Simulating moisture transport over the Tibetan Plateau in Summer across hydrostatic to non-hydrostatic scales with a global variable-resolution model

Abstract

Moisture transport in summer induces annual precipitation peak over the Tibetan Plateau (TP) thus being one crucial sustentation of water cycle between the TP and its surrounding areas. Simulating moisture transport accurately over the TP remains uncertain for current numerical models with one important influencing factor as horizontal resolution. In this study, in order to investigate the difference in moisture transport at resolutions from hydrostatic to non-hydrostatic scales, three experiments are conducted for summer of 2015 using a global variable-resolution model, including one with a globally quasi-uniform resolution of 60 km (U60km) and two with regional refinements over the TP at resolutions of 16 km (V16km) and 4 km (V4km), respectively. The differences in moisture transport among three simulations are significantly influenced by the changes in wind fields through the Himalayas and eastern TP at two layers, 700~600 and 600~400 hPa, which is largely modulated by their difference in large-scale circulations particularly monsoon depression. At hydrostatic scale (from 60 km to 16 km), the monsoon depression is slightly stronger and shifts northward along with the mid-latitude westerlies, which is due to the combination of the sensitivity of convection scheme to integrating timestep and different extents of resolved dynamical processes at different resolutions. With horizontal resolution increasing to convection-permitting scale (from 16 km to 4 km), the resolved moist convection along with its associated less latent heat leads to weaker monsoon depression over the south of TP, which is much larger than the resolution induced difference at hydrostatic scale.