside Magnetopause

“…In a recent study by Trattner, Burch, et al (), predictions of the dayside magnetopause reconnection locations by the Maximum Magnetic Shear model were tested against an MMS database of confirmed encounters with the reconnection location during Phase 1a. The model showed an accuracy of 80% to predict the dayside reconnection region within the 2 R E model uncertainty, in agreement with earlier smaller studies (e.g., Fuselier et al, , Dunlop et al, ; Petrinec et al, ; Trattner et al, 2012; Vines et al, ). The study also revealed two major anomalies in the ability to predict the dayside reconnection location, (1) for events observed around the equinoxes (no dipole tilt) and (2) for events around December (maximum dipole tilt).…”

“…The model also predicts that during IMF clock angles (arctan ( B Y / B Z ), where 0° is defined as pointing due north) within ±25° of a southward magnetic field or events occurring during a mainly radial magnetic field (IMF| B X |/ B > 0.7) the reconnection process reverts to an antiparallel reconnection scenario with no component reconnection tilted X‐line present. Several magnetopause reconnection studies and MHD simulations have successfully used and confirmed the model predictions (e.g., Dunlop et al, ; Fuselier et al, ; Komar et al, ; Petrinec et al, ; Trattner et al, 2012, Trattner, Thresher, et al, , Trattner, Burch, et al, ; Vines et al, ).…”

The MMS Dayside Magnetic Reconnection Locations During Phase 1 and Their Relation to the Predictions of the Maximum Magnetic Shear Model

“…This model suggests that magnetopause reconnection occurs where the magnetic shear angle between the magnetospheric and draped magnetosheath magnetic fields is a maximum. It has been used in many studies involving observations from various satellites (Polar, Cluster, THEMIS, IBEX, Cassini) (Dunlop et al, ; Fuselier et al, , ; Petrinec et al, ; Trattner et al, , ; Vines et al, ) and magnetohydrodynamic (MHD) simulations (Komar et al, ) and was successfully validated. The maximum magnetic shear model was also used during the MMS design effort to optimize and predict the number of reconnection location encounters for the dayside phases 1a and 1b (Fuselier et al, ).…”

The 18 November 2015 Magnetopause Crossing: The GEM Dayside Kinetic Challenge Event Observed by MMS/HPCA

“…All magnetopause boundary layer encounters are characterized by the presence of mixed plasma distributions from the magnetosphere and the magnetosheath, where the ambient magnetic field rotates from the northward geomagnetic field to the (in this case) southward oriented IMF. An additional identifier of the LLBL during intervals of southward IMF is the presence of counter‐streaming, heated electrons as compared to uni‐directionally streaming electrons seen in the MSBL (e.g., Fuselier et al, 2011; Vines et al, 2017). The magnetopause boundary layers for the GEM kinetic challenge event show the presence of southward accelerated ion jets, indicating an active X‐line north of the MMS satellites.…”

“…For all MMS boundary layer encounters including the single magnetopause crossing event, there are no instances when the ion jet in the magnetopause boundary layer switches direction. Such ion jet switches are indicative of an X‐line passing by the satellite location and are a well‐known signature to identify the magnetopause reconnection location at the instant of the direction switch (e.g., Cowley, 1982; Dunlop et al, 2011; Gosling et al, 1982; Paschmann et al, 1979; Pu et al, 2007; Vines et al, 2017).…”