Annual variation of ionospheric total electron contents near the equatorial anomaly region during the solar minimum period

SINGH KUMAR; SINGH R. P.; AZPILICUETA FRANCISCO; BRUNINI CLAUDIO

Monteal, Canadá

Congreso; 37th COSPAR Scientific Assembly; 2008

Committe on Space Research

The ionospheric total electron content (TEC), derived by analyzing dual frequencysignals from the Global Positioning System (GPS) recorded near the equatorial anomalyregion, Varanasi (geomag. lat. 140, 55/ N, geomag. long.1540 E) is studied. Specifically,we studied monthly, seasonal and annual variations as well as solar and geomagneticeffects on the equatorial ionospheric anomaly (EIA) during the solar minimum periodfrom May 2007 to April 2008. It is found that TEC at equatorial anomaly crest yield theirmaximum values during the equinox months and their minimum values during thesummer and winter. Using monthly averaged peak magnitude of TEC, a clear semiannualvariation is seen with two maxima occurring in both spring and autumn. Statisticalstudies indicate that the monthly mean values of peak magnitude of TEC are poorlycorrelated with Dst-index (r= 0.-0.03) but correlated very well with Kp-index (r= 0.82).During this period the TEC were also pooly correlated with solar indices, solar flux F10.7(r= -0.42) and sunspot number(r= -.09). The maximum occurrence of the daily maximumEIA crest is found around 12:30 LT. We have also studied effect of geomagnetic stormsand substorms on variation of TEC by choosing two most strong storms found during thisperiod. Some characteristics of plasma bubbles are also studied by analyzing GPS slantTEC (STEC) data. The depletion size of observed plasma bubbles varies up to 6.65 TECunits with maximum time interval of 176 minutes. These results are also discussed withthe recent published works.