IONOSPHERIC CONVECTION DURING THE MAGNETIC STORM OF 20-21-MARCH-1990

We report on the response of high-latitude ionospheric convection duri ng the magnetic storm of March 20-21 1990. IMP-8 measurements of solar wind plasma and interplanetary magnetic field (IMF), ionospheric conv ection flow measurements from the Wick and Goose Bay coherent radars, EISCAT, Millstone Hill and Sondrestrom incoherent radars and three dig isondes at Millstone Hill, Goose Bay and Qaanaaq are presented. Two in tervals of particular interest have been identified. The first starts with a storm sudden commencement at 2243 UT on March 20 and includes t he ionospheric activity in the following 7 h. The response time of the ionospheric convection to the southward turning of the IMF in the dus k to midnight local times is found to be approximately half that measu red in a similar study at comparable local times during more normal so lar wind conditions. Furthermore, this response time is the same as th ose previously measured on the dayside. An investigation of the expans ion of the polar cap was nonuniform. A subsequent reconfiguration of t he nightside convection pattern was also observed, although it was not possible changes in B-y and effects due to substorm activity. The sec ond interval, 1200-2100 UT 21 March 1990, included a southward turning of the IMF which resulted in the B-z component becoming - 10 nT. The response time on the dayside to this change in the IMF at the magnetop ause was approximately 15 min to 30 min which is a factor of similar t o 2 greater than those previously measured at higher latitudes. A move ment of the nightside flow reversal, possibly driven by current system s associated with the substorm expansion phases, was observed, implyin g that the nightside convection pattern can be dominated by substorm a ctivity.