Abstract

Tibetan Plateau (TP), a high elevation region in the Asian subcontinent, play an influential role in the Indian summer monsoon. In this numerical model study, sensitivity to the local changes in the microphysics over Tibet on the model forecast of circulation and precipitation over Indian monsoon regions is assessed. The local modification of the cloud microphysical parameters, riming, over TP is attempted. The simulation experiments have been carried out for different synoptic situations during the summer monsoon season. The riming gave differing responses in the two synoptic cases with the ice to rain conversion displaying a uniform distribution throughout the atmospheric column for the active monsoon case, whereas it is restricted up to an altitude of 8000 m in pre-monsoon case. The experiment over TP gives a 1.97% increase (0.54% reduction) in the all India rainfall for the pre-monsoon (active monsoon) case, which are mainly driven by the changes in the monsoon core zone. The maximum impact is found in Western Ghats rainfall with a 3.74% reduction (10.49% increases) for the pre-monsoon (active monsoon) case. Modulations in Tropical Easterly Jet and surface circulations in the experiments have substantial effect over the head Bay and the Western Ghats.

Research highlights

• Tibet Plateau (TP) played a significant role in the circulation and precipitation over Indian monsoon region. In this study, the impact of locally modified microphysics parameters (riming) over TP is estimated through NCMRWF Unified Model sensitivity experiments.

• Precipitation distribution in both pre-monsoon and active monsoon synoptic situation shows a different response with the riming modification.

• The experiment gives a 1.97% increase (0.54% reduction) in the all India rainfall for the pre-monsoon (active monsoon) case, with maximum impact in Western Ghat region.

• Current modelling approach may be useful for the different cloud observation projects.