I need to estimate the actual solar radiation value from clear sky solar radiation data. So, I need to multiply the clear sky solar radiation by cloud cover. But I am not clear about total sky cover and opaque sky cover. Can anybody explain to me about this.
There are not many radiation models that can use both inputs. Most only use the total sky cover, also known as cloud fraction. One notable exception is METSTAT by Maxwell et al. (Solar Energy, 1998), which used hourly cloud data then available in the US. Such ground observations do not exist anymore, however, All human observers in North America have been replaced with automatic cloud sensors that have a lot of limitations. See https://www.researchgate.net/publication/236314670_Towards_production_of_an_updated_National_Solar_Radiation_Data_Base_%28NSRDB%29?ev=srch_pub&_sg=MyRqJuKI4u4lHPFFkDIXa2az8zvLfzeMIbUa3YrzYmZQEFmU1o7ey9ChoO-WG56p.buRnA8wzvtAsNG-JnhkfB-sZ-XinlDIaS5tx-CzOmyCZHgWVXLNpglNMeYnAlzqW.5VkB3iXcc_746hwKxP4Xf1ZUDVi2stoBnVND5SAF6O0OS7wZxVf7eQUZ9nNXgJ73 for more details about how the difficulties of adapting the METSTAT model to the newer cloud data were handled.
Of course, the majority of solar radiation modeling efforts now use satellite imagery to evaluate cloud effects and to provide gridded solar irradiance products at high spatial and temporal resolution--with also normally better accuracy than estimates based on ground observations.
Conference Paper Towards production of an updated National Solar Radiation Da...
In surface weather observations, a term used to denote one or more of the following:
1) the amount of sky covered but not necessarily concealed by clouds or by obscuring phenomena aloft;
2) the amount of sky concealed by obscuring phenomena that reach the ground; or
3) the amount of sky covered or concealed by a combination of 1) and 2).
Opaque sky cover is the amount of sky completely hidden by clouds or obscuring phenomena, while total sky cover includes this plus the amount of sky covered but not concealed (transparent). Sky cover, for any level aloft, is described as thin if the ratio of transparent to total sky cover at and below that level is one-half or more. Sky cover is reported in tenths, so that 0.0 indicates a clear sky and 1.0 (or 10/10) indicates a completely covered sky. Amount of sky cover for any given level is determined according to the summation principle. The following classifications of sky cover are used in aviation weather observations: clear, scattered, broken, overcast, partial obscuration, obscuration.
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