Comparison of NMC/NCAR reanalysis with 1987 FIFE data

Data from the FIFE experiment of the Summer of 1987 are used to assess the diurnal and seasonal cycles of the surface energy budget and boundary layer in the NMC/NCAR reanalysis, which uses the current (June, 1995) Medium-Range Forecast model. The seasonal agreement is quite good, reflecting the improvements in land-surface parameterizations in recent years. Detailed studies however identify several places where still further improvements in model parameterizations are possible. Clear-sky short-wave absorption and cloudiness may be underestimated in the model as has been noticed in other global models. More frequent updates of the model cloud cover (currently every 3 h) would improve the land surface interaction after the initial onset of precipitation. The model produces a realistic well-mixed boundary layer, but underestimates boundary layer deepening by entrainment. For much of the summer precipitation is close to that observed, but for a period in June and early July, the reanalysis model has excess precipitation, which comes from daytime interactions between the surface evaporation, boundary layer, and convection schemes. The model, which has a deep 2-m soil reservoir, has adequate soil moisture storage for several weeks without rain, although surface Bowen ratio fluctuates more strongly after rain than is observed. Surface evaporation is generally too high at night, especially in high winds. This analysis suggests several improvements to the model parameterizations which are currently being tested. Alan K. Betts, Song-You Hong, and Hua-Lu Pan. "September 1995." "This is an unreviewed manuscript, primarily intended for informal exchange of information among the NMC staff members." System requirements: Adobe Acrobat Reader. Includes bibliographical references (pages 38-41). 1995 NWS (National Weather Service) NCEP (National Centers for Environmental Prediction) Library Public Domain 1931