Evaluating Midlatitude Fall-off Dependencies of the High Latitude Convection Pattern

Abstract:

It is well known that the polar cap convection pattern is highly dependent on the orientation of the interplanetary magnetic field (IMF) and its radius depends significantly on geomagnetic activity. In contrast, the midlatitude fall-off of the high latitude electric field is relatively less understood. This region connects the high latitude polar cap convection to the region where the ring currents cancel out the low latitude electric field. The electric field in this midlatitude region is typically modeled as a simple fall-off, but magnetosphere-ionosphere dynamics may create structure in this region that has previously been neglected by ionospheric models. We investigate the IMF and Kp dependencies and the fall-off using plasma drift data from the Defense Meteorological Satellite Program (DMSP) and a simplified polar cap convection model. The model uses an inverse fourth power function to approximate the fall-off and incorporates two offsets (one dusk to dawn and one noon to midnight) and a potential skew to replicate the convection pattern. First the northern hemisphere polar cap passes from DMSP were separated into categories based on IMF clock angle and magnitude. Two methods were used to account for the delay from the time of the IMF measurement by the Advanced Composition Explorer (ACE) satellite to the time the plasma reaches earth. The first method uses a standardized delay value based on a typical solar wind speed while the second method used actual solar wind measurements from ACE to calculate the time delay. The groupings obtained using these two methods will be compared to determine if they produce significantly different results. The groupings will also be compared to the model results to determine what offsets are required to match the IMF orientation. Groupings based on geomagnetic activity using the Kp index will then be examined and compared to the model fall-off at midlatitudes. We will discuss the differences in the time delay methods and the results of the IMF orientation and Kp grouping comparison to the model.