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Air Pollution and Turbulence: Modeling and Applications
seen that the MF term gives the leading contribution to the heat fl ux, except in the
lower part of the BL. In particular, in the inversion layer this dominance assumes an
important role, since it enhances considerably the buoyancy fl ux associated with the
top-entrainment process, crucial to the BL growth. LES results (Sullivan et al. 1998)
confi rm the important role of thermals in top-entrainment.
In spite of the simplicity of the parcel model, in what concerns its basic equation,
and of the lateral mixing formulation, the vertical profi les of vertical velocity computed with Equation 4.55 are quite close to those diagnosed through LES simulations
as fractions of the stronger ascents (Figure 4.15).
4.4.4.1 Top-Entrainment
The top-entrainment is a typical interface process, present in all geophysical fl ows.
Although crucial to the BL growth, it is still not a well-understood process and is often
2.0
10 h
LES
hr
cr
5 h
Height (km)
1.5
1.0
0.5
0.0
–0.02
0.00
0.02
0.04
w΄θ΄ (ms
–1 K)
0.06
FIGURE 4.13 Vertical profi les of the vertical fl ux of potential temperature. Hourly average
of the 5th and 10th hour. Results of the new scheme, (hr) 20 m resolution and (cr) ecmwf-40
levels resolution, and LES model.
2.0
1.5
1.0
0.5
0.0
–0.02
0.00
0.02
0.04
0.06
w΄θ΄ (ms
–1 K)
Height (km)
MF
ED
Total
FIGURE 4.14 The ED and MF contributions for the vertical fl ux of potential temperature.
Hourly average of the 10th hour.
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