ISSN 1006-9895

CN 11-1768/O4

Distribution of Different Cloud Types and their effects on Near-surface Air Temperature during Summer Daytime in Central Eastern China
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Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences

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    Abstract:

    The spatial-temporal variation characteristics of the daytime cloud fraction and cloud optical thickness of various cloud types over central and eastern China in summer are explored based on ERA5 reanalysis data and CERES satellite data during the period of 2001-2017. Then, the effects of various cloud types on near-surface air temperature are analyzed quantitatively using a Radiative-Convective Model. The observations show that the annual mean daytime total cloud fraction and its optical thickness decrease gradually from south to north, while upper-middle cloud fraction dominates the total cloud fraction over central and eastern China in summer. For annual mean changing rates, the total cloud fraction shows a significant decrease of 0.3% a-1 with the largest contribution from low cloud (-0.27% a-1).The increasing trend of total cloud optical thickness ranges from 0 to 0.1 a-1, with low and lower-middle cloud optical thickness show an increasing trend of 0.06 a-1 and 0.03 a-1, respectively, while the upper-middle and high cloud optical thickness show a decreasing trend of 0.08 a-1 and 0.03 a-1, respectively. The model results show that the annual mean CETs of the four different cloud types are negative, with values of 2.9 ℃, 2.7 ℃, 2.2 ℃, and 1.7 ℃ for low, lower-middle, upper-middle and high cloud, respectively, indicating the cooling effects of various cloud types. The low cloud CET in the North China Plain can be up to -5 ℃, while the lower-middle and upper-middle cloud can both come up to -7.8 ℃ in Sichuan Basin and Yunnan-Guizhou Plateau. The interannual variations of CETs of different cloud types and near-surface air temperature have a good consistency. The near-surface air temperature decreases (increases) before (after) 2004, while the CETs of different cloud types decrease (increase) during this period, which indicates a good correspondence between the strengthening (weakening) of the cloud cooling effect and the decrease (increase) of near-surface temperature. It means, in other words, a positive correlation relationship appearing in four cloud types and near-surface air temperature over central and eastern China during daytime in summer. In particular, the annual mean daytime upper-middle cloud fraction plays an important role in all types of clouds over central and eastern China in summer, and the correlation coefficient between the CET and near-surface air temperature is as high as 0.63. In summary, the effects of different cloud types on near-surface air temperature over central and eastern China in summer are different, but all of them show positive correlations. The quantitative analysis of the influence of different cloud types on near-surface air temperature can provide scientific references for the accurate measurement of global warming, the role of cloud feedback in regional warming, and the accurate prediction of regional warming scenarios, respectively.

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History
  • Received:May 07,2019
  • Revised:August 01,2019
  • Adopted:September 06,2019
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