A Study on the Lower Tropospheric Thermal Inversion Over the Arabian Sea Using Radiosonde and IASI Data

摘要

Over the temperature inversion regions, tropospheric temperature increases with height and clouds are unable to grow vertically. Over the western Arabian Sea, thermal inversion (TI) is seen at the lower troposphere during the Indian summer monsoon season of June to September. Characteristics of this TI are studied using radiosonde data collected over two stations viz., Muscat (23.5°N; 58.5°E) and Salalah (17.0°N; 54.1°E), located close to the TI region and compared with satellite data. Results suggest that the inversion pattern is highly variable on day-to-day basis over Muscat but is nearly constant over Salalah. Three distinct inversion patterns are identified over Muscat. They are: Type-1: temperature increases with height from surface to about 900 hPa and decreases thereafter; Type-2: temperature decreases with height in a shallow region close to the surface followed by an increase up to about 900 hPa and decreases thereafter; and Type-3: multiple inversions up to about 850 hPa. Salalah always showed type-2 inversion with peak temperature around 950 hPa. Statistics of the occurrence of different inversion types are computed for Muscat and Salalah. This paper also evaluates the ability of Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOP satellite in identifying the TI over the Arabian Sea. IASI data are able to capture type-1 and type-2 inversions over Muscat but is unable to capture the type-3 inversions due to its coarser vertical resolution. IASI data are also unable to capture the sharp inversion over Salalah for the same reason.