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A Climatology of Midlatitude Continental Clouds from the ARM SGP Central Facility:Part IV: Comparison of Cloud Fraction and Radiation Fluxes between the Surface Observation and the NCEP NWP Forecast

Dong, Xiquan University of North Dakota

Baike Xi(a), Xiquan Dong(a), and Fanglin Yang(b) University of North Dakota (a), NOAA National Centers for Environmental Prediction(b) Contact: Baike Xi, baike@aero.und.edu ; Phone: 701-777-2767 Three years (From Jan. 1, 2001 to Dec. 31, 2003) of observational data from Department of Energy Atmospheric Radiation Measurement (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) central facility have been statistically compared with the outputs of National Centers for Environmental Prediction (NCEP) NWP forecasts at the same time period. In this study, we compared the following parameters: cloud fraction and downwelling and upwelling shortwave (SW), longwave (LW) fluxes, and radiation budgets under the conditions of all skies and total clouds. The total cloud fraction derived from the paired upward-looking narrow field-of-view radar/lidar measurements is simply the percentage of returns that are cloudy within a specified sampling time period, and the NCEP total cloud fraction is selected from the max. value of the 65-layer cloud fractions. The SW and LW fluxes are measured by up- and down-looking standard precision spectral pyranometers and precision infrared radiometers and provided by NCEP model. The monthly variations of cloud fractions from measurement and forecast have the same trend with the annual averages of 0.505 and 0.365, respectively. The monthly variations of SW, LW, and Net fluxes and budgets under the conditions of total clouds and all skies are also analyzed in this study. The annual averages of cloudy SW, LW, and Net budgets are 127.8 (163.0), -44.7 (-67.7), and 83.1 (95.3) W m-2 from PSP/PIR measurements (NCEP forecast), respectively. The measured cloudy downwelling SW flux (161.3 W m-2) is systematically lower than those of NCEP forecast (203.6 W m-2), while LW flux (352.1 W m-2) is higher than NCEP result (324.1 W m-2). These comparisons are consistent with the cloud fraction comparison. The upwelling SW and LW fluxes between measurement and forecast have a good agreement (5-7 W m-2) under cloudy condition. For all-sky condition, the annual averages of SW, LW, and Net budgets are 180.7 (165.6), -71.3 (-68.8), and 109.4 (96.8) Wm-2 from measurement (forecast), respectively. Although the monthly variations of all-sky down/upwelling forecasted SW and LW fluxes are close to the measured values, they are inconsistent with the cloud fraction comparison. Since the NCEP NWP provides the 48-hour forecasts extended at 00Z, we compare the first and second 24-hour NCEP forecasts against the surface measurements. The hourly variations of cloud fractions and SW/LW fluxes and budgets will be studied.

This poster will be displayed at the ARM Science Team Meeting.