Numerical Weather Prediction (NWP) models such as the Weather Research and Forecasting (WRF) model are essential for forecasting one-day-ahead solar irradiance. In order to evaluate the performance of the WRF in forecasting solar irradiance over the Korean Peninsula, we compared WRF prediction data from 2008 to 2010 corresponding to weather observation data (OBS) from the Korean Meteorological Administration (KMA). The WRF model showed poor performance at polluted regions such as Seoul and Suwon where the relative Root Mean Square Error (rRMSE) is over 30%. Predictions by the WRF model alone had a large amount of potential error because of the lack of actual aerosol radiative feedbacks. For the purpose of reducing this error induced by atmospheric particles, i.e., aerosols, the WRF model was coupled with the Community Multiscale Air Quality (CMAQ) model. The coupled system makes it possible to estimate the radiative feedbacks of aerosols on the solar irradiance. As a result, the solar irradiance estimated by the coupled system showed a strong dependence on both the aerosol spatial distributions and the associated optical properties. In the NF (No Feedback) case, which refers to the WRF-only stimulated system without aerosol feedbacks, the GHI was overestimated by 50–200 W m-2 compared with OBS derived values at each site. In the YF (Yes Feedback) case, in contrast, which refers to the WRF–CMAQ two-way coupled system, the rRMSE was significantly improved by 3.1–3.7% at Suwon and Seoul where the Particulate Matter (PM) concentrations, specifically, those related to the PM10 size fraction, were over 100 g m-3. Thus, the coupled system showed promise for acquiring more accurate solar irradiance forecasts.

Abstract
 1. Introduction
 2. Methods
  2.1. Numerical weather prediction model
  2.2. Coupled system with the air quality model
  2.3. Modeling periods and statistical metrics
 3. Results
  3.1. Evaluation of solar irradiance archived by the WRF system
  3.2. Case study: improvement of solar irradiance forecasting by the WRF–CMAQ coupled system
 4. Concluding remarks
 REFERENCES

• Dong Hyeok Kim(Seohaean Research Institute, ChungNam Institute)
• Jung Woo Yoo(Department of Atmospheric Environment, Pusan National University)
• Hwa Woon Lee(Department of Atmospheric Environment, Pusan National University) Corresponding author
• Soon Young Park(Institute of Environmental Studies, Pusan National University)
• Hyun Goo Kim(New & Renewable Energy Resource Center, Korea Institute of Energy Research)