March of Buoyancy Elements during Extreme Monsoon Rainfall

A major rain storm in Uttarakhand caused heavy rains and a major loss of life from floods and land slide during June 16 to 18, 2013. The observed daily rainfall during the 16th and 17th were 220 mm and 370 mm respectively. However, the actual rainfall could have been much more at Kedarnath, Gangotri and Badrinath which are located above 3000 m. At these locations the rain gauge sites of the India Meteorological Department (IMD) were all located largely in the lower parts of the Himalayas (i.e. below 2,000 m) and there are no raingauge sites at the higher elevations (above 3000 m). The faster movement of onset isochrones across the country in June 2013, a stronger westerly system, the interaction between the well-formed low-pressure system and the upper air westerly trough, a large incursion of moist air from the Bay of Bengal and favorable geography and orography were considered as some of the important factors for this event of devastating floods and landslides. The streaming of moist air from the east south east and warmer air from the south west contributed to the sustained large magnitudes of buoyancy and CAPE of clouds that contribute to the longer period heavy rains. The arrival of a western disturbance was an additional factor in the time history of this event. Our work addresses enhanced and sustained buoyancy/CAPE of clouds through sensitivity studies using a cloud resolving model. Here the buoyancy enhancement is studied as a function of moist rivers and warm/moist air entrainment into the interior of clouds using a cloud resolving non hydrostatic model with detailed microphysics. This study also addresses a post-processing algorithm that provides an analysis of a time rate of change for the buoyancy equation. Moist air streams and warm/moist air intrusions into heavily raining clouds are part of this buoyancy enhancement framework. We have designed a control experiment that has benefited from the post processing to produce the best results for the heavy sustained Uttaranchal rains. A number of other experiments show the sensitivity and the degradation of these control run results. The areas covered in this study include: i) Use of high resolution modeling, 1 km cloud resolving resolution, ii) Now casting of rains using physical initialization with a Newtonian relaxation, iii) use of an adaptive observational strategy, iii) sensitivity of the evolution of fields and populations of buoyancy elements to boundary layer moisture, iv) role of orography and details of buoyancy budget. The heavy rains of the order of 300 + mm/day over Uttaranchal are modeled and the role of the buoyancy growth is illustrated as an important element in this study.