The formation of mesoscale fluctuations by boundary layer convection
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Transcript of The formation of mesoscale fluctuations by boundary layer convection
Multi-Scale Physics Faculty of Applied Sciences
The formation of mesoscale fluctuations by boundary layer
convection
Harm Jonker
Multi-Scale Physics Faculty of Applied Sciences
A spectral gap?
(Stull)
Multi-Scale Physics Faculty of Applied Sciences
Cold Air Outbreak
time
L = 6.4km(8hr)
Dx = Dy = 100m
L = 12.8km
(12hr)
L = 25.6km (16hr)
LES of Sc (ASTEX) Liquid water path
“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
w
qt u
lwp
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 ZhangFiedler, van Delden, Muller and Chlond, Randall and Shao,Dornbrack, ……
Multi-Scale Physics Faculty of Applied Sciences
Convective Atmospheric Boundary Layer
penetrative convection
zi
heat flux
entrainment
entrainment
tracer flux
Saline convection tank
Laser Induced Fluorescence (LIF)
fresh water
salt water (2%)
fresh water + fluorescent dye
buoyancy flux & tracer flux
Laser
(z)
digital camera
p
Han van Dop, IMAUMark Hibberd, CSIROJos Verdoold, Thijs Heus, Esther Hagen
Laser Induced Fluorescence
Laser Induced Fluorescence (LIF)“bottom-up” tracer
boundary layer depth structure
(Verdoold, Delft, 2001)(see also van Dop, et al. BLM 2005)
Multi-Scale Physics Faculty of Applied Sciences
Conclusions1) 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