Improvement Of The Atmospheric Radiation Model And Its Application In Climate Modeling

Atmospheric radiation model is an important part in climate models. On the onehand, radiative flux in surface and at the top of atmosphere calculated byatmospheric radiation model can influence radiative energy balance in climatemodel; on the other hand, radiative heating rates calculated by atmospheric radiationmodel can affect atmospheric vertical and horizontal motion. In this thesis, thelongwave gas absorption is updated using HITRAN2008molecular spectroscopicdatabase and MT_CKD2.5.2vapor continuum absorption model. A k-distributionwater cloud optical properties parameterization method which matched thecorrelated k distribution radiation scheme is constructed. Four-stream sphericalharmonic function algorithm is used in the atmospheric radiation model. All theseimprovements are based on the National Climate Center radiation model calledBCC_RAD. The k-distribution water cloud optical properties parameterizationmethod, four-stream spherical harmonic function algorithm and solar radiation inlongwave region are applied in National Climate Center atmospheric generalcirculation model called BCC_AGCM2.0.1. The major conclusions are as follows:(1) Four HITRAN editions (HITRAN1996, HITRAN2000, HITRAN2004, andHITRAN2008) are compared using a line-by-line radiative model in longwave region.The results show the largest difference is1.70W m-2in downward radiative flux and0.28W m-2in upward radiative flux. The largest cooling rate difference is0.12KDay-1. Uncertainties caused by line intensity and air-broadened half-widths areevaluated using the uncertainty codes given in HITRAN08. The uncertainty is±10%for optical depth,±1.92W m-2for upward flux,±1.97W m-2for downward flux and±0.5K day-1for cooling rate.(2) Gas absorption coefficient in longwave is updated using HITRAN2008molecular spectroscopic database and MT_CKD2.5.2continuum model. Thereference pressure used in correlated k distribution is changed from100mb to700mb. Compared with observations from CIRC, these changes can improve theaccuracy of radiative flux and cooling rate. Add the absorption of CO2, N2O andCH4in shortwave in BCC_RAD radiation model.(3) Correlated k distribution radiative model using the band average watercloud optical properties parameterization overestimates the heating rate at the top of cloud in shortwave. To reduce the error, a k-distribution water cloud opticalproperties parameterization scheme which matched the correlated k distributionradiative model is constructed. It can reduce half of the overestimation caused by theband average water cloud optical properties. The k-distribution water cloud opticalproperties parameterization method is also applied in climate model. The resultsshow compared with band average water cloud optical properties parameterizationmethod, it can reduce0.87W m-2of shortwave downward radiative flux in surface,increase2.15W m-2of shortwave upward radiative flux at the top of atmosphere inwhole sky. It can also increase0.32%of total cloud fraction.(4) Using single-layer four stream spherical harmonic function algorithmcombined adding method is applied in radiation model. The results show using thefour stream spherical harmonic function can improve the accuracy of heating rate atthe top of cloud. Four stream spherical harmonic function algorithm is also appliedin climate model. The results show compared with Eddington method, four streamspherical harmonic function algorithm can reduce1.16W m-2of downward radiativeflux in surface and increase0.24W m-2of upward radiative flux at the top ofatmosphere in whole sky. It can also increase0.18K for the tropopause temperature.(5) Solar radiation in longwave region is studied in climate model. The resultsshow the method considering the solar radiation in longwave region can improve2.03W m-2of downward radiative flux in surface and improve0.53W m-2ofupward radiative flux at the top of atmosphere in clear sky; improve1.37W m-2ofdownward radiative flux in surface and improve0.75W m-2of upward radiative fluxat the top of atmosphere in whole sky. It can also improve the result of temperaturein the region of upper troposphere and lower stratosphere, especially the tropopausetemperature in the tropical Pacific area.