TY - JOUR
T1 - Response of the atmospheric hydrological cycle over the tropical Asian monsoon regions to anthropogenic aerosols and its seasonality
AU - Takahashi, Hiroshi G.
AU - Watanabe, Shingo
AU - Nakata, Makiko
AU - Takemura, Toshihiko
N1 - Funding Information:
This work was partly supported by the Environment Research and Technology Development Fund (S-12) of the Environmental Restoration and Conservation Agency. HGT was partly supported by the Cooperative Program of Atmosphere and Ocean Research Institute, The University of Tokyo. JRA-55 was provided by the Japan Meteorological Agency. GPCP Precipitation data were provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA. This work was partly supported by the Environment Research and Technology Development Fund (S-12) of the Environmental Restoration and Conservation Agency. The HIST experiments are provided under the CMIP5. Please contact the authors for data requests regarding the piAERO experiments.
Publisher Copyright:
© 2018, The Author(s).
PY - 2018/12/1
Y1 - 2018/12/1
N2 - This study investigates the impact of anthropogenic aerosols on the atmospheric hydrological cycle over the tropical Asian monsoon region (South Asian, Southeast Asian, and western North Pacific monsoons), using a coupled atmosphere-ocean global climate model (CGCM), Model for Interdisciplinary Research on Climate-Earth System Models. Three-ensemble historical (HIST) and sensitivity (piAERO) experiments for the period 1985–2005 are conducted. The piAERO experiment is the same as HIST, but with anthropogenic aerosol emissions kept at preindustrial values. The results show that, as a whole, the Asian monsoon precipitation is reduced by the increase in aerosol loading during boreal summer and winter. This decrease in precipitation corresponds to a decrease in precipitable water due to the cooling in surface air temperature (SAT), mainly over adjacent oceans. The cooling is explained by the sum of the direct and indirect effects of aerosols. A modulation of the Walker circulation occurs, which can be explained by the east-west horizontal SAT gradient over the tropics due to the spatially heterogeneous increase in aerosols. Concurrent with the modulation of the Walker circulation, the anomalous descending motions over the tropical Asian monsoon region are consistent with the decrease in precipitation. In addition, the changes in local Hadley circulation (or a shift of the inter-tropical convergence zone) are unclear over the Asian monsoon region and thus cannot explain the decrease in precipitation. Moreover, the detailed spatial pattern of the response of the atmospheric hydrological cycle over the Asian monsoon region has distinct seasonality. Interestingly, signals are distinct in regions where tropical disturbance activity is vigorous during both boreal summer and winter. However, uncertainties regarding aerosol-cloud-precipitation interactions in current climate models and internal variability in the climate models may have affected the results.[Figure not available: see fulltext.].
AB - This study investigates the impact of anthropogenic aerosols on the atmospheric hydrological cycle over the tropical Asian monsoon region (South Asian, Southeast Asian, and western North Pacific monsoons), using a coupled atmosphere-ocean global climate model (CGCM), Model for Interdisciplinary Research on Climate-Earth System Models. Three-ensemble historical (HIST) and sensitivity (piAERO) experiments for the period 1985–2005 are conducted. The piAERO experiment is the same as HIST, but with anthropogenic aerosol emissions kept at preindustrial values. The results show that, as a whole, the Asian monsoon precipitation is reduced by the increase in aerosol loading during boreal summer and winter. This decrease in precipitation corresponds to a decrease in precipitable water due to the cooling in surface air temperature (SAT), mainly over adjacent oceans. The cooling is explained by the sum of the direct and indirect effects of aerosols. A modulation of the Walker circulation occurs, which can be explained by the east-west horizontal SAT gradient over the tropics due to the spatially heterogeneous increase in aerosols. Concurrent with the modulation of the Walker circulation, the anomalous descending motions over the tropical Asian monsoon region are consistent with the decrease in precipitation. In addition, the changes in local Hadley circulation (or a shift of the inter-tropical convergence zone) are unclear over the Asian monsoon region and thus cannot explain the decrease in precipitation. Moreover, the detailed spatial pattern of the response of the atmospheric hydrological cycle over the Asian monsoon region has distinct seasonality. Interestingly, signals are distinct in regions where tropical disturbance activity is vigorous during both boreal summer and winter. However, uncertainties regarding aerosol-cloud-precipitation interactions in current climate models and internal variability in the climate models may have affected the results.[Figure not available: see fulltext.].
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U2 - 10.1186/s40645-018-0197-2
DO - 10.1186/s40645-018-0197-2
M3 - Article
AN - SCOPUS:85052095174
SN - 2197-4284
VL - 5
JO - Progress in Earth and Planetary Science
JF - Progress in Earth and Planetary Science
IS - 1
M1 - 44
ER -
