Patterns of potential magnetic field merging sites on the dayside magnetopause

Abstract

Models of the magnetospheric and magnetosheath magnetic fields are used to determine the relative orientations of these fields at the dayside magnetopause in order to locate potential merging sites. Areas on the magnetopause with different fractional antiparallel components are displayed by contour diagrams for a variety of interplanetary field orientations. For interplanetary fields oriented perpendicular to the solar wind velocity the areas of nearly antiparallel field agree with those obtained by Crooker using simplified representations for the magnetic field geometry. Here, the application of more realistic models gives the locations of areas where any antiparallel component occurs. Potential merging sites for interplanetary fields with radial components are also illustrated. The results suggest that the topology of the magnetosheath and magnetospheric fields provides antiparallel components over a substantial fraction of the magnetopause for most interplanetary field orientations.

Multi-site observations of the association between aurora and plasma convection in the cusp/polar cap during a southeastward(<i>B<sub>y</sub></i> <u>~</u> |<i>B<sub>z</sub></i>|) IMF orientation

“…Their data set was found to be consistent with antiparallel, steady state merging, as described by Crooker (1979) and Luhmann et al (1984). That interpretation is based on the observation of certain convection vortices involving strong equatorward flow at cusp latitudes at noon, and an ion dispersion signature consistent with steady-state reconnection.…”

“…According to this view, reconnection can take place over large areas of the dayside magnetopause, for example, along a tilted reconnection line traversing the subsolar region and extending to high latitudes in both hemispheres. In the antiparallel model, on the other hand, reconnection is restricted to high latitudes during B y -dominated IMF conditions (Crooker, 1979;Luhmann et al, 1984;Rodger et al, 2000;Coleman et al, 2001). Auroral observations of relevance to this issue are reported in this paper.…”

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

“…Under these conditions, the antiparallel regions are aligned with the location of the tilted ''component'' reconnection line. In addition, the study showed that the actual reconnection line has the tendency to be located where [Crooker, 1979;Luhmann et al, 1984]. The alternative to this reconnection scenario is a tilted X-line or component reconnection model [e.g., Gonzalez and Mozer, 1974;Cowley and Owen, 1989] where the reconnection line does not continue along the antiparallel reconnection regions but continues to cross the dayside magnetopause regardless of the magnitude of the B Y component.…”

“…More typical than the purely southward or northward IMF are conditions with a significant IMF westeast component (B Y 6 ¼ 0). For such conditions, Crooker [1979] and Luhmann et al [1984] demonstrated that the antiparallel reconnection region splits at local noon, producing two separate reconnection regions in different hemispheres. Such a scenario was observationally confirmed by Trattner et al [2005] who used a Cluster cusp crossing in the Northern Hemisphere and observed a double cusp structure which could be associated with the dawn and dusk convection cells and reconnection sites in different hemispheres close to the antiparallel reconnection regions.…”

X lines in the magnetotail for southward and northward IMF conditions

“…For a southward IMF, the X line is most likely to occur near the equatorial plane [e.g., Sonnerup, 1970;Øieroset et al, 1997;Moore et al, 2002;Fuselier et al, 2011;Tan et al, 2011]. For a northward IMF, the X line may take place at high-latitude boundary layer [Cowley, 1976;Crooker et al, 1979;Maezawa, 1976;Luhmann et al, 1984;Song et al, 1999].…”