EQUATORIAL PLASMA FOUNTAIN AND ITS EFFECTS OVER 3 LOCATIONS - EVIDENCE FOR AN ADDITIONAL LAYER, THE F3 LAYER

The equatorial plasma fountain and equatorial anomaly in the ionospher es over Jicamarca (77 degrees W), Trivandrum (77 degrees E), and Forta leza (38 degrees W) are presented using the Sheffield University plasm asphere-ionosphere model under magnetically quiet equinoctial conditio ns at high solar activity. The daytime plasma fountain and its effects in the regions outside the fountain lead to the formation of an addit ional layer, the F-3 layer, at latitudes within about plus or minus 10 degrees of the magnetic equator in each ionosphere. The maximum plasm a concentration of the F-3 layer, which occurs at about 550 km altitud e, becomes greater than that of the F-2 layer for a short period of ti me before noon when the vertical E x B drift is large. Within the F-3 layer the plasma temperature decreases by as much as 100 K. The ionogr ams recorded at Fortaleza on January 15, 1995, provide observational e vidence for the development and decay of an F-3 layer before noon. The neutral wind, which causes large north-south asymmetries in the plasm a fountain in each ionosphere during both daytime and nighttime, becom es least effective during the prereversal strengthening of the upward drift. During this time the plasma fountain is symmetrical with respec t to the magnetic equator and rises to over 1200 km altitude at the eq uator, with accompanying plasma density depletions in the bottomside o f the underlying F region. The north-south asymmetries of the equatori al plasma fountain and equatorial anomaly are more strongly dependent upon the displacement of the geomagnetic and geographic equators (Jica marca and Trivandrum) than on the magnetic declination angle (Fortalez a).