Multi-altitude observations of the lower atmospheric disturbances and its ionospheric signatures over the Indian region

Abstract

Tropospheric disturbances like tropical cyclones produce a spectrum of gravity waves which can propagate to higher altitudes and can even perturb the ionosphere-thermosphere system. The observations of a severe cyclonic storm Hudhud during 7–14 October 2014 using vertical total electron content (VTEC) from 11 stations and the brightness temperature from AIRS (atmospheric infrared sounder) imagery are analysed. Main results show ring-arc structures resembling concentric gravity waves (CGWs) in the brightness temperature and widespread, synchronized and episodic perturbations in VTEC during 10, 11 and 12 October. The stratospheric perturbations are found to spread in a range of radial distance between ∼ 730 and 2500 km with horizontal wavelengths between 307 and 541 km. A wavelet analysis of the daytime band-pass (5–60 min) filtered dVTEC perturbations shows enhancements in the spectral power associated with periods of ∼ 30–50 min on different days following the cyclone movement from east to west. The radial phase speed of the dVTEC for different temporal bands is found to vary between 114 and 320 m/s at different intervals during 10–11 October. Additionally, a comparative analysis of the past and present results is performed using the established dispersion relations which shows a compatible range of variability of wave parameters among all the studies including the present results. The results substantiate strong signatures of the Hudhud cyclone at multiple altitudes and depict vertical coupling of the atmosphere–ionosphere system through a theoretical framework.