Effects of the IMF BY inferred from the FAC-based convection model and radar observations

Lukianova, R.1, Kozlovsky, A.2, Christiansen, F.3 and Turunen, T.4

1 Arctic and Antarctic Research Institute, St. Petersburg, Russia
2 Sodankylä Geophysical Observatory, Oulu unit, Oulu, Finland
3 National Space Center DTU, Copenhagen, Denmark
4 Sodankylä Geophysical Observatory, Sodankylä, Finland

We present the results of modeling and radar observations of the ionospheric electric fields in the polar cap, where the electrodynamic processes are strongly controlled by the IMF BY component. The polar-orbiting satellites such as the Orsted, Magsat, Champ, Iridium detect intense field-aligned currents (FAC) above ±75° MLat which depends on a sign of BY. These current density numbers are comparable with the density of the corresponding pair of R1 currents. The near-pole FAC imply large and variable electric fields in the polar cap, which is not presented adequately in the statistical convection models published up to now. Recently, a new approach for modeling the global distribution of ionospheric electric potentials utilizing high-precision maps of FACs derived from measurements by the Orsted, Magsat and Champ satellites as input to a comprehensive numerical scheme has been developed. We show that the FAC-based convection model reproduces nicely the polar cap effects. We combine the model’ predictions with the European IS Svalbard radar (ESR) and SuperDARN observations for specific cases of strong interhemispheric asymmetry caused by the sign of BY, season, universal time (UT) to adress the following questions. To what degree the FAC-based model does reproduce the radar observation? How does the difference in electric potential between the near-pole region and the auroral zone depend on the magnitude of BY? Are the observed peculiarities of plasma flow controlled by FAC, ionospheric conductance or both? What can be the reason of observed variability of the polar cap potential? Also, the simulation in frame of the FAC-based model as well as observations shows that the solar zenith angle (both seasonal and UT variation) should be linked to the IMF clock angle to fully characterize the convection patterns. That confirms the necessity to link season with the sign of IMF By to fully characterize the dependence of the convection patterns on season. Finally, we show that when the seasonal interhemispheric asymmetry in conductivity and in FAC intensity is amplified with the By–related redistribution of FACs, the plasma flow at middle latitude is also modified. Specifically, the flow is strongly affected by the corresponding summer polar cap convection pattern.