Abstract:
The influence of east-west component of interplanetary magnetic field (IMF-By) on
ionospheric plasma convection over polar region is well established by both observation and modeling studies. However, its influence beyond polar latitudes has rarely been addressed. To understand the effects of IMF-By at low-latitudes during geomagnetic storm times, we have designed simulation experiments using Thermosphere-Ionosphere-Electrodynamics General Circulation Model. This communication shows that strong IMF-By and its polarity has effects on the storm-time ionosphere-thermosphere dynamics even near equator. It can change zonal electric field, magnitude of morning/evening time prereversal-enhancements (PRE) and meridional winds. At the storm onset when prompt penetration electric fields prevail, a strong IMF-By, in general, reduces the vertical plasma drifts over the equator and the largest effects are observed near sunrise and sunset terminators. Later when disturbance dynamo is active, morning PRE appears, and a strongly positive IMF-By strengthens morning PRE and weakens evening PRE, with respect to zero IMF-By conditions. A strongly negative IMF-By just shows the reverse, thus indicates dawn-dusk asymmetry due to IMF-By. It is also seen that the meridional winds are oppositely directed during positive and negative IMF-By conditions. The effects of IMF-By transition are observed on the evening PRE within 2 h from the transition. The new insights successfully explain the observations from a few earlier available works. However, the presented results should be treated with caution in view of model limitations associated with the empirical patterns of high latitude convection and preliminary scheme of merging high latitude-low latitude potentials.
