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