• Document: Theoretical Study of the High-Latitude Ionosphere s Response to Multicell Convection Patterns
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Utah State University DigitalCommons@USU All Physics Faculty Publications Physics 1987 Theoretical Study of the High-Latitude Ionosphere’s Response to Multicell Convection Patterns Jan Josef Sojka Utah State University Robert W. Schunk Utah State University Follow this and additional works at: http://digitalcommons.usu.edu/physics_facpub Part of the Physics Commons Recommended Citation Sojka, J. J., and R. W. Schunk (1987), Theoretical Study of the High-Latitude Ionosphere’s Response to Multicell Convection Patterns, J. Geophys. Res., 92(A8), 8733–8744, doi:10.1029/JA092iA08p08733. This Article is brought to you for free and open access by the Physics at DigitalCommons@USU. It has been accepted for inclusion in All Physics Faculty Publications by an authorized administrator of DigitalCommons@USU. For more information, please contact dylan.burns@usu.edu. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 92, NO. A8, PAGES 8733- 8744, AUGUST 1, 1987 Theoretical Study of the High-Latitude Ionosphere's Response to Multicell Convection Patterns J. J. SOJKA AND R. W. SCHUNK Center for Atmospheric and Space Sciences, Utah State University, Logan It is well known that convection electric fields have an important effect on the ionosphere at high latitudes and that a quantitative understanding of their effect requires a knowledge of the plasma convection pattern. When the interplanetary magnetic field (IMF) is southward, plasma convection at F region altitudes displays a two-cell pattern with antisunward flow over the polar cap and return flow at lower latitudes. However, when the IMF is northward, mUltiple convection cells can exist, with both sunward flow and auroral precipitation (theta aurora) in the polar cap. The characteristic ionospheric signatures associated with multicell convection patterns were studied with the aid of a three-dimensional time-dependent iono- spheric model. Two-, three-, and four-cell patterns were considered and the ionosphere's response was calculated for the same cross-tail potential and for solar maximum and winter conditions in the northern hemisphere. As expected, there are major distinguishing ionospheric features associated with the different convection patterns, particularly in the polar cap. For two-cell convection the antisunward flow of plasma from the dayside into the polar cap acts to maintain the densities in this region in winter. For four-cell convection, on the other hand, the two additional convection cells in the polar cap are in darkness most of the time, and the resulting 0+ decay acts to produce twin polar holes that are separated by a sun-aligned ridge of enhanced ionization due to theta aurora precipitation. For three-cell convection, only one polar hole forms in the total electron density, but in contrast to the four-cell case, an additional 0+ depletion region develops near noon owing to large electric fields causing an increased 0+ + N2 loss rate. These general distinguishing features do not display a marked universal time variation in winter. 1. INTRODUCTION Nevertheless, this approach has led to a significant improve- During the last decade, a major effort has been devoted to ment in our understanding of magnetospheric processes and studying the effect that magnetospheric electric fields and par- how they vary with Kp and the interplanetary magnetic field ticle precipitation have on the high-latitude ionosphere and (lMF). neutral atmosphere. Very early, it became apparent that a quan- When the IMF Bz component is southward, the average con- titative understanding of the effect of these magnetospheric vection patterns display a two-cell structure with antisunward processes could not be obtained without a knowledge of the flow over the polar cap and return flow at lower latitudes. The "global" plasma convection and particle precipitation patterns. size of the dawn and dusk convection cells depends on the sign of Experimentally, information on the plasma convection pattern the By component of the IMF, and at times, a dayside throat and associated electric fields has been obtained by a variety of and a Harang discontinuity are important features of the two- techniques, including satellite and rocket-borne probes cell convection pattern. These convection characteristics are [Heppner, 1977; M

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