Average structure and storm-time change of the polar topside ionosphere at sunspot minimum

A synoptic model of the topside ionosphere above 40°N at sunspot minimum is constructed by statistically summarizing more than 3000 Alouette 1 N-h profiles obtained in 1962, 1963, and 1964 during geomagnetically quiet intervals. The characteristic features of ‘polar peak,’ ‘auroral peak,’ ‘trough,’ ‘winter spur,’ and ‘midlatitude evening increase’ are shown. The storm-time change is derived by comparing a storm-time (Kp = 9−) profile with the average quiet-interval profile. Physical explanations are discussed with emphasis on the role of ionospheric drift and plasma escape from the magnetospheric tail.