Ionospheric and atmospheric response to extremely severe cyclonic storm Nida of 29 July-02 August 2016

Abstract

Tropical cyclones are one of the biggest threats to life and property. During cyclone period storm surge, flooding, extreme winds, tornadoes and lighting cause significant impacts on life and property and hence affects life of human being to a great extent. Nida was the third tropical cyclone requiring the issuance of tropical cyclone warning signals by the Hong Kong Observatory in 2016 and maximum hourly mean winds of 158 km/hr was recorded in Hong Kong. It affected many cities of China and about 500,000 people, more than 300 houses collapsed and made economic loss of about 500 million RMB. Investigation of lightning discharges around the cyclone track line revealed that the strong lightning activity is noticed during the cyclone period with a super lightning maxima on 30 July and 01 August. The effect of this typhoon on the ionosphere is studied using the TEC data from GPS measurements taken around the cyclone track and satellite based COSMIC measurements. Strong convective activity which is driver for the thunderstorm and gravity waves activity noticed from the negative cloud top temperature as low as −50°C observed from AIRS satellite during the cyclone period. Significant enhancement is atmospheric ozone is observed during the cyclone period which could be attributed to thunderstorm activity present during the cyclone period. The analysis found decrease in GPS-TEC data at stations around Hong Kong region during the landfall of the cyclone. The magnitude of perturbation in TEC is found larger at stations lying toward right/eastward of the cyclone track as compared to those in the left/westward from the cyclone track. In addition, periodic signatures in ionospheric TEC data were also detected. Continuous wavelet transform to DTEC data has been made to estimate period and found the periodic structure in ionospheric TEC belongs to AGWs with period 9–20 min and frequency 1–2 mHz. Strong scintillation activity as high as S4-index 1.35 from GPS measurements has been noticed at Sanya station during cyclone period on 02 August which is further confirmed by satellite based measurements from COSMIC. Both measurements show maximum scintillation activity during 1400–1600 UT. The strong scintillation activity as compared to normal days observed during the cyclone period is attributed to lightning induced electric filed as well as generation of AGWs due to deep convection which could act as seed perturbation for generation of ionospheric irregularities by Rayleigh-Taylor instability mechanism.