[GTP] MMM SEMINAR 7/28/10 @ 10:30AM--Mironov

[Silvia Gentile]

MMM SEMINAR NCAR
Effect of Surface Temperature Heterogeneity on Turbulent Mixing in a 
Stably Stratified Atmospheric Boundary Layer
Dmitrii V. Mironov
German Weather Service, Offenbach am Main, Germany
Peter P. Sullivan National Center for Atmospheric Research, Boulder CO, USA



Idealized LES of two stably stratified boundary layer (SBL) flows driven 
by fixed winds and homogeneous and heterogeneous surface temperature are 
compared. The LES data are used to compute statistical moments of the 
fluctuating fields (mean wind and mean potential temperature, 
second-order and third-order turbulence moments, pressure-velocity and 
pressure-scalar co-variances), to estimate terms in the second-moment 
budgets, and to assess the relative importance of various terms in 
maintaining the budgets. The budgets of the turbulence kinetic energy 
(TKE), of the temperature variance, and of the vertical temperature flux 
are analyzed. As different from most previous studies, the LES-based 
second-moment budgets are estimated with due regard for the sub-grid 
scale contributions. These contributions may be substantial, 
particularly in the SBL, and should be retained in order to close the 
second-moment budgets to a good order. We find the SBL over a 
heterogeneous surface is more turbulent with larger variances and TKE, 
is better mixed and is deeper compared to its homogeneous counterpart. 
The latter results are similar to those described by Stoll and 
Porte-Agel (2009). Perhaps the most striking difference between the 
cases is exhibited in the temperature variance and its budget. Due to 
surface heterogeneity, the third-order moment, i.e. the vertical flux of 
temperature variance, is non-zero at the surface. Hence, the turbulent 
transport term (divergence of the above third-order moment) not only 
redistributes the temperature variance in the vertical, but is a net 
gain. As a result, the temperature variance in the heterogeneous case is 
large near the surface. Motivated by the LES results, possible ways to 
incorporate the effect of the sub-grid scale surface temperature 
heterogeneity into the SBL turbulence models (parameterization schemes), 
including the surface-layer flux-profile relationships, are discussed.


Wednesday, 28 July 2010, 10:30 AM
Refreshments 10:15 AM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg 3, Room 2072