Long-term vertical air motion characteristics over the gateway of Indian Summer Monsoon using direct measurements using Cochin ST Radar

One of the most important meteorological parameters is the vertical air motion. Accurate measurement is only possible using the vertical profiling radars. This paper presents the first long-term characteristics of vertical air motion over the gateway of Indian summer monsoon using the Cochin ST radar. It is seen that the lower troposphere (< 4 km) generally presents a downward mean motion all throughout the year. While centred around the summer monsoon months, 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 the 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 the monsoon months represents a “two-step process” of transport of air mass from lower the troposphere to the lower stratosphere and vice versa. Hourly mean characteristics show that the clear two-step structure persists in the monsoon months with clear reversal around 12-13 km during 10-19 IST. The consistent downdrafts can be called representative of the region and attributed to the gentle subsidence associated with intermittent convective activity away from the location of observation. In contrasting seasons such as winter no clear established transport mechanisms are seen, barring a few windows where such transport maybe feasible.