The interaction of Indian monsoon depressions with northwesterly midlevel dry intrusions

Fletcher, J.K. and Parker, D.J. and Hunt, K.M.R. and Vishwanathan, G. and Mrudula, G (2018) The interaction of Indian monsoon depressions with northwesterly midlevel dry intrusions. Monthly Weather Review, 146 (3). pp. 679-693. ISSN 00270644

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Abstract

Monsoon depressions (MDs) bring substantial monsoon rainfall to northern and central India. These events usually form over the Bay of Bengal and travel across northern India toward Pakistan. Using European Centre for Medium-Range Weather Forecasts interim reanalysis, an MD-tracking algorithm, and an objective identification method, the authors find that about 40% of MDs interact with northerly intrusions of dry desert air masses as the MDs traverse the subcontinent. MD interactions with dry intrusions are often preceded by positive potential vorticity (PV) anomalies on the subtropical jet and low-level anticyclonic anomalies over the north Arabian Sea. Dry intrusions nearly halve the precipitation rate in the southwest quadrant of MDs, where MDs rain the most. However, dry intrusions increase the rainfall rate near the MD center. Similarly, ascent is reduced west of the MD center and enhanced at the MD center, especially in the upper troposphere. The reduced ascent west of MD centers is likely attributable to changes in vertical shear reducing differential cyclonic vorticity advection. Dry intrusions slightly reduce MDs’ propagation speed. For the mid- to upper-level vortex, this can be explained by anomalous westerlies reducing propagation by adiabatic advection. For the lower-tropospheric vortex, it is likely that reduced diabatic generation of PV plays a role in slowing propagation, along with reduced adiabatic advection.

Item Type: Article
Subjects: RENEWABLE ENERGY > Wind Energy
CHEMISTRY AND MATERIALS > Chemistry and Materials (General)
ENGINEERING > Electronics and Electrical Engineering
Depositing User: Mrs SK Pratibha
Date Deposited: 28 Jan 2022 04:55
Last Modified: 28 Jan 2022 04:55
URI: http://nal-ir.nal.res.in/id/eprint/13214

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