Turbulent Flux Parameterization And Numerical Study On Thermal Boundary Layer

This paper documents, discusses, and investigates turbulent flux observation, flux parameterization, and PBL schemes via1-D vertical profiles and3-D simulations using WRF. The study, indicating some weaknesses even some specific problems in the current widely-used flux parameterization and PBL scheme, suggests that development of a general PBL scheme be the right direction. While, non-local parameterization is more suitable for convective boundary layer (CBL) so far.As the first part of this study, the validation of three heat flux parameterizations using observational data is discussed and addressed. The three parameterizations for CBLhave been developed by Deardorff(1972), Holtslag and Moeng (1991), and liu (2000,2001). With part of published database obtained from WL-ARPDD94Experiment in Xianghe, the three schemes are tested and compared. The result analysis shows that Deardorff’s scheme systematically underestimates the heat flux within entire CBL. Holtslag and Moeng’s is in good agreement with observation in the middle and upper portion of CBL, where the heat counter-gradient transport becomes predominant. However, Liu’s parameterization exhibits good agreement with observations in whole CBL. The counter-gradient as function of eddy length scale varies with height in Liu’s rather than a constant in the aforementioned two. The analysis suggests that Liu’s scheme, first used to determine heat flux based on field experiment data, enable to represent heat flux profile for CBL. On the basis of review of physical interpretation about counter-gradient transport phenomenon by the different closure schemes, a universal scheme for planetary boundary layer suitable for numerical weather forecast models is urgently needed.In the second part of this study, WRF simulations with three PBL schemes including YSU, MYJ, and ACM2are performed. The model validation using observational data from4stations is discussed in very details. The modeled and observed T2m, U10associated with a dust storm episode occurred in4-10April,2002is well-compared and analyzed. The results show that the simulations are good in agreement with observations, and the non-local YSU scheme is the best one among the three. Meanwhile, the profiles of wind and moisture as well as PBL height are validated by observed data from those stations. In general, the WRF with YSU scheme enable to capture major features of desert PBL, and performs better than others. Therefore, the WRF simulation is helpful to fill the gap between the observation stations which are scarce in this region.