Simulation of intense organized convective precipitation observed during the Arabian Sea Monsoon Experiment (ARMEX)

Abstract

[1] We examine a deep precipitating system that formed over the west coast of India during 26-28 June 2002 producing heavy rainfall of 2-61 cm day À1 . The system developed into a well-marked low pressure area due to interaction between an eastward moving westerly trough and a westward moving monsoon low. We used the PSU/NCAR Mesoscale Model (MM5) to make 10-day interactively nested simulations at 90, 30, and 10 km grid-resolutions. We used observations from a special data set collected during an Arabian Sea Monsoon Experiment (ARMEX) conducted June-August, 2002. Nudging the observations produced a balanced atmosphere which, in turn, matched the location of vortex with cloud clusters observed from satellite. The simulated rainfall corresponded well with observations. We then use the simulated fields as forcing and boundary conditions for MM5 run in cloud-system resolving mode at 2 km grid-resolution to detail cloud-clusters embedded within the monsoon disturbance. We examined the sensitivity to different physical parameterizations and also the effect of continuous nudging four dimensional data assimilation (FDDA) on the rainfall forecasts. While the simulation of the convective event improved with certain combinations of physical parameterizations, the rainfall was not forecasted at the correct location, no matter which parameterization was used, unless continuous FDDA was performed in all domains throughout the integrations. Finally, cloud-cluster properties of the cloud-system resolving simulations were compared with observations.

Composite characteristics of Nor'westers based on observations and simulations

“…Rain water exists in the lower levels below 600 hPa. Das et al (2006aDas et al ( , 2006bDas et al ( , 2007 studied detailed microphysics of a Himalayan cloudburst event and a heavy rainfall event over the west coast of India and verified the results with the profiles obtained from TRMM (2A12 products). Their results showed that the profile of cloud liquid water had a maximum in the lower troposphere and a secondary maximum in the middle troposphere.…”

“…Studies by Das et al (2007) indicated that the hydrometeor profiles observed by TRMM (2A12 products) are usually higher than the simulated values for the clouds off the west coast of India, but are less than the values for cloudburst events over Himachal Pradesh region (northwestern parts of India). The cloud liquid water (CLW) measured aboard P3 aircraft over the Bay of Bengal during MONEX-79 (Houze and Churchill, 1987) were about 0.1 g m −3 .…”

Simulation of a Flash Flooding Storm at the Steep Edge of the Himalayas*

“…2 At the same time, relatively stationary low-pressure systems over north-central India were situated so that moist lower-level flow was directed into the Leh region from the south-southeast. The vortex over northwest India (seen most strongly at 700 hPa; see RH) was a midlevel monsoon cyclone of the type described by Krishnamurti and Hawkins (1970), 216 Mak (1975), Carr (1977), Goswami et al (1980), and Das et al (2007). The lower row of panels of Fig.…”

A Flash-Flooding Storm at the Steep Edge of High Terrain: Disaster in the Himalayas

“…However, during the 3 days leading up to the Leh flood, the 500-mb geopotential height field showed an easterly jet . Transient vortices of this type have proved to be somewhat elusive, and have been treated only occasionally in the literature (Krishnamurti and Hawkins 1970;Mak 1975;Carr 1977;Goswami et al 1980;Das et al 2007). Winds above 500 mb also were generally easterly-northeasterly.…”