Summary of issues and conclusions from DMQC-4

1. Summary of issues and conclusions from DMQC-4 Pressure Issues, especially Surface pressure offset, Druck microleak, APEXs that truncate negative pressures Other issues

2. All delayed-mode groups to be aware of increased possibility of SBE CTDs developing the Druck microleak disease. • This disease manifests itself as a negative pressure error that increases with time, with the end stage being bad data that are uncorrectable. • Expect about 30% occurrence rate for floats deployed in 2007 and later. Oil leak rate varies.

3. Some floats die early, others take a long time to diagnose Combined Apf-9 data from BSH, UW, and CSIRO, up until 22 August 2009. Occurrence rate up until Mar 09 Pre-2008 ~ 3% UW ice floats Jan 2008 18% (after 14 months) UW + SIO floats Kaharoa Oct 2008 28% (after 5 months) Both occurrence rate and oil leak rate have increased!

4. Stephanie Guinehut’s altimetry QC can detect errors that correspond to about 5 cm of dynamic height. Because of the thermal structure of the ocean, this is equivalent to about 10 dbar pressure error in the tropics, but about 50 dbar at high latitude. Therefore the altimetry QC will be most useful at latitudes < 30.

5. APEX APF8 with Truncated Negative Pressure Drift (TNPD) For such APEX floats, if the Surface Pressure ‘hovers around zero’ there is no problem. If Surface Pressure becomes ‘persistently’ zero, but other data are ‘sensible’ the unknown surface pressure offset is negative. The magnitude is unknown but probably < ~ 20 dbar if the other data have no obvious problem. When such a float is identified, DM proposes: (see next page)

6. Recommendations from DMQC-4 For TNPD floats with persistently zero surface pressure For APEX Apf-5, Apf-7, Apf-8 (all firmwares that truncate negative surface pressure values), when a large portion of the SP time series (nominally 80%) records absolute zero AND T/S does not show anomaly, it means the float may be experiencing undetectable negative pressure error. In those cases: PRES_ADJUSTED_QC = ‘2’ TEMP_ADJUSTED_QC = ‘2’ PSAL_ADJUSTED_QC = ‘2’ SCIENTIFIC_CALIB_COMMENT = “TNPD: APEX float that truncated negative pressure drift. Other operator comments,……”

7. Recommendations from DMQC-4 For TNPD floats with persistently zero surface pressure If fhere is an apparent T/S anomaly, it is very likely that there is a pressure problem and the flags should be ‘3’ or ‘4’ depending on severity of the anomaly. A negative PRES error will lead to a positive PSAL error, and a cold TEMP anomaly whose size depends on vertical TEMP gradient If the float is telemetering highly erratic data, it is a sign that the microleak problem is about to reach its endpoint. Previous cycles may need to be reviewed.

8. Recommendations from DMQC-4 For TNPD floats with persistently zero surface pressure(continued) Justin Buck & Mathieu Ouellet to consult their assimilation groups about how they use PRES_ADJUSTED_ERROR and to suggest to DM community what value should be assigned for APEX TNPDs to ensure that these data are treated appropriately by those groups.

9. To be decided by the RT DACs For the cases of APEX TNPDs, what to do with PRES_QC, TEMP_QC, PSAL_QC? Comment: When the pressure goes really bad, the float will go on the greylist. Before that time, DM suggests that in real time, PRES_QC, TEMP_QC, PSAL_QC should be ‘2’ in the GDAC files. Should these data be transmitted on the GTS ?

10. Other considerations from DMQC-4 For floats with microleaks Be aware that if the pressure offset is <~ 10 dbar, the error may be independent of depth, so a simple pressure adjustment is appropriate; but if pressure offset is >~ 10 dbar, the error may vary with both PRES & TEMP Chair AST will write to SBE and ask them to characterise pressure errors from microleaks for the sensors they have already identified as bad in their laboratory tests

11. DMQC-4 other issues CellTM • 6. Birgit Klein to study effects of CellTM correction in the North Atlantic with currently available coefficients and estimated ascent rate.

12. DMQC-4 other issues D format checks • 7. All delayed-mode groups to download D file format check output from ftp kakapo.ucsd.edu (anonymous login) cd /pub/gilson/DMQC4 and to correct the format errors. (GDAC checks new files and rejects failures) • 8. In order to squeeze D format errors out of existing D files, John Gilson to perform D file format check every quarter in conjunction with updating the SIO Argo climatology. Summary table to be published in the AIC Monthly Report. Detail output to be made available via ftp from Coriolis in conjunction with the SIO Argo climatology.

13. DMQC-4 collating information about DMQC detailed practices • 9. Annie Wong to collate regional parameter information from all delayed-mode operators. Sylvie to host DMQC webpage at the Coriolis Data Management website. User login or public? Web page is not interactive, but is updated as new information is collated. • 10. All delayed-mode operators to edit raw qc flags (PARAM_QC) in delayed-mode, to preserve pointwise information about spikes, jumps, etc incorrectly flagged by automatic RT tests. Editing raw flags

14. DMQC-4 Editing raw flags (continued) 11. A suggestion was made that if PSAL is adjusted in delayed-mode, then PSAL_QC should be ‘3’ because ‘These data should not be used without scientific correction’. Agreement was not reached on whether to instruct all DM operators to adopt this. Some DACs/DM operators may choose to do this if they wish.

15. DMQC-4 other issues 12. The question was posed: ‘Should we remove D files that haven’t been reprocessed for surface pressure offset, and restore them when the DM operator has completed the task ?’ The answer was: ‘No. We cannot afford to lose that many D files; DACs should fix them as a high priority’. If it is critical to users to know whether surface pressure has been adjusted, they must read the SCIENTIFIC_CALIBRATION_COMMENT.’

16. Change in thinking of data variables (reflects the way DM community has viewed data for some time) REAL-TIME versus DELAYED-MODE → 2 stages of data quality control RAW versus ADJUSTED → 2 types of data

17. Change definitions of PARAM and PARAM_QC in User’s Manual and QC Manual: ▪ PARAM contains the raw values telemetered from the floats. PARAM = PRES, TEMP, CNDC, PSAL. (DOXY will have its own definition.) ▪ PARAM_QC contains qc flags that give information about the values in PARAM. Values in PARAM_QC are set initially in ‘R’ and ‘A’ modes by the automatic real-time tests. They are later modified in ‘D’ mode at levels where the qc flags are set incorrectly by the real-time procedures, and where erroneous data are not detected by the real-time procedures.

18. DMQC-4 other issues: TEOS-10 Thermodynamic Equation Of Seawater - 2010 www.teos-10.org, (top hit for “teos-10” in google) TEOS-10: Approved by IOC June 2009 for use from Jan 2010 onwards DMQC-4 reviewed the impact of TEOS-10 on the DM process, which will be small TEOS-10 libraries available in Matlab & FORTRAN; c will come in due course Note that the salinity argument for the TEOS-10 algorithms is Absolute Salinity SA =~ 1.004715 *PSAL + regional composition anomaly of magnitude <~ 0.02. function SA = gsw_ASal(PSAL,PRES,LON,LAT) function result = gsw_pden(SA,t,p,pr) function result = gsw_ptmp(SA,t,p,pr) Extends algorithms to larger ranges, which were not defined for PSAL & EOS80 ( 0 < S < 120; T < 80) Units of SA are g/kg