Zhuorui Wei1, Hongsheng Zhang1*, Xuhui Cai2, Yu Song2
1. Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, P.R. China
2. State Key Joint Laboratory of Environmental Simulation and Pollution Control, Department of Environmental Science, Peking University, Beijing 100871, P.R. China
* Correspondence to: Hongsheng Zhang (hsdq@pku.edu.cn)
Abstract
Using multi-layer pressure fluctuations and other conventional turbulence observational data over a nearly flat and homogeneous dune underlying surface, the temporal and spatial characteristics of pressure flux and its profile were analyzed to illustrate the physical mechanism of pressure flux convergence/divergence and the impact of pressure transport terms on the estimation of turbulent fluxes in this study. The flux-variance (FV) method is an effective approach to indirectly obtain pressure flux through momentum flux when no fast-response observations of pressure fluctuations are available. The fitted functions are 
and , where and are the height normalized functions for vertical and horizontal directions. Under the circumstance of pressure flux divergence (FD), the transport efficiency of pressure and contribution of larger-scale eddies to pressure flux at higher levels are greater than those at lower levels, and flows in the atmospheric surface layer (ASL) are mainly dominated by the sweep events; while the pressure flux convergence (FC) cases are exactly the opposite situations. A good quadratic function relationship was found between the vertical gradient of pressure flux and friction velocity under different atmospheric stabilities: . Turbulence kinetic energy (TKE) and its vertical transport are greater in the FD cases than those in the FC cases. The momentum and sensible heat fluxes in the convective boundary layer (CBL) were overestimated by their common second-order diagnostic equations and Rotta model (pressure redistribution term parameterization) which neglect the diffusion terms. After adding the contribution of pressure transport terms into the diagnostic equations and Rotta model and modifying the original Rotta constants, the overestimations were well corrected and the estimated turbulent fluxes were more consistent with the observations. This work provides a novel direction and idea for the future improvement of the planetary boundary layer (PBL) parameterization schemes in many numerical weather and climate models.
Keywords
Vertical gradient of pressure flux; Flux convergence and divergence; Diagnostic equations for Turbulent Fluxes; Rotta model
Acknowledgments
This work was supported by the National Natural Science Foundation of China (42090031, 42175092, 92044301, 91837209); the Second Tibetan Plateau Scientific Expedition and Research (STEP) program (grant no. 2019QZKK0105); and Flexible Talents Introducing Project of Xinjiang (2018).
Citation
Wei, Z., Zhang, H., Cai, X., & Song, Y. (2022). Physical mechanism of vertical gradient of pressure flux and its impact on turbulent flux estimation. Agricultural and Forest Meteorology, 323, 109032. https://doi.org/10.1016/j.agrformet.2022.109032.
