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The formation of mesoscale fluctuations by boundary layer convection

The formation of mesoscale fluctuations by boundary layer convection. Harm Jonker. Cold Air Outbreak. Peter Duynkerke, IMAU Utrecht University. Agee, Atkinson and Zhang ……. Stratocumulus Aircraft Observations. log E(k). log k. Sun and Lenschow, 2006. Sun and Lenschow, 2006.

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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. Cold Air Outbreak Peter Duynkerke, IMAU Utrecht University Agee, Atkinson and Zhang ……

  3. Stratocumulus Aircraft Observations log E(k) log k

  4. Sun and Lenschow, 2006

  5. Sun and Lenschow, 2006

  6. Sun and Lenschow, 2006

  7. LES of Stratocumulus L = 25.6km Dx = Dy = 100m t = 1...16hr, liquid water path

  8. 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

  9. qt u lwp w

  10. - 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) ?

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

  12. LES passive scalar c passive scalar c q q w w w variance spectra c FFT (2D) Jonker,Duynkerke,Cuypers, JAS, 1999

  13. 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

  14. Laser Induced Fluorescence

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

  16. Intermediate Conclusions 1) the formation of dominating mesoscale fluctuations is an integral part of PBL dynamics! 2) latent heat and radiation are not essential • - latent heat release • - radiative cooling • - entrainment • inverse cascade

  17. Inverse Cascade? E(k) E(k) P D P P D k k 2-D or not 2-D: that’s the question

  18. spectral interaction dissipation production scale by scale variance budget Spectral variance budget

  19. source Scale Interaction MatrixCml 16 sections sink l m passive scalar

  20. source Scale Interaction MatrixCml 16 sections sink l m dynamics

  21. E(k) k pdf of spectral flow f or

  22. upscale transfer downscale transfer

  23. Intermediate Conclusions 1) the formation of dominating mesoscale fluctuations is an integral part of PBL dynamics! 2) latent heat and radiation are not essential 3) budgets show: no inverse cascade (significant backscatter on all scales) - latent heat release - radiative cooling - entrainment - inverse cascade

  24. Mechanism… E(k) E(k) P D P P D k k

  25. weak production, weak transfer E(k) P P D k

  26. mechanism (CBL) (Leith, 1967) spectral (Corrsin, ‘68) large scales weak production, weak transfer. w crucial! (Jonker, Vila, Duynkerke, JAS, 2004) transport

  27. qt u lwp w

  28. Spectral budget w spectral transfer subgrid dissipation buoyancy production pressure correlation

  29. spectrum budget

  30. Spectral budget u subgrid dissipation spectral transfer shear production pressure correlation

  31. spectrum budget

  32. spectrum budget

  33. Spectral budget scalar variance budget gradient production subgrid dissipation spectral transfer spectral budget

  34. spectrum budget

  35. buoyancy production pressure break the chain … production

  36. test 1: w lwp u reference w filtered

  37. reference

  38. test 1:

  39. buoyancy production pressure break the chain … production

  40. test 2: w lwp u reference q,q filtered

  41. reference

  42. test 2:

  43. Concluding: The spectral gap … (Stull)

  44. time Cold Air Outbreak

  45. 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

  46. Jonker,Duynkerke,Cuypers, JAS, 1999

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