Earth Planets Space, Vol. 52 (No. 11), pp. 1055-1060, 2000LETTER
René Warnant and Eric Pottiaux
Royal Observatory of Belgium, Avenue Circulaire, 3, B-1180 Brussels, Belgium
(Received December 31, 1999; Revised September 25, 2000; Accepted September 25, 2000)
Abstract: The paper outlines a method allowing to compute the TEC with a precision of about 2-3 TECU and to detect Travelling Ionospheric Disturbances using GPS measurements. We describe the solar cycle dependance of the TEC and TIDs. Since the beginning of 1998, we have observed a stronger ionospheric activity due to the increasing solar activity. This ionospheric activity is characterized by larger TEC values which are regularly reaching the level of 60 TECU and by a larger number of Travelling Ionospheric Disturbances. During the winter 1999-2000, the mean daily TEC was above 45 TECU; at solar minimum the mean daily TEC is ranging from 4 TECU to 12 TECU. In January 2000 (close to solar maximum) more than 1300 events due to TID's were detected: it is 6.5 more than in January 1996 (at solar minimum).