Based on an attribution analysis of the global mean temperature biases in the Flexible Global Ocean- AtmOsphere-Land System model, spectral version 2 （FGOALS-s2） through a coupled atmosphere-surface ch- mate feedb...Based on an attribution analysis of the global mean temperature biases in the Flexible Global Ocean- AtmOsphere-Land System model, spectral version 2 （FGOALS-s2） through a coupled atmosphere-surface ch- mate feedback-response analysis method （CFRAM）, the model＇s global surface-atmosphere energy balance in boreal winter and summer is examined. Within the en- ergy-balance-based CFRAM system, the model temperature biases are attributed to energy perturbations resulting from model biases in individual radiative and non-radia- tive processes in the atmosphere and at the surface. The results show that, although the global mean surface tem- perature （Ts） bias is only 0.38 K in January and 1.70 K in July, and the atmospheric temperature （Ta） biases from the troposphere to the stratosphere are only around ＋3 K at most, the temperature biases due to model biases in rep- resenting the individual radiative and non-radiative proc- esses are considerably large （over -4-10 K at most）. Spe- cifically, the global cold radiative Ts bias, mainly due to the overestimated surface albedo, is compensated for by the global warm non-radiative Ts bias that is mainly due to the overestimated downward surface heat fluxes. The model biases in non-radiative processes in the lower tro- posphere （up to 5-15 K） are relatively much larger than in upper levels, which are mainly responsible for the warm Ta biases there. In contrast, the global mean cold ira biases in the mid-to-upper troposphere are mainly dominated by radiative processes. The warm/cold Ta biases in the lower/upper stratosphere are dominated by non-radiative processes, while the warm ira biases in the mid-strato- sphere can be attributed to the radiative ozone feedback process.展开更多
Biases in shortwave cloud radiative forcing(SWCF), which cause overestimates in tropical regions and underestimates in subtropical marine stratocumulus regions, are common in many climate models. Here, two boundary la...Biases in shortwave cloud radiative forcing(SWCF), which cause overestimates in tropical regions and underestimates in subtropical marine stratocumulus regions, are common in many climate models. Here, two boundary layer processes are investigated in the atmospheric model GAMIL2, entrainment at the top of the boundary layer and longwave radiative cooling at the top of stratocumulus clouds, in order to reduce biases and reveal the mechanisms underlying these processes. Our results show that including the entrainment process in the model can reduce negative SWCF biases in most tropical regions but increases positive SWCF biases in subtropical marine stratocumulus regions. This occurs because entrainment reduces the low-level cloud fraction and its cloud liquid water content by suppressing the vertical turbulent diffusion in the boundary layer and decreasing the relative humidity when warm and dry free atmosphere is entrained in the boundary layer. Longwave radiative cooling at the top of stratocumulus clouds can enhance turbulent diffusion within the stratocumulus-topped boundary layer. When combined with the entrainment process, longwave radiative cooling reduces the positive SWCF biases in subtropical marine stratocumulus regions that are observed using the entrainment process alone. The incorporation of these two boundary layer processes improves the simulated SWCF in tropical and subtropical regions in GAMIL2.展开更多
基金jointly supported by the Special Fund for Public Welfare Industry(Meteorology)(Grant No.GYHY201406001)Science Foundation of the Chinese Academy of Sciences(Grant No.XDA11010402)the National Natural Science Foundation of China(Grant No.91437105)
文摘Based on an attribution analysis of the global mean temperature biases in the Flexible Global Ocean- AtmOsphere-Land System model, spectral version 2 （FGOALS-s2） through a coupled atmosphere-surface ch- mate feedback-response analysis method （CFRAM）, the model＇s global surface-atmosphere energy balance in boreal winter and summer is examined. Within the en- ergy-balance-based CFRAM system, the model temperature biases are attributed to energy perturbations resulting from model biases in individual radiative and non-radia- tive processes in the atmosphere and at the surface. The results show that, although the global mean surface tem- perature （Ts） bias is only 0.38 K in January and 1.70 K in July, and the atmospheric temperature （Ta） biases from the troposphere to the stratosphere are only around ＋3 K at most, the temperature biases due to model biases in rep- resenting the individual radiative and non-radiative proc- esses are considerably large （over -4-10 K at most）. Spe- cifically, the global cold radiative Ts bias, mainly due to the overestimated surface albedo, is compensated for by the global warm non-radiative Ts bias that is mainly due to the overestimated downward surface heat fluxes. The model biases in non-radiative processes in the lower tro- posphere （up to 5-15 K） are relatively much larger than in upper levels, which are mainly responsible for the warm Ta biases there. In contrast, the global mean cold ira biases in the mid-to-upper troposphere are mainly dominated by radiative processes. The warm/cold Ta biases in the lower/upper stratosphere are dominated by non-radiative processes, while the warm ira biases in the mid-strato- sphere can be attributed to the radiative ozone feedback process.
基金supported by the CAS Strategic Priority Research Program (Grant No. XDA05110304)the National Basic Research Program of China (Grant No. 2015CB954102)the National Natural Science Foundation of China (Grant Nos. 41205079 & 41305040)
文摘Biases in shortwave cloud radiative forcing(SWCF), which cause overestimates in tropical regions and underestimates in subtropical marine stratocumulus regions, are common in many climate models. Here, two boundary layer processes are investigated in the atmospheric model GAMIL2, entrainment at the top of the boundary layer and longwave radiative cooling at the top of stratocumulus clouds, in order to reduce biases and reveal the mechanisms underlying these processes. Our results show that including the entrainment process in the model can reduce negative SWCF biases in most tropical regions but increases positive SWCF biases in subtropical marine stratocumulus regions. This occurs because entrainment reduces the low-level cloud fraction and its cloud liquid water content by suppressing the vertical turbulent diffusion in the boundary layer and decreasing the relative humidity when warm and dry free atmosphere is entrained in the boundary layer. Longwave radiative cooling at the top of stratocumulus clouds can enhance turbulent diffusion within the stratocumulus-topped boundary layer. When combined with the entrainment process, longwave radiative cooling reduces the positive SWCF biases in subtropical marine stratocumulus regions that are observed using the entrainment process alone. The incorporation of these two boundary layer processes improves the simulated SWCF in tropical and subtropical regions in GAMIL2.
