Long‐term vertical air motion characteristics over the gateway of Indian summer monsoon using direct measurements by the Cochin stratosphere–troposphere radar

Abstract

Abstract This article presents the first long‐term characteristics of vertical air motion over the gateway of Indian summer monsoon using the Cochin stratosphere–troposphere radar (10.04°N, 76.33°E). It is seen that the lower troposphere (<4 km) generally presents a downward mean motion throughout the year. While centred around June–July–August (JJA), downdrafts below 12–13 km and updrafts above that (both generally <5 cm·s −1 in magnitude) are noted. It is ensured that the dataset considered does not suffer from any significant bias due to several possible factors, including possible jet contamination, and the results are thus representative of real atmospheric features. The structure of mean vertical velocity as seen in JJA represents a ‘two‐step process’ of transport of air mass from the lower troposphere to the lower stratosphere and vice versa. Hourly mean vertical motion shows that the clear two‐step structure persists during JJA with clear reversal around 12–13 km during 1000–1900 Indian Standard Time (IST = UTC + 0530). The consistent downdrafts can be called representative of the region and attributed to the gentle subsidence associated with intermittent yet widespread convective activity away from the location of observation. In contrast, like during December–January–February (DJF), such a mechanism of transport is not discernible.