Status of ECCO v4r3 extension and ice-shelf melt-rate optimization

UT Austin: PATRICK HEIMBACH

MIT: GAEL FORGET

AER: RUI PONTE

© 2018. All rights reserved.

Ou Wang, Ichiro Fukumori, and Ian Fenty

Estimating the Circulation and Climate of the Ocean

Part I: V4r3 extension

Part II: Ice-shelf melt rate optimization

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Release 1 Release 2

2014 2016

Timeline of ECCO Version 42017

J F M A M J J A S O N D J F M A M J J A S O

Release 3Updating forcing and new observations.

Extension iterations

2018

Part I: V4r3 extension

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• Optimization first conducted for 2014-2017 when the

majority of new observations are added:

• Turning on time-anomaly data costs only;

• Adjusting time-variable atmospheric controls;

• Using V4r3’s other control adjustments;

• ~50 iterations conducted for 2014-2017;

• Conducting iterations for the whole 26-year of 1992-

2017 with everything turned on.

V4r3 being extended thru 2017

Variable R3 Ext. Comments

cg2dTargetResWunit 1e-12 N/ANow using non-dimensional

convergence criteria

SEAICEadvScheme 30 33From 3rd-order direct space

& time to flux-limited 3rd-DST (suggested by Martin Losch)

• Improve accuracy of the 2D conjugate-gradient solver (CG2D) by applying non-dimensional convergence criteria;

• Revised sea-ice time-stepping scheme.

Model:

ECCO V4 Release 3 Ext. (what’s different)

~5000W/m2 oceQnet caused by SEAICEadvScheme=30

Maps for March 2014 from runs over 2014-2017

5000W/m2

SEAICEadvScheme = 33(3-DST flux limited);Similar results if using SEAICEadvScheme=77 (Non-linear flux limited).

SEAICEadvScheme = 30(3rd Order Direct Space & Time).The adv. scheme generated large unphysical negative HEFF that needs ~5000W/m2 to the ocean to make HEFF non-negative.This large heat flux causes >10m increase of sea-ice at a neighboringgrid point in one month.

AmundsenSea

12m

+ is downward

Updated forcing and observation:

AERMIT

UT

JPLSIO

ITP, GOSHIP (S. Escher)

CTD, XBT, GLD, APB/Seals, MRB, sea-ice (I. Fenty);SSH, SST (O. Wang);Forcing (H. Zhang).

GRACE, Aquarius, GMSL, GMBP, MDT (R. Ponte)

Argo (G. Forget)

MEOP/Seals, TAO (D. Trossman)

ECCO V4 Release 3 Ext. (what’s different)

‘92 ‘00 ‘05 ‘10 ‘15 ‘17SSHSSTSIOBPSSSGMSLGMBP

Data CoverageRed = R3, Blue = extension

SI: Sea-ice concentration

In situ T Coverage Red = R3, Blue = extension

‘92 ‘00 ‘05 ‘10 ‘15 ‘17ArgoXBTCTDITPCLIMODESealsGliderGOSHIPBeaufort GyreDavis Str.TAO/other moorings

In situ S Coverage: Red = R3, Blue = extension‘92 ‘00 ‘05 ‘10 ‘15 ‘17

ArgoCTDITPCLIMODE

SealsGliderGOSHIPBeaufort GyreDavis Str.Bering Str.

Fram Str.TAO/other moorings

Number of T profiles vs. dataset:Red = R3, Blue = Ext., Black = Ext./R3

ext./

v4r3

Num

ber (

in m

illion

s)

Argo CTDXBT APB (marine mammals)

ITP

Novel profiles:Red = R3/Extension, Blue = Extension only

APB (marine mammals)

Glider

ITP

Novel mooring data:Red = R3/Extension, Blue = Extension only

Moorings

1. Convert to MITprof profile format2. Map data to model grid3. Add corresponding monthly climatology4. Map data to geodesic grids

• Supports mean and anomaly profile cost formulation

5. Add spatially-varying weights6. Convert in-situ T to potential T (when

necessary)7. Change weights to zero for bad or

missing data8. Multiply weights by relative grid-cell

area factor (γ)• γ = A(i)/max(A)

9. Remove profiles with zero weights

In situ Data Processing Sequence

Ten tests to zero out in-situ data weights

1. Inherited weight = 02. Nonzero QC flag3. Missing value4. T or S value identically zero5. T or S value outside physical range6. No corresponding climatology value7. Invalid date or time8. Invalid location9. Average average cost of entire profile

vs. climatology exceeds threshold10. Average cost of individual

observation vs. climatology exceeds threshold

update_zero_weight_points_on_prepared_profiles.m

Processing code:https://github.com/ECCO-GROUP/OBS_DATA_PROCESSING

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COST REDUCTION AND NORMALIZED COST VS. Ext. ITER0

% COST REDUCTION

NORMALIZED COST(COST PER DATUM)

1

2

3

-0.6

-0.4

0

-0.2

-0.8

0.2

-

+

fc

OBP

Prof

mn

T

prof

mn

S

For 2014-2017; black: iter0; magenta to red: iter10 to 52.

Fit to GRACE (Normalized Cost)

Iter52Iter0

2014-2107

Profile T and S:Uncertainty normalized model-data before and after novel APB data

Pre-new APB

Post-new APB

300-m, 2014-2017

T S

Large-scale SSH: Variance through time (cm2)

2000 2005 2010 20151995

model data

residual

0

20

40

60

AMOC: Rapid vs. Model (in Sv)

V4r3 extensiondata

2004 2006 2008 2010 2012 2014 2016 2018

10

20

30

26.5 N

• Configuration based on v4r3;• Updated bathymetry in Antarctic;• Data: Rignot et al. (2013) estimate of mean melt rate;• Code: Merged shelf-ice & ice-front packages (I. Fenty);• Control: ice-ocean heat transfer coefficient

• 3-d varying, but temporally invariant;• Initial guess is constant.

One-year (2010) experimental runsConfiguration:

Part II: Antarctic ice-shelf melt rate optimization

land

ice-shelfX

Y

ice-frontZ

Ice-shelf vs. ice-front:

Area-wise, ice-shelf >> ice-front in Antarctic.

ocean

T,S,& FW (q)

Thermodynamics of ice-ocean interactions:3 equations and 3 unknowns

TB = aSB + b+ cpB

Ice-shelf (Tice, Sice)

Unknowns: ice-ocean boundary layer TB and SB, and melt-rate q

Ocean (T, S)

ice-ocean boundary layer (TB, SB)

heat conservation

salt conservation

Linearized version of sea-water freezing point

Holland & Jenkins (1999)

q

Assumptions: • Ice-shelf and ice-front are

infinite reservoirs;• Heat and salt transfer

coefficients (m/s) are linearly related

• …

Sea-floor depth: v4 vs. IBCSO

v4

IBCSO

0-3000-6000

10000-1000

IBCSO-v4

(in meters)

Sea-floor depth vs. ice-shelf thickness (m):

Ice-shelf thickness (BEDMAP-2)

0

-4000

-2000

0

4000

2000

Sea-floor depth

Ice shelf cavity thickness (m):

0

500

200

100

300

400

Melt rate estimate (m/yr):

Rignot et al. (2013)

Melt rate (m/yr)Rignot et al. (2013)

Fractional cost vs. iterations

iteration 0

iteration 27

0.2

0.4

0.6

0.8

1

0 10 205 15 25

758Gt/yr, 16%

1156Gt/yr, 100%681Gt/yr

Data constraint: mean melt rate;Control: ice-ocean heat transfer coefficient(3d varying)

Freshwater flux

m/yr

ERA-interim precipitation2300 Gt/yr

River runoff in v42205 Gt/yr

Melt rate 682 Gt/yr

Rignot et al. (2013)Fekete et al. (2002)

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Summary• V4r3 being extending thru 2017 with

extended datasets;• Experimental ice-shelf melt rate

optimization working;• Adding ice-shelf melt to model requiring

modification of v4 runoff.