A semidiurnal tide in the meridional wind at F region heights at low latitudes

Arecibo data for equinox conditions at solar cycle minimum are presented which show the existence of an important semidiurnal meridional wind oscillation at F region heights at low latitudes. The inferred structure of the semidiurnal tide is in reasonable agreement with theoretical predictions based on in situ EUV and ion drag forcing and tidal energy propagating upward from the lower atmosphere. The post‐midnight descent of the F layer that is observed at low latitudes is shown to be the result of the semidiurnal winds. The height‐varying semidiurnal winds cause gradients in the vertical ion velocity which reach 2 × 10−4 s−1. Thus the semidiurnal winds have important effects not only on the F layer height but also on the layer shape and peak density.