Model-Based Investigation of the Upper Tropospheric–Lower Stratospheric Composition during the Field Campaign StratoClim 2017

Abstract:

In the upper troposphere and lower stratosphere (UTLS) region over South Asia, the prevailing large-scale anticyclonic circulation during boreal summer and the associated overshooting convection have a major impact on the hydration/dehydration mechanisms. Both numerical and observational studies acknowledge that microphysical properties of ice phase hydrometeors linked to deep convection are not fully understood. Therefore, adequate quantification of the updraft/ice-particles relationship is crucial for better formulation of deep convection. The StratoClim project enabled significant samplings of UTLS region in July and August 2017, over the southern slopes of the Himalayas. In addition to the comparison with measurements from the field campaign, this model-based study aims to quantitatively evaluate the effect of key processes associated with deep convection that modulate water vapor in the tropical tropopause layer (TTL) and lower stratosphere. Also, we explore micro- and macrophysical properties of TTL cirrus clouds related to deep convection. The numerical experiment involves a real case study to reproduce convective overshoots and TTL properties captured during the M55-Geophysica flight no. 8 on August 10, 2017. The simulation is carried out using an isotope-enabled version of the Weather Research and Forecasting (WRF-ARW) Model. The model configuration involves four telescoping domains of 9-, 3-, 1-, and ~ 0.3 km horizontal grid spacings, encompassing the trajectory of flight no. 8. A stretched vertical grid is used with a high-resolution vertical grid spacing of 100 m within and around the TTL. WRF is driven with ERA5 reanalysis and Isotope-Incorporated Global Spectral Model (IsoGSM). An additional post-processing of model output includes the use of Cloud Resolving Model Radar Simulator (CR-SIM v3.3). An in-depth analysis of the four-dimensional model-based data is carried out and compared to observations from the StratoClim campaign.