Precipitation response of monsoon low-pressure systems to an idealized uniform temperature increase

Abstract

The monsoon low-pressure systems (LPSs) are one of the most rain-bearing synoptic-scale systems developing during the Indianmonsoon.We have performed high-resolution, convection-permitting experiments of 10 LPS cases with the Weather Research and Forecasting regional model, to investigate the effect of an idealized uniform temperature increase on the LPS intensification and precipitation. Perturbed runs follow a surrogate climate change approach, in which a uniform temperature perturbation is specified, but the large-scale flow and relative humidity are unchanged. The differences between control and perturbed simulations are therefore mainly due to the imposed warming and moisture changes and their feedbacks to the synoptic-scale flow. Results show that the LPS precipitation increases by 13%/K, twice the imposed moisture increase, which is on the same order as the Clausius-Clapeyron relation. This large precipitation increase is attributed to the feedbacks in vertical velocity and atmospheric stability, which together account for the high sensitivity. In the perturbed simulations the LPSs have higher propagation speeds and aremore intense. The storms intensification to the uniformtemperature perturbation can be interpreted in terms of the conditional instability of second kind mechanism where the condensational heating increases along with low-level convergence and vertical velocity in response to temperature and moisture increases. As a result, the surface low deepens.