Terdiurnal migrating-tide signature in ionospheric total electron content

We report the latitudinal, seasonal and solar cycle variations of terdiurnal migrating tide (i.e., terdiurnal westward wave number 3, TW3) signature in ionospheric total electron content (TEC). Our investigations are based on the JPL global ionospheric maps (GIMs) during 1999-2011. The absolute amplitude of TW3 exhibits maximum values in the magnetic equatorial region, which reaches about 8 TECu under high solar activity and 1.5 TECu under low solar activity. The relative amplitude of zonal mean TEC in equatorial region, however, shows persistent patterns from 1999 to 2011 with little solar activity dependence. The relative amplitude of TW3 has a peak of similar to 10% in the magnetic equatorial region and a second one of similar to 7% at magnetic middle latitudes (30 degrees-50 degrees). At high latitudes in local winter seasons, the maximum relative amplitude occurs, which varies between 8 and 15% with slightly larger amplitudes in the Northern Hemisphere. The global structure of TW3 signature in TEC should shed some light on the coupling between the ionosphere-thermosphere and the lower atmosphere.