Evolution of tracer and ice crystal distribution in the young plumes of overshooting turrets from the StratoClim golden flight

Deployment of the high-altitude M55-Geophysica aircraft in Kathmandu during Summer 2017 within StratoClim campaign has yielded a wealth of unique high-resolution measurements in the Asian Monsoon Anticyclone (AMA). In a particular flight (F8, 10 August 2017) the aircraft flew at the cold-point tropopause level through active overshoots and their outflows minutes to hours old. The measurements reveal up to 2500 ppmv of ice water above 17 km in large aggregated ice crystals up to 700 µm in diameter. Smaller crystals were observed as high as 18.8 km (410 K). Tracer and thermodynamical measurements show manifestations of vigorous vertical motions and provide evidence for ongoing mixing of tropospheric and stratospheric air around the tropopause. We use an ensemble of airborne and satellite measurements inside and downwind of convective overshoots together with trajectory modeling to characterize the impact of overshooting convection on the thermodynamical structure and chemical composition of the Asian tropopause layer. The effect of cross-tropopause convective transport on the Asian lower stratospheric water vapour is discussed.