Persistent Heavy Downpour in Desert Areas of Pakistan in South Asian Monsoon 2011

Cheema S B, Q. Zaman, G. Rasul


This diagnostic study carried out to understand the phenomenon of heavy rainfall which gripped up the Sindh in August and September 2011. National Center for Environmental Prediction (NCEP) Reanalysis data alongwith satellite and high resolution model (HRM) outputs are used for the post analyses of this downpour. The model output and satellite imagery captured well spatial and temporal distribution of the rainfall event. The analysis showed that heavy rainfall occurred over this province due to orientation of monsoon currents. A low pressure system developed over Bay of Bengal (BoB) passed over India and entered in Pakistan fro m 07 August, afterwards this tropical depression merged into seasonal low on 10th Aug and accentuated the weather system. Moisture was supplied from (BoB) and Arabian Sea (AS) during the monsoon season. Orientation of Tibetan high also played a crucial role for spatial distribution of precipitation over Sindh. This high blocked the monsoon current from penetration in north. At same time, another high pressure system was lying over Iran and its ridge was extended up
to Baluchistan and Karachi Region. It bloc ked westward movement of monsoon depressions. A mid tropospheric cyclone (MTC) generated along the coastal boundary of Mumbai (India) and caused another heavy rainfall event from 29thAug to 16th September. The structure and intensification of this MTC has been discussed in this study.
This paper also brings out the relationship between precipitation and large scale circulation such as monsoon orientation, tilting of Tibetan High, generation of MTC which are main causes for this rainfall event in 2011.

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