Detection of monsoon inversion by TIROS-N satellite

Abstract

Colon¹ and Ramage² have investigated the thermal stratification of the summer monsoon air and presented evidence of a well-defined temperature inversion in the lower atmosphere over the Arabian Sea. This inversion is low (base between 900 and 800 mbar) and strong over the western Arabian Sea and weakens and rises (base at ∼700 mbar) towards the coast of India and is not observed east of 70 °E, especially during the active monsoon³. The presence of dry warm continental air from Africa and Arabia above the maritime air is thought to be associated with this inversion. This inversion is very important to the rain producing potential of the monsoon current because once the inversion is destroyed there is a favourable stratification for rapid release of moisture upwards leading to precipitation. Observations of the western Arabian Sea inversion features have previously been reported only from in situ ship radiosonde and aircraft dropsonde measurements. Although the basic accuracy and the vertical resolution of the present-day satellite sensors cannot delineate the small-scale variations of temperature⁴ such as monsoon inversions we have detected these features from just the TIROS-N derived sea-surface temperatures and the 1,000–850 mbar layer-mean temperatures using a simple differencing procedure. From these temperatures and simultaneous satellite-derived mid-tropospheric water vapour content, we show here the close link between the extent of inversion regions and the convective processes with the Indian monsoon at its different phases.