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History of these DMQC Workshops

History of these DMQC Workshops Gatherings of delayed-mode operators and PIs to work out problems, when the amount of problems becomes too much to be handled during the short sessions at the annual AST and ADMT meetings. DMQC-1 April 2005, ~20,000 D files

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History of these DMQC Workshops

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  1. History of these DMQC Workshops Gatherings of delayed-mode operators and PIs to work out problems, when the amount of problems becomes too much to be handled during the short sessions at the annual AST and ADMT meetings. DMQC-1 April 2005, ~20,000 D files Problem: How to start Argo delayed-mode processing for all groups. Solution: Established standard procedures for processing Argo salinity data. Other problems that popped up: WJO or BS? Reference datasets!! Conductivity cell thermal mass inertia error. DMQC-2 October 2006, ~70,000 D files Problem: Consistency of the Argo delayed-mode dataset and timely delivery of Argo delayed-mode data. Solution: OW was introduced. The basis for a complete Argo DMQC reference database was established. An algorithm for correcting cell thermal mass inertia error was offered. Preliminary results from the Argo delayed-mode data intercomparison were presented. Other problems that popped up: Pressure correction. Use of float data in the reference database.

  2. Since DMQC-2 … •Several AST and ADMT meetings have passed, and so have many resolutions. Some of these resolutions may not have reached all delayed-mode operators. •Operators have gained more expertise in delayed-mode processing of float data, as evident from the fact that in DMQC-3, each topic has a contributing speaker. •More dialogue between scientists, engineers, manufacturers to identify instrument errors. •New operators, new Argo groups, new qc techniques. DMQC-3, ~195,000 D files as of July 2008 Problem: Consistency! Solution: …

  3. Ascent rate of an UW APEX Iridium float with Sbe41Cp. The float monitors pressure P in fixed time intervals dT (e.g. 5 min). If dP/dT < 0.08, adds buoyancy X. If dP/dT > 0.08, keeps the same buoyancy for that time interval. When ascending through the thermocline, the rate of change of density is greater than the rate that buoyancy is added, therefore the float slows down when passing through the thermocline. This ascent rate control algorithm is used in all APEX floats. The pattern of ascent rate cannot be estimated. It is only known accurately when the data are reported, such as in Iridium floats.

  4. Implication for the thermal mass inertia correction to salinity in APEX floats Without known ascent rate, the current practice of assuming a constant ascent rate will over-correct salinity, especially at the thermocline.

  5. When the same breakpoints are chosen, salinity data calibrated by all 3 methods should agree to within error bars.

  6. 4 levels with minimum S variance on P 4 levels with minimum θ variance on P 2 levels with minimum S variance on θ

  7. Results from the Delayed-mode Data Intercomparison 2006 PSAL_ADJUSTED ●The biggest discrepancies occurred around sudden calibration jumps where the groups using a large time-window in estimating drifts could not model the sudden calibration changes. ●Cases exist where ocean variability has been interpreted as sensor drift and the data needlessly adjusted. PSAL_ADJUSTED_ERROR ●Adjustments came close to agreeing within the formal error bars, but did not quite reach this optimum state. This suggest that our error bars are too small and we should consider increasing their size to reflect the subjective nature of the adjustments. PSAL_ADJUSTED_QC ●The first step in DMQC should be to check the real-time qc flags. ●IFMGEOMAR set PSAL_ADJUSTED_QC = ‘5’ and is the only group to take this approach. We must all agree to a clear policy of assigning qc flags else it will be confusing for users.

  8. APEX floats only! AST-8 Action Item #18 All Paine and Ametek pressure errors need to be adjusted, no matter the size. The AST endorses the pressure report from Kobayashi & Johnson and accepts its recommendation. (Adjustment of all known pressure drifts in Argo data.) AST-9 Further investigation of techniques to assess the identification and impact of lost negative pressure offsets (in APEX floats with Apf-8 controllers) will be undertaken prior to DMQC-3 by a working group led by S Wijffels. The intention is to have a firm and revised recommendation for DMQC-3 of the circumstances under which pressure should be adjusted to account for surface pressure offset.

  9. Argo APEX pressure issues progress report Susan Wijffels and Paul Barker, September 2008 (Annie has an electronic copy of the report.) Problem 1): DACs are not adjusting APEX pressure values for known pressure biases, as found via the surface pressure value. We urge DACs to populate the technical files with the reported surface pressure offset. We also urge the adoption of common names in the technical files. We agree with the Kobayashi & Johnson paper that all DACs should adjust pressure both in real-time and delayed-mode. Problems 2): APEX floats with APF8 controller boards with truncated sfc_pressure_offset – THESE MAY EXHIBIT NEGATIVE DRIFT. Actions: 1) Identify the WMOs of these floats for users. 2) Attempt to bound the possible error in this group of floats – use altimetric methods. Drucks should be separated out from other sensors. 3) Possibly derive a pressure error to add to netcdf files at GDACs.

  10. For Druck pressure sensors, surface pressure readings are often bound within the noise level of +/- 1 dbar. About 5% of them show a slow negative drift, which has been identified to be caused by microleaks past a glass-metal seal. 214 UW floats with Apf-9 Most of the remaining 95% have surface pressure readings that don’t follow systematic trends. Such noise can be due to surface waves, changes in atmospheric pressure, etc. Not all mechanisms result in depth-independent pressure offsets.

  11. Druck pressure sensors on APEX floats • Problems • Adjust or not adjust? • ●Under what circumstances should we adjust? • ●How to adjust? Extract a trend? • 2. What about the negative offsets truncated in Apf-8 floats? • 3. Real-time correction (in ‘A’ mode)?

  12. Profiles without LATITUTDE, LONGITUDE, JULD From Argo QC Manual PSAL_ADJUSTED = FillValue; PSAL_ADJUSTED_ERROR = FillValue; PSAL_ADJUSTED_QC = FillValue. Considerations 1. (from Claudia Schmid) Some users may only be interested in the data as a time series and do not care if the data have no positions. For these users, they would like to be able to extract data from the _ADJUSTED fields, even if the data have no positions. 2. Ice floats! What should we do?

  13. AST-8, Action Item #13 (post dm data intercomparison) Wijffels & King to compose a statement and send it out to argo-dm-dm/argo-dm-rt lists saying:- When QC flags are re-examined and edited in DMQC, these edits should be made to the raw QC fields and not the _ADJUSTED_QC fields. Raw QC flags “1” & “2” should then be propagated to _ADJUSTED_QC; “3” & “4” should be set to “4” in _ADJUSTED_QC and filled with missing values as per the Argo QC Manual. Update Argo Data User’s Manual? Users continue to find bad data in delayed-mode files!

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