A diagnostic study of convective environment leading to heavy rainfall during the summer monsoon 2010 over Pakistan

Abstract

Observational data and outputs from the Weather Research and Forecasting (WRF) model were used to investigate the atmospheric processes that led to an unusual extreme precipitation resulting to a destructive flash flooding, loss of life and property in northern Pakistan on 28–29 July, 2010. In this work, the model's inner most domain with horizontal grid spacing of 3km, successfully simulated the extreme precipitation with values up to 120mm within 24h. The useful dynamic and thermodynamic variables ζ→a⋅∇θ/ρ and ζ→a⋅∇θe/ρ are used to understand their roles in the atmospheric environment conducive to severe weather system. The results show that prior to the extreme rainfall, distribution of high potential vorticity anomaly in the mid-tropospheric level is conducive for the development of strong mesoscale convective vortex and large-scale cyclonic circulation. Moreover, the resulting symmetric instability due to negative moist potential vorticity anomaly located over the area significantly enhanced the vertical ascending and precipitation in the convective region. Another prominent factor was the interaction between the upper-level westerly trough and the east–west moving monsoon low clearly discernible from the synoptic situation. The aforementioned findings may be responsible for the extreme rainfall over the selected area.