Super Dual Auroral Radar Network observations of ionospheric multicell convection during northward interplanetary magnetic field

There have been a number of reports on the ionospheric convection during northward interplanetary magnetic field (IMF). Multicell convection patterns with two reverse cells within the polar cap have been derived from statistical magnetometer data and individual satellite passes over the high-latitude ionosphere. The reverse convection cells are also reproduced with some data assimilation techniques. However, there have been few direct observations of complete reverse cells. In this paper, we present HF radar observations of ionospheric convection with two reverse cells in the winter hemisphere during northward IMF. The prenoon reverse cell is focused around 1000 magnetic local time (MLT) near 82 degrees magnetic latitude; the postnoon reverse cell is focused around 1400 MLT near 82 degrees magnetic latitude. The reverse convection cells are stable as long as the IMF is stable. The focus location of the reverse cells does not show noticeable change when the IMF B-y component has different signs. The ionospheric convection at lower latitudes with the normal two-cell rotational sense for southward IMF is also observed. In particular, the clockwise convection cell is focused around 1800 MLT near 77 degrees magnetic latitude. The reversal boundary of the low-latitude convection during northward IMF appears at around 77 degrees-78 degrees magnetic latitude in both the morning and afternoon sectors. It is observed that the reverse cells take similar to 10 min to form after a northward turning of the IMF. Our observations show that the four-cell convection does exist during strongly northward IMF.