The formation of an additional layer in the equatorial topside ionosphere

Calculations using the Sheffield University plasmasphere ionosphere model have shown that under certain conditions an additional layer can form in the low latitude topside ionosphere, This layer (the F3 layer) has subsequently been observed in ionograms recorded at Fortaleza in Brazil, It has not been observed in ionograms recorded at the neighbouring station, Sao Luis, Model calculations have shown that the F3 layer is most likely to form in summer at Fortaleza due to a combination of the neutral wind and the E x B drift acting to raise the plasma, At Fortaleza the horizontal wind moves the plasma up the inclined field lines; at Sao Luis the field lines are nearly horizontal and the wind cannot raise the plasma further. (C) 1997 COSPAR. Published by Elsevier Science Ltd.