Characteristics of Vertical Air Motion During Summer Monsoon Over the Central Himalayan Region Using 206.5 MHz ARIES Stratosphere-Troposphere (ST) Radar

Abstract

First observations on the characteristics of vertical velocity during the Asian Summer Monsoon (ASM) months, over the central Himalayan region using 206.5 MHz Stratosphere-Troposphere radar are presented. Clear air zenith observation data have been extracted and analyzed to determine the distribution of vertical velocity occurrence and the mean vertical velocity profiles up to 16 km from June to October. Results show that the mean updraft and downdraft characteristic velocity ∼4 km did not generally exceed 5 cm s⁻¹ for all the months. An exception to this feature is observed as a layer of persistent downdraft between 10 and 11 km with a maximum mean vertical velocity of ∼−7 cm s⁻¹ in August, which is new observation. Consistent downdrafts in the lower troposphere and consistent updrafts in the upper troposphere above 12 km show that direct transport of airmass from lower to upper level and vice versa is not climatologically supported. In turn, such profile shows similarity to the two-step process of upliftment of air mass in the tropical region. Notably this height corresponds to the lower level of ASM Anticyclone and gives insight in to the entrapment and slow upliftment of airmass toward stratosphere. Further analysis of inter-period variability of vertical velocity for forenoon, afternoon, and evening periods for all the months show notable variations in the mid-tropospheric region with barely any change in the upper troposphere above 12 km, indicating that the slow upward transport does not directly depend on the inter-period variability for any of the months.