Evaluation of HYCOM Upper Ocean Mixing Parameterizations

S. Daniel Jacob1, Lynn K. Shay2, George R. Halliwell2 and David Le Vine3

1 GEST, UMBC/ NASA GSFC, Greenbelt, MD 207712 MPO, RSMAS, University of Miami, Miami, FL 331493 NASA GSFC , Greenbelt, MD 20771

A. Wallcraft (NRL Stennis), M. Powell (NOAA HRD), O. M. Smedstad Partial Funding from NOAA Joint Hurricane Testbed, NSF US Weather Research Program

Upper Ocean Mixing and Hurricane Intensity

• Based on Observational Analysis (Jacob et al., JPO 2000)

– Entrainment is the dominant mechanism in the mixed layer cooling.

– Mixed layer heat and mass budgets strongly depend upon the entrainment scheme used.

• Numerical Modeling (Jacob and Shay, JPO, 2003):

– Measured and simulated quantities based on different hypothesis are used to compute entrainment mixing.

– Bulk schemes in using MICOM

MOVIE 1

Gaspar KT

PRT DDF

GILBERT UPPER OCEAN RESPONSE EXPERIMENTShay et al. JGR 1992

MODEL-DATA COMPARISON

ALL

STORM

WAKE1

WAKE2

OBJECTIVES

Mixing Schemes

Hybrid Coordinate Ocean Model

• Evaluate higher order turbulence closure schemes for hurricane forcing based on the data acquired during the three storms

Precipitation Effects

• TRMM measurements

• Large rain-rates of more than 15 mm/hr have been observed.

• Mixing effects

• Heat Fluxes

Data Resources

Data were acquired in 2002 as part of the NSF USWRP in two additional storms Isidore and Lili in the Caribbean and Gulf of Mexico Region.

•Overall, number of profiles available for comparison include:

• 339 Temperature Profiles from AXBTs, AXCPs and AXCTDs

• 178 Current Profiles from AXCPs

• 134 Salinity Profiles from AXCTD

• Other data includes

• Aircraft acquired atmospheric forcing data for specifying boundary layer forcing

• 1988 year day 200 data for model initialization for Gilbert

Hurricane Gilbert Case

• Configuration– Domain: Gulf of Mexico– Resolution: 0.07– 20/22/50 Levels/ Layers– Closed Boundaries

• Initial Conditions– Quiescent and Realistic– No Precip vs Precip for

Quiescent conditions

TEMPERATURE-SALINITY DIAGRAM

WIND FIELD STRUCTURE 16 SEP 88 06UTC

Hycom Q MovieGaspar

MY2.5

KPP

PWP

2 Rmax

TEMPERATURE-SALINITY DIAGRAM

Case E Case E GCW

Case C Case Q

1988 Yearday 200 to 258 with COADS climatological forcing with KT scheme

Center position is accurate within 0.3°, Strength consistent with data

MICOM HYCOM

KPPPWP

MY GISS

PRECIP STRUCTURE 16 SEP 88 06UTC

mm/day

OCEAN RESPONSE at 06 UTC, 16 SEP 1988

KPP KPP

NO PRECIP

KPP

WITH PRECIP

KPP

MLT MLS

ΔOCEAN RESPONSE at 06 UTC, 16 SEP 1988

ΔMLT

KPP PWP

MY2.5 GISS

ΔOCEAN RESPONSE at 06 UTC, 16 SEP 1988

ΔMLS

KPP PWP

MY2.5 GISS

2 RmaxNo Precip Precip

2 Rmax PWP

WIND FIELD STRUCTURE 22 SEP 02 12UTC

KPP

GISS

SUMMARY

• HYCOM simulations also show a strong oceanic ML budget dependence on the entrainment closure scheme in the directly forced region.– Implications for storm intensity.

• Initial comparisons with data indicates better performance of KPP and MY2.5 for the Gilbert case. Comparisons will be performed with 50 levels/layers and also in Isidore and Lili cases.

• The PWP scheme simulates coolest and most saline mixed layer without precipitation. Due to the stabilizing effect of precipitation, mixed layer cooling is reduced by ~0.5° C when rainfall is added.

• A freshening of 0.25 PSU is seen in simulations with added precipitation. This counteracts mixing of more saline water from below.