Numerical Study Of Radiative In Three-dimensional Cloudy Atmospheres

One-dimensional radiative transfer model is widely used in numerical atmospheric model, which neglects radiation transport process in three-dimensional cloudy atmosphere and thus produces inaccurate numerical simulation and even weather forecast. In order to assess these uncertainties, In this paper, three-dimensional broadband radiative transfer model SHDOM are used to studies the effects of three-dimensional radiation interaction between clouds on their thermodynamic and dynamic structures in order to optimize the radiation parameterization in numerical weather forecast system.First, we discuss the difference between one-dimensional and three-dimensional radiative transfer with radiative flux and heating rate, respectively high-order diffusion attenuation, low-order scattering radiative enhancement and low-order scattering radiative decrease were classified as the three-dimensional cloud radiative distribution characteristics of radiative escape, cloud edge lighting effects and cloud shadow effect.In order to discuss the three-dimensional radiative effect on cloud dynamic, using the light cumulus fields as input, using buoyancy formula to preliminarily discuss the relationship between three-dimensional cloud heating rate and cloud buoyancy. The following conclusions are obtained by the numerical simulation. For longwave bands, Cloud side buoyancy is inversely proportional to the distance between clouds. When each clouds have long distance, cloud side emitting longwave radiation cause cooling itself to form negative buoyancy; When the distance is short, the longwave radiative interaction between the clouds form positive buoyancy. For short wave bands, cloud buoyancy is related to the sun radiation direction and three dimensional structure of cloud. When the sun obliquely incident, radiative warming occur in the sun-facing part of the cloud body, which result in positive buoyancy. Cloud nightside cooling result in negative buoyancyIn order to analyze the three-dimensional radiative effects of clouds, using the I3RC II cumulus and stratocumulus fields as input, the center of which are assumed as the targeted domain and the others of which as adjacent domain, we simulate the spatial distribution of shortwave and longwave radiative heating rates by the broadband three-dimensional radiative transfer model SHDOM to illustrate the impacts of adjacent-cloud on targeted-cloud thermodynamic structure. The following conclusions are obtained by the numerical simulation. For longwave bands, adjacent-cloud produces radiative warming effects for the whole targeted domain. The warming zone is mainly situated around the surface layer of cloud, the depth of which is negatively correlated with liquid water content; the warming value are proportional to cloud coverage and the reciprocal of the distance between the targeted and adjacent cloud, and its maximum value is 3.08 K/h. For shortwave bands, adjacent-cloud simultaneously results in scattering-induced warming effects and shadowing-induced cooling effects for targeted-cloud. For small sun zenith angle, warming effects are dominant although they are quite weak and are distributed uniformly; As sun zenith angle grows, cooling effects become more important, significantly causing temperature reductions (the maximum reduction value of 1.72 K/h) of surface layer of one side of targeted-cloud hidden by adjacent-cloud, the value of which may even exceed the value of longwave radiative warming effects. In conclusion, adjacent-cloud could strongly change the local heating rate of the target-cloud. Therefore, it is crucial to introduce three-dimensional radiative effects into the numerical weather forecast system to improve the radiation parameterization.