Climatological patterns of high‐latitude convection in the Northern and Southern hemispheres: Dipole tilt dependencies and interhemispheric comparisons

Abstract

Using line‐of‐sight measurements of horizontal plasma drift from the Super Dual Auroral Radar Network (SuperDARN) located in the Northern and Southern hemispheres over a period extending from 1998 to 2002, statistical models of the high‐latitude convection electric field are derived for various ranges of interplanetary magnetic field (IMF) magnitude and orientation and for several ranges of dipole tilt angle. Direct comparison of the corresponding convection patterns in each hemisphere shows that under neutral tilt conditions (dipole tilt angle magnitude <10°) the patterns are most similar. However, a strong dipole tilt angle dependence is observed under northward (Bz+) and By dominated IMF conditions. For IMF Bz+, reverse convection is observed to be much stronger during positive tilt than negative tilt. For IMF By dominated conditions (IMF Bz = 0), the round convection cell is more enhanced for positive tilt than for negative tilt, particularly for IMF By < 0 in both hemispheres. The presence of a lobe cell is a likely cause of this enhancement, although it is not entirely clear why it occurs preferentially under IMF By < 0. In addition, the crescent‐shaped cells are weakened as tilt angle progresses from negative to positive, most likely due to vastly different solar produced conductivities under different tilt angles. For IMF Bz−, asymmetric values of the cross‐polar cap potentials (ΦPC) are observed between hemispheres, with ΦPC in the south being systematically larger than ΦPC in the north. Although neutral tilt patterns are similar enough to be used interchangeably, convection has a strong dipole tilt dependence and a Northern Hemisphere convection model should not be applied to the Southern Hemisphere if dipole tilt angle is not taken into account. When dipole tilt is accounted for, ΦPC differs between hemispheres by less than 10% on average, but the strength of the convection in the individual cells differs by 15% to 20% on average.