Climatology of longitudinal structure observed in the TOPEX TEC measurements

Abstract

Since the launch on 10 August 1992, the TOPEX/Poseidon mission provided an extensive database of vertical TEC over the ocean until it ended its mission on October 2005. Data from about 14 years of TOPEX TEC observations were analyzed to study the climatology of longitudinal structure at low and middle latitude regions. For the analysis, TEC data were binned by season and solar activity for geomagnetically quiet conditions (Kp < 2) to create TEC maps in magnetic latitude and longitude for several local time sectors. These maps show not only the annual and semiannual anomalies well-known from climatological studies of NmF2, but also the wavenumber-4 structure of the equatorial anomaly. In particular, the latter is the ionospheric feature recently identified from satellite measurements and closely correlated with the longitudinal structure of the vertical E×B drift. Furthermore, this strongly indicates the coupling between the upper atmosphere and the lower atmosphere.