Stéphanie Guinehut CLS, Space Oceanography Division

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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The use of Satellite Altimeter data in Argo quality control

Limitations of the method in terms of pressure and salinity signals to be detected

Stéphanie GuinehutCLS, Space Oceanography Division

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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Reminder of the method The main idea is to compare co-located :

– Altimeter Sea Level Anomalies (SLA) – and Dynamic Height Anomalies (DHA) from Argo T/S profiles

for each Argo float time series

Method :DHA = DH – Mean-DH / SLA

2 times series co-located in time and spaceSLA : AVISO combined mapsDHA : Argo Coriolis-GDAC data baseDH calculated from T/S profiles using a ref. level at 200, 400, 900, 1200 or 1900

dbar only data with : POSITION_QC = ‘0’, ‘1’, ‘5’, ‘8’

JULD_QC = ‘0’, ‘1’, ‘5’, ‘8’ PRES/TEMP/PSAL_QC = ‘1’ (DATA_MODE=‘R’) PRES_ADJ/TEMP_ADJ/PSAL_ADJ_QC = ‘1’ (DATA_MODE=‘A’/’D’)

Mean-DH : contemporaneous Argo mean dynamic height

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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Impact of the reference level

Good data

Bad data

- Impact of the salinity drift increases with the ref level

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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Representative anomalies

Spike Float : 5900155

Bad salinity data at depth

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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Representative anomalies

Offset

Float : 1900581r : 0.61rms-diff : 2187.00 %mean-diff : 15 cmsamples : 69* statistics on DHA-Real

Salinity offsetVertically averaged correction applied= -0.243 psu

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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SLA DHA (real-time)

Representative anomalies

Drift Float : 5900963

Evidence of a negative pressure drift

Figure : courtesy of Annie Wong

SP ~ –14 dbar

CYCLE NO ~ 119

SLA-DHA ~ 6 cm

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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Little geographical variations of the impact Impact with reference level and offset

Limitations of the method in terms of pressure and salinity signals to be detected

Theoretical study using WOA05 fields salinity offset

Impact of a salinity offset of +0.05 psu on a (0-900)dbar DH

-3.41 -3.38 -3.35 -3.31 -3.28 -3.25 cm

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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Limitations of the method in terms of pressure and salinity signals to be detected

Theoretical study using WOA05 fields pressure offset

Impact of a pressure offset of -10 dbar on a (0-900)dbar DH

-6 -4.9 -3.8 -2.7 -1.6 -0.5 cm

Large geographical variations of the impact + small seasonal variations Impact with offset, small differences with ref level

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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Limitations of the method in terms of pressure and salinity signals to be detected

Tests on a particular float : WMO 5900963

Simulatedpressure offset of -15 dbar

Simulated pressure offset of +15 dbar

Pressure offset

cycles corr. mean(SLA-DHA)(cm)

rms(SLA-DHA)(cm)

rms(SLA-DHA) % rms(SLA)

corr. rms(SLA-DHA) % rms(SLA) ref

no offset 203 0.91 0.91 2.53 20.8 0.85 28-15 dbar 203 0.90 5.14 5.75 107.4 0.85 28+15 dbar 203 0.91 -3.36 4.12 55.1 0.85 28

Impact of the observed mean SLA-DHA differences Impact of the time series length

SL

A /

DH

A

SL

A -

DH

A

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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Limitations of the method in terms of pressure and salinity signals to be detected

Observed mean SLA-DHA differences

Large-scale consistent signal Higher values in high variability regions

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 cm

Argo Delayed-Mode Quality Control Workshop (DMQC-4) – 28/09/2009 – Toulouse

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Limitations of the method in terms of pressure and salinity signals to be detected

Limitation of the method :

If 5 cm is considered to be the smallest offset to be detected between SLA and DHA

No much help for small offset/drift - compared to P/T/S analysis …

Reference level (dbar)

Min salinity offset (psu)

200 0.3400 0.17900 0.081200 0.061900 0.04

-50 -30 -25 -20 -15 -10 -5 dbar

Min pressure offset that can be detected – 900 dbar DH

Min salinity offset that can be detected