Evolution of ionospheric multicell convection during northward interplanetary magnetic field with vertical bar B-z/B-y vertical bar > 1

During northward interplanetary magnetic field (IMF), it is generally belie ved that ionospheric convection appears as a four-cell structure for /B-2/B -y/ > 1 and as a distorted two-cell structure for /B-z/B-y/ < 1, where B-y and B-z are the Y and Z components of the IMF. In this paper we present Sup er Dual Auroral Radar Network (SuperDARN) observations of ionospheric conve ction in the Northern Hemisphere during northward IMF for /B-z/B-y/ > 1 on November 11, 1998. We show in detail the evolution of the convection patter ns as /B-z/B-y/ changes. Nearly symmetric fourcell convection, with two rev erse cells in the polar cap and two normal cells at lower latitudes, occurs for /B-z/B-y/ approximate to 7. The ionospheric flow associated with the r everse cells is closed almost completely on the dayside. A shifted four-cel l convection pattern, with the reverse cells shifted toward earlier magneti c local time (MLT) for negative B-y and toward later MLT for positive B-y, is observed for /B-z/B-y/ approximate to 2.3. When /B-z/B-y/ decreases to s imilar to1.7, the convection appears as a three-cell pattern, with a single reverse cell focused near noon and two normal cells. The normal morning an d afternoon cells are focused at quite high magnetic latitudes (between 76 degrees and 80 degrees); the spatial extent of the normal cells is 10 degre es -15 degrees or 1000-1500 km in the latitudinal direction. We also presen t Defense Meteorological Satellite Program (DMSP) satellite data which show sunward convection over the polar cap in the Southern Hemisphere at the sa me time as the Northern Hemisphere radar observations. We propose a new mod el of convection patterns during northward IMF for /B-z/B-y/ > 1 and B-y < 0 on the basis of the combined observations. In the model the convection ap pears as a symmetric four-cell structure for /B-z/B-y/ <greater than or equ al to> 3, a shifted four-cell structure for /B-z/B-y/ = 2-3, and a three-ce ll structure for /B-z/B-y/ = 1-2.