Distribution Of Different Cloud Types And Their Effects On Near-surface Air Temperature During Summer In China

The spatial-temporal variation characteristics of the cloud fraction,cloud optical thickness and cloud water path of various cloud types over China in summer are explored based on ERA5reanalysis data,CERES satellite data and MODIS 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.Finally,combined with the ISCCP data and CMIP5 model data,the change of total cloud fraction under the different types of external radiative forcing are obtained,and the response of the total cloud fraction to external radiative forcing is analyzed.The main conclusions are as follows:?1?The total cloud and high cloud fraction showed a decreasing distribution trend from south to north in China.Most of areas in china are dominated by upper-middle cloud,which are mainly related to the East Asian monsoon in summer.The high-value areas of total cloud optical thickness and four different cloud types of optical thickness are located in the Sichuan Basin and the Yunnan-Guizhou region,and the cloud optical thickness in western China is generally lower than that in central and eastern China.The total and different types of liquid cloud water path show a higher distribution pattern in central and eastern China than in the west.The ice water path of total cloud and high cloud are located in central and eastern China.Large-value areas are mainly concentrated in Xinjiang and the Qinghai-Tibet Plateau.Except for low cloud,the ice water path of total cloud and other types of cloud are larger than liquid water path in most parts of China.In most areas of China,low cloud are mainly liquid cloud,while lower-middle,upper-middle,high cloud are mainly ice-phase cloud.?2?The total,low,lower-middle cloud fraction showed a downward trend in most areas of China.The upper-middle cloud fraction all showed an increasing trend,the high cloud fraction showed an increasing trend in the northeast and the western Qinghai-Tibet Plateau.The central region showed a weak downward trend.Except for the Qinghai-Tibet Plateau and the Sichuan Basin,the optical thickness of total cloud,low cloud,and lower-middle cloud is increasing from0 to 0.1y^-1 in most parts of China,and the upper-middle cloud optical thickness is decreasing in China as a whole.High cloud optical thickness showed a significant increase trend of 0.24 y^-1in Xinjiang and western Inner Mongolia.The distribution of the annual variability of the liquid water path of the total cloud,lower-middle cloud,and upper-middle cloud is roughly the same.Most of the western and northeastern regions of China have a weakly increasing trend,and the Sichuan-Guizhou region has a weakly decreasing trend.The low-cloud liquid water path has a weak increasing trend in most parts of eastern and central China.The high-cloud liquid water path in western China increased significantly at 0.96 g m^-2 y^-1,while that in southern China decreased.Except for the high-cloud ice water path in Xinjiang,which has a significant increase trend(0.40 g m^-2 y^-1),the total cloud and other types of cloud ice water path in other regions of China have both decreased.?3?The CETs of the four different cloud types are negative in central and eastern China.The lower-middle cloud?CET=-1.1 ^oC?and upper-middle cloud?CET=-2.2 ^oC?also showed a cooling effect in western China,but were weaker than those in central and eastern China.The high cloud has a warming effect in western China?CET=2.3 ^oC?.The CETs of different cloud types are in good agreement with the interannual changes of near-surface temperature.The increase?decrease?in the cooling effect of cloud corresponds to the decrease?rise?of near-surface temperature,which reflects the four different types of cloud in China in summer.The CET has a positive correlation with the near-surface temperature.In particular,upper-middle cloud cover in central and eastern China is dominant in summer,and the correlation coefficient between CET and near-surface air temperature is as high as 0.63,which indicates that the near-surface air temperature in central and eastern China in summer is more closely related to the CET of upper-middle cloud.?4?The change in the total cloud fraction in most regions of China under the greenhouse gas forcing are in line with the spatial distribution of the ISCCP cloud cover.The total cloud cover in southeast China showed an increasing trend under anthropogenic aerosol forcing?AA?,ozone forcing?OZ?and natural radiative forcing?Nat?.The global cloud amount change is likely to be affected by external radiative forcing,of which greenhouse gas forcing and natural forcing dominate,while the global cloud amount change in summer is mainly affected by greenhouse gases.The change of ISCCP cloud fraction in China in summer is also significantly correlated with the change of cloud fraction under the external forcing of greenhouse gases,which indicates that the change of total cloud fraction in China in summer is closely related to greenhouse gases.