Delay-mode quality control of Argo float salinity data in the Tyrrhenian Sea

1
Delay-mode quality control of Argo float salinity
data in the Tyrrhenian Sea

• Giulio Notarstefano
• OGS Trieste - Italy

Third Argo Delay-Mode Quality Control Workshop
(DMQC-3) University of Washington Seattle,
Washington USA - September 10-12, 2008
2
Contents

• Argo Profilers
• Float and historical data
• Application of DMQC in the Tyrrhenian Sea
• Results
• Conclusions

3
ARGO profilers

• APEX ( Webb Research Corporation, USA)

SBE-CTD sensor (model 41 pumped
MicroCAT) Accuracies 0.002C 0.005 PSU 2.4 dbar
4
ARGO profilers

• Configuration
• Parking depth 350 m (LIW).
• Profiling depths700 m and 2000 m (every 10
  cycles).
• Cycles 5-10 days.

5
Float data

• Float data extracted from CORIOLIS in NetCDF
  format
• Float data from August 2004 to March 2008

• ftp//ftp.ifremer.fr/ifremer/argo/dac/coriolis/

Tyrrhenian Sea
6
Float data
50 floats (16 active) in the Mediterranean Sea
7
Float data

• two APEX floats (WMO number 6900280 and 6900281)
• deployed in the Tyrrhenian Sea in August 2004
• float 6900280 228 cycles, the last one in
  November 2007
• float 6900281 still active with 280 cycles in
  August 2008

8
Historical data

• Two types of historical CTD data were used
• MEDAR/MEDATLAS climatology (1975-1997)
• Data kindly made available by Borghini and
  Santoleri (2004)

Tyrrhenian Sea
9
Historical data

• Mean profile (black line) of salinity vs
  pressure standard deviation (red bars) is an
  indicator of the large variability along the
  water column of the Tyrrhenian Sea. The green
  points are the number of data used to compute the
  statistics.

10
DMQC method in the Tyrrhenian Sea

• apply the DMQC method in the various sub-basin of
  the Mediteranean Sea separately
• Two Argo floats in the Tyrrhenian WMO numbers
  6900280 and 6900281

11
DMQC method in the Tyrrhenian Sea

• Parameters used
• CONFIG_MAX_CAST 300
• MAP_USE_PV yes (0.5 and 0.1)
• MAPSCALE 6, 2 (longitude), 5, 1.67
  (latitude)
• MAPSCALE_AGE 10 years
• MAP_P_EXCLUDE 200 dbar
• MAP_P_DELTA 250 dbar
• Theta/pres range default values

12
Results for Argo float 6900280

• More than 3 years of data, from August 2004 and
  November 2007, were collected by float 6900280
  that performed 228 cycles
• The black line represents the mean profile of
  the salinity from float versus pressure. In the
  first 150-200 meters the highly variability of
  the shallower water is shown by the amplitude of
  the standard deviation

13
Results for Argo float 6900280

• The conductivity sensor worked quite well
  during its life but it seems that the salinity
  measurements from the float are almost always a
  bit fresher than the climatology (r gt 1)
• The application of the calibration method
  proposed a correction of less than 0.02 PSU to
  the float salinity measurements

14
Results for Argo float 6900281

• Deployed in August 2004, the float 6900281 is
  still active and performed more than 250 cycles
• The black line represents the mean profile of
  the salinity from float versus pressure

15
Results for Argo float 6900281

• The conductivity sensor seems to be stable and
  r is close to 1 for more than 150 cycles after
  the deployment
• The application of the calibration method
  proposed a correction that is smaller than the
  Argo accuracy (0.01 PSU)

16
Conclusions

• There is quite a good agreement between the
  historical and float measurements, given the
  natural variability of both datasets
• Despite the long operational floats life (gt 3
  years), the conductivity sensor worked well and
  demonstrated to be quite stable in time
• The corrections proposed by the DMQC method are
  small (less than 0.02 PSU) and, over long
  periods, less than the Argo accuracy (0.01 PSU)
• The corrections proposed by the DMQC method are
  smaller than the variability of the climatology,
  so we do not think that any correction is needed
  at the moment

17
Future work

• Increase climatology historical data until 2006
  for the Tyrrhenian sea. More recent data for
  other areas of the Mediterranean Sea
• Apply the DMQC method to other sub-basins of the
  Mediterranean Sea
• Use other available floats