In this study, an analysis of the monthly mean values of the fraction of the sky covered by clouds (C) of all types and the duration of bright sunshine hours (S) and global solar radiation on the horizontal surface (H) was carried out to establish relationship for solar radiation estimation for Bangladesh. The relationship between C and (1 − S/S 0), where S 0 is the maximum possible hours of sunshine, was found to be nonlinear. The relationship between C and (1 − H/H 0), where H 0 is the extraterrestrial solar radiation, was also found to be nonlinear. Few quadratic regression equations were derived for different regions of Bangladesh. The data were separated in Zone 1 (below the tropic of cancer, i.e., ≤23.5°N) and Zone 2 (above the tropic of cancer, i.e., ≥23.5°N). All the developed models were checked statistically. It was found that it is always better to estimate solar radiation from sunshine duration as it gives the best estimation and accuracy, but if there is no sunshine duration data available for a site, then solar radiation can be estimated directly from cloud cover data. Estimating sunshine duration first from cloud data to estimate solar radiation introduces more error as it has to go through the modeling stage twice. In case of the need of sunshine duration data only, the estimation from cloud cover is quite helpful. It was also found from the study that for small country like Bangladesh separating data according to latitude has insignificant effect.

中文翻译：

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根据孟加拉国的云量数据估算太阳辐射

在这项研究中，对所有类型的云层覆盖的天空比例（C）的月平均值，明亮的日照时间的持续时间（S）和水平表面的全球太阳辐射（H）进行了分析。建立孟加拉国太阳辐射估算的关系。发现C和（1- S / S 0）之间的关系是非线性的，其中S 0是最大可能的日照时间。还发现C与（1- H / H 0）之间的关系是非线性的，其中H 0是地外太阳辐射。对于孟加拉国的不同地区，很少有二次回归方程。数据在区域1（在热带地区以下，即≤23.5°N）和区域2（在热带地区以上，即≥23.5°N）分开。对所有开发的模型进行统计检查。已经发现，从日照时长估算太阳辐射总是更好的方法，因为它可以提供最佳的估计和准确性，但是如果没有站点的日照时长数据可用，则可以直接从云量数据中估算日照辐射。首先要从云数据估计日照持续时间以估计太阳辐射会引入更多误差，因为它必须经过两次建模阶段。仅在需要日照持续时间数据的情况下，根据云量的估算非常有帮助。从研究中还发现，对于像孟加拉国这样的小国，按纬度分离数据的影响不大。然后可以直接从云量数据估算太阳辐射。首先要从云数据估计日照持续时间以估计太阳辐射会引入更多误差，因为它必须经过两次建模阶段。仅在需要日照持续时间数据的情况下，根据云量的估算非常有帮助。从研究中还发现，对于像孟加拉国这样的小国，按纬度分离数据的影响不大。然后可以直接从云量数据估算太阳辐射。首先要从云数据估计日照持续时间以估计太阳辐射会引入更多误差，因为它必须经过两次建模阶段。仅在需要日照持续时间数据的情况下，根据云量的估算非常有帮助。从研究中还发现，对于像孟加拉国这样的小国，按纬度分离数据的影响不大。