Moist convection and water vapour transport into the upper troposphere over the Third Pole in multi-scale ICON-CLM simulations

Abstract

Water vapour exchange into the upper troposphere (UT) remains poorly understood over the Third Pole region. Previous studies have mainly focused on monsoon related moistening of the UT using reanalysis and satellite data. In this study, we employ km-scale (Dx = 3.3 km) ICON-CLM simulations to investigate the role of convection in transporting water vapour into the UT over the Third Pole. We analyse three extreme precipitation and snowfall events, each associated with different atmospheric processes and seasons, to better understand the impact of model resolution and convection-scheme configuration on UT moisture transport. The km-scale ICON-CLM simulations provide a substantially improved representation of these extreme events compared to coarser (Dx = 13 km) ICON-CLM simulations and reanalyses (IMDAA, ERA5) that use deep convection parameterisation. A km-scale simulation with parameterised shallow convection of a mesoscale Tibetan Plateau (TP) vortex event over the east of TP showed more water vapour transport to the UT region (above 300 hPa) than a km-scale simulation without any parameterisation (i.e. with explicit simulation) of convection. The opposite was simulated for an event with extreme precipitation during monsoon over the central Himalayas. All ICON-CLM simulations and reanalyses failed to capture the extreme snow event driven by lake effect processes over the Tibetan Plateau and exhibited only a slight water vapour enhancement in the UT. For all the events, km-scale simulated water vapour in the UT was consistent with satellite observations over the TP. Additionally, Lagrangian air parcel tracking and CALIPSO observations indicate that the extreme events over the Himalayan region transported more water vapour into the UT than the other analysed events. Only a few air parcels reached near the tropopause (100 hPa) within a few hours of the Lagrangian tracking initiation; once air parcels reach the upper troposphere, they advect eastward. The three analysed events suggest that, in the simulations, extreme events can enhance water vapour transport into the UT but may not convectively penetrate the lower stratosphere over the Third Pole region. Additionally, for the investigated events, the vertical transport processes associated with convection are better represented in the km-scale simulations than in the coarser, convection parameterised simulations and reanalyses.