Modeling Tides for Southern Ocean GLOBEC

Modeling Tides for Southern Modeling Tides for Southern Ocean GLOBECOcean GLOBEC

Susan Howard and Laurence Padman

Earth & Space ResearchEarth & Space Research

MotivationMotivation

• Tidal currents are “noise” in ship ADCP

records. A model helps us remove them to

highlight the mean circulation.

• Tides contribute to benthic stirring and

pycnocline mixing.

• Ocean-applied stresses on the sea-ice base

affect ice kinematics and surface buoyancy

exchanges.

TopicsTopics

• 2-D model

Description of model

Results

Validation

• 3-D model (preliminary work):

Description of model

Results

2-D Model: CATS2-D Model: CATS

Resolution: The resolution is 1/4o E/W and 1/12o N/S (~10 km at 70oS).

Forced by height fields along 58oS obtained from the Oregon State University TPXO5.1 global tidal solution.

CATSCATS

Model

Domain

2-D Model: CATS2-D Model: CATS

Resolution: The resolution is 1/4o E/W and 1/12o N/S (~10 km at 70oS).

Forced by height fields along 58oS obtained from the Oregon State University TPXO5.1 global tidal solution.

Bathymetry: modified ETOPO-5.

Constituents: K1,O1,P1,Q1, M2,S2,N2,K2,Mm,Mf.

K1 M2

CATS ModelCATS Model

• Mean tidal speed

10 Constituents

• Weak tides except at shelf break

• Tides at shelf break diurnal (TVW)

• Currents will be affected by bathymetry

Tidal Signal in DriftersTidal Signal in Drifters

• Max speeds

15 cm s-1

• Diurnal band

only

• Speed varies

with position &

spring neap cycle

• Evidence of

strong tides near

shelf break

CATS vs. Moorings CATS vs. Moorings

3-D Model: POM3-D Model: POM

Resolution: The resolution is 1/8o E/W and 1/15o N/S (~8 km).

(we want to work toward a 2-4 km res.)

Forced by normal flow at open boundaries (taken from CATS).

POMPOM

Model Domain

(preliminary)

3-D Model: POM3-D Model: POM

Resolution: The resolution is 1/8o E/W and 1/15o N/S (~8 km).

Forced by normal flow at open boundaries (taken from CATS).

Bathymetry: modified ETOPO5.

Constituents: K1 and M2, modeled separately.

K1K1

Adelaide Island

M2

Adelaide Island

K1

Adelaide Island

M2

M2 M2

ConclusionsConclusions

• Tidal currents are quite weak except at the shelf break.

• Internal tides may be generated by both diurnal and semidiurnal flows across the upper continental slope.

• Surface tidal currents move the ice pack around, and may also increase open-water fraction.

• Lots of room for model improvements!

AcknowledgementsAcknowledgements

We would like to thank Dick Limeburner

for providing us with drifter data and Lana

Erofeeva for help with tide modeling.