On the response of equatorial and low latitude ionosphere over Indian region to the tropical cyclones

Abstract

This paper presents, for the first time, the distinct impacts of two tropical cyclones Ockhi (2017) and Burevi (2020) on the equatorial and low-latitude ionosphere using multiple ionospheric parameters, including the Equatorial Electrojet (EEJ)-induced magnetic field, foF2, h′F, and GPS TEC. As the cyclones traversed the Indian equatorial region, the study investigates how modified electrodynamics over the dip equator (Trivandrum: 8.5°N, 77°E, 0.5°N dip latitude) influenced the low-latitude ionosphere (Hyderabad: 17.4°N, 78.4°E, 11.7°N dip latitude). During the passage of Tropical Cyclone Ockhi, a strong Counter-Electrojet (CEJ) with varying strength (–22 to −5 nT) was observed, accompanied by a decrease in foF2, and TEC at the equatorial site. Correspondingly, the low-latitude ionosphere also exhibited a decrease in TEC. In contrast, Tropical Cyclone Burevi, which was weaker than Ockhi, exhibited a weaker CEJ (−13 to −2.6 nT) along with an increase in critical frequency of F2 layer, and TEC at the equatorial site. Similarly, the low-latitude ionosphere showed an increase in TEC during Burevi’s passage. Ockhi, being a more intense cyclonic storm, demonstrated the presence of strong blanketing Es layers over Trivandrum, particularly near the peak of its cyclonic activity. On these days, although the Pre-Reversal Enhancement (PRE) was weaker, the presence of Equatorial Spread-F (ESF) was still observed. The wavelet periodogram of the EEJ-induced magnetic field, h′F and TEC revealed an intensification of gravity waves with ∼1-hour periodicity during the cyclones’ passage. Similarly, wavelet analysis of TEC over Trivandrum indicated the presence of enhanced terdiurnal tides during these events. It is proposed that. gravity waves generated by the cyclones likely caused the observed CEJs and ESF events. The observed variability in ionospheric parameters and TEC is attributed to modifications in E-region electrodynamics and subsequent changes in the plasma fountain. Strong tropical cyclones can disrupt the ionosphere through intense convection and lightning activity. Therefore, identifying the disturbances associated with cyclones is important for the studies pertaining to ionospheric modelling and space weather forecasting.