Measurements and (preliminary) Modeling of Turbulent properties in the Adriatic Sea

Measurements and (preliminary) Measurements and (preliminary) Modeling Modeling

of Turbulent properties in the Adriatic of Turbulent properties in the Adriatic SeaSea

Sandro Carniel – Mauro Sclavo (CNR-ISMAR, Venice)Sandro Carniel – Mauro Sclavo (CNR-ISMAR, Venice)Lakshmi Kantha (Univ. of Boulder, CO, USA)Lakshmi Kantha (Univ. of Boulder, CO, USA)

Hartmut Prandke (ISW, Germany)Hartmut Prandke (ISW, Germany) Jacopo Chiggiato (ARPA-SIM, Bologna)Jacopo Chiggiato (ARPA-SIM, Bologna)

ROMS-TOMS European Workshop, ROMS-TOMS European Workshop, November November 6-8, 20066-8, 2006

Sub-grid Scale parameterizationSub-grid Scale parameterization

…WHY?... important to air-sea exchange, weather, climate, biolog. productivity, oil-spill tracking, counter-mine warfare, S&R etc.

Mixing in the upper ocean is primarily surface-driven: 1. Momentum flux from winds and waves 2. Negative buoyancy flux due to cooling and evap.Below the active ML: Shear instabilities, Double-diffusion

……HOW?...HOW?...1) Acquiring microstructure measurements via turbulence 1) Acquiring microstructure measurements via turbulence profilerprofiler2) Starting from this picture of turbulent parameters, to test 2) Starting from this picture of turbulent parameters, to test and accordingly modify SCM employed in 3-D and accordingly modify SCM employed in 3-D hydrodynamical modelshydrodynamical models

ONR NICOP Grant (ONR NICOP Grant (N00014-05-1-0759)N00014-05-1-0759)

DART region

2006: measuring turbulentproperties, during the period of DART06 A & B

(March and August)

2007: - assessment Turbulenceparameterization in 3-D ocean models- other measurements (June)

2008: refinement of

parameterization and delivery

ONR NICOP and DART ProjectONR NICOP and DART Project

Location and InstrumentsLocation and Instruments

Free-falling profilerFree-falling profiler

2 velocity microstr. Shear sensors

1 microstructure Temp. sensor

standard CTD sensors for prec. measurements

turbidity (light scattering) sensor

vibration control sensor (ACC)

surface detection sensor

1024 s.p.s., 16 bit

MSS ProfilerMSS Profiler

1.1. The microstructure sensors are placed at the tip of a The microstructure sensors are placed at the tip of a slim shaft, about 150 mm in front of the CTD slim shaft, about 150 mm in front of the CTD sensors.sensors.

2.2. Shear sensor is a piezoceramic beam: if VShear sensor is a piezoceramic beam: if V~sinking ~sinking velocity, G is sensor gain, Evelocity, G is sensor gain, Ess~signal, du/dz ~ (~signal, du/dz ~ (GVGV22))--

11 dE dEss/dt /dt TKE dissipation rate TKE dissipation rate

3.3. TKE Dissipation RateTKE Dissipation Rate

1.1. The microstructure sensors are placed at the tip of a The microstructure sensors are placed at the tip of a slim shaft, about 150 mm in front of the CTD slim shaft, about 150 mm in front of the CTD sensors.sensors.

2.2. Shear sensor is a piezoceramic beam: if VShear sensor is a piezoceramic beam: if V~sinking ~sinking velocity, G is sensor gain, Evelocity, G is sensor gain, Ess~signal, du/dz ~ (~signal, du/dz ~ (GVGV22))--

11 dE dEss/dt /dt TKE dissipation rate TKE dissipation rate

3.3. TKE Dissipation RateTKE Dissipation Rate 7.5 du / dz 2

2

5.7

dz

duDissipation rate for isotropic turbulence:( water kinemat. viscosity)

i.o. = ui/xj (ui/xj + uj/xi) 2

6

dz

dTT

Dissipation rate of microstruct. Temperature variance:(KT molecular diff. for heat in water)

Eddy Diffusivity from Diss. Rate: 2 NK

2

2

dz

dTK h

Eddy Diffusivity of Heat:

Useful Info from Measurements…

ISW Wassermesstechnik

MSS profiler - Example of MSS profiler - Example of measurementsmeasurements

ISW Wassermesstechnik

MSS profiler - Example of MSS profiler - Example of measurementsmeasurements

MSS profiler - Example of MSS profiler - Example of measurementsmeasurements

ISW Wassermesstechnik

ISW Wassermesstechnik

MSS profiler - Example of MSS profiler - Example of measurementsmeasurements

Meteo Conditions during DART06-B Meteo Conditions during DART06-B (August 2006)(August 2006)

Red= air TRed= air TBlue= SSTBlue= SST

March 2006:252 profiles

August 2006:More than 300 profiles,

160 of them at B90 site in 5 days, divided into 5 O.P.

Heat & Buoyancy Fluxes, DART06-BHeat & Buoyancy Fluxes, DART06-B

Estimated errorsBulk formulae

VSmeasured turbulent

fluxes are

easilyup to 40%

OP-1 (39 casts, 13.09-15.26 UTC)OP-1 (39 casts, 13.09-15.26 UTC)Weak surface forcings caseWeak surface forcings case

Weak w, 4.9 m/s Weak w, 4.9 m/s Wstar= 1.2 cm/sWstar= 1.2 cm/s

D=13m > MO=5mD=13m > MO=5mLLTT=0.5 m =0.5 m (RMS of Thorpe displ., (RMS of Thorpe displ., length scale of turb. length scale of turb. oveturns, i.e. weak oveturns, i.e. weak mixing)mixing)

N freq. indicates N freq. indicates strong pycnoclinestrong pycnocline

T variance diss. rate

U*=(/)1/2

W*=(Jb0D)1/3

MO=U*3/(Jb0)

R=(W*/U*)3

OP-2 (24 casts, 17.03-18.48 UTC)OP-2 (24 casts, 17.03-18.48 UTC)Wind-driven caseWind-driven case

Stronger w, 11 m/sStronger w, 11 m/sCooling, -150 W/mCooling, -150 W/m22

Wstar= 1. cm/sWstar= 1. cm/sUstar=1.3 cm/sUstar=1.3 cm/s(R=0.4, i.e. wind (R=0.4, i.e. wind driven)driven)

D=13m < MO=60m D=13m < MO=60m (large, indicating wind (large, indicating wind driven case)driven case)LLTT=up to 2 m =up to 2 m

d

U*=(/)1/2

W*=(Jb0D)1/3

MO=U*3/(Jb0)

R=(W*/U*)3

OP-3 (40 casts, 23.29-02.17 UTC)OP-3 (40 casts, 23.29-02.17 UTC)Convection-driven caseConvection-driven case

Weak w, 3.4 m/sWeak w, 3.4 m/sClear sky, high cooling, Clear sky, high cooling, -200 W/m200 W/m22

Wstar=1.1 cm/sWstar=1.1 cm/sUstar=0.4 cm/sUstar=0.4 cm/s(R=20, convection)(R=20, convection) D=20m > MO=2.6mD=20m > MO=2.6m(buoyancy dominated(buoyancy dominated))LLTT=3 m (strong =3 m (strong convection mixing)convection mixing)

d

U*=(/)1/2

W*=(Jb0D)1/3

MO=U*3/(Jb0)

R=(W*/U*)3

March 2006 – late winter (DART06-A)March 2006 – late winter (DART06-A)

Weak wind (4 m/s)Weak wind (4 m/s)

Layered density Layered density structure.structure.Double diffusivities Double diffusivities convection from cold convection from cold fresh water masses fresh water masses over warm salty ones?over warm salty ones?

Turbulence Scaling: Dissipation Turbulence Scaling: Dissipation ratesrates

=c+ s ,z D =i ,z >D

…better scaling in the interior

good scaling in the ML...

c=0.58 Jb0

s=1.76 u*3 / z

=c+ s

Below the ML,i=0.03 L2

TN3

Original resolution: 15 arc seconds (1/240°). Source: data collected during the project ADRIA 02-03 with various contributions from CNR-ISMAR Bologna, CNR-ISMAR Venice, HHI Split, IIM Genova, IRB Zagreb, NIB Piran, NURC La Spezia.

Grid 160 x 60 w/ variable resolution

~ 3 Km (north)~ 10 Km (south)

20 levels

LAMI

• wind 10 m • mean sea level pressure• air temperature 2 m• dew temperature 2 m• total cloud cover• net short-wave radiation

MediterraneanGCM

(OPA-MFSTEP)daily forecasted

temperature and salinity+

tidal elevation and currents (M2, S2, O1,

K1) from QUODDY model

48 rivers and springs

-Resolution 6x6 km or Resolution 6x6 km or 2x2 km (running)2x2 km (running)- Restart file from - Restart file from

operational operational version version ARPA-SIM ARPA-SIM 6km6km-TCMs: TCMs: GLS as “gen”GLS as “gen” GLS as “k-kl”GLS as “k-kl”

-Wave-breakingWave-breaking onon (6km)/off (2km) (6km)/off (2km)

-Radiation Stresses Radiation Stresses onon (one-way, 6km) (one-way, 6km)via SWAN runvia SWAN run

ROMS turbulence modeling: March ROMS turbulence modeling: March

Validation (CTDs Urania)

RMSE suggest:

• Similar behaviour as for CTD-Alliance in the SAd and MAd (actually the temperature

is a little bit colder compared to observations)

• Low errors for temperature in the NAd, salinity fresher by 0.5 PSU

• Major errors are located along the WACC

RMSE suggest:

•Southern Adriatic: AdriaROMS is colder by 1°C and fresher by 0.3 PSU. The two bias

cancel each other, and resulting sigma-t is nearly unbiased.

•Middle Adriatic: AdriaROMS has a negligible temperature bias but is still fresher by 0.2÷0.3 PSU; the resulting

sigma-t is now slightly biased

Validation (CTDs Alliance)

ROMS turbulence modeling: March 2006ROMS turbulence modeling: March 2006

6x6 km6x6 km 2x2 km2x2 km

CB wave-CB wave-breakingbreakingonon

Radiation Radiation stressesstressesonon via SWAN via SWAN runrun

NO CB wave-NO CB wave-breakingbreaking

NO radiation NO radiation stressesstresses

ROMS turbulence modeling: March 2006ROMS turbulence modeling: March 2006

5x5 km5x5 km 2x2 km2x2 km6x6 km6x6 km 2x2 km2x2 km

NO CB Wave-NO CB Wave-breakingbreaking

NO Radiation NO Radiation stressesstresses

CB wave-CB wave-breakingbreakingonon

Radiation Radiation stressesstressesonon via SWAN via SWAN runrun

ROMS turbulence modeling: March 2006ROMS turbulence modeling: March 2006

6x6 km6x6 km

CB wave-CB wave-breakingbreakingonon

Radiation Radiation stressesstressesonon via via SWAN runSWAN run

ROMS turbulence modeling: March 2006ROMS turbulence modeling: March 2006

2x2 km2x2 km

NO CB wave-NO CB wave-breakingbreaking

NO Radiation NO Radiation stressesstresses

ConsiderationsConsiderations

1. Dissipation measurements and data processing have to be carried out carefully to avoid falsification resulting from pseudo shear, sensor bottom hits, high particle conc., strong shear layers and pycnoclines (change of profiler sinking leads to falsified dissipation rates)

2. Despite this, modern turbulence profilers enable routinely TKE dissipation measurements in marine environment and useful diffusivity estimations

3. Need of longer „time-series“, i.e. repeated measurements in the same spot (intermittency…) combined with other info (shear, meteo…)

ConsiderationsConsiderations

4. 2-eqs TCMs are now integral part of ocean models

(POM, ROMS, NCOM, ICOM?), but experience gained over

past 2 decades indicates that these models can be made more skillful.

OF COURSE, influence of W-B, radiation stress, horiz. resolution, proper initialization to be investigated!!! We need to have a correct vertical structure, first.

5. However, outstanding issues are: a) Better performance under free convection b) Inclusion of surface wave effects on mixing in the

OML

ConsiderationsConsiderations

6. Surface Wave Effects have not been included properly in OML models until recently. Two kinds of effects:

a) TKE injection at the surface into the water column by wave breaking – has a surface effect (Umlauf, JSR 2003; Kantha, OM 2004). ROMS is following one approach (Warner GLS), but…

b) Stokes production of TKE by the interaction of waves and turb. in the OML, can enhance turb. in the interior

7. Langmuir cells (wind driven shear+Srokes drift) can also produce strong vertical velocities in the OML

8. simple non-local models (counter-gradient term) need to be constructed for free convection situations.

9. Can we possibly think of “assimilating” these typology of measurements?

TKE prod. by LC

U j

t

xk

UkU j jkl fk Ul VSl 1

0

x j

g j xk

uku j jplVSpl l lmn

Un

xm

p 0

2Ui VSi Ui VSi VSiVSi

VS VSiVSi 12 VS0 exp 2kz C ka 2 exp 2kz

andwhere

D

Dtq2

zqlSq

z

q2

2(P B ) 2uw

U

zuS

z

2vw

V

zvS

z

2gw 2q3

B1l

D

Dtq2l

zqlS1

z

q2l

E1l uw

U

z vw

V

z

E6l uw

uS

z vw

vS

z

E3 gw E2

q3

B1

1 E4

l l w

2

Adding additional production terms…

#define craig_banner

#define tke_wavediss

Surface TKE fluxes Two formulations to account for surface injection of TKE due to breaking waves.For GLS each formulation requires boundary conditions for k and .

wc *su ~ 100; = surface stress

…how get Zos ?#define charnok#define zo_hsig

~ 0.25 w = wave energy dissipationw

sk

t

z

k

3*sw

sk

t ucz

k

nnsft

m p

μswn

sftm p

μk

s

t zzLkcn

uczzLkmcz

ψ0

12/1103*0

10 )(

nnsft

m p

μn

sftm p

μk

s

t zzLkcn

zzLkmcz

ψ0

12/1100

10 )(

guaZos /2* a = 1400

ss aHZo a = 0.5; Hs = significant wave height

End of Presentation

ConclusionsConclusions

1. Modern turbulence profilers enable routinely TKE dissipation measurements in marine environment

2. Dissipation measurements and data processing have to be carried out carefully to avoid falsification resulting from pseudo shear

3. Dissipation measurements in coastal waters require special attention due to sensor bottom hits, high particle conc. (falsified shears), strong shear layers and pycnoclines (change of profiler sinking leads to falsified dissipation rates)

4. Need of longer „time-series“, i.e. repeated measurements in the same spot (intermittency…) combined with other info (shear, meteo…)

Theoretical Dissipation ratesTheoretical Dissipation rates

Dz

DzDJ

zJ

b

bc

0

9.01.0 39.0

0

0

0

In the convective layer:

Dz

DzDDu

Dzzus

0

3.0 33.3

3.00 3*

3*

In the wind-stress driven ML:

03.0 32 NLTi

Assuming LT proportional to Ozmidov scale

3N

Lo

For turbulence generated by momentum flux + destabilizing buoyancy flux:

=c+ s ,z D =i ,z >D

Wit

hin

ML

Belo

w

ML

A length scale for the description of turbulent flows under stable stratification, defined as… In flows where turbulence and wave motion are simultaneously present, the inverse of the Ozmidov scale defines the buoyancy wavenumber, which separates the buoyancy subrange from the inertial subrange.

Friction & Convective Velocity scaleFriction & Convective Velocity scale

U*=(/)1/2

Wstar=(Jb0D)1/3

MO=U*3/(Jb0)

R=(Wstar/U*)3

ADCP velocitiesADCP velocities

OP-6 (6 casts, 14.45-15.13 UTC)OP-6 (6 casts, 14.45-15.13 UTC)

-Stronger wind Stronger wind (7 m/s)(7 m/s)-Insolation decreased Insolation decreased to 300 W/mto 300 W/m22

Ustar=0.95 cm/sUstar=0.95 cm/s

D=18m, MO=21m, D=18m, MO=21m, LLTT=3 m =3 m (strong mixing above (strong mixing above pycnocline)pycnocline)

Shear probe data processing

From the lift force at the airfoil caused by potential flow (Allen and Perkins, 1952):

F = 1/2 U2A sin2 ( 15)Definition of S (F E) E = U2 S sin2rms. measurement for S E = 2 U2 Srms sin2sin 2 = 2sin cos E = 22 Vu Srms Differentiation, gain du/dt = (22 VG Srms)

-1 dE/dtdu/dt = V du/dz du/dz = (22 V2G Srms)

-1 dE/dt

TKE dissipation rate definition: = ui/xj (ui/xj + uj/xi)

… and assuming isotropic turbulence: = 7.5 (du/dz)2

…from the voltage output of the probe we then obtain an estimate of the TKE diss. rate

Where to improve/What to includeWhere to improve/What to include

1.1. Wave breaking effects were ignored on Epsilon Wave breaking effects were ignored on Epsilon scaling (upper 2-3 m are not covered by scaling (upper 2-3 m are not covered by measurements)measurements)

2. Langmuir circulation, Stokes production2. Langmuir circulation, Stokes production

3. Wave observation (Wave rider, buoy)3. Wave observation (Wave rider, buoy)

4. Measurements of turbulent fluxes at sea VS bulk 4. Measurements of turbulent fluxes at sea VS bulk fluxesfluxes

5. Measurements of shear (ADCP) and of the broad 5. Measurements of shear (ADCP) and of the broad context around OPcontext around OP