Modeling the Summertime Heat Budget of Southeast New England Shelf WatersModeling the Summertime Heat Budget of Southeast New England Shelf Waters John Wilkin and Lyon LanerolleJohn Wilkin and Lyon Lanerolle

Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, N.JInstitute of Marine and Coastal Sciences, Rutgers University, New Brunswick, N.J..

C

O O

L O A S T A L C E A N B S E R V A T I O N

A B

R

U

U T G E R S N I V E R S I T Y

CBLAST: Coastal Boundary CBLAST: Coastal Boundary Layers and Air-Sea TransferLayers and Air-Sea Transfer

CBLAST Modeling using ROMS CBLAST Modeling using ROMS

The ONR CBLAST-Low program focuses on air-sea interaction and coupled The ONR CBLAST-Low program focuses on air-sea interaction and coupled atmosphere/ocean boundary layer dynamics at low wind speeds where atmosphere/ocean boundary layer dynamics at low wind speeds where processes are strongly modulated by thermal forcing. (There is a companion processes are strongly modulated by thermal forcing. (There is a companion CBLAST-Hurricane program.)CBLAST-Hurricane program.)

Turbulence and mean flow observations are being used to quantify the turbulent kinetic energy, momentum, mass, and heat budgets in the oceanic mixed-layer and atmospheric boundary layer.

The field program is centers on the Martha’s Vineyard Coastal Observatory (MVCO) and Air-Sea Interaction Tower.

• Split-explicit, free-surface, hydrostatic, primitive equation model [1,2]Split-explicit, free-surface, hydrostatic, primitive equation model [1,2]• Generalized, terrain-following vertical coordinatesGeneralized, terrain-following vertical coordinates• Orthogonal curvilinear, horizontal coordinates, Arakawa C-gridOrthogonal curvilinear, horizontal coordinates, Arakawa C-grid• 33rdrd- and 4- and 4thth-order advection and time-stepping; weighted temporal averaging; reduced -order advection and time-stepping; weighted temporal averaging; reduced pressure gradient and mode-splitting errorpressure gradient and mode-splitting error• Simultaneous conservation and constancy preservation for tracer equations in combination Simultaneous conservation and constancy preservation for tracer equations in combination with evolving coordinate system due to free-surface [2]with evolving coordinate system due to free-surface [2]• High-order accurate continuous, monotonic reconstruction of vertical gradientsHigh-order accurate continuous, monotonic reconstruction of vertical gradients• Adjoint and tangent-linear implemented; 4-D variational assimilation under testAdjoint and tangent-linear implemented; 4-D variational assimilation under test• MPI and OpenMP shared and distributed memory parallel F-90 codeMPI and OpenMP shared and distributed memory parallel F-90 code• All input/output via NetCDFAll input/output via NetCDF• NPZD biology; EcoSim bio-optics; Community sediment transport model, Lagrangian floatsNPZD biology; EcoSim bio-optics; Community sediment transport model, Lagrangian floats

Vertical turbulence closure optionsVertical turbulence closure options• Mellor-Yamada level 2.5Mellor-Yamada level 2.5• K-profile parameterization (KPP) surface and bottom boundary layers [3]K-profile parameterization (KPP) surface and bottom boundary layers [3]• Generalized Length Scale scheme [4,5]: Eddy viscosity and diffusivity are the product of a Generalized Length Scale scheme [4,5]: Eddy viscosity and diffusivity are the product of a non-dimensional stability function, TKE, and length scale. Stability functions are the result of non-dimensional stability function, TKE, and length scale. Stability functions are the result of various 2various 2ndnd-moment closures. TKE and length scales are calculated by dynamic (as in k--moment closures. TKE and length scales are calculated by dynamic (as in k- or or M-Y) or algebraic formulations. GLS encompasses M-Y) or algebraic formulations. GLS encompasses kk--, , kk-- and M-Y in a single code. and M-Y in a single code.

Qualitative comparison to subsurface validation data (below) shows Qualitative comparison to subsurface validation data (below) shows realistic vertical stratification and mixed layer depths. In 2003, an array realistic vertical stratification and mixed layer depths. In 2003, an array of 5 subsurface moorings between ASIT and ASIMET mooring-of 5 subsurface moorings between ASIT and ASIMET mooring-AA will will enable validation of the modeled evolution of the diurnal mixed layer. enable validation of the modeled evolution of the diurnal mixed layer.

Circulation around the Circulation around the Nantucket Shoals is Nantucket Shoals is augmented by strong tidal augmented by strong tidal rectified cyclonic flow that rectified cyclonic flow that carries water northward into carries water northward into Vineyard Sound through Vineyard Sound through Muskegat Channel (between Muskegat Channel (between Nantucket and the Vineyard). Nantucket and the Vineyard).

1 km horizontal resolution1 km horizontal resolution20 s-levels (stretched toward surface)20 s-levels (stretched toward surface)

ReferencesReferences[1] Haidvogel, D.B., H. Arango, K. Hedstrom, A. Beckmann, P. Rizzoli and A. Shchepetkin, 2000: Dyn. Atm. Oceans, 32, 239-281.[2] Shchepetkin, A., and J.C. McWilliams, 1998: Monthly Weather Review, 126, 1541-1580.[3] Large, W., J. McWilliams, and S. Doney, 1994: Rev. Geophys., 32, 363-403. [4] Umlauf, L. and H. Burchard. A generic length-scale equation for geophysical turbulence models, J. Mar. Res., accepted 2003.[5] Warner, J., Sherwood, C., Butman, B., Arango, H., Signell, R., Implementation of a generic length scale turbulence closure in a 3D oceanographic model." Ocean Modelling, submitted.[6] Fairall, C., E. Bradley, D. Rogers, J. Edson, and G. Young, 1996: JGR, 3747-3764.[7] Bi-monthly regional climatology provided by C. Naimie, Dartmouth University[8] Marchesiello, P., J.C. McWilliams, and A. Shchepetkin, 2001: Ocean Modelling, 3, 1-20.[9] Luettich, R. A., Westerink, J. J., and Scheffner, N. W., 1992: ADCIRC: An advanced three-dimensional circulation model for shelves, coasts, and estuaries, Tech. Report DRP-92-6, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.

Regional Ocean Modeling System Regional Ocean Modeling System (ROMS) numerical features (ROMS) numerical features

Mean circulation and heat budgetMean circulation and heat budget

wilkin@marine.rutgers.eduwilkin@marine.rutgers.edu http://marine.rutgers.edu/~wilkin/wip/cblast http://marine.rutgers.edu/~wilkin/wip/cblast

http://ocean-modeling.orghttp://ocean-modeling.org

Precise observations of air-sea fluxes and turbulent mixing from CBLAST are Precise observations of air-sea fluxes and turbulent mixing from CBLAST are ideal for evaluating the suite of ocean model vertical turbulence closure ideal for evaluating the suite of ocean model vertical turbulence closure schemes implemented in ROMS.schemes implemented in ROMS.

This comparison will be possible provided the model captures the essential This comparison will be possible provided the model captures the essential features of the ocean heat budget on diurnal to several day time-scales, and features of the ocean heat budget on diurnal to several day time-scales, and spatial scales of order 1 km.spatial scales of order 1 km.

Modeling complements the interpretation of the field observations by Modeling complements the interpretation of the field observations by quantifying unobserved lateral transport and mixing of heat.quantifying unobserved lateral transport and mixing of heat.

CBLAST-Low Observing System:CBLAST-Low Observing System:

Observational assets deployed in July/August of 2002 and 2003 include in situ observations of vertical fluxes and mixing rate profiles from fixed towers and moorings, satellite and aircraft remote sensing, and measurements of small-scale and breaking waves. Irradiance

Irradiance

23m

15m

U, T, QU, T, Q Heat, mass & Heat, mass &

mom. flux, mom. flux, εεWavesWaves

WavesWaves T, ST, S

Heat, mass Heat, mass mom. flux, mom. flux, εε

Solar, IR, rain, Solar, IR, rain, U, T, QU, T, Q Heat, mass & Heat, mass & momentum flux, momentum flux, εε

MVCOMVCO

Nantucket SODARNantucket SODARK

ASITASIT

ASIMET moorings with ASIMET moorings with ocean T(z) and ADCPocean T(z) and ADCP

RemoteRemoteSensingSensing

AircraftAircraft

3-D3-DMooringMooring

Coherent Coherent structures structures

(Fanbeam)(Fanbeam) Heat & mom. fluxHeat & mom. flux

U(z), U(z), WavesWaves (ACDP(ACDP))

ROMS CBLAST configuration ROMS CBLAST configuration

Open boundary conditions:Open boundary conditions:

Inflow climatology [7] + outflow Inflow climatology [7] + outflow radiation [8] on T,S, u, vradiation [8] on T,S, u, vClimatology, tides [9], radiation (Climatology, tides [9], radiation (gh) gh) on on and depth average u,v and depth average u,v

160 x 380 x 20 grid requires 160 x 380 x 20 grid requires approximately 2 CPU mins per model approximately 2 CPU mins per model day on 16-processor HP/Compaqday on 16-processor HP/Compaq

Tidal stirringTidal stirring

COAMPS 72-hour forecast is generated every 12 COAMPS 72-hour forecast is generated every 12 hours at ARL.HPC.mil and transferred to IMCS where hours at ARL.HPC.mil and transferred to IMCS where ROMS runs for the same forecast cycle.ROMS runs for the same forecast cycle.

Real-time validation is available using CODAR on Real-time validation is available using CODAR on Nantucket (operational after July 7, 2003).Nantucket (operational after July 7, 2003).

ROMS forecasts will be factored into the deployment ROMS forecasts will be factored into the deployment strategy for drifting instrument strings providing strategy for drifting instrument strings providing Lagrangian observations of evolving mixed-layer.Lagrangian observations of evolving mixed-layer.

Operational forecasts commence mid-July, 2003Operational forecasts commence mid-July, 2003 M2 displacement ellipses from ADCIRC

3-day composite SST for 30-Aug-2002

Vigorous tidal mixing generates a region of perpetually cold SST on the eastern flank of the Nantucket Shoals

CTD temperature section between ASIT and mooring-A, late July 2001.

Observed Modeled

Tidal phase eddies transport cold tidally-mixed Tidal phase eddies transport cold tidally-mixed Nantucket Shoals water into Vineyard Sound, Nantucket Shoals water into Vineyard Sound, and warmed VS water toward MVCO. and warmed VS water toward MVCO.

COAMPS CBLAST, 3km, 91x91

9 km

27 km, 151x121x30

The open boundary climatology imposes The open boundary climatology imposes a south and westward flow from the Gulf a south and westward flow from the Gulf of Maine, through Great South Channel of Maine, through Great South Channel and around Nantucket Shoals.and around Nantucket Shoals.

Southwest of Martha’s Vineyard, and Southwest of Martha’s Vineyard, and within Vineyard Sound, winds drive within Vineyard Sound, winds drive eastward depth averaged flow.eastward depth averaged flow.

Air-sea flux (QAir-sea flux (Qnetnet) is greatest east of ) is greatest east of

Vineyard Sound where SST is cold, but Vineyard Sound where SST is cold, but is largely balanced by divergence due is largely balanced by divergence due to tidal mixing. to tidal mixing.

Ocean temperature increase (storage) Ocean temperature increase (storage) is largest south of The Islands, primarily is largest south of The Islands, primarily due to surface heating. Horizontal due to surface heating. Horizontal divergence is small in the region of the divergence is small in the region of the B-CB-C ASIMET moorings - indicating a ASIMET moorings - indicating a region of approximate 1-D vertical heat region of approximate 1-D vertical heat balance suited to evaluating ROMS balance suited to evaluating ROMS vertical turbulence closures. vertical turbulence closures.

July 2002

Tides significantly affect the mean circulation and heat Tides significantly affect the mean circulation and heat budget. Lateral heat transport is large in much of the region, budget. Lateral heat transport is large in much of the region, including near MVCO, and will need to be considered in the including near MVCO, and will need to be considered in the analysis of ASIT heat budgets. analysis of ASIT heat budgets.

Wind-driven upwelling circulation contributes to the heat Wind-driven upwelling circulation contributes to the heat budget southwest of Martha’s Vineyard.budget southwest of Martha’s Vineyard.

A 1-D heat balance occurs near the A 1-D heat balance occurs near the B-A-CB-A-C ASIMET mooring ASIMET mooring sites, and these data will be used for evaluation of model sites, and these data will be used for evaluation of model turbulent closures. turbulent closures.

July 2002 mean

SummarySummary

MVCO

Time series of the heat budget (below) in a box near MVCO Time series of the heat budget (below) in a box near MVCO shows half the air-sea flux goes to warming the water column, shows half the air-sea flux goes to warming the water column, and half is removed by lateral divergence. and half is removed by lateral divergence.

The time mean advection cools The time mean advection cools the box at, on average, 200 W/mthe box at, on average, 200 W/m22. . The net “eddy” divergence (The net “eddy” divergence (u’T’u’T’) ) warms the MVCO region at about warms the MVCO region at about 150 W/m150 W/m22. .

Episodic positive divergence Episodic positive divergence (cooling) events briefly arrest the (cooling) events briefly arrest the warming trend. warming trend.

Surface forcing:Surface forcing:

Heat and momentum fluxes from bulk Heat and momentum fluxes from bulk formulae [6] with model SST, formulae [6] with model SST, observed downward long-wave at observed downward long-wave at MVCO, and TMVCO, and Tairair, p, pairair, rel. humidity, , rel. humidity,

UU1010, , VV1010, and short-wave radiation , and short-wave radiation

from 3 km resolution nested from 3 km resolution nested COAMPS 6--36 hr forecastCOAMPS 6--36 hr forecast