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Large Eddy Simulations of Entrainment and Inversion Structure

Large Eddy Simulations of Entrainment and Inversion Structure. Alison Fowler Supervisor: Ian Brooks. Convectively driven entrainment. Example of LES. The IMPORTANCE of the EZ. The EZ is responsible for the growth of the ML.

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Large Eddy Simulations of Entrainment and Inversion Structure

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  1. Large Eddy Simulations of Entrainment and Inversion Structure Alison Fowler Supervisor: Ian Brooks

  2. Convectively driven entrainment

  3. Example of LES

  4. TheIMPORTANCE of the EZ • The EZ is responsible for the growth of the ML • The depth of the ML is important for determining concentrations of variables within, for example, pollution. • Formation and distribution of clouds

  5. Defining the EZ i) However, Entrainment is a localised event: these definitions are area averaged so may not be useful for fully understanding individual entrainment events. Davis, K. J., D. H. Lenshow, S. P. Oncley, C. Kiemle, G. Ehret, A. Giez, J. Mann, 1997: Role of entrainment in surface- atmosphere interactions over the boreal forest. J. Geophys. Res., 120, 219-230.

  6. Defining the EZ ii) Brooks, I. M., 2003: Finding Boundary Layer Top: Application of a Wavelet Covariance Transform to Lidar Backscatter Profiles. J. Atmos. Ocean. Tech., 20, 1092-1105.

  7. Comparison of Definitions Comparing relationship with the convective Richardson number : Large Ri => little turbulence, there will be no entrainment unless it is strongly influenced from below small Ri =>the interface is dynamically unstable and may become or remain turbulent entraining without any influence from large eddies bellow

  8. Statistics of the EZ

  9. Statistics of the EZ

  10. Statistics of the EZ

  11. Conclusions • Definitions of the EZ using area-averaged profiles cannot help in understanding entrainment events • The variability of the EZ top and bottom important for estimating Ri • Ri important for understanding dynamics of BL and has been used in parameterizations of the entrainment velocity. • Sullivan, P. P., C.-H. Moeng, B. Stevens, D. H. Lenshow and S. D. Mayor, 1998: Structure of the Entrainment Zone Capping the Convective Boundary Layer. J. Atmos. Sci,. 55, 3042-3064. • Entrainment velocity is important in modelling cloud distribution and the budgets of pollution and heat.

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