Evolutionary phases of equatorial spread F including L band scintillations and plumes in the context of GPS total electron content variability: A case study

Abstract

The evolution of large-scale (few kilometers), medium-scale (few hundreds of meters), and small-scale (meters) size plasma density irregularities in the postsunset equatorial F region, in the context of characteristic GPS total electron content (GTEC) variations, are reported from Indian longitudes. The ionograms and GTEC from a GPS receiver installed as a part of the GPS Aided Geo Augmentation Network (GAGAN) project for satellite-based navigation are obtained from an equatorial station at Trivandrum (8.5N, 76.91E, dip latitude 0.5N). The variations in the GTEC with respect to TEC are considered to represent the seed perturbations for the plasma instability that results in the equatorial spread F (ESF) irregularities and are treated as a perturbation factor (P). The VHF radar at Gadanki (13.5N, 79.17E, dip latitude 6.4N) provided the small-scale structures of ESF. The background thermospheric conditions that affect the growth of the plasma instability through ion-neutral collision frequency ( in) are estimated using the F region base height (hF)and the representative scale height of the neutral atmosphere and are represented by a growth factor (G). The present case study reveals a close coupling between the background ionospheric conditions and the baseline perturbations in deciding the evolutionary phases of ESF. It has been shown that although large-scale (kilometer scale) irregularities are formed without any constraints when the background ionospheric-thermospheric conditions are favorable in the presence of fluctuations in GTEC, consistently, the medium-scale and small-scale irregularities show remarkable similarity with the variations in the product of the perturbation and growth factors. Copyright 2011 by the American Geophysical Union.