The Grid-point Atmospheric Model of IAP LASG version 2 （GAMIL2） has been developed through upgrading the deep convection parameterization, cumulus cloud fraction and two-moment cloud microphys- ical scheme, as well ...The Grid-point Atmospheric Model of IAP LASG version 2 （GAMIL2） has been developed through upgrading the deep convection parameterization, cumulus cloud fraction and two-moment cloud microphys- ical scheme, as well as changing some of the large uncertain parameters. In this paper, its performance is evaluated, and the results suggest that there are some significant improvements in GAMIL2 compared to the previous version GAMIL1, for example, the components of the energy budget at the top of atmosphere （TOA） and surface; the geographic distribution of shortwave cloud radiative forcing （SWCF）; the ratio of stratiform versus total rainfall; the response of atmospheric circulation to the tropical ocean; and the east- ward propagation and spatiotemporal structures of the Madden Julian Oscillation （MJO）. Furthermore, the indirect aerosols effect （IAE） is -0.94 W m-2, within the range of 0 to -2 W m-2 given by the IPCC 4th Assessment Report （2007）. The influence of uncertain parameters on the MJO and radiation fluxes is also discussed.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supported by the CAS Strategic Priority Research Program(Grant No.XDA05110304)the National"973"Project(Grant No.2010CB951904)+2 种基金the China Meteorological Administration R&D Special Fund for Public Welfare(meteo-rology)(Grant No.GYHY201006014)the National"863"Project(Grant No.2010AA012304)the National Natural Science Foundation of China(Grant Nos.40923002 and 41005053)
文摘The Grid-point Atmospheric Model of IAP LASG version 2 （GAMIL2） has been developed through upgrading the deep convection parameterization, cumulus cloud fraction and two-moment cloud microphys- ical scheme, as well as changing some of the large uncertain parameters. In this paper, its performance is evaluated, and the results suggest that there are some significant improvements in GAMIL2 compared to the previous version GAMIL1, for example, the components of the energy budget at the top of atmosphere （TOA） and surface; the geographic distribution of shortwave cloud radiative forcing （SWCF）; the ratio of stratiform versus total rainfall; the response of atmospheric circulation to the tropical ocean; and the east- ward propagation and spatiotemporal structures of the Madden Julian Oscillation （MJO）. Furthermore, the indirect aerosols effect （IAE） is -0.94 W m-2, within the range of 0 to -2 W m-2 given by the IPCC 4th Assessment Report （2007）. The influence of uncertain parameters on the MJO and radiation fluxes is also discussed.
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.
