Satellite and human visual observation are two of the most important observation approaches for cloud cover. In this study, the total cloud cover （TCC） observed by MODIS onboard the Terra and Aqua satellites was com...Satellite and human visual observation are two of the most important observation approaches for cloud cover. In this study, the total cloud cover （TCC） observed by MODIS onboard the Terra and Aqua satellites was compared with Synop meteorological station observations over the North China Plain and its surrounding regions for 11 years during daytime and 7 years during nighttime. The Synop data were recorded eight times a day at 3-h intervals. Linear interpolation was used to interpolate the Synop data to the MODIS overpass time in order to reduce the temporal deviation between the satellite and Synop observations. Results showed that MODIS-derived TCC had good consistency with the Synop observations; the correlation coefficients ranged from 0.56 in winter to 0.73 in summer for Terra MODIS, and from 0.55 in winter to 0.71 in summer for Aqua MODIS. However, they also had certain differences. On average, the MODIS-derived TCC was 15.16% higher than the Synop data, and this value was higher at nighttime （15.58%-16.64%） than daytime （12.74%-14.14%）. The deviation between the MODIS and Synop TCC had large seasonal variation, being largest in winter （29.53%-31.07%） and smallest in summer （4.46%-6.07%）. Analysis indicated that cloud with low cloud-top height and small cloud optical thickness was more likely to cause observation bias. Besides, an increase in the satellite view zenith angle, aerosol optical depth, or snow cover could lead to positively biased MODIS results, and this affect differed among different cloud types.展开更多
The Grid-point Atmospheric Model of IAP LASG version 1.0（GAMIL1.0） is used to investigate the impacts of different convective schemes on the radiative energy budget.The two convective schemes are Zhang and McFarlanc...The Grid-point Atmospheric Model of IAP LASG version 1.0（GAMIL1.0） is used to investigate the impacts of different convective schemes on the radiative energy budget.The two convective schemes are Zhang and McFarlance（1995）/Hack（1994）（ZM） and Tiedtke（1989）/Nordeng（1994）（TN）.Two simulations are performed：one with the ZM scheme（EX_ZM） and the other with the TN scheme（EX_TN）.The results indicate that during the convective process,more water vapor consumption and temperature increment are found in the EX_ZM,especially in the lower model layer,its environment is therefore very dry.In contrast, there is a moister atmosphere in the EX_TN,which favors low cloud formation and large-scale condensation, and hence more low cloud fraction,higher cloud water mixing ratio,and deeper cloud extinction optical depth are simulated,reflecting more solar radiative flux in the EX_TN.This explains why the TN scheme underestimates the net shortwave radiative flux at the top of the atmosphere and at surface.In addition, convection influences longwave radiation,surface sensible and latent heat fluxes through changes in cloud emissivity and precipitation.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 41590874 and 41590875)the Ministry of Science and Technology of China (Grant No. 2014CB953703)
文摘Satellite and human visual observation are two of the most important observation approaches for cloud cover. In this study, the total cloud cover （TCC） observed by MODIS onboard the Terra and Aqua satellites was compared with Synop meteorological station observations over the North China Plain and its surrounding regions for 11 years during daytime and 7 years during nighttime. The Synop data were recorded eight times a day at 3-h intervals. Linear interpolation was used to interpolate the Synop data to the MODIS overpass time in order to reduce the temporal deviation between the satellite and Synop observations. Results showed that MODIS-derived TCC had good consistency with the Synop observations; the correlation coefficients ranged from 0.56 in winter to 0.73 in summer for Terra MODIS, and from 0.55 in winter to 0.71 in summer for Aqua MODIS. However, they also had certain differences. On average, the MODIS-derived TCC was 15.16% higher than the Synop data, and this value was higher at nighttime （15.58%-16.64%） than daytime （12.74%-14.14%）. The deviation between the MODIS and Synop TCC had large seasonal variation, being largest in winter （29.53%-31.07%） and smallest in summer （4.46%-6.07%）. Analysis indicated that cloud with low cloud-top height and small cloud optical thickness was more likely to cause observation bias. Besides, an increase in the satellite view zenith angle, aerosol optical depth, or snow cover could lead to positively biased MODIS results, and this affect differed among different cloud types.
基金Supported by the Knowledge Innovation Program of the Chinese Academy of Sciences under Grant No.KZCX2-YW-Q11-04the China Meteorological Administration R & D Special Fund for Public Welfare(meteorology)(Grant Nos.GYHY200806007, GYHY200806006,and GYHY200906020)+1 种基金Informalization Construction Project of Chinese Academy of Sciences during the 11th Five-Year Plan Period(No.INFO-115-B01)LASG State Key Laboratory Special Fund and LASG Free Exploration Fund
文摘The Grid-point Atmospheric Model of IAP LASG version 1.0（GAMIL1.0） is used to investigate the impacts of different convective schemes on the radiative energy budget.The two convective schemes are Zhang and McFarlance（1995）/Hack（1994）（ZM） and Tiedtke（1989）/Nordeng（1994）（TN）.Two simulations are performed：one with the ZM scheme（EX_ZM） and the other with the TN scheme（EX_TN）.The results indicate that during the convective process,more water vapor consumption and temperature increment are found in the EX_ZM,especially in the lower model layer,its environment is therefore very dry.In contrast, there is a moister atmosphere in the EX_TN,which favors low cloud formation and large-scale condensation, and hence more low cloud fraction,higher cloud water mixing ratio,and deeper cloud extinction optical depth are simulated,reflecting more solar radiative flux in the EX_TN.This explains why the TN scheme underestimates the net shortwave radiative flux at the top of the atmosphere and at surface.In addition, convection influences longwave radiation,surface sensible and latent heat fluxes through changes in cloud emissivity and precipitation.
