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Temperature, Salinity and Sea Level: climate variability from ocean reanalyses (Intercomparison Items 3 & 4). Magdalena A. Balmaseda Anthony Weaver. Outline. Defining the variability: signal and noise Seasonal cycle removed: Anomalies with respect to the common period (1994-2000)

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Temperature, Salinity and Sea Level:climate variability from ocean reanalyses(Intercomparison Items 3 & 4)

Magdalena A. Balmaseda

Anthony Weaver

GSOP Workshop, Reading, 31 Agust-1 September 2006


Outline
Outline

  • Defining the variability: signal and noise

    • Seasonal cycle removed: Anomalies with respect to the common period (1994-2000)

    • 12-month/3-month running mean

    • Focus on the upper ocean (upper 300m): Equator, Mid latitudes

  • Temperature and salinity:

    • What can we say about climate variability?

    • Time variation of uncertainty

    • Outliers?

  • Source of uncertainty (forcing, model, assimilation method)?

  • Sea Level variations: volume or mass changes?

  • Summary and conclusions

GSOP Workshop, Reading, 31 Agust-1 September 2006


Focus regions for items 3 4
Focus Regions for Items 3 & 4

GSOP Workshop, Reading, 31 Agust-1 September 2006


Uncertainty in the mean
Uncertainty in the Mean

  • Ambiguity in the definition

    • closest level, interpolated values…?

  • Real Uncertainty?

We will use anomalies…

GSOP Workshop, Reading, 31 Agust-1 September 2006


T300 equatorial regions

T300: Equatorial regions

  • Eq Pac: Uncertainty decreases with time.

  • Relatively robust interannual variability.

  • Increased uncertainty after 2000. Why?

GSOP Workshop, Reading, 31 Agust-1 September 2006


What can we say about tropical variability
What can we say about Tropical variability?

How should we interpret the outliers?

Need to understand the reasons

An outlier for the good reason is very valuable

An outlier for the wrong reason is damaging

GSOP Workshop, Reading, 31 Agust-1 September 2006


T300 mid latitudes northern

T300: Mid latitudes (northern)

  • The North Atlantic is dominated by a warming trend, especially post 1997

  • Large uncertainty after 2000.

  • Phase/amplitude of decadal variability is poorly resolved.

GSOP Workshop, Reading, 31 Agust-1 September 2006


Global signals

GLOBAL: Upper T-300m of a rapid shift in the early 90’s

GLOBAL Upper T-750m

GLOBAL Upper T-3000m

GLOBAL SIGNALS

Warming occurs ~ in first 750m

GSOP Workshop, Reading, 31 Agust-1 September 2006


Salinity variability
Salinity Variability of a rapid shift in the early 90’s

  • Salinity variability dominated by spin-up effects in several cases.

  • There is no consistency among reanalyes

GSOP Workshop, Reading, 31 Agust-1 September 2006


Signal noise ratio long period

T300-12m-rm of a rapid shift in the early 90’s

S300-12m-rm

T750-12m-rm

S750-12m-rm

T3000-12m-rm

S3000-12m-rm

Signal/Noise Ratio (long period)

EQPAC

EQATL

EQINDTRPAC

TRATL

NPAC

NATL

GLOBAL

GSOP Workshop, Reading, 31 Agust-1 September 2006


Signal noise ratio short period interannual

T300-3m-rm of a rapid shift in the early 90’s

S300-3m-rm

T750-3m-rm

S750-3m-rm

T3000-3m-rm

S3000-3m-rm

Signal/Noise Ratio (Short period, interannual)

EQPAC

EQATL

EQINDTRPAC

TRATL

NPAC

NATL

GLOBAL

GSOP Workshop, Reading, 31 Agust-1 September 2006


Sources of uncertainty
Sources of Uncertainty of a rapid shift in the early 90’s

All

ERA40

ERA40-No data

ERA40-Assim

GSOP Workshop, Reading, 31 Agust-1 September 2006


Equatorial atlantic assimilation increases spread
Equatorial Atlantic: Assimilation increases spread of a rapid shift in the early 90’s

All

ERA40

ERA40-No data

ERA40-Assim

GSOP Workshop, Reading, 31 Agust-1 September 2006


Assimilation and uncertainty t300
Assimilation and Uncertainty T300 of a rapid shift in the early 90’s

1956-2005

EQPAC EQATL EQIND TRPAC

Long period 1956-2005:

Assimilation decreases uncertainty everywhere

1993-2005

EQPAC EQATL EQIND TRPAC

TRATL NPAC NATL GLOBAL

Latest period 1993-2005

Only in EQPAC the assimilation reduces uncertainty

TRATL NPAC NATL GLOBAL

GSOP Workshop, Reading, 31 Agust-1 September 2006


Assimilation and uncertainty s300
Assimilation and Uncertainty S300 of a rapid shift in the early 90’s

1956-2005

EQPAC EQATL EQIND TRPAC

Long period 1956-2005:

Assimilation increases uncertainty everywhere

1993-2005

EQPAC EQATL EQIND TRPAC

TRATL NPAC NATL GLOBAL

Latest period 1993-2005

Assimilation increases uncertainty

TRATL NPAC NATL GLOBAL

GSOP Workshop, Reading, 31 Agust-1 September 2006


Global sea level variations i
GLOBAL SEA LEVEL VARIATIONS I of a rapid shift in the early 90’s

  • Prior to 2002, changes in sea level and steric height are correlated:

  • Volume rather than mass

  • Changes in bottom pressure are not consistent amont analyses?

GSOP Workshop, Reading, 31 Agust-1 September 2006


Global sea level variations ii
GLOBAL SEA LEVEL VARIATIONS II of a rapid shift in the early 90’s

Temperature contribution to dynamic height dominates the trend

GSOP Workshop, Reading, 31 Agust-1 September 2006


Sea level variations seasonal cycle
Sea level variations: Seasonal cycle of a rapid shift in the early 90’s

Seasonal variations in global sea level are attributed to mass variations that affect the bottom pressure.

GSOP Workshop, Reading, 31 Agust-1 September 2006


Summary and conclusions
Summary and Conclusions of a rapid shift in the early 90’s

  • There is large uncertainty in climate signals

    • Signal to noise ratio > 1 in the Eastern Pacific for Temperature

    • Signal to noise ratio <1 for salinity in most regions

    • Warming trend in the 90’s is consistently reproduced

    • What is happening now? There is not consistent picture

  • Forcing fluxes and analysis methods are largest source of uncertainty

    • Data Assimilation does not always collapse the spread: We need to pay more attention to the assimilation methods.

  • Global Sea level trends

    • 1993-2002: Consistently attributed to temperature rise.

    • 2002-present: It is not clear. Mass increase?

    • Seasonal variations related to mass variations.

GSOP Workshop, Reading, 31 Agust-1 September 2006


NEXT of a rapid shift in the early 90’s

  • Web page to collect. WHERE? GSOP web page?

  • Maps of signal to noise ratio, and so on

  • Need to define the variables so there are not “so” dependent on the vertical model grid.

  • There are currently 20 analysis… are there more there?

  • Agreement on colour coding and naming convention?

  • Other?

GSOP Workshop, Reading, 31 Agust-1 September 2006


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