Certain behavior of the ionospheric F2 region at low latitudes

The continuity equation of electron density is solved for the conditions of the F 2 region at low latitude along 69°W meridian in the equinox of high solar activity. The transport term includes the electromagnetic drift observed at Jicamarca, the plasma diffusion, the vertical motion due to thermal expansion and contraction, and the neutral wind for which the direction reversal in the morning is rather late. The large‐scale irregularity which forms a bifurcated F 2 layer is generated at the geomagnetic equator and travels as far as 15° latitude with a speed of about 10 km min −1 . Other features of this bifurcation and the probable mechanism of its formation are described. The height of maximum electron density is strongly controlled by the electromagnetic drift at very low latitude from 0700 to midnight. The computation also shows that the large postsunset peak of N m F 2 at a subtropical region is caused by the rapid sunset increase of upward drift at the equator. The late reversal of neutral wind favors the observed diurnal pattern of N m F 2 . Other effects of neutral wind and that of loss rate on the low latitude ionosphere are discussed.