Models - Atmospheric Model

A new cumulus convective scheme (Wu, 2011) has been implemented in the BCC_AGCM2.1. The scheme is based on a bulk-cloud approach and has the following properties:

(1) Deep convection is launched at the level of maximum moist static energy above the top of the boundary layer. It is triggered if there is positive convective available potential energy (CAPE) and relative humidity of the air at the lifting level of convection cloud is greater than 75%;

(2) Convective updrafts for mass, dry static energy, moisture, cloud liquid water and momentum are parameterized by a one-dimensional entrainment/detrainment bulk-cloud model. The lateral entrainment of the environmental air into the unstable ascending parcel before it rises to the lifting condensation level is considered. The entrainment/detrainment amount for the updraft cloud parcel is separately determined according to the increase/decrease of updraft parcel mass with altitude, and the mass change for the adiabatic ascent cloud parcel with altitude is derived from a total energy conservation equation of the whole adiabatic system in which involves the updraft cloud parcel and the environment;

(3) The convective downdraft is assumed saturated and originated from the level of minimum environmental saturated equivalent potential temperature within the updraft cloud;

(4) The mass flux at the base of convective cloud is determined by a closure scheme suggested by Zhang (J Geophys Res 107(D14), doi:10.1029/2001JD001005, 2002) in which the increase/decrease of CAPE due to changes of the thermodynamic states in the free troposphere resulting from convection approximately balances the decrease/increase resulting from large-scale processes.

CO2 is a prognostic variable in BCC-AGCM2.1. It is no more a passive tracer, and it is calculated through a budget equation, as a function of global integrated anthropogenic CO2 emissions, and interactive CO2 fluxes at the interfaces with land and ocean.

The COSP implementation has been added to work with the model physics.

According to the CMIP5 design, BCC_AGCM2.1 run the AIMP simulations, which include AMIP, sstClim, sstClim4xCO2, sstClimAerosol, sstClimSulfate, amip4xCO2, amipFuture, amip4K runs. At the same time, BCC_AGCM2.1 is the atmospheric component of BCC_CSM1.1 and run the CMIP5 most experiments. 

Tongwen Wu (2012), A mass-flux cumulus parameterization scheme for large-scalemodels: description and test with observations, Clim Dyn, 38:725–744,DOI 10.1007/s00382-011-0995-3. (full text)