Equatorial bubbles as observed with GPS measurements over Pune, India

Abstract

Ionospheric total electron content (TEC) and scintillations have been recorded continuously since April 2003 using a dual‐frequency GPS receiver at Pune, India (geographic latitude 19.1°N, longitude 74.05°E; 24°N dip), situated in between the magnetic equator and the northern crest of the equatorial anomaly. The TEC often shows bite‐outs when severe amplitude scintillations are observed on the GPS L1 carrier level. The apparent duration of the bite‐outs may be different from the true east‐west duration, as observed with geostationary links, because of the presence of a relative velocity between the irregularity cloud and the satellite. The trajectory of a GPS satellite plays an important role in observing the bubble characteristics. The distributions of amplitude and duration of the bubbles have been obtained during the equinoctial months February through April of 2004. The median values are found to be 9 TEC units (1 TECU = 1016 el/m2) and 3.3 min, respectively. The range error at GPS L1 frequency corresponding to the median TEC depletion is 1.4 m, while that corresponding to the 95th percentile value is 4.5 m. An asymmetry in the east‐west walls of the bubble and sharp edges of the depletions resulting in high range error rates ∼30 cm/min has been noted.