云天地表总辐射和净辐射瞬时值的计算方法

Estimation of global and net solar radiation at the Earth surface under cloudy-sky condition

为减少计算机时,满足实时预报要求,全球数值预报模式中的辐射计算频率通常设定为3 h。这样处理会大大减少计算量,但同时导致较大的辐射日变化偏差,并影响模式对地面能量平衡、对流及降水的模拟。为改进这一缺陷,建立了一种辐射快速计算方案,可用于计算瞬时地面太阳总辐射和净辐射,使到达地面的太阳辐射计算可与模式积分同步进行,改善地面太阳辐射日变化模拟。本文介绍云天情况下的总辐射和净辐射计算方案,该方案所用的输入变量均为预报模式或卫星观测提供。结果表明:该方案既可用于数值预报模式,也可利用观测资料独立计算地面太阳辐射。通过使用美国能源部大气辐射观测资料检验,证明该方案的精度高,地面总辐射瞬时值的平均计算误差小于7%。

Radiation calculations in global numerical weather prediction（NWP）and climate models are usually con-ducted in 3-hourly time interval in order to reduce the computational cost.Although great reduction in time consu-ming,this treatment can lead to an incorrect solar radiation at the Earth′s surface which could be one of the error sources in modeled surface energy budget,convection and precipitation.In order to improve the simulation of the diurnal cycle of the solar radiation,a fast scheme has been developed based on detailed radiative transfer calcula-tions for a wide range of atmospheric conditions and can be used to determine the surface solar radiation at each model integration time step with affordable costs.This scheme is divided into components of clear-sky and cloudy-sky conditions.The cloudy-sky component is introduced in this paper.The results indicate that the input variables required by this scheme are all available in NWP and climate models or can be obtained from satellite observa-tions.Therefore,the scheme can be used in a global model to determine the surface solar radiation.It can also be used as an offline scheme to calculate the surface radiation using data from satellite measurements.The scheme has been tested using observations obtained from three Atmospheric Radiation Measurements （ARM）stations estab-lished by the U.S.Department of Energy.The results show that a half hourly mean relative error of global solar ra-diation under all-sky conditions is less than 7%.