Comparison of an ionosonde drift model at a single station with polar convection patterns

A study of convection at a single point in the polar cap is made by compari ng vertical incidence ionosonde Doppler drift data with the Weimer 96 (W96) convection model. Four years of data are used to construct a local convect ion model at Casey, Antarctica (geographic 66.3 degrees S, 110.5 degrees W, geomagnetic 80.8 degrees S). The Casey 97 (C97) model is capable of produc ing a drift velocity for any time and interplanetary magnetic field (IMF) v ector in the B-y-B-z plane for either summer or winter seasons. The direct comparison of vectors predicted by C97 and W96 shows there is generally ver y good agreement between them at all IMF angles. Because of this, our findi ngs consequently support the existence of multiple convection cells for IMF angles within 30 degrees of northward (+Z), For all other angles there is a distortion of the two-cell pattern that becomes a minimum when the IMF is strongly southward with slightly a positive By component. Drawing on an ea rlier study with the Heppner-Maynard model [Smith et al,, 1998], but now us ing the C97 model for comparison, we also find their patterns only begin to match the Casey results when \ B-y\ much greater than B-z. A significant s easonal dependence also exists within the C97 and W96 models, although the agreement with each other in winter is not as good. The presence of additio nal summer lobe cells embedded within the merging cells is supported, parti cularly for a rounder, expanded dusk cell.