RESPONSE-TIME OF THE POLAR IONOSPHERIC CONVECTION PATTERN TO CHANGES IN THE NORTH-SOUTH DIRECTION OF THE IMF

A three-day period from January 27 through January 29, 1992 is analyze d using one minute resolution solar wind data from the IMP-8 satellite and the ionospheric convection pattern data derived from the four ope rational DMSP satellites. During this period there were several clear reversals of the sign of the z component of the interplanetary magneti c field (IMF) which is known to have a direct effect on the convection patterns observed in the polar ionosphere. Polar convection patterns observed by the frequent passes of four DMSP satellites are examined f ollowing each sign change to determine the time lag between the change in the IMF at the magnetopause and the establishment of a new global convection signature in the ionosphere. After removing the transit tim e for the IMF to travel from the position of the IMP-8 satellite to th e magnetopause, a further time lag of about 17 to 25 minutes is observ ed for the five cases where the IMF turned from northward to southward . A longer lag of between 28 and 44 minutes is observed for the two ca ses where the IMF turned from southward to northward. These lags are i nterpreted as the inertial response time of the ionosphere in reacting to the change in the IMF.