1. The formation of mesoscale fluctuations by boundary layer convection
Harm Jonker

2. A spectral gap?
(Stull)

3. Cold Air Outbreak
time

4. LES of Sc (ASTEX) Liquid water path L = 25.6km (16hr) L = 12.8km
Dx = Dy = 100m
L = 25.6km (16hr)
L = 12.8km
(12hr)
L = 6.4km
(8hr)
“Large Eddy Simulations:
How large is large enough?”,
de Roode, Duynkerke, Jonker, JAS 2004
“How long is long enough when measuring fluxes and other turbulence statistics?”,
Lenschow, et al. J. Atmos. Oceanic Technol., 1994

5. qt u
lwp w

6. Intermediate Conclusions
1) the formation of dominating mesoscale fluctuations is an integral part of PBL dynamics!
- no mesoscale forcings
- what is the origin (mechanism) ?
- latent heat release
- radiative cooling
- entrainment
- inverse cascade
Atkinson and Zhang
Fiedler, van Delden,
Muller and Chlond,
Randall and Shao,
Dornbrack, ……

7. Convective Atmospheric Boundary Layer
penetrative convection 
entrainment
entrainment zi
heat flux
tracer flux

8. Saline convection tank Laser Induced Fluorescence (LIF)
digital camera
Han van Dop, IMAU
Mark Hibberd, CSIRO
Jos Verdoold,
Thijs Heus,
Esther Hagen
fresh water
Laser
salt water (2%)
r(z)
buoyancy flux & tracer flux
fresh water + fluorescent dye Dp

9. Laser Induced Fluorescence

10. Laser Induced Fluorescence (LIF)
“bottom-up” tracer
boundary layer depth structure
(Verdoold, Delft, 2001)
(see also van Dop, et al. BLM 2005)

11. Conclusions
1) the formation of dominating mesoscale fluctuations is an integral part of PBL convective dynamics!
2) latent heat and radiation are not essential
(but speed up the process considerably)
3) budgets: no inverse cascade on average.
significant backscatter (on all scales)
4) production: ineffective (slow), but spectral transfer is just as ineffective
5) the spectral behaviour of w at large scales is crucial