Interplanetary magnetic field B-y and auroral conductance effects on high-latitude ionospheric convection patterns

T. Tanaka, Interplanetary magnetic field B-y and auroral conductance effects on high-latitude ionospheric convection patterns, J GEO R-S P, 106(A11), 2001, pp. 24505-24516
Citations number
Categorie Soggetti
Space Sciences
Journal title
ISSN journal
2169-9380 → ACNP
Year of publication
24505 - 24516
SICI code
The dependence of the ionospheric electric potential (convection) on the in terplanetary magnetic field (IMF) and the ionospheric conductivity is inves tigated to understand the generation of convection patterns in the framewor k of the solar wind-magnetosphere-ionosphere (S-M-I) coupling scheme and th e merging concept. A numerical magnetohydrodynamic (MHD) simulation is adop ted for the study of the present problem. To achieve a high resolution in t he ionosphere, the MHD calculation employs the finite volume (FV) total-var iation diminishing (TVD) scheme with an unstructured grid system. The two-c ell convection patterns reproduced from simulation are shown for several ca ses under the southward IMF condition during the growth-phase interval. In the investigation of these results, special attention is paid to the analys is of mirror symmetry in the convection patterns with respect to the IMF BY . On the dayside in the Northern Hemisphere, IMF By- (By+) generates flow d eflection on newly opened field lines toward the dusk dawns without a sever e violation of the mirror symmetry. While the mirror symmetry of the convec tion pattern is maintained even on the nightside when the ionospheric condu ctivity is uniform, it is not maintained on the nightside when the ionosphe ric conductivity is nonuniform. A realistic ionospheric conductivity modifi es the convection pattern in the Northern (Southern) Hemisphere so as to em phasize distinctive features seen for IMF By+ (By-) under a uniform conduct ivity, and the reproduced convection patterns coincide with the observation quite well including fine signatures on the nightside, both for IMF By- an d By+. Because of the nonuniform conductivity, cell centers of convection a re shifted to the earlier magnetic local times, and the antisunward flow in the northern polar cap is nearly aligned with noon-midnight meridian for I MF By-, while the flow in the northern polar cap has a significant inclinat ion from prenoon to premidnight for IMF By+. These convection patterns can be understood by considering the effect due to the Hall current closure of the region-1 field-aligned current. The analysis for the dependence of nigh tside convection on IMF B-y and ionospheric conductivity shows that the Har ang discontinuity is attributed partially to the structure of magnetospheri c driver but mainly to the effect of nonuniform auroral conductivity. As a consequence, it is more adequate to say that convection patterns are more o r less caused by the synthesized effect of more than one process rather tha n a single elementary process. Reproduced convection patterns in this paper show a particular coincidence with satellite observations summarized by ad opting the pattern-recognition-based approach.