Effect of displaced geomagnetic and geographic poles on high‐latitude plasma convection and ionospheric depletions

Abstract

We assumed that the ionospheric plasma at high latitudes has a tendency to corotate about the geographic pole and that magnetospheric convection is relative to the geomagnetic pole. With this assumption we calculated plasma drift patterns over the polar cap for a range of constant magnetospheric electric fields as well as for asymmetric electric fields with enhanced plasma flow on either the dawnside or the duskside of the polar cap. We calculated the drift patterns in both the geographic inertial and the geomagnetic inertial frame taking into account the displacement between the geographic and geomagnetic poles. We found that this displacement between the poles has an important effect on the plasma drift patterns. In particular, we found the following: (1) A time‐independent magnetospheric electric field produces a flow pattern in the magnetic inertial frame that does not vary with universal time. (2) This flow pattern becomes UT dependent in the geographic inertial frame because of the motion of the geomagnetic pole about the geographic pole. (3) The UT variation of the plasma flow pattern in the geographic inertial frame occurs on a time scale that is comparable to satellite orbital periods and that is much less than typical plasma convection flow times over the polar cap. (4) In the geographic inertial frame the main region of very low speed flow is not centered at 1800 LT but moves from about 1300 to 2300 LT during the course of a day. (5) In the geographic inertial frame a throatlike feature appears at certain universal times owing to the relative motion of the geographic and geomagnetic poles. This feature is not seen in the geomagnetic inertial frame and is not connected with our model of the magnetospheric electric field. These results and others described in the paper have important implications for both the interpretation of satellite data related to high‐latitude ionospheric dynamics and the formation of ionospheric troughs.