Tec climatology derived fromtopex/poseidonmeasurements

Abstract

We have used the TOPEX data sets available from JPL to create a customizeddatabase of the TOPEX TEC measurements that contain data from 1992 through part of 1996.Thedata base includes time, geographic and geomagnetic coordinates of themeasurement,geomagnetic indices ( Kp, previous K p , HemisphericPower, andintegral of hemispheric power over the previous 36 h), solar index ( F 10.7),andInternational Reference Ionosphere (IRI) results corresponding to the TOPEX measurements.Inthis paper we present global maps of TEC for low solar activity conditions ( F 10.7 ⩽ 120) for quiet (integral of hemispheric power less than 800 GWh, roughly correspondingto K p = 2), moderately disturbed (integral of hemispheric power greaterthan 800GWh but less than 1200 GWh, roughly corresponding to K p = 3),anddisturbed (integral of hemispheric power greater than 1200 GWh, roughly corresponding to K p = 4) geomagnetic conditions, derived by binning all appropriateTOPEX TECdata from 1992 to 1996. The analysis is performed in a Magnetic-Local-Time,Magnetic-Latitudecoordinate system. The most prominent feature of the global TEC maps is thefeaturecorresponding to the equatorial anomaly. The feature becomes wider in magnetic latitudeandmore pronounced in amplitude as the activity level increases. The equatorward shift of thecrests,with increased magnetic activity, can produce apparent decreases in TEC at their quiettimelocation for individual storms as evident in the conflicting conclusions of TECgeomagneticdependence studies of the 1960s. For the same activity level, TEC values in theequatorialanomaly are higher during equinox compared to solstice.