GPS phase fluctuations in the equatorial region during the MISETA 1994 campaign

In this gaper we present the first coordinated use of Global Positioning System (GPS) multisite and multisatellite observations with ground based radar and optical diagnostics to investigate equatorial irregularity patterns. Thirty second samples of total electron content (TEC) obtained from GPS phase differences between 1.2- and 1.6-GHz signals are used to study phase fluctuations at several stations. Comparisons were made with various types of ground measurements during the multi-instrument studies of the equatorial thermosphere aeronomy (MISETA) period. Depletions of 6300 Angstrom airglow emission from Arequipa, Peru, correlated with phase fluctuations recorded at the same site. Phase fluctuations at Arequipa occurred at the times when the Jicamarca radar backscatter returns from plumes were noted but were also seen on other nights when there were no radar returns from plumes. Levels of phase fluctuations noted at Arequipa varied considerably on nights when only thin layers of irregularities were observed by the Jicamarca radar. Differences of ionospheric conditions between the two sites, separated by only 5.5 degrees geographic longitude, may account for the different behavior patterns of irregularities noted. Similar differences in the general behavior pattern of phase fluctuations were shown when data from Arequipa and Fortaleza, Brazil, were compared. These stations, 33 degrees apart, but at the same dip latitude had different patterns for some days. During a magnetic storm a very high altitude plume was observed by the radar and by phase fluctuations noted at Santiago at 18 degrees dip latitude. This correlation of high plume altitude during some periods of magnetic activity was validated by additional examples of phase fluctuations from three other magnetic storms in the solar minimum years of 1994 and 1995.