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Changing Circulation Structure and Precipitation Characteristics in Asian Monsoon Regions: Greenhouse Warming vs. Aerosol EffectsUsing model outputs from CMIP5 historical integrations, we have investigated the relative roles of anthropogenic emissions of greenhouse gases (GHG) and aerosols in changing the characteristics of the large-scale circulation and rainfall in Asian summer monsoon (ASM) regions. Under GHG warming, a strong positive trend in low-level moist static energy (MSE) is found over ASM regions, associated with increasing large-scale land-sea thermal contrast from 1870's to present. During the same period, a mid tropospheric convective barrier (MCB) due to widespread reduction in relative humidity in the mid- and lower troposphere is strengthening over the ASM regions, in conjunction with expanding areas of anomalous subsidence associated with the Deep Tropical Squeeze (DTS) [Lau and Kim, 2015]. The opposing effects of MSE and MCB lead to enhanced total ASM rainfall, but only a partial strengthening of the southern portion of the monsoon meridional circulation, coupled to anomalous multi-cellar overturning motions over ASM land. Including anthropogenic aerosol emissions strongly masks MSE but enhances MCB via increased stability in the lower troposphere, resulting in an overall weakened ASM circulation with suppressed rainfall. Rainfall characteristics analyses indicate that under GHG, overall precipitation efficiency over the ASM region is reduced, manifesting in less moderate but more extreme heavy rain events. Under combined effects of GHG and aerosols, precipitation efficiency is unchanged, with more moderate, but less extreme rainfall.
Document ID
20180003058
Acquisition Source
Goddard Space Flight Center
Document Type
Accepted Manuscript (Version with final changes)
Authors
William K M Lau
(University of Maryland, College Park College Park, Maryland, United States)
Kyu-myong Kim
(Goddard Space Flight Center Greenbelt, Maryland, United States)
L Rudy Leung
(Pacific Northwest National Laboratory Richland, Washington, United States)
Date Acquired
May 25, 2018
Publication Date
November 28, 2017
Publication Information
Publication: Geoscience Letters
Publisher: SpringerOpen
Volume: 4
Issue: 28
Issue Publication Date: January 1, 2017
e-ISSN: 2196-4092
Subject Category
Geophysics
Report/Patent Number
GSFC-E-DAA-TN51593
Funding Number(s)
CONTRACT_GRANT: 80NSSC17K0213
CONTRACT_GRANT: DE-AC05-76RLO1830
Distribution Limits
Public
Copyright
Use by or on behalf of the US Gov. Permitted.
Keywords
Asian monsoon
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