Surface Dispersion by Mesoscale Eddies Using Altimeter Data

Long Zhou

3nd Student Seminar, 11/06/2006

Outline

• Objectives and Applications

• Dataset

• Method

• One example of model output

• Results

• Summary and future work

Objectives • Examine absolute dispersion at ocean

surface

• Find out the relative diffusivities

at different separation distances

Applications • Improve parameterization of eddy diffusivity in climate numerical modeling

• Pollutant fate (e.g. oil spills)

• Larval transport

Dataset: Satellite altimetry

JETEG along-track sea level anomalies (SLA) for three years

02/25/2003 to 02/25/2006

Jason1 Envisat Topex2 ERS GFO

Note: GFO=Geosat Follow-on

Method

a. Objective mapping of JETEG with a space-time correlation

model => daily SLA maps (02/25/2003 to 02/25/2006).

b. Derive stirring velocities Vs from SLA assuming geostrophic

balance holds.

c. Random walk numerical model with a daily time step and

1/6 degree of spatial resolution.

, where randnRDVVm VmVsVtotal

Longitude

latitu

de

mean eddy KE (cm/s)2 over 3 years(02/25/2003 to 02/25/2006)

38oW 34oW 30oW 26oW 22oW 18oW

2oN

4oN

6oN

8oN

10oN

12oN

3565.9084 3565.9084 2077.8211 1848.8846

589.7338

131.8608

200 400 600 800 1000 1200 1400 1600 1800

One example of model output: where to deploy

KE: kinetic energy

One example of model output

03/02/2003-07/30/2003

0 10 20 30 40 50 60 70 80 900

1

2

3

4

5

6

7

8x 10

4

days

zonal

abs.

dis

p.(km

2 )

zonal absolute dispersion changing with random velocity

0.10.20.30.40.50.60.70.80.9 11.5 22.5 3

0.5-0.9

3

0.1

Results

• Find RDV to be 0.75 to reasonably represent submesoscale process.

N

iitia xx

NtxD

1

20,, )(

1),(

1

1 1

2,, )(

)!1(

1),(

N

i

N

ijtjtir xx

NtxD

0 10 20 30 40 50 60 70 80 900

5

10

15x 10

4

days

zonal

rel

.dis

p.(km

2 )

zonal relative dispersion changing with random velocity

0.10.20.30.40.50.60.70.80.9 11.5 22.5 3

3

0.5-0.9

0.1

• Absolute dispersion: zonal > meridional

a b

c d

• At scale of less than 200 km, relative diffusivity grow quadratically.

• Later can be scaled as distance to the 2/3 power.

0 200 400 600 800 1000 1200 1400-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5x 10

4

distance(km)

diffu

sivi

ties

(m2 /s

ec)

relative diffusivities vs. mean square separation

mu vs. msd

msd2/3

msd2

Summary

• RDV=0.75 to reasonably represent submesoscale process.

• Absolute dispersion: zonal > meridional.

• Relative diffusivities can be scaled with separation distance.

Future Work

• Statistical analysis of ensembles

• Add larva growth rate

Acknowledgement

GSO:

Dave Hebert

Tom Rossby

WHOI:

Valery Kosnyrev

Dennis McGillicuddy

Real-time Altimeter Data Research Group at Colorado Center for Astrodynamics

CLS Space Oceanography Division

longitude

latitu

de

rms SLA (mm)

38oW 34oW 30oW 26oW 22oW 18oW

2oN

4oN

6oN

8oN

10oN

12oN

10 15 20 25 30 35 40 45 50

RDV=0.1

RDV=3