changes to the kpp vertical mixing parameterization g. danabasoglu and w. g. large shallowness of...

Changes to the KPP Vertical Mixing

ParameterizationG. Danabasoglu and W. G.

Large•Shallowness of summer-time

boundary/mixed layer depths

•Presence of some grid-point noise in boundary /mixed layer depths, particularly in the Tropics•General review of physics and numerics

ENERGY INPUT AND DISSIPATION NOT CONSIDERED

TEST BED

x1 POP forced with QSCAT, NCEP, ISCCP, and MSU / Xie-Arkin data sets for July 1999 – December 2001

The initial conditions are for July 1, 1999, obtained from a 42-year forcing cycle experiment.The results shown are from the last years of 2.5-year experiments.

Short-wave heat flux has a diurnal cycle.

For simplicity, the internal wave mixing is the only interior mixing allowed.

BOUNDARY LAYER DEPTH

= HBLT

= 0.3

This value of the critical bulk Richardson number is based on some sensitivity studies where comparisons with observed ocean responses during the Ocean Storm Experiment were made. The vertical grid resolution was 1 m.

Large et al. (1994)

CRITICAL BULK RICHARDSON NUMBER

Large et al. (1994) suggests that the critical bulk Ri should somewhat increase as the vertical resolution degrades.

Obtained by matching 1-m vertical resolution results

= 1.8

This value is chosen to satisfy the empirical rule of pure convection, i.e. the ratio of entrainment flux to surface buoyancy flux should be 0.2.Large et al. (1994)

Obtained by satisfying the above rule

No dependence on resolution

BOUNDARY LAYER DEPTH

CONTROL Ri and Cv MODS

Jan

July

TURBULENT VELOCITY SCALES

Figure 2 of Large et al. (1994)

QUADRATIC INTERPOLATION

BOUNDARY LAYER DEPTH

CONTROL Quadratic Interpolation MODS

Jan

July

SUMMARY OF CHANGES• Diurnal cycle in short-wave heat flux

• Critical bulk Ri as a function of the vertical resolution

• Cv as a function of N

• Turbulent velocity scale limit in stable regions

• Quadratic interpolation for HBLT

• Use 4-pt maximum instead of 4-pt average for resolved shear

• Consider interior convection after HBLT is determined• Correct the Ekman and Monin-Obukhov depth limit computations

• Modify usage of N in turbulent shear computation

BOUNDARY LAYER DEPTH

CONTROL All Physics MODS

Jan

July

SUMMARY OF CHANGES• Diurnal cycle in short-wave heat flux

• Critical bulk Ri as a function of the vertical resolution

• Cv as a function of N

• Turbulent velocity scale limit in stable regions

• Quadratic interpolation for HBLT

• Use 4-pt maximum instead of 4-pt average for resolved shear

• Consider interior convection after HBLT is determined• Correct the Ekman and Monin-Obukhov depth limit computations

• Modify usage of N in turbulent shear computation

• Use OLDTIME level data in KPP to eliminate temporal noise• Use a Gaussian filter to smooth HBLT

BOUNDARY LAYER DEPTH

CONTROL All Physics + Numerical MODS

Jan

July

MIXED LAYER DEPTH

CONTROL All Physics + Numerical MODS

Jan

July

EQUATORIAL TEMPERATURE

CONTROL All MODSJan

July

LEVITUS

EQUATORIAL TEMPERATURE

CONTROL All MODSLEVITUS

PMEL