Ocean Reanalyses -- Carton 1

Ocean Reanalyses: Prospects for Climate Studies

James A. Carton (University of Maryland) Thanks: Gennady Chepurin, Anthony Santorelli, You-Soon Chang

# pubs refering to 'ocean reanalysis'

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Ocean Reanalyses -- Carton 2

Some motivating questions

• What climate signals can we detect?– Where and when?– How large?– What level of diagnostic analysis is possible?

• How biased are the results?– Are the signals we see real?

• How do we evaluate the error (and bias) in our analyses?

• What comes next?

Ocean Reanalyses -- Carton 3

Profile Obs Coverage

1930-1939

1960-1969

Ocean Reanalyses -- Carton 4

OSD cast data with time at NODC (picture from NODC)

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GODAR as of WOD01 (2001): 1,050,509 castsNODC (1991): 783,912 casts

Ocean Reanalyses -- Carton 5

Growth of ARGO since 2003

(pictures from ARGO website and S. Wilson)

Time �

Ocean Reanalyses -- Carton 6

In-situ SST observation coverageSST obs

Ocean Reanalyses -- Carton 7

Remotely sensed SST since 1981

Source: John Maurer, UC Boulder http://cires.colorado.edu/~maurerj/class/SST_presentation.htm

Ocean Reanalyses -- Carton 8

Most of this talk will focus on the time period 1960-2001 corresponding to ERA40. At the end I will consider the full 20th century.

I’ll begin by looking at ocean heat content, essentially the vertical integral of temperature. Then I’ll look at water masses.

Ocean Reanalyses -- Carton 9

Global Heat Content 0/700m

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-2

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1960 1970 1980 1990 2000

Hea

t C

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nt

(x10

8 Jm

-2)

Trend: 0.77x108 Jm-2/10yr

Problem of time-dependent bias in the profile data

Levitus et al., 2005

Why would the ocean warm up for a decade, and then cool off again??

‘no-model’ analysis of

Ocean Reanalyses -- Carton 10

Assimilation/synthesis methodologies

• Sequential filters

• Smoothers

frictionstressp

UUUxkft

U++

∇−=∇⋅++

∂

∂

ρ

rrr)r

nsobservatioxbackgroundx

xHxRxHxxxBxxxJob

oTobTb

:;:

)()()()()( 11 −−+−−= −−

ECMWF Training manual

ECMWF Training manual

J=J[X(t)]

‘physically consistent’

Ocean Reanalyses -- Carton 11

Eight examples

Objective Analysis1962-2001UK-OI

sequential1962-2001ECMWF

Sequential1962-1998UK-FOAMBell. (2000), Bell et al. (2004)

Sequential 1958-2005SODACarton and Giese(2007)

Objective analysis1955-2003LEVITUSLevitus et al.(2005)

Objective analysis1945-2005ISHIIIshii et al. (2006)

Sequential1962-2001INGV Davey(2005)

Sequential1979-2005GODAS Behringer(2005)

Sequential, Coupled Sequential

1955-19991980-2005

GFDL 1,2Sun et al. (2007)

4DVar1950-1999GECCOKöhl et al. (2006)

Sequential1962-2001CERFACS Davey(2005)

Analysis procedureTime SpanAnalysis

Ocean Reanalyses -- Carton 12

Global heat content

Global Heat Content 0/700m

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-2

0

2

4

1960 1970 1980 1990 2000

Hea

t C

onte

nt

(x10

8 Jm

-2)

GECCO LEVITUSINGV UKOIGODAS SODACERFACS GFDLISHII MEANSato

Trend: 0.77x108 Jm-2/10yr

Aerosolforcing

Ocean Reanalyses -- Carton 13

Bathythemograph fall rate corrections

L09

W08

XBT

(from Sippican)

Ocean Reanalyses -- Carton 14

Global heat content after obs correction

Assimexperiment using L09

Assimexperiment using W08

Ocean Reanalyses -- Carton 15

Impact of bias correction on mean tropical circulation

Ocean Reanalyses -- Carton 16

Heat Content by decade

Vertical/Time Structure �

1960-1969 1970-1979 1980-1989 1990-1999

Ocean Reanalyses -- Carton 17

Correlation with Pacific Decadal Oscillation

Colors – heat content

Contours - SST

North Pacific Heat Content 0/700m

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1960 1970 1980 1990 2000

Hea

t Con

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(x1

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m-2

)

Much of the decadal variability is correlated with PDO

Ocean Reanalyses -- Carton 18

Decadal N. Pacific density variations

Depth of sigma 25.5 surface (Miller and Schneider, 2000)

Ocean Reanalyses -- Carton 19

Heat Content by Decade: Indian Sector1960s 1980s1970s 1990s

Ocean Reanalyses -- Carton 20

Quick Look at Upper Ocean Water Masses

Examples of the upper ocean response to freshwater events:• HOT• Bermuda• Great Salinity Anomalies

SSTAnal-SSTOBS during winter

Ocean Reanalyses -- Carton 21

McPhaden and Zhang (2002)

Change in depth (meters) of the 24.5σsurface averaged 1990-1999 minus 1970-1977

Ocean Reanalyses -- Carton 22

Response of the North Pacific to Heavy precipitation (’95-’97)

Hawaii Ocean Time seriesLukas (2001)

Salinity Anomalies at HOT showing penetration of near-surface freshwater

Heavy rainfall

Time �

Dep

th �Salinity

Precip

Ocean Reanalyses -- Carton 23

PV variability at BermudaJoyce and Robbins (1996)

Normalized PV from the Analyses

Our analysis of OBS

Ocean Reanalyses -- Carton 24

Dickson et al (1988) revised: Ellett and Blindheim (1992, Fig. 6)

Ocean Reanalyses -- Carton 25

Great Salinity Anomalies

Annually averaged upper ocean salinity (0-500m) in the Norwegian Basin (0-5oE, 63oN-69oN) for the seven analyses spanning the time period. ECMWF becomes quite fresh after 1990.

0/250m Salinity changes within the southern Labrador Sea (53oW-59oW, 50oN-56oN).

ECMWF gets extremely fresh

Lab Sea GSAs appear in 5 of the analyses

Ocean Reanalyses -- Carton 26

Spatial structure of 0/500 salinity’

0/250m Salinity changes within the southern Labrador Sea (53oW-59oW, 50oN-56oN).

Ocean Reanalyses -- Carton 27

20th Century Reanalysis:ENSO

From: Giese et al. (2009)

reconstructed SST simulated SST reanalysis SST (blue)

Ocean Reanalyses -- Carton 28From: Giese et al. (2009)

Ocean Reanalyses -- Carton 29From: Giese et al. (2009)

Ocean Reanalyses -- Carton 30From: Giese et al. (2009)

Ocean Reanalyses -- Carton 31

What have we learned?• What climate signals can we detect?

– See above.• How biased are the results?

– Observation bias is certainly present, but seems mainly to afflict basin-or global integral quantities. Model bias (including bias in meteorological forcing) does not seem insurmountable. But we still aren’t sure just how large it is.

• Are the signals we see real? Are we learning new things?– Yes. Beginning to. This is a new tool and the community is just getting

used to it.• How do we evaluate the error (and bias) in our analyses?

– Unbiased data sets like ctd/osd are uniquely valuable for this.• What next?

– Ensemble methods seem like a logical next step.– Analyses really should be done in the coupled system.– Impact of circulation on ecosystem models.