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A New Combined Local and Non-Local Boundary Layer Model: ACM2

Jonathan Pleim NOAA/ARL USEPA/ORD RTP, NC. A New Combined Local and Non-Local Boundary Layer Model: ACM2. Outline. Model development 1-D testing and evalution Large Eddy Simulation (LES) GABLS Experiment (CASES99) WRF testing and evaluation Surface stats PBL Heights Vertical Profiles

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A New Combined Local and Non-Local Boundary Layer Model: ACM2

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  1. Jonathan Pleim NOAA/ARL USEPA/ORD RTP, NC A New Combined Local and Non-Local Boundary Layer Model: ACM2

  2. Outline • Model development • 1-D testing and evalution • Large Eddy Simulation (LES) • GABLS Experiment (CASES99) • WRF testing and evaluation • Surface stats • PBL Heights • Vertical Profiles • Preliminary CMAQ testing

  3. Purpose • Develop a simple PBL model that: • Produces realistic fluxes and profiles in PBL • Accurate PBL height simulations • Equally applicable to both meteorology and chemistry models • Appropriate for all stability conditions without discontinuities • Computationally efficient

  4. Background • Local flux-gradient proportionality (i.e. Eddy diffusion) is not appropriate for Convective Boundary Layers • Upward heat flux penetrates to ~80% of h while potential temperature gradients are very small through most of the PBL • Eddies in CBL are larger that vertical grid spacing (local closure is not appropriate) • Two common alternative approaches: 1. Gradient adjustment term: Deardorff 1966,Troen and Mahrt 1986, Holstlag and Boville 1993,Noh et al. 2003 2. Transilent or non-local closure: • Stull 1984, Blackadar 1976, • Pleim and Chang 1992

  5. Asymmetric Convective Model (ACM) • Modification of the Blackadar convective scheme • Simple Transilient model with very sparse, efficient semi-implicit matrix solver • Rapid upward transport by convectively buoyant plumes • Gradual downward transport by compensatory subsidence • Part of the PX-LSM in MM5

  6. ACM ACM2

  7. ACM2 • Added eddy diffusion to ACM • Allows local mixing at all levels • More realistic profiles in lower layers • Gradual transition from stable to unstable • Full column integration (PBL and FT together)

  8. ACM Model equations Where Ciis mass mixing ratio at center of Layer i Ki+1/2 is eddy diffusivity at top of layer i [m2s-1] Mu is upward convective mixing rate [s-1] Mdiis downward mixing rate from layer i to layer i-1 [s-1] h is top of PBL

  9. Non-local Mixing rates Convective mixing rate derived by conservation of buoyancy flux: Buoyancyflux at top of first layer defined by eddy diffusion: Where: Thus, Convective mixing rate is a function of Kz but not a function of potential temperature gradient:

  10. ACM2 Model equations Mixing rate, defined by Kz, is partitioned into local and non-local components

  11. Partitioning of local and non-local components The Question is: How to define fconv? Clearly it should increase with increasing instability, but what is its upper limit for free convection? and what should be its stability function? First a sensitivity study for convective conditions

  12. 1-D experiments – Variations in partitioning of local and non-local transport

  13. Normalized heat flux and potential temperature profiles LES (Stevens 2000) ACM2

  14. Non-local partitioning • These tests suggest that the upper limit of fconv should be about 50% • An expression for fconv can be derived from gradient adjustment models (e.g. Holstlag and Boville 1993) at top of surface layer:

  15. Non-local fraction (fconv) as function of stability

  16. LES experiment low heat flux (Q* = 0.05 K m s-1), weak cap

  17. LES experiment low heat flux (Q* = 0.05 K m s-1), strong cap

  18. LES experiment high heat flux (Q* = 0.24 K m s-1), strong cap

  19. Comparison of ACM2, ACM1, and EDDYNL (Holtslag and Boville 1993) compared to the 05WC LES experiment.

  20. Profiles of sensible heat flux. Local, non-local, and total sensible heat flux compared to LES

  21. The second GABLS model intercomparison • Multi-day Intercomparison of 23 PBL models for CASES99 field study • Given initial profiles • Tg time series • Constant geostrophic wind • Large scale subsidence • 2.5% of potential evaporation • P, zo

  22. GABLS T-2m Intercomparison

  23. GABLS Experiment – Simulation of CASES99October 22-24, 1999

  24. GABLS Profile intercomparison

  25. CASES99 profiles

  26. Near surface Temperature profile from CASES99 main tower

  27. WRF • ARW • NOAH LSM • 12 km resolution • FDDA • PBL comparisons • ACM2 • MYJ • YSU • August 2006

  28. PBL Heights from TexAQS II • PBL heights derived from 10 radar wind profilers in Texas area by Jim Wilczak and Laura Bianco NOAA/ESRL • Observations and models averaged by hour of the day for August 1-31, 2006

  29. Average PBL ht for Aug 2006

  30. Average PBL ht for Aug 2006

  31. Ozonesonde 2006

  32. Beltsville - Aug 28, 18Z

  33. Houston – 8/31, 18Z

  34. Houston windspeed and O3

  35. Narragansett – Aug 2, 17Z

  36. Narragansett Ozone, CO

  37. Huntsville – Aug 28, 18Z

  38. Huntsville – Aug 29, 18Z

  39. Huntsville – Ozone, CO

  40. Valparaiso – Aug 31, 19Z

  41. Egbert – Aug 29, 19Z

  42. Egbert WS and O3

  43. CMAQ • Configuration: • Domain: 199 x 205 x 34 @ 12 km res • V4.5 CB4 AE3 • ACM2 vs Eddy • Preliminary evaluation • Ground level statistics (AMET) • Ozonesondes from ICARTT 2004

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