Ih. Cairns et Jg. Lyon, MAGNETIC-FIELD ORIENTATION EFFECTS ON THE STANDOFF DISTANCE OF EARTHSBOW SHOCK, Geophysical research letters, 23(21), 1996, pp. 2883-2886
Three-dimensional, global MHD simulations of solar wind flow onto a pr
escribed magnetopause obstacle are used to show that a bow shock's nos
e location a, and the relative subsolar magnetosheath thickness Delta(
ms)/a(mp) are strong functions of the IMF cone angle theta (between v(
sw) and B-sw) and the Alfven Mach number M(A). For a given M(A) the sh
ock is more distant for higher theta (restricted to the interval 0 - 9
0 degrees by symmetries), while a(s)/a(mp) and Delta(ms)/a(mp) increas
e with decreasing M(A) for theta greater than or similar to 20 degrees
but decrease with decreasing M(A) for theta similar to 0 degrees. Lar
ge differences in Delta(ms)/a(mp) are predicted between theta = 0 degr
ees and 90 degrees at low M(A), with smaller differences remaining eve
n at M(A) similar to 10. The theta = 0 degrees results confirm and ext
end the previous work of Spreiter and Rizzi [1974]. The simulations sh
ow that successful models for the subsolar shock location cannot subsu
me the dependences on M(A) and theta into a sole dependence on M(ms).
Instead, they confirm a recent prediction [Cairns and Grabbe, 1994] th
at a(s)/a(mp) and Delta(ms)/a(mp) should depend strongly on theta and
M(A) for M(A) less than or similar to 10 (as well as on other MHD vari
ables). Detailed comparisons between theory and data remain to be done
. However, preliminary comparisons show good agreement, with distant s
hock locations found for low M(A) and large theta greater than or simi
lar to 45 degrees and closer locations found for theta less than or si
milar to 20 degrees even at M(A) similar to 8.