Forecast of UV-index over Korea with improved total ozone prediction and effects of aerosols, clouds and surface albedo

New ultraviolet (UV) index forecast model was developed by using radiative transfer model and improved multiple linear regression for total ozone prediction using new predictors based on extensive investigation on their correlations with total ozone, and new modification factor for clouds, aerosols and surface reflectance. For clear sky case, root mean square error (RMSE) of newly-forecasted UV index with respect to observations is reduced by 16.0% with using improved forecast of total ozone, by 25.2% with cloud modification factor (CMF) applied, and by 32.7% with CMF and aerosol modification factor (AMF) compared to the existing forecast at Korea Meteorological Administration (KMA), which utilized the state-of-the-art UV radiative transfer model together with multiple regression model. The percentage improvement is estimated to be 16.0% through the application of new total ozone forecast, 9.2% with the new CMF, and 7.5% with the new AMF. The accuracy of UV index forecast for cloudy skies is subjected to the errors of next day's cloud forecast for the modification, but the forecast of UV index for clear sky conditions shows significant improvement.