Spatio-temporal distribution of tropospheric water vapour over Arabian Sea and Equatorial Indian Ocean in boreal winter of 2018

Abstract

Balloon-borne experiments carried out onboard ORV Sagar Kanya over the Arabian Sea (AS) and Equatorial Indian Ocean (EIO) during the period 16 January 2018–14 February 2018 in northern hemisphere winter are used to study the spatio-temporal distribution of tropospheric water vapour. The column-integrated water vapour (IWV) showed an increase of ~10 kg/m2 over the Equatorial Indian Ocean (EIO) compared to that over Arabian Sea (AS). Amount of water vapour in the free troposphere increases towards south with water vapour enhancement observed up to an altitude of 12 km over the equator. This is mainly due to convective outflows emanating from the Inter Tropical Convergence Zone (ITCZ). Along 2°S, the IWV showed an east–west (75–65°E) gradient with high values in the east. During the return leg of the ship cruise, when the AS is convectively disturbed with cloud tops extending up to mid-troposphere, the IWV showed an increase of about 10–15 kg/m2 compared to that observed during onward leg under fair weather conditions, particularly due to the accumulation of water vapour in the 2–7 km altitude region. Over the deep ocean the diurnal amplitude of water vapour shows a clear altitude variation with lesser amplitude in the lower troposphere compared to land.