Large Eddy Simulations of Entrainment and Inversion Structure

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Large Eddy Simulations of Entrainment and
Inversion Structure
Alison Fowler Supervisor Ian Brooks
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Convectively driven entrainment
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Example of LES
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The IMPORTANCE 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

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