Characterization of Turbulent Kinetic Energy Budget in the Atmospheric Surface Layer

Urban activities and pollutant dispersions take place in the atmospheric surface layer, the bottom of the atmosphere, whose depth is on the order of several tens or hundreds meters. Characterizing turbulence in the surface layer is of great significance in urban air quality research, and has a major role in policy and regulatory decision, urban design, and air pollution control. The turbulence kinetic energy (TKE) budget, which associates the change of turbulence per unit time to mechanical production, buoyancy production or destruction, turbulent energy dissipation, and transport by mean flow, turbulent fluctuations, and pressure fluctuations, finds its applications in both empirical and computational approaches. This study utilizes experimental data collected in an open filed in Hanford, WA in 2002 to investigate the TKE budget in the surface layer. The TKE budget was normalized and all terms were parameterized as functions of a stability parameter z/L, where z is a distance from the ground and L is the Monin-Obukhov length. The mechanical, buoyancy and dissipation terms, are found to be imbalanced due to a large net transport term. This imbalance suggests imperfection of the Monin-Obukhov Similarity Theory (MOST), which is widely used as the major parameterization in the surface layer. Modifications on the TKE parameterization derived from MOST were attempted and generated good agreement with the experimental data.