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Air Pollution and Turbulence: Modeling and Applications
cycle of cumulus clouds over land. Lenderink et al. (2004) presented a single- column
intercomparison study based on this case. This intercomparison was based on several single column versions of (semi)-operational models. The MesoNH was one of
the models included, using its standard options, referred above. Like the majority of
the other models, MesoNH produced too large values of cloud cover, and unlike the
other models too small values of cloud liquid water.
In this case, surface latent and sensible heat fl uxes were prescribed, with values
close to zero in early morning and the evening, and a maximum at midday of 500
and 140 Wm −2 , respectively. The initial profi les of potential temperature and humidity are displayed in Figure 4.27. The mean wind initial vertical profi les correspond
to (u, v) = (10, 0) ms −1 .
Figures 4.25 and 4.26 show the time series of cloud properties. The EDMF scheme
captures well the diurnal cycle of shallow convection. Both the timing of the onset
and disappearance of the cumulus clouds are well described. The cloud cover and
liquid water path (LWP), given by the sub-grid condensation scheme, are in a rather
good agreement with LES results, revealing both the proper time evolution and order
of magnitude. The maximum of cloud cover (Figure 4.25a) around 0.2 is very close
to the LES simulation result, and is reached after 18 UTC (12 LT) only slightly later
than in the LES. The cloud base height also agrees well with LES results. The diagnostic of cloud base height given by the updraft condensation level (“new up” in
Figure 4.25b) indicates the onset of cumulus clouds at 15.30 UTC (9.30 LT), above
700 m. The cloud base goes up in time, attaining a maximum of around 1200 m after
24.00 UTC (18 LT).
Some of the models that participated in the intercomparison study of Lenderink
et al. (2004) were able to reproduce the cumulus onset time. However, most models
were unable to correctly predict the dissipation of clouds by the end of the day. With
the EDMF scheme, the cumulus fi eld dissolves at approximately the correct time,
and shows a low level of intermittency. In its standard version, MesoNH had a rather
high cloud fraction (around 50%) and almost no liquid water during the simulation.
These features appear much improved mainly due to a better estimate of the variance, associated with the contribution of the MF term in Equation 4.84.
Figure 4.25c shows that the cloud scheme is able to reproduce the height of maximum cloud cover given by the LES model. The cloud-top height (Figure 4.25d)
is underestimated, probably due to the over simplistic constant entrainment profi le
used. The LWP results in Figure 4.26a show a realistic evolution but with a slight
underestimation by the EDMF model. The cloud base MF time series shown in
Figure 4.26b resembles the one diagnosed from LES by Neggers et al. (2004).
The vertical profi les of potential temperature and humidity are shown in Figure
4.27. The subcloud layer potential temperature evolution is very much realistic. The
specifi c humidity is too high in the sub-cloud layer due to insuffi cient transport into
the cloud layer. This defi ciency is consistent with the cloud fraction and liquid water
profi les displayed in Figure 4.28; they tend to have the right order of magnitude but
they lack suffi cient vertical extension. This is also refl ected in the potential temperature profi le in the cloud layer (Figure 4.27a). The discrepancy again is the result of
insuffi cient turbulent mixing in the cloud layer.
© 2010 by Taylor and Francis Group, LLC
Air Pollution and Turbulence: Modeling and Applications
cycle of cumulus clouds over land. Lenderink et al. (2004) presented a single- column
intercomparison study based on this case. This intercomparison was based on several single column versions of (semi)-operational models. The MesoNH was one of
the models included, using its standard options, referred above. Like the majority of
the other models, MesoNH produced too large values of cloud cover, and unlike the
other models too small values of cloud liquid water.
In this case, surface latent and sensible heat fl uxes were prescribed, with values
close to zero in early morning and the evening, and a maximum at midday of 500
and 140 Wm −2 , respectively. The initial profi les of potential temperature and humidity are displayed in Figure 4.27. The mean wind initial vertical profi les correspond
to (u, v) = (10, 0) ms −1 .
Figures 4.25 and 4.26 show the time series of cloud properties. The EDMF scheme
captures well the diurnal cycle of shallow convection. Both the timing of the onset
and disappearance of the cumulus clouds are well described. The cloud cover and
liquid water path (LWP), given by the sub-grid condensation scheme, are in a rather
good agreement with LES results, revealing both the proper time evolution and order
of magnitude. The maximum of cloud cover (Figure 4.25a) around 0.2 is very close
to the LES simulation result, and is reached after 18 UTC (12 LT) only slightly later
than in the LES. The cloud base height also agrees well with LES results. The diagnostic of cloud base height given by the updraft condensation level (“new up” in
Figure 4.25b) indicates the onset of cumulus clouds at 15.30 UTC (9.30 LT), above
700 m. The cloud base goes up in time, attaining a maximum of around 1200 m after
24.00 UTC (18 LT).
Some of the models that participated in the intercomparison study of Lenderink
et al. (2004) were able to reproduce the cumulus onset time. However, most models
were unable to correctly predict the dissipation of clouds by the end of the day. With
the EDMF scheme, the cumulus fi eld dissolves at approximately the correct time,
and shows a low level of intermittency. In its standard version, MesoNH had a rather
high cloud fraction (around 50%) and almost no liquid water during the simulation.
These features appear much improved mainly due to a better estimate of the variance, associated with the contribution of the MF term in Equation 4.84.
Figure 4.25c shows that the cloud scheme is able to reproduce the height of maximum cloud cover given by the LES model. The cloud-top height (Figure 4.25d)
is underestimated, probably due to the over simplistic constant entrainment profi le
used. The LWP results in Figure 4.26a show a realistic evolution but with a slight
underestimation by the EDMF model. The cloud base MF time series shown in
Figure 4.26b resembles the one diagnosed from LES by Neggers et al. (2004).
The vertical profi les of potential temperature and humidity are shown in Figure
4.27. The subcloud layer potential temperature evolution is very much realistic. The
specifi c humidity is too high in the sub-cloud layer due to insuffi cient transport into
the cloud layer. This defi ciency is consistent with the cloud fraction and liquid water
profi les displayed in Figure 4.28; they tend to have the right order of magnitude but
they lack suffi cient vertical extension. This is also refl ected in the potential temperature profi le in the cloud layer (Figure 4.27a). The discrepancy again is the result of
insuffi cient turbulent mixing in the cloud layer.
© 2010 by Taylor and Francis Group, LLC