Drier North American Monsoon in Contrast to Asian–African Monsoon under Global Warming

2020 ◽  
Vol 33 (22) ◽  
pp. 9801-9816
Author(s):  
Chao He ◽  
Tim Li ◽  
Wen Zhou
Keyword(s):  
North American ◽  
Radiative Forcing ◽  
Monsoon Rainfall ◽  
Summer Monsoon Rainfall ◽  
North American Monsoon ◽  
Global Monsoon ◽  
African Monsoon ◽  
High Emission ◽  
Continental Area ◽  
Sst Warming

AbstractSummer monsoon rainfall supplies over 55% of annual precipitation to global monsoon regions. As shown by more than 70% of models, including 30 models from CMIP5 and 30 models from CMIP6 under high-emission scenarios, North American (NAM) monsoon rainfall decreases in a warmer climate, in sharp contrast to the robust increase in Asian–African monsoon rainfall. A hierarchy of model experiments is analyzed to understand the mechanism for the reduced NAM monsoon rainfall in this study. Modeling evidence shows that the reduction of NAM monsoon rainfall is related to both direct radiative forcing of increased CO2 concentration and SST warming, manifested as fast and slow responses to abrupt CO2 quadrupling in coupled GCMs. A cyclone anomaly forms over the Eurasian–African continental area due to enhanced land–sea thermal contrast under increased CO2 concentration, and this leads to a subsidence anomaly on its western flank, suppressing the NAM monsoon rainfall. The SST warming acts to further reduce the rainfall over the NAM monsoon region, and the El Niño–like SST warming pattern with enhanced SST warming over the equatorial Pacific plays a key role in suppressing NAM rainfall, whereas relative cooling over the subtropical North Atlantic has no contribution. A positive feedback between monsoon precipitation and atmospheric circulation helps to amplify the responses of monsoon rainfall.

scholarly journals Understanding Future Change of Global Monsoons Projected by CMIP6 Models

2020 ◽  
Vol 33 (15) ◽  
pp. 6471-6489 ◽  
Author(s):  
Bin Wang ◽  
Chunhan Jin ◽  
Jian Liu
Keyword(s):  
North American ◽  
Rainy Season ◽  
Monsoon Rainfall ◽  
North American Monsoon ◽  
Convective Heating ◽  
Monsoon Circulation ◽  
Future Change ◽  
Global Monsoon ◽  
African Monsoon ◽  
The Future

AbstractProjecting future change of monsoon rainfall is essential for water resource management, food security, disaster mitigation, and infrastructure planning. Here we assess the future change and explore the causes of the changes using 15 models that participated in phase 6 of the Coupled Model Intercomparison Project (CMIP6). The multimodel ensemble projects that, under the shared socioeconomic pathway (SSP) 2–4.5, the total land monsoon rainfall will likely increase in the Northern Hemisphere (NH) by about 2.8% per one degree Celsius of global warming (2.8% °C−1) in contrast to little change in the Southern Hemisphere (SH; −0.3% °C−1). In addition, in the future the Asian–northern African monsoon likely becomes wetter while the North American monsoon becomes drier. Since the humidity increase is nearly uniform in all summer monsoon regions, the dynamic processes must play a fundamental role in shaping the spatial patterns of the global monsoon changes. Greenhouse gas (GHG) radiative forcing induces a “NH-warmer-than-SH” pattern, which favors increasing the NH monsoon rainfall and prolonging the NH monsoon rainy season while reducing the SH monsoon rainfall and shortening the SH monsoon rainy season. The GHG forcing induces a “land-warmer-than-ocean” pattern, which enhances Asian monsoon low pressure and increases Asian and northern African monsoon rainfall, and an El Niño–like warming, which reduces North American monsoon rainfall. The uncertainties in the projected monsoon precipitation changes are significantly related to the models’ projected hemispheric and land–ocean thermal contrasts as well as to the eastern Pacific Ocean warming. The CMIP6 models’ common biases and the processes by which convective heating drives monsoon circulation are also discussed.

scholarly journals Uncertainty in aerosol radiative forcing impacts the simulated global monsoon in the 20th century

2020 ◽  
Vol 20 (23) ◽  
pp. 14903-14915
Author(s):  
Jonathan K. P. Shonk ◽  
Andrew G. Turner ◽  
Amulya Chevuturi ◽  
Laura J. Wilcox ◽  
Andrea J. Dittus ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Monsoon Rainfall ◽  
Scaling Factor ◽  
Global Monsoon ◽  
Tropical Rainfall ◽  
Aerosol Forcing ◽  
Monsoon Area ◽  
Hemispheric Temperature ◽  
Temperature Contrast ◽  
Aerosol Emissions

Abstract. Anthropogenic aerosols are dominant drivers of historical monsoon rainfall change. However, large uncertainties in the radiative forcing associated with anthropogenic aerosol emissions, as well as the dynamical response to this forcing, lead to uncertainty in the simulated monsoon response. We use historical simulations from the “SMURPHS” project, run using HadGEM3-GC3.1, in which the time-varying aerosol emissions are scaled by factors from 0.2 to 1.5 to explore the monsoon sensitivity to historical aerosol forcing uncertainty (present-day versus preindustrial aerosol forcing in the range −0.38 to −1.50 W m−2). The hemispheric asymmetry in emissions generates a strong relationship between scaling factor and both hemispheric temperature contrast and meridional location of tropical rainfall. Averaged over the period 1950–2014, increasing the scaling factor from 0.2 to 1.5 reduces the hemispheric temperature contrast by 0.9 ∘C, reduces the tropical summertime land–sea temperature contrast by 0.3 ∘C and shifts tropical rainfall southwards by 0.28∘ of latitude. The result is a reduction in global monsoon area by 3 % and a reduction in global monsoon intensity by 2 %. Despite the complexity of the monsoon system, the monsoon properties presented above vary monotonically and roughly linearly across scalings. A switch in the dominant influence on the 1950–1980 monsoon rainfall trend between greenhouse gases and aerosol is identified as the scalings increase. Regionally, aerosol scaling has a pronounced effect on Northern Hemisphere monsoon rainfall, with the strongest influence on monsoon area and intensity located in the Asian sector, where local emissions are greatest.

SST data improve modeling of North American monsoon rainfall

Eos ◽  
2003 ◽  
Vol 84 (43) ◽  
pp. 457 ◽  
Author(s):  
X. Gao ◽  
S. Sorooshian ◽  
J. Li ◽  
J. Xu
Keyword(s):  
North American ◽  
Monsoon Rainfall ◽  
North American Monsoon

Seasonal Shifts in the North American Monsoon

2007 ◽  
Vol 20 (9) ◽  
pp. 1923-1935 ◽  
Author(s):  
Katrina Grantz ◽  
Balaji Rajagopalan ◽  
Martyn Clark ◽  
Edith Zagona
Keyword(s):  
United States ◽  
North American ◽  
Gulf Of California ◽  
Monsoon Rainfall ◽  
Monsoon Season ◽  
North American Monsoon ◽  
Southwestern United States ◽  
Monsoon Period ◽  
The North ◽  
Ocean Conditions

Abstract Analysis is performed on the spatiotemporal attributes of North American monsoon system (NAMS) rainfall in the southwestern United States. Trends in the timing and amount of monsoon rainfall for the period 1948–2004 are examined. The timing of the monsoon cycle is tracked by identifying the Julian day when the 10th, 25th, 50th, 75th, and 90th percentiles of the seasonal rainfall total have accumulated. Trends are assessed using the robust Spearman rank correlation analysis and the Kendall–Theil slope estimator. Principal component analysis is used to extract the dominant spatial patterns and these are correlated with antecedent land–ocean–atmosphere variables. Results show a significant delay in the beginning, peak, and closing stages of the monsoon in recent decades. The results also show a decrease in rainfall during July and a corresponding increase in rainfall during August and September. Relating these attributes of the summer rainfall to antecedent winter–spring land and ocean conditions leads to the proposal of the following hypothesis: warmer tropical Pacific sea surface temperatures (SSTs) and cooler northern Pacific SSTs in the antecedent winter–spring leads to wetter than normal conditions over the desert Southwest (and drier than normal conditions over the Pacific Northwest). This enhanced antecedent wetness delays the seasonal heating of the North American continent that is necessary to establish the monsoonal land–ocean temperature gradient. The delay in seasonal warming in turn delays the monsoon initiation, thus reducing rainfall during the typical early monsoon period (July) and increasing rainfall during the later months of the monsoon season (August and September). While the rainfall during the early monsoon appears to be most modulated by antecedent winter–spring Pacific SST patterns, the rainfall in the later part of the monsoon seems to be driven largely by the near-term SST conditions surrounding the monsoon region along the coast of California and the Gulf of California. The role of antecedent land and ocean conditions in modulating the following summer monsoon appears to be quite significant. This enhances the prospects for long-lead forecasts of monsoon rainfall over the southwestern United States, which could have significant implications for water resources planning and management in this water-scarce region.

scholarly journals Uncertainty in aerosol radiative forcing impacts the simulated global monsoon in the 20th century

2020 ◽  
Author(s):  
Andrew Turner ◽  
Jonathan Shonk ◽  
Laura Wilcox ◽  
Andrea Dittus ◽  
Ed Hawkins
Keyword(s):  
Radiative Forcing ◽  
Monsoon Rainfall ◽  
Strong Relationship ◽  
Dynamical Response ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Global Monsoon ◽  
Monsoon Area ◽  
Hemispheric Temperature ◽  
Aerosol Emissions

<div> <div> <div> <p>Anthropogenic aerosols are dominant drivers of historical monsoon rainfall change.  However, large uncertainties in the radiative forcing associated with anthropogenic aerosol emissions, and the dynamical response to this forcing, lead to uncertainty in the simulated monsoon response.  We use historical simulations in which aerosol emissions are scaled by factors from 0.2 to 1.5 to explore the monsoon sensitivity to aerosol forcing uncertainty (−0.3 W m−2 to −1.6 W m−2).  Hemispheric asymmetry in emissions generates a strong relationship between scaling factor and both hemispheric temperature contrast and meridional location of tropical rainfall.  Increasing the  scaling from 0.2 to 1.5 reduces the global monsoon area by 3% and the global monsoon intensity by 2% over 1950–2014, and changes the dominant influence on the 1950–1980 monsoon rainfall trend from greenhouse gas to aerosol.   Regionally, aerosol scaling has a pronounced effect on Northern Hemisphere monsoon rainfall.</p> </div> </div> </div>

scholarly journals Intensification of the North American Monsoon Rainfall as Observed From a Long‐Term High‐Density Gauge Network

2019 ◽  
Vol 46 (12) ◽  
pp. 6839-6847 ◽  
Author(s):  
Eleonora M. C. Demaria ◽  
Pieter Hazenberg ◽  
Russell L. Scott ◽  
Menberu B. Meles ◽  
Mary Nichols ◽  
...  
Keyword(s):  
North American ◽  
Monsoon Rainfall ◽  
High Density ◽  
North American Monsoon ◽  
The North

scholarly journals Uncertainty in Aerosol Radiative Forcing Impacts the Simulated Global Monsoon in the 20th Century

2020 ◽  
Author(s):  
Jonathan K. P. Shonk ◽  
Andrew G. Turner ◽  
Amulya Chevuturi ◽  
Laura J. Wilcox ◽  
Andrea J. Dittus ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Monsoon Rainfall ◽  
Strong Relationship ◽  
Dynamical Response ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Global Monsoon ◽  
Monsoon Area ◽  
Hemispheric Temperature ◽  
Aerosol Emissions

Abstract. Anthropogenic aerosols are dominant drivers of historical monsoon rainfall change. However, large uncertainties in the radiative forcing associated with anthropogenic aerosol emissions, and the dynamical response to this forcing, lead to uncertainty in the simulated monsoon response. We use historical simulations in which aerosol emissions are scaled by factors from 0.2 to 1.5 to explore the monsoon sensitivity to aerosol forcing uncertainty (−0.38 W m−2 to −1.50 W m−2). Hemispheric asymmetry in emissions generates a strong relationship between scaling factor and both hemispheric temperature contrast and meridional location of tropical rainfall. Increasing the scaling from 0.2 to 1.5 reduces the global monsoon area by 3 % and the global monsoon intensity by 2 % over the period 1950–2014, and switches the dominant influence on the 1950–1980 monsoon rainfall trend between greenhouse gas and aerosol. Regionally, aerosol scaling has a pronounced effect on Northern Hemisphere monsoon rainfall.

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