TEC variations during low solar activity period (2005ndash;2007) near the Equatorial Ionospheric Anomaly Crest region in India

摘要

The dual frequency signals from the GPS satellites recorded at Rajkot(22.29° N, 70.74° E, Geographic, 14.03° N Geomagnetic) near theEquatorial ionization anomaly crest in India have been analyzed to study theionospheric variations in terms of Total Electron Content (TEC) for the low solar activity periodfrom April 2005 to December 2007. In this study, we describe the diurnal andseasonal variations of TEC, solar activity dependence of TEC and effects ofa space weather related event, a geomagnetic storm on TEC. The diurnalvariation of TEC shows pre-dawn minimum for a short period of time, followedby a steep early morning increase and then reaches maximum value between 14:00 LTand 16:00 LT. The mean diurnal variations during different seasons arebrought out. It is found that TEC at Rajkot is at its maximum during Equinoctialmonths (March, April, September, October), and minimum during the Wintermonths (November, December, January, February), with intermediate valuesduring Summer months (May, June, July, August), showing a semi annualvariation. TEC values have been decreasing since 2005, onwards showing positivecorrelation with solar activity. TEC variations during the geomagnetic stormcommencing 24 August 2005 with =−216 nT are analysed. TEC showsa positive ionospheric storm effect on the first day of the storm and negativeionospheric storm effect on the next day. The equatorial Electrojet controlon the development of the equatorial anomaly is also demonstrated.