Origin and maintenance of upper tropospheric inversion over the northern Indian Ocean during boreal winter of 2018

摘要: Radiosonde observations over the Indian Ocean on board ORV Sagar Kanya showed the presence of a sharp thermal inversion layer in the upper troposphere during the onward leg of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) ship cruise in winter 2018 (12° N–2° S, 75° E; 16–24 January 2018). This temperature inversion layer having a thickness of ~ 300 m, referred to as upper tropospheric inversion (UTI) observed near 15 km altitude at 12° N showed a gradual descent towards the equator reaching about 13 km altitude at 2° S. Daily radiosonde observations at a nearby island station Minicoy (8.27° N, 73.05° E) revealed similar UTI structure for about 20 days during the period 5–24 January 2018, indicating that the UTI features observed during the cruise period were temporal in nature. The persistent inversion layer which is situated on the top of a ~ 2 km thick moist layer is …