Nonlobe Reconnection at the Earth's Magnetopause for Northward IMF

Abstract

Under northward interplanetary magnetic field conditions, magnetic reconnection at the Earth's magnetopause is usually thought to operate through the merging of magnetosheath magnetic field lines and open magnetic field lines from the magnetospheric lobe. However, reconnection also occurs between magnetosheath field lines and closed magnetic field lines in the magnetosphere. Under certain conditions, this nonlobe field line reconnection has distinct plasma and magnetic field signatures that distinguish it from reconnection of lobe field lines. A survey of these conditions suggests that nonlobe reconnection at the Earth's magnetopause may be common even for relatively strong northward IMF.Plain Language Summary Magnetic reconnection interconnects magnetic field lines across a current sheet like that at the Earth's magnetopause or like that in the solar corona. This paper describes a type of interconnection of magnetic field lines at the magnetopause that was first reported for the solar corona. It appears that this type of reconnection is fairly common at the magnetopause. The different topology of this reconnection suggests a different type of interaction between the magnetic field lines in the solar wind and the field lines of the Earth.Lobe reconnection is not the only magnetic topology possible when the IMF is northward. Cowley (1983) suggested several different magnetic topologies that may result from reconnection when the IMF is northward. Two of these topologies are illustrated in Figure 1. The topology on the left-hand side results from lobe reconnection. The Sun is to the left, and a magnetosheath field line, 1, convecting toward the magnetopause reconnects in the southern hemisphere with a lobe field line, 2, poleward of the cusp. A lobe field line is defined, prior to reconnection, as a field line with one foot in the ionosphere and the other far downtail and essentially not connected to the Earth. After reconnection, the resulting open field line, 1 0 , still has one FUSELIER ET AL. 8275

DMSP Observations of High‐Latitude Dayside Aurora (HiLDA)

“…The main body of the TPA is in both events associated with BPS-like precipitation, suggesting a formation mechanism on closed field lines. This is in agreement with many previous reports that large-scale TPAs appear commonly in the boundary region reconnection, which has been suggested to be a common feature at high latitudes in a recent survey based on Cluster observations (Fuselier et al, 2018). This means that there are two possibilities of reconnection associated with the formation of HiLDA: lobe reconnection or non-lobe reconnection.…”

“…The reconnection poleward of the cusp separates the TPA and the HiLDA into two different regions with the former on closed field lines and latter on open field lines. Moreover, reconnection with closed magnetic field lines poleward of the cusp is sometime called non‐lobe reconnection, which has been suggested to be a common feature at high latitudes in a recent survey based on Cluster observations (Fuselier et al., 2018). This means that there are two possibilities of reconnection associated with the formation of HiLDA: lobe reconnection or non‐lobe reconnection.…”

Magnetopause Reconnection and Indents Induced by Foreshock Turbulence

“…Magnetopause reconnection enabled by foreshock turbulence presents a new possible scenario of dayside reconnection when the IMF clock angle (between the IMF B yz and z GSM ) is ~0, as in the simulated case. The known scenarios are: (1) reconnection of IMF with open cusp field lines (lobe reconnection), and (2) reconnection of IMF with closed field lines that thread through the nightside of the magnetosphere (non-lobe reconnection), as illustrated inFuselier et al [2018]. Foreshock turbulence makes possible for local bursty reconnection to occur near the subsolar magnetopause by creating large shear angles between the magnetosheath and the magnetosphere fields.…”

Electron Dispersion and Parallel Electron Beam Observed Near the Separatrix

“…These phenomena have not been observed previously for electrons, but similar phenomena have been studied for ions. The decrease of the cutoff velocity of the curved D shape ion distribution caused by the E×B drift has been observed in PIC simulation (Broll et al, 2017; ignoring the effect of wave-particle interactions) and cluster observation (Fuselier et al, 2018). Therefore, both of these two dispersions are caused by the E×B drift; however, the time for E×B drift is different.…”