Motivation

1. Evaluation of Surface Flux Parameterizations.Surface momentum, sensible and latent heat fluxes are critical processes that need to be accurately represented in large scale weather and climate models. However, direct observational evaluation of the parameterization schemes for these fluxes is rare. DOE scientists at the Brookhaven National Laboratory have evaluated the six surface flux parameterization schemes used in the Weather Research and Forecasting (WRF) model and three US global climate models (GCMs) under a variety of stability conditions, diurnal cycles and seasons using the long-term observations of surface fluxes collected at the ARM Southern Great Plains site. Statistical analyses show that the momentum flux parameterization agrees best with the observations, followed by latent heat flux, sensible heat flux, and the evaporation ratio/Bowen ratio. The overall performance of these parameterizations depends on atmospheric stability, and is best under neutral stratification conditions, deteriorating under both more stable and more unstable conditions. The results also demonstrate the need for improving land-surface models and for the measurement of surface properties that allow their full evaluation. Reference: Liu, G., Y. Liu and S. Endo, 2012L “Evaluation of Surface Flux Parameterizations with Long-Term ARM Observations” Wea. Mea. Rev., (accepted) Contact: Dorothy Koch, SC23.1, 301-903-0105.

2. Evaluation of major surface flux parameterizations with 7 years of ARM measurements • Motivation • Parameterizations of surface momentum, sensible heat and latent heat fluxes are critical for large scale weather and climate models; however, direct evaluation against observations is rare due to limited observations. • Approach • 7 year ARM measurements at SGP with the eddy correlation (EC) and Energy Balance Bowen Ratio (EBBR) methods are used to evaluate the six parameterizations used in WRF, NCAR, GFDL and GISS GCMs. • Result • The momentum flux scheme agrees best with the EC observations, followed by latent heat flux, sensible heat flux, and evaporation ratio/Bowen ratio. The results demonstrate the need for improving land-surface models and for the measurement of surface properties that allow their full evaluation. Comparison of the relative Euclidean distances between the momentum flux, sensible heat flux, latent heat fluxes, and Bowen ratio, and between the six parameterization schemes. The relative Euclidean distance measures the overall agreement between the parameterization and EC observation in terms of mean bias, standard deviation and correlation coefficient, with a smaller value indicating a better overall agreement. Note that the parameterized Bowen ratio is actually worse than shown here due to deletion of some “extreme” values. G. Liu, Y. Liu and S. Endo, 2012L “Evaluation of Surface Flux Parameterizations with Long-Term ARM Observations” Wea. Mea. Rev., (accepted)