Nighttime Enhancements in IEC at Low Latitudes — A Study with Reference to F Region Dynamics

The nighttime enhancement (NTE) in the ionospheric electron content (IEC) are observed over Waltair (17.7°N) and Calcutta (22°N), when the equatorial F region rises to higher altitudes during the post-sunset hours over Kodaikanal (10°N). No significant enhancement is seen at either of the stations if the altitude of the F region near the equatorial region is confined to lower altitudes. In addition to the altitude rise at the equatorial region, an earlier post-sunset reversal in the meridional neutral wind direction from poleward to equatorward also seems to be a requisite condition for the enhancements in IEC to occur at off-equatorial regions. The observed features are discussed in the light of the F region dynamics.