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The formation of mesoscale fluctuations by boundary layer convection

The formation of mesoscale fluctuations by boundary layer convection. Harm Jonker. A spectral gap?. (Stull). time. Cold Air Outbreak. Liquid water path. LES of Sc (ASTEX). Dx = Dy = 100m. L = 25.6km (16hr). L = 12.8km (12hr). L = 6.4km (8hr). “Large Eddy Simulations:

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The formation of mesoscale fluctuations by boundary layer convection

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

  2. A spectral gap? (Stull)

  3. time Cold Air Outbreak

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

  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. boundary layer depth structure Laser Induced Fluorescence (LIF) “bottom-up” tracer (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

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