THE RESPONSE OF HIGH-LATITUDE CONVECTION TO A SUDDEN SOUTHWARD IMF TURNING

We describe the response of the high-latitude convection to a sudden s outhward turning of the IMF. In this event B-z recorded at the WIND sa tellite switched from +6 nT to -6 nT in 21/2 minutes and effects in th e ionosphere were observed by the SuperDARN HF radars. In the vicinity of noon MLT, the convection switched suddenly (similar to 2 min) from sunward to antisunward with the velocity change reaching magnitudes a s great as 1500 m/s in about 6 minutes. Surprisingly, the responses at the other MLTs distributed from noon to midnight began at virtually t he same time. Meridional flows near 22 MLT were observed to reverse di rection in about 4 minutes with the velocity change reaching magnitude s as great as 750 m/s in about 8 minutes. This example shows that the convection can respond to a sudden IMF change practically simultaneous ly (similar to 2 min) over the entire high-latitude zone and reconfigu re from a pattern characteristic of B-z+ to one characteristic of B-z- in a very short (2-4 min) time.