scholarly journals The effect of regional changes in anthropogenic aerosols on rainfall of the East Asian Summer Monsoon

2013 ◽  
Vol 13 (3) ◽  
pp. 1521-1534 ◽  
Author(s):  
L. Guo ◽  
E. J. Highwood ◽  
L. C. Shaffrey ◽  
A. G. Turner
Keyword(s):  
Surface Temperature ◽  
Black Carbon ◽  
Land Surface Temperature ◽  
Land Surface ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Surface Cooling ◽  
Anthropogenic Aerosols ◽  
Asian Summer

Abstract. The response of East Asian Summer Monsoon (EASM) precipitation to long term changes in regional anthropogenic aerosols (sulphate and black carbon) is explored in an atmospheric general circulation model, the atmospheric component of the UK High-Resolution Global Environment Model v1.2 (HiGAM). Separately, sulphur dioxide (SO2) and black carbon (BC) emissions in 1950 and 2000 over East Asia are used to drive model simulations, while emissions are kept constant at year 2000 level outside this region. The response of the EASM is examined by comparing simulations driven by aerosol emissions representative of 1950 and 2000. The aerosol radiative effects are also determined using an off-line radiative transfer model. During June, July and August, the EASM was not significantly changed as either SO2 or BC emissions increased from 1950 to 2000 levels. However, in September, precipitation is significantly decreased by 26.4% for sulphate aerosol and 14.6% for black carbon when emissions are at the 2000 level. Over 80% of the decrease is attributed to changes in convective precipitation. The cooler land surface temperature over China in September (0.8 °C for sulphate and 0.5 °C for black carbon) due to increased aerosols reduces the surface thermal contrast that supports the EASM circulation. However, mechanisms causing the surface temperature decrease in September are different between sulphate and BC experiments. In the sulphate experiment, the sulphate direct and the 1st indirect radiative effects contribute to the surface cooling. In the BC experiment, the BC direct effect is the main driver of the surface cooling, however, a decrease in low cloud cover due to the increased heating by BC absorption partially counteracts the direct effect. This results in a weaker land surface temperature response to BC changes than to sulphate changes. The resulting precipitation response is also weaker, and the responses of the monsoon circulation are different for sulphate and black carbon experiments. This study demonstrates a mechanism that links regional aerosol emission changes to the precipitation changes of the EASM, and it could be applied to help understand the future changes in EASM precipitation in CMIP5 simulations.

scholarly journals The effect of regional changes in anthropogenic aerosols on rainfall of the East Asian Summer Monsoon

2012 ◽  
Vol 12 (9) ◽  
pp. 23007-23038 ◽  
Author(s):  
L. Guo ◽  
E. J. Highwood ◽  
L. C. Shaffrey ◽  
A. G. Turner
Keyword(s):  
Surface Temperature ◽  
Black Carbon ◽  
Land Surface Temperature ◽  
Land Surface ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Surface Cooling ◽  
Anthropogenic Aerosols ◽  
Asian Summer

Abstract. The response of East Asian Summer Monsoon (EASM) precipitation to long term changes in regional anthropogenic aerosols (sulphate and black carbon) is explored in an atmospheric general circulation model, the atmospheric component of the UK High-Resolution Global Environment Model v1.2 (HiGAM). Separately, sulphur dioxide (SO2) and black carbon (BC) emissions in 1950 and 2000 over East Asia are used to drive model simulations, while emissions are kept constant at year 2000 level outside this region. The response of the EASM is examined by comparing simulations driven by aerosol emissions representative of 1950 and 2000. The aerosol radiative effects are also determined using an off-line radiative transfer model. During June, July and August, the EASM was not significantly changed as either SO2 or BC emissions increased from 1950 to 2000 levels. However, in September, precipitation is significantly decreased when emissions are at the 2000 level. The cooler land surface temperature over China in September due to increased aerosols reduces the surface thermal contrast that supports the EASM circulation. However, mechanisms causing the surface temperature decrease in September are different between sulphate and BC experiments. In the sulphate experiment, the sulphate direct and the 1st indirect radiative effects contribute to the surface cooling. In the BC experiment, the BC direct effect is the main driver of the surface cooling, however, a decrease in low cloud cover due to the increased heating by BC absorption partially counteracts the direct effect. This results in a weaker land surface temperature response to BC changes than to sulphate changes. The resulting precipitation response is also weaker, and the responses of the monsoon circulation are different for sulphate and black carbon experiments. This study demonstrates a mechanism that links regional aerosol emission changes to the precipitation changes of the EASM, and it could be applied to help understand the future changes in EASM precipitation in CMIP5 simulations.

Relationship between sea surface temperature anomalies over tropical Atlantic in late spring and East Asian summer monsoon

2020 ◽  
Author(s):  
Joong-Bae Ahn ◽  
Yeon-Woo Choi
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Late Spring ◽  
Sea Surface ◽  
Tropical Atlantic ◽  
Asian Summer

<p>This study investigates the relationship between the preceding late spring Sea Surface Temperature (SST) over the tropical Atlantic and the East Asian Summer Monsoon (EASM) based on the observational data and Coupled Model Intercomparison Project Phase 5 (CMIP5) historical simulations. The results show that warm (cold) tropical Atlantic SST (TASST) during May tends to be followed by a strong (weak) EASM with positive (negative) precipitation anomalies over the subtropical frontal area. Evidence is also provided that the atmospheric teleconnections propagating in both east and west directions are the key mechanisms linking the EASM with the preceding May TASST. That is, the warm TASST anomaly during late spring can persist through the subsequent summer, which, in turn, induces the Gill-type Rossby wave response in the eastern Pacific, exciting the westward relay of the Atlantic signal, as well as the eastward propagation of the Rossby wave along the jet stream. Furthermore, the westward (eastward) propagating teleconnection signal may induce the anomalous anticyclone in the lower troposphere over the Philippine Sea (anomalous tropospheric anticyclone with barotropic structure over the Okhotsk Sea). The anomalous anticyclonic circulation over the Philippine Sea (Okhotsk Sea) brings warm and humid (cold) air to higher latitudes (lower latitudes). These two different types of air mass merge over the Baiu-Meiyu–Changma region, causing the enhanced subtropical frontal rainfall. To support the observational findings, CMIP5 historical simulations are also utilized. Most state-of-the-art CMIP5 models can simulate this relationship between May TASST and the EASM.</p><p>Reference: Choi, Y., Ahn, J. Possible mechanisms for the coupling between late spring sea surface temperature anomalies over tropical Atlantic and East Asian summer monsoon. Clim Dyn <strong>53, </strong>6995–7009 (2019) doi:10.1007/s00382-019-04970-3</p><p>Acknowledgment: This work was funded by the Korea Meteorological Administration Research and Development Program under Grant KMI2018-01213.</p><p> </p>

scholarly journals Distinct effects of anthropogenic aerosols on the East Asian summer monsoon between multidecadal strong and weak monsoon stages

2016 ◽  
Vol 121 (12) ◽  
pp. 7026-7040 ◽  
Author(s):  
Xiaoning Xie ◽  
Hongli Wang ◽  
Xiaodong Liu ◽  
Jiandong Li ◽  
Zhaosheng Wang ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Anthropogenic Aerosols ◽  
Asian Summer

scholarly journals Effects of Nonuniform Land Surface Warming on Summer Anomalous Extratropical Cyclone Activity and the East Asian Summer Monsoon: Numerical Experiments with a Regional Climate Model

2020 ◽  
Vol 33 (24) ◽  
pp. 10469-10488
Author(s):  
Wanxin Zhang ◽  
Haishan Chen ◽  
Liming Zhou ◽  
Botao Zhou ◽  
Jie Zhang ◽  
...  
Keyword(s):  
East Asia ◽  
Land Surface ◽  
East Asian Summer Monsoon ◽  
Climate Model ◽  
Asian Summer Monsoon ◽  
Regional Climate ◽  
East Asian ◽  
Anticyclonic Circulation ◽  
Surface Warming ◽  
Asian Summer

AbstractPrevious studies detected significant negative correlations between the nonuniform land surface warming and the decadal weakened activities of the summer extratropical cyclones (ECs) over East Asia and the East Asian summer monsoon (EASM) after the early 1990s. Here such relationships are further examined and the possible mechanisms are explored via numerical sensitivity experiments with a regional climate model (RegCM4.5). The positive/negative sensible heat flux (SH) anomalies were added as a forcing to a key region near 50°N of East Asia in RegCM4.5 to simulate the observed ground surface temperature (GST) anomalies. The model results suggest that the nonuniform land surface warming over the Lake Baikal area (50°–60°N, 90°–120°E) can indeed cause the weakening of the extratropical cyclogenesis and affect the decadal weakening of the EASM. Warm (cold) GST forcing over the key GST region can lead to decreasing (increasing) atmospheric baroclinicity and related energy conversion of the EC activity over the key EC region (40°–50°N, 90°–120°E), resulting in an evidently weakening (enhancing) of the ECs over East Asia. Meanwhile, precipitation shows a dipole pattern with significantly suppressed (enhanced) precipitation in northern and northeastern China, and slightly enhanced (suppressed) rainfall south of 40°N of East Asia, mainly over the East China Sea. Lake Baikal and its adjacent areas are occupied by a strong anticyclonic (cyclonic) circulation while the southeast coastal areas of China have a relatively weak cyclonic (anticyclonic) circulation accompanied with an anomalous northeasterly (southwesterly) wind to the southeast of the anticyclonic circulation, which is opposite to (coincident with) the atmospheric circulation anomalies that are associated with the second mode of the EASM.

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