GPS PHASE FLUCTUATIONS IN THE EQUATORIAL REGION DURING THE MISETA-1994 CAMPAIGN

In this gaper we present the first coordinated use of Global Positioni ng System (GPS) multisite and multisatellite observations with ground based radar and optical diagnostics to investigate equatorial irregula rity patterns. Thirty second samples of total electron content (TEC) o btained from GPS phase differences between 1.2- and 1.6-GHz signals ar e used to study phase fluctuations at several stations. Comparisons we re made with various types of ground measurements during the multi-ins trument studies of the equatorial thermosphere aeronomy (MISETA) perio d. Depletions of 6300 Angstrom airglow emission from Arequipa, Peru, c orrelated with phase fluctuations recorded at the same site. Phase flu ctuations at Arequipa occurred at the times when the Jicamarca radar b ackscatter returns from plumes were noted but were also seen on other nights when there were no radar returns from plumes. Levels of phase f luctuations noted at Arequipa varied considerably on nights when only thin layers of irregularities were observed by the Jicamarca radar. Di fferences of ionospheric conditions between the two sites, separated b y 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 f rom 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 obs erved by the radar and by phase fluctuations noted at Santiago at 18 d egrees dip latitude. This correlation of high plume altitude during so me periods of magnetic activity was validated by additional examples o f phase fluctuations from three other magnetic storms in the solar min imum years of 1994 and 1995.