Presentation on theme: "Yeon S. Chang, Xiaobiao Xu, Tamay M. Özgökmen, Eric P. Chassignet, Hartmut Peters, Paul F. Fischer 1 MPO/RSMAS University of Miami 1 Mathematics and Computer."— Presentation transcript:
Yeon S. Chang, Xiaobiao Xu, Tamay M. Özgökmen, Eric P. Chassignet, Hartmut Peters, Paul F. Fischer 1 MPO/RSMAS University of Miami 1 Mathematics and Computer Science Division Argonne National Laboratory Gravity current mixing parameterization and calibration of HYCOM
Objectives 1.To explore how common mixing parameterizations, particularly KPP and TP, perform using an idealized setting and high- resolution nonhydrostatic solution 2.To quantify the differences and limitations of the two schemes, understanding why and how these parameterizations can be modified to produce consistent results.
Outline 1.Numerical test of gravity currents over idealized sloped basin using a OGCM, HYCOM 2.Comparison with 3-D LES (Nek5000) in terms of Entrainment, E(t) 3.Tuning the vertical mixing parameters of KPP and TP 4.Adjustment of parameterization over varying slopes 5.Also testing it as a function of the grid resolution
Nek5000HYCOM Configuration of experiments and initial conditions
Distribution of salinity surface, Nek5000 3-D 2-D averaged in span-wise T=9350s
TP (Hallberg, 2000) : developed for overflows based on Ellison and Turner(1959) KPP (Large et al., 1994, 99) : shear-induced, multi-purpose
HYCOM, before tuning KPP : LES studies of upper tropical ocean (e.g., Large, 1998)
TP HYCOM, before tuning : Lab. Exp. by Ellison and Turner(1959), Turner(1986)
Why significant modification is necessary to adjust the entrainment curves ? - Turbulence parameterization should include a dependence on the forcing as well as a dependence on the Ri ; this holds for TP but not for KPP. KPP: 1.KPP-modeled Mediterranean outflow sinks deeper: insufficient mixing 2.K max should vary with the strength of the forcing, and a particular value of K max cannot hold in bottom gravity current mixing Maximum turbulence forcing Peters et al. (1988) TP: 1.Papadakis et al.(2003) : applied TP every 144 th steps 2. Turner (1986): small tank (0.1x2 m), large slopes ( >10°) 3. Replacement of bulk Ri in original Turner scheme by shear Ri in Hallberg(2000)
Test of adjustment to forcing by employing different low-slopes
Conclusion 1.With appropriate tuning of parameters, both KPP and TP can be well matched with the nonhydrostatic 3-D solution, and the results are fairly independent of the horizontal grid resolution. 2.But there’s substantial difference between KPP and TP KPP: the amplitude of mixing term is quite dependent on its peak diffusivity, K max, but this given constant cannot respond to the variation of ambient forcing, TP: by relating W E to ΔU, TP avoids hard limit for peak diffusivity, and the implied diffusivity is dependent both on Ri and on the forcing via ΔU. 3. Further experiments with stratified flows are necessary.