Characterizing global equatorial sporadic-E layers through COSMIC GNSS radio occultation measurements

Abstract

The Global Navigation Satellite System Radio Occultation (GNSS-RO) technique has proven to be a powerful tool for studying E-region irregularities, i.e., Sporadic E (Es) which is primarily associated with the amplitude and phase scintillations. In the present study, an extensive 7-year GNSS-RO scintillation indices data from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations was employed to investigate the global distribution and seasonal variation of the Es occurrences under solar activity near the magnetic dip equator. Our analysis from the Earth’s magnetic field parameters such as horizontal intensity and inclination estimated by the International Geomagnetic Reference Field model (IGRF) reveals that Earth’s magnetic field plays a crucial role in determining the global distribution of Es layers. Moreover, the abundance of Es shows a clear dependence on season/longitude, and the occurrence statistics of Es are closely aligned with the earlier reports. The solar activity dependence of the Es occurrence characteristics demonstrates its significant reduction with increased solar activity for most of the seasons in all longitude sectors. We address the Gradient Drift instability as a source mechanism of the Es layer’s appearance at the magnetic dip equator, where wind shear theory fails to operate because of the minimal inclination of the geomagnetic field.