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

Abstract

A study of convection at a single point in the polar cap is made by comparing vertical incidence ionosonde Doppler drift data with the Weimer 96 (W96) convection model. Four years of data are used to construct a local convection model at Casey, Antarctica (geographic 66.3°S, 110.5°W, geomagnetic 80.8°S). The Casey 97 (C97) model is capable of producing a drift velocity for any time and interplanetary magnetic field (IMF) vector in the By–Bz plane for either summer or winter seasons. The direct comparison of vectors predicted by C97 and W96 shows there is generally very good agreement between them at all IMF angles. Because of this, our findings consequently support the existence of multiple convection cells for IMF angles within 30° 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 earlier study with the Heppner‐Maynard model [Smith et al., 1998], but now using the C97 model for comparison, we also find their patterns only begin to match the Casey results when |By| ≫ Bz. A significant seasonal dependence also exists within the C97 and W96 models, although the agreement with each other in winter is not as good. The presence of additional summer lobe cells embedded within the merging cells is supported, particularly for a rounder, expanded dusk cell.