TEC climatology derived from TOPEX/POSEIDON measurements

We have used the TOPEX data sets available from JPL to create a customized data base of the TOPEX TEC measurements that contain data from 1992 through part of 1996. The data base includes time, geographic and geomagnetic coor dinates of the measurement, geomagnetic indices (Kp, previous K-p, Hemisphe ric Power, and integral of hemispheric power over the previous 36 h), solar index (F 10.7), and International Reference Ionosphere (IRI) results corre sponding to the TOPEX measurements. In this paper we present global maps of TEC for low solar activity conditions (F 10.7 less than or equal to 120) f or quiet (integral of hemispheric power less than 800 GWh, roughly correspo nding to K-p = 2), moderately disturbed (integral of hemispheric power grea ter than 800 GWh but less than 1200 GWh, roughly corresponding to K-p = 3), and disturbed (integral of hemispheric power greater than 1200 GWh, roughl y corresponding to K-p = 4) geomagnetic conditions, derived by binning all appropriate TOPEX TEC data from 1992 to 1996, The analysis is performed in a Magnetic-Local-Time, Magnetic-Latitude coordinate system. The most promin ent feature of the global TEC maps is the feature corresponding to the equa torial anomaly. The feature becomes wider in magnetic latitude and more pro nounced in amplitude as the activity level increases. The equatorward shift of the crests, with increased magnetic activity, can produce apparent decr eases in TEC at their quiet time location for individual storms as evident in the conflicting conclusions of TEC geomagnetic dependence studies of the 1960s. For the same activity level, TEC values in the equatorial anomaly a re higher during equinox compared to solstice. (C) 1999 Elsevier Science Lt d. All rights reserved.