The influence of hemispheric asymmetries on field-aligned ion drifts at the geomagnetic equator

In the topside ionosphere, equatorial field-aligned ion drifts are driven by field-aligned gradients in the plasma pressure. These gradients form due to hemispheric asymmetries in plasma temperature and density, which are caused by the sun and the neutral atmosphere. The role of the neutral atmosphere in creating a field-aligned plasma pressure gradient and driving ion drifts across the geomagnetic equator is examined for several local times during solar minimum. Using satellite observations and complimentary modeled data, the field-aligned ion drifts are found to correlate with the vertical displacement between conjugate ion density peaks in both the observed and modeled data sets. In the modeled data sets, an even stronger correlation is seen between the field-aligned ion drift and the total neutral wind along the magnetic meridian at the height of the ion density peak. This correlation is seen to improve in the absence of an E x B drift. Citation: Burrell, A. G., and R. A. Heelis (2012), The influence of hemispheric asymmetries on field-aligned ion drifts at the geomagnetic equator, Geophys. Res. Lett., 39, L19101, doi:10.1029/2012GL053637.