The diurnal variation of the equatorial anomaly in the topside ionosphere at sunspot maximum.

Over sixty ionograms taken by the Alouette II and ISISA satellites from November 1969-January 1970 were analyzed and converted to give electron density-true height data. The equatorial anomaly was observed to appear by 1000 LT, reach a maximum by 1500 LT, with the subsequent decay arrested by 1700 LT. Around 1900 LT, an enhancement, particularly of the Southern Hemisphere crest became apparent. It was found that an increase of solar activity from sunspot minimum to maximum produced an increase of vertical upthrust of ionization above the magnetic equator, with probably little change in the meridional wind velocity near the time of the maximum development of the equatorial anomaly.