Stability of the high‐latitude reconnection site for steady northward IMF

Abstract

The stability of the high-latitude reconnection site under steady northward Interplanetary Magnetic Field (IMF) conditions was investigated using observations in the Earth's magnetospheric cusp. Using proton distributions with characteristic low-energy cutoffs, the distance to the high-latitude reconnection site was monitored during four cusp crossings that had relatively steady solar wind dynamic pressure and IMF clock angle. For these four events, the reconnection site location remained approximately fixed, indicating that the high-latitude magnetic reconnection site remains stable for many minutes under steady IMF conditions. A possible explanation for this stability is that the magnetosheath flow remains sub-Alfvenic even at high latitudes because of the presence of a plasma depletion layer.

Probing the boundary between antiparallel and component reconnection during southward interplanetary magnetic field conditions

“…The plane of the two-dimensional cut contains the magnetic field direction (y-axis) and the axis perpendicular to the Sun- Earth line. Three-dimensional flux measurements from the TIMAS instrument within ±45°of this plane are rotated into the plane by preserving total energy and pitch angle to produce the distribution shown in Figure 2a [see also Fuselier et al, 2000].…”

“…This outflow distribution is seen in the energy-time spectrogram in Figure 1 at energies below 300 eV in the region of interest. The low-velocity cutoffs in Figure 2 needed for the distance calculation are defined at the lowerspeed side of the precipitating and mirrored ion beams where the flux is 1/e lower than the peak flux [see also Fuselier et al, 2000;Trattner et al, 2005]. To ensure a clear reproducible identification of the low-velocity cutoffs, especially for the mirrored distribution embedded within ionospheric outflow distribution, former magnetopause boundary layer distributions and high-velocity magnetosheath ions injected onto the field line while it was already convecting, the precipitating and mirrored ion peaks are fit with Gaussian distributions (blue curves in Figure 2) that are subsequently used to define the 1/e reduced flux location.…”

“…[28] The low-velocity cutoff method has been successfully used to pinpoint the location of the dayside reconnection line [e.g., Fuselier et al, 2000;Trattner et al, 2004Trattner et al, , 2005. The stability of the method has been recently demonstrated by Trattner et al [2006], who compared the results of fieldline traces derived from a Northern Hemisphere cusp crossing by the Cluster satellites with field line traces from a southern cusp crossing by Polar during similar solar wind and IMF conditions.…”

“…[3] Magnetic reconnection has been shown to occur somewhere at the Earth's magnetopause for any orientation of the IMF [e.g., Sonnerup et al, 1981;Kessel et al, 1996;Fuselier et al, 1991Fuselier et al, , 2000. More typical than the purely southward or northward IMF are conditions with a significant IMF westeast component (B Y 6 ¼ 0).…”

Solar wind entry into the high-latitude terrestrial magnetosphere during geomagnetically quiet times

“…Although previous studies have demonstrated that enhanced amounts of plasma enter to form a relatively thick, lowlatitude boundary layer 2,12,13 and a denser plasma sheet 13,14 when the IMF is northward even during quiet times, the dominant mechanism of solar wind entry into the magnetosphere (and entry location on the magnetopause) under these conditions is less clear and still controversial. It is still not very clearly understood whether the entering plasma is a result of the highlatitude MR 12,[15][16][17][18][19][20][21][22] , impulsive penetration 23,24 , or from the low latitudes through instabilities 25,26 or gradient drift 27 .…”