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GFS Vertical Turbulent Mixing Scheme

GFS Vertical Turbulent Mixing Scheme. Jongil Han. Introduction. (1). (2). Φ : θ , q, u, v , …. Tendency due to subgrid cumulus convection, turbulent mixing, and gravity wave drag. (2) All tendency terms due to advection and diabatic processes. GFS vertical mixing scheme (moninq).

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GFS Vertical Turbulent Mixing Scheme

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  1. GFS Vertical Turbulent Mixing Scheme Jongil Han

  2. Introduction (1) (2) • Φ: θ, q, u, v, …. • Tendency due to subgrid cumulus convection, turbulent mixing, and gravity wave drag. • (2) All tendency terms due to advection and diabatic processes. NEMS/GFS Modeling Summer School

  3. GFS vertical mixing scheme (moninq) • It is a first order K-theory-based scheme under down-gradient diffusion assumption, where K is eddy-diffusivity. • For the daytime planetary boundary layer (PBL), an eddy-diffusivity (profile) counter-gradient (EDCG) mixing approach is adopted to take into account nonlocal transport by strong updraft. • For the vertical diffusion in nighttime stable boundary layer and layers above PBL, a local K is used (which is a function of local gradient Richardson number, local wind shear, and a mixing length). • Include stratocumulus-top driven turbulence mixing based on Lock et al.’s (2000) study. • Enhance stratocumulus top driven diffusion when the condition for cloud top entrainment instability is met. NEMS/GFS Modeling Summer School

  4. EDCG approach for unstable PBL NEMS/GFS Modeling Summer School

  5. Stratocumulus-top driven turbulence mixing (Lock et al., 2000) NEMS/GFS Modeling Summer School

  6. Stratocumulus-top driven turbulence mixing (Buoyancy reversal term is neglected) c=0.2 (Moeng et al., 1999) c=1.0 (CTEI condition; MacVean and Mason, 1990) NEMS/GFS Modeling Summer School

  7. PBL height (h) in unstable BL • Daytime PBL grows by surface heating and entrainment flux at the PBL top. • h is intentionally enhanced with a thermal excess to have an implicit entrainment flux at the PBL top Rbcr=0.25 h = height of zero heat flux, not that of minimum heat flux NEMS/GFS Modeling Summer School

  8. NEMS/GFS Modeling Summer School

  9. Diffusion in the stable boundary layer and the layers above the PBL • Use a local diffusion scheme (Louis, 1979) Stable condition Unstable condition l0 = 150 m for unstable condition 30 m for stable condition NEMS/GFS Modeling Summer School

  10. Near future development: Eddy-Diffusion Mass-Flux (EDMF) PBL scheme (Siebesma et al., 2007) • The GFS EDCG scheme under-predicts the PBL growth for the convection-dominated (strongly unstable) PBL (Noh et al., 2003; Siebesma et al., 2007) . • Siebesma et al. (2007) show that the underestimation of the daytime PBL growth EDCG is due to too weak entrainment flux at the PBL top which is caused by positive constant CG term over the entire. • With the EDMF scheme, the CG term in the EDCG scheme is replaced by a mass-flux scheme. NEMS/GFS Modeling Summer School

  11. SCM (single column model) test with EDCG scheme NEMS/GFS Modeling Summer School

  12. SCM test with EDCG scheme NEMS/GFS Modeling Summer School

  13. SCM test with EDCG scheme NEMS/GFS Modeling Summer School

  14. EDMF PBL scheme GFS PBL scheme (EDCG scheme) EDMF scheme NEMS/GFS Modeling Summer School

  15. EDMF PBL scheme Fig. 1. Sketch of a convective updraft embedded in a turbulent eddy structure. (from Siebesma et al., 2007) NEMS/GFS Modeling Summer School

  16. EDMF PBL scheme Updraft velocity equation: b1=2.0, b2=4.0 (Soares et al., 2004) Soares et al. (2004) ce=0.37, h: height of wu=0 NEMS/GFS Modeling Summer School

  17. EDMF PBL scheme Rbcr=0.25 EDCG: h = height of zero heat flux for ED part EDMF: h=height of wu=0 for MF part NEMS/GFS Modeling Summer School

  18. SCM test with EDMF scheme NEMS/GFS Modeling Summer School

  19. SCM test with EDMF scheme NEMS/GFS Modeling Summer School

  20. SCM test with EDMF scheme NEMS/GFS Modeling Summer School

  21. Thank you !! NEMS/GFS Modeling Summer School

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