Monthly Means Of Daily Solar Radiation (Mj/M2/Day) September

These daily estimates of solar radiation were derived using modifications for South African conditions of the Bristow and Campbell (1984) equation. The daily values can be used as input in other equations such as the Penman-Monteith equation for potential crop evaporation. The method of estimation of daily solar radiation loadings over South Africa and its verification are as follows: based on the premise that clear sky solar radiation is determined essentially by extraterrestrial solar radiation modulated by an atmospheric extinction function, and dependent on high maximum temperatures associated with a high diurnal range in temperature, while cloudy/rainy conditions are associated with a low diurnal temperature range, the Bristow and Campbell (1984) equation was modified for South African conditions by regionally optimised expressions of clear sky depletion for atmospheric water vapour content, and by month-by-month regionalised expressions for solar radiation extinction by cloudy/rainy conditions. Other than the optimised regional/monthly coefficients and the computation of extraterrestrial radiation, which is undertaken with trigonometrical geometry functions, the only other variables used were daily maximum and minimum temperatures. The latter were determined for the 50 year period 1950 - 1999 at each of 429 700 one arc minute (1.7 x 1.7 km) raster points over South Africa by techniques outlined in Schulze and Maharaj (2004).本数据集的每日太阳辐射估算值，是针对南非本土条件优化改造布里斯托-坎贝尔（Bristow and Campbell，1984）方程后生成的。 该每日辐射数据可作为其他模型方程的输入参数，例如用于计算作物潜在蒸发量的彭曼-蒙特斯（Penman-Monteith）方程。 南非地区每日太阳辐射负荷的估算方法及其验证流程如下：研究基于以下核心前提——晴空太阳辐射本质上由受大气消光函数调制的地外太阳辐射决定，且与伴随高昼夜温差的最高气温强相关；而阴雨多云天气则对应低昼夜温差。据此，针对南非本土条件对布里斯托-坎贝尔（1984）方程完成两处针对性改造：一是针对大气水汽含量的晴空衰减项采用区域优化表达式，二是针对阴雨多云天气下的太阳辐射衰减项采用逐月度区域化表达式。 除了优化后的区域/月度系数，以及通过三角几何函数计算得到的地外太阳辐射项之外，模型仅使用每日最高、最低气温作为输入变量。 上述气温数据是依据Schulze与Maharaj（2004）提出的方法，针对南非全境429700个1弧分（对应实地尺度1.7×1.7公里）的栅格点，于1950至1999年这50年周期内计算得到的。