Abstract
Abstract. In an earlier study, Thampi et al. (2006) have shown that the strength and asymmetry of Equatorial Ionization Anomaly (EIA), obtained well ahead of the onset time of Equatorial Spread F (ESF) have a definite role on the subsequent ESF activity, and a new "forecast parameter" has been identified for the prediction of ESF. This paper presents the observations of EIA strength and asymmetry from the Indian longitudes during the period from August 2005–March 2007. These observations are made using the line of sight Total Electron Content (TEC) measured by a ground-based beacon receiver located at Trivandrum (8.5° N, 77° E, 0.5° N dip lat) in India. It is seen that the seasonal variability of EIA strength and asymmetry are manifested in the latitudinal gradients obtained using the relative TEC measurements. As a consequence, the "forecast parameter" also displays a definite seasonal pattern. The seasonal variability of the EIA strength and asymmetry, and the "forecast parameter" are discussed in the present paper and a critical value for has been identified for each month/season. The likely "skill factor" of the new parameter is assessed using the data for a total of 122 days, and it is seen that when the estimated value of the "forecast parameter" exceeds the critical value, the ESF is seen to occur on more than 95% of cases.
Highlights
The Equatorial Ionization Anomaly (EIA) and Equatorial Spread F (ESF) are two well known daytime and nighttime processes in the equatorial and low-latitude ionosphere thermosphere system
The observations of the strength and asymmetry of Equatorial Ionization Anomaly (EIA) using a ground-based beacon receiver located at Trivandrum (8.5◦ N, 77◦ E, 0.5◦ N dip lat) for a period spanning from August 2005–March 2007 are presented
It is seen that the seasonal variability of EIA strength and asymmetry are manifested in the latitudinal gradients obtained using the relative Total Electron Content (TEC) measurements
Summary
The Equatorial Ionization Anomaly (EIA) and Equatorial Spread F (ESF) are two well known daytime and nighttime processes in the equatorial and low-latitude ionosphere thermosphere system Both these processes have been investigated in quite detail through a number of ground and space based instruments (Rishbeth, 2000, and references therein). From a limited sample of eight geomagnetically quiet nights, during September 1998, 85% successful “forecasts” had been achieved by them using the strength of the EIA derived from GPS data for predictions They speculated that the GPS derived proxy for electrodynamical vertical drift may turn out to be site and season dependent in its quantitative sense. On similar grounds, Based on the Jicamarca digital ionosonde data and SCINDA 250 MHz scintillation observations obtained by receiving signals from the FLEETSAT-7 geostationary satellite during July 1998–July 1999, Anderson et al (2004) have demonstrated that there exists a threshold for the maximum E×B drift velocity (between 18:30 and 19:00 LT) of 20 m/s that determines whether or not the subsequent UHF S4 values will be below or above 0.5
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