Study of intra-hour direct normal irradiance variability effects on hourly WRF-Chem outputs
Abstract
Reliable and accurate solar resource information can be obtained, ideally, through direct ground measurements of the incoming solar irradiance; however, greater temporal and spatial coverages require most of the time some sort of modelling, commonly by directly deriving irradiance from satellite imaging or through physical, empirical, or numerical models. Operationally running the Weather Research and Forecasting (WRF) model provides the current values of irradiance as well as forecasts up to a few days ahead, and great efforts are being made to reduce the relatively high uncertainties from these models. While NWP models can provide forecasts at hourly intervals, which is relatively high for some applications, for solar radiation applications this temporal resolution cannot correctly capture the intra-hour variability and can be a source of errors especially during changing atmospheric conditions, in which hourly averages do not necessarily reflect representative enough conditions, particularly in the case of direct (or beam) normal irradiance, which is especially sensitive to clouds and aerosols. A study is presented here on the effects of intra-hour (within the hour) variability of beam radiation for cloud- and aerosol-variable conditions, in the use of hourly values in the advanced WRF-Chem model to predict beam irradiances in desert conditions.