The Study Of Atmospheric Longwave Radiation Schemes And Their Applications In The Climate Model

Atmospheric radiative transfer plays a critical role in the climate system.However,there is still room for improvement in the process of longwave radiation in climate models.The studies mainly include following several points to improve the parameterization of longwave radiative transfer in climate models,(1)Firstly,an analytical adding algorithm is proposed based on the infrared invariance principle to solve the infrared radiative transfer of the multiple layers with a vertically inhomogeneous atmosphere and improve the accuracy of the atmospheric radiation scheme in the climate model.The adding method for ?-four-stream discrete-ordinates approximation method(referred to as ?-4DDA)and ?-four-stream spherical harmonic expansion approximation(referred to as ?-4SDA)are developed.And the calculation accuracy and efficiency of these two four-stream schemes are also evaluated.(2)Several kinds of Gaussian quadrature(GQ)are applied to the four-stream solar and infrared radiative transfer algorithms to study the influence of different GQ on the accuracy of the approximate solution of the single-layer solar/infrared four-stream discrete ordinate.Several single-column ideal experiments are run to find the best GQ for accuracy.The results are confirmed in evaluations by using satellite observation data.(3)A new parameterization,the double-?-function adjustment which incorporating the backward peak contribution to multiple scattering along with the forward peak contribution,is proposed.We apply it into an adding method of two-stream discrete-ordinates approximation(2DDA)for infrared radiative transfer.The double-?-2DDA(2?-2DDA)produces smaller errors than the ?-2DDA for thick optical depths,and produce similar errors with ?-2DDA for thin optical depths.(4)Besides,a new scheme is proposed to deal with the solar and thermal infrared spectra overlap,and compared with two schemes commonly used in current climate models.It is shown that the new scheme produces the smallest error in the flux and heating rate compared to the other two schemes,especially in the infrared spectrum of 4-7.14 ?m.(5)The newly infrared four-stream approximation method is applied to the Canadian Atmospheric Global Climate Model Version 4.3(Can AM4.3).Differences simulated by three different longwave radiation schemes with Can AM4.3 are compared to discuss the influence of the new longwave radiation scheme and longwave cloud effect on the climate simulation and its sensitivity.