Comparison of MM5 Forecast Shortwave Radiation with ARM SGP Data

Armstrong, M.A. and Ellingson, R.G., University of Maryland
Eleventh Atmospheric Radiation Measurement (ARM) Science Team Meeting

The performance of the Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model 5 (MM5), in particular the shortwave downwelling (SW) flux calculations, is examined in this paper. Selected quantities output from the MM5 were compared with ARM SGP data gathered during the SCM intensive observation period (IOP) from June 18 to July 18, 1997. MM5 was run 29 times with a forecast length of 24 hours. The data were saved and then compared to radiosonde and pyranometer data. SW flux calculated from the MM5 deviated severely from that observed at the SGP site. Much of the error probably results from the method by which cloud fraction is calculated within the radiation parameterization. Additional error in the SW flux could be attributed to an overly moist upper troposphere generated by the model. Despite the enormous SW flux errors, the model reproduced the observed surface temperature quite well, with only a slight cold bias. These results echo a number of other verification studies of the MM5, and the SW flux problem bears some resemblance to a SW flux verification study conducted with the Eta regional model.

Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).