Downward Solar Radiation at the Surface Difference<br>
aer_opt2 minus standard case<br>
4-km domain, forecast hour 24<br>
aer_opt2 Case uses:<br>
 GEOS 3-hourly aerosol optical depth<br>
 fixed aerosol angstrom exponent   = 1.3<br>
 fixed single scattering albedo    = 0.85<br>
 fixed aerosol asymmetry parameter = 0.9<br>