Assessment of the ECCO2 optimized solution in the Arctic

An T. Nguyen, R. Kwok, D. MenemenlisJPL/Caltech

ECCO-2 Team Meeting, MIT Sep 23-24, 2008

Outline: Optimized solution in the Arctic Ocean:

• hydrography• fresh water & heat content• heat & volume fluxes

Sea ice:• Extent summer 2007• Velocities & fluxes• Thickness• Volume

Summary• Arctic solution total cost reduction• Greenland Sea

Regional optimized solution: Data:

• Sea-ice velocity, sea-ice thickness, CTD profiles, • Initial conditions, Forcings

Parameters: • salt-plume parameters• air / sea-ice drag coefficients• sea-ice and ocean albedos• sea-ice strength and H0• initial conditions• freshwater content• GMredi

Sea ice velocity

Sea ice extent

Sea ice extent

c37: NCEP

c47: c37, WOCE climatology , without specifying net shortwave radiation, bug fixes in growth.F , including Peter Winsor's new monthly Arctic Ocean runoff

c55: first blend integration (c49) , more realistic initial sea-ice conditions from a PSC estimate SEAICEadvSnow=.true. , SEAICEuseFlooding=.TRUE.

c62: c55, but with blend forcing and blend wind NCEP at high lat

arc1: First integration of Arctic domain, open boundary, NCEP wind, c55 param

Passive Microwave data: 1991-2002

Sea Ice flux: Fram Strait

gree

nlan

d

Annual c37 c47 c55 c62 arc1Mean() -22 301 503 419 325Std() 134 147 190 159 141 % 2.5 35 58 48 38

model – data

Sea Ice flux: comparison

Sea ice extent: Arctic Ocean

Sea ice thickness

Apr

May

Aug

Apr

Apr A

prSep

Sep

Sep

Aug

Oct

Arctic sea ice: too thin Mean STDApr-May: -0.93 0.37Aug-Sep: -0.74 0.20Oct: -0.25 0.19

greenland

siberia

alaska

ULS data from submarine: 1991-2002

Sea Ice thickness:

ULS data at Fram Strait: 1991-2002greenland

Sea ice volume

Note:c37: specifying net shortwave radiation

c47: remove net shortwave radiation specification and fix growth.F reduces sea-ice volume

c55 & c62: starts with higher initial sea-ice thickness increases volume

c57: increase dry-ice & dry-snow albedos increases ice-thickness & volume

c56: increase wet-ice & wet-snow albedos higher increase in volume

Dropping too fast?

Positive trend 96-02

Sea ice velocity

Expect: • ice velocity direction to the right of wind at ~ 25-40o

Model:• Turns to the right, but not enough• Sometimes: parallel to the wind dir• turning angles correlate with |vel|

Sea ice velocityA

ngle

dif

fere

nce

betw

een

data

and

mod

el ic

e ve

lV

elocity residuals (mm

/yr)

Sensitivity experimen

t

%cube Oct-Dec Jan-May Mar-May29 19.0 4.4 1.7 %NCEP?31 20.0 12.4 10.7 %NCEP37 19.7 12.4 10.0 %NCEP47 20.0 10.4 2.0 %NCEP55 20.3 9.8 1.3 %75%CORE62 20.7 9.6 1.0 %NCEP-1 20.3 10.6 3.0 %NCEP

Consistently high, essentially // to the wind dir

Summary-1: Sea Ice

1. Sea Ice flux: over-estimates net ice export across Fram Strait by 40% to 60%

2. Sea ice thickness/extent/volume: too much ice extent in winter, too little in summer ice thickness small relative to ULS data in Arctic ocean closer to data in Greenland sea ice volume too small, with positive trend!

3. Sea ice velocity: parallel to wind direction, consistently to the left of data turning angles correlate with magnitude of vel

Arctic ocean (5): Fresh water volume:

12

34

5

Expect:~7.5x104km3

Too low

Arctic ocean : freshwater input through Bering Strait

Expect: ~0.053Sv[Aagaard and Carmack, 1989]

Arctic ocean: SST and Dynamic Topography:

Summary-2: Arctic ocean

1. Fresh water volume: Between 60,000km3 to 67,000km3

2. Fresh water input through Bering Strait: ~ 0.031Sv

3. Arctic domain: SST does not drift ETAN drifting Ice velocity across Bering Strait: significantly larger than both c47 and

c55 ice import increases by 8% to 10% (NOT SHOWN HERE)

END

List of things to do (04/13/07):

1) Fix drifts in Arctic domain2) Fix vertical mixing

fix ice thickness + ice vol + fresh water vol?3) Jinlun’s comments:

• Initial condition for ice thickness: in the wrong season?• Ice extent problem in summer: thermodynamics• Tear-drop vs. elliptical yield curves:

might not solve discrepancies of vel near coast• Need to check if stresses lie on the yield curve

Arctic ice thickness PDF

too thin, lacking modes

Sea Ice strength