Ionospheric imaging of the northern crest of the Equatorial Anomaly

The dominant structure in free electron concentration in the tropical ionosphere is the Equatorial Anomaly, where the largest values of TEC are found. This structure follows the geomagnetic equator and extends some 40degrees in latitude. The edges of the structure (crests) are characterised by steep, latitudinal gradients in TEC, which are temporally as well as spatially variable. This phenomenology is traditionally explained in terms of the theory of "fountain effect", which is shortly reviewed in this work before presenting our results. Here we study the northern crest of the Equatorial Anomaly using a program that can perform multi-instrument two- or three-dimensional time-evolving mathematical inversions. This program is designed to unify a number of different measurement techniques, thus allowing the spatial and temporal study of the ionospheric features at hand. The paper reports on experimental results from winter 2000/2001. This is a highly significant period to study the ionospheric anomalies because it is around the maximum of the 11-year solar cycle and TEC is at a maximum. (C) 2003 Elsevier Ltd. All rights reserved.