| The Weather Research and Forecast (WRF) model is used to explore the influence of aerosol direct radiative effects on regional climate of California. Aerosol data is provided by the MOZART global chemistry transport model and includes sulfate, black carbon, organic carbon, dust and sea salt. To investigate the sensitivity of aerosol radiative effects to different aerosol species and to the quantity of sulfate and dust, tests are conducted by using different combinations of aerosols and by resetting the quantity of sulfate and dust. The model results show that all the considered aerosols could have a cooling effect of one half to one degree in terms of temperature and that dust and sulfate are the most important aerosols. However, large uncertainties exist. The results suggest that the dust from MOZART is greatly overestimated over the simulation domain. The single scattering albedo (SSA) values of dust used in some global climate models are likely underestimated compared to recent studies on dust optical properties and could result in overestimating the corresponding cooling effects by approximately 0.1 degree. Large uncertainties exist in estimating the roles of different forcing factors which are causing the observed temperature change in the past century in California. |
