Collection of examples of floats for which the salinity shows a TBTO-like adjustment during the first few profiles.

[cabanesc]

During the last DMQC discussions, several examples were reported of floats for which the salinity was too fresh in the first cycle and then gradually recovered. The purpose of this issue is to start collecting examples of floats where the same behaviour has been observed.

If you have an example to share, please comment on this issue. Don't forget to include the float number, a brief description of its programming (cycle length...) and any figures you think might be useful (e.g. Figure 3 & 6 from OWC, Theta/S diagram...).

[tatianarykova]

WMOID 5905432 experienced TBTO like freshening for the first 50 or so cycles - see attached comparison to nearby floats and to climatology. Float located in the Indian Ocean, 15S, moved very little: 4 or so degrees Lat and 6 degrees Lon.

[jlovellcsiro]

WMOID 5905441 was fresh offset initially (~0.1PSU) and returned to agreement with reference data over 20 cycles. It was a BGC float launched in the Tasman sea just west of Brisbane (during RV Investigator East Australia Current voyage) and was initially on a 1-day cycle for 14 days, then changed to the standard 10-day mission. The following plots show comparison with climatology and nearby floats. OWC was used to fit an adjustment for the first 20 cycles. The first 4 cycles have had PSAL_ADJUSTED_QC set to 4 because the adjustment was very large and the linear OWC fit was not perfect. This float has recently been recovered so that BGC sensor can be reconditioned. This gives an opportunity for the CTD to be examined. What should we look for? Who is best to do this and how should we go about it?

[cabanesc]

Here are two examples in the Atlantic.

6903072 is a deep float that shows a fresh bias (0.016 at the begining) which tends to stabilise thereafter. It is on a standard mission with a 10-day cycle.

6903080 is a deep float that shows a similar adjustment over the first 10 cycles (although much weaker ~0.003) and then a slight salty drift. It is on a standard mission with a 10-day cycle.

[Anto79124]

Example in Medditerranea Sea - WMO 6903247
The float shows a TBTO during the first 8 profiles (high ΔS ranged [0.02-0.08]) then a salty drift. I thought not to correct the first 8 ccyles and put QC 4. Then I applied OWC correction for the salinity drift detected. Anyone have any comments or suggestions?

[cabanesc]

Thanks for your example Antonella.

From fleetmonitoring.euro-argo.eu, it seems that your float is on a 1-day cycle, at least for the first ~twenty cycles, right?

Your correction seems appropriate as it makes sense to set PSAL_ADJUSTED_QC to 4 when the correction is very strong and the OWC linear fit is not perfect.

[jlovellcsiro]

@Anto79124 - Antonella, I agree also, that looks like a good approach. did you nee to set the initial break point in the OWC fit by specifying the 'breaks' variable in the config, or did the OWC set the breaks?

[ksato-aopc]

WMOID 5905871, which is the JAMSTEC's float, experienced TBTO like freshening error. It was deployed at December 1st, 2021 in the Southern Ocean off coast of Australia. The fresh bias at the first cycle is about 0.02. The float is equipped with SBE41CP whose SN is 13535, and it is active.

[BSHbirgit]

During the last DMQC discussions, several examples were reported of floats for which the salinity was too fresh in the first cycle and then gradually recovered. The purpose of this issue is to start collecting examples of floats where the same behaviour has been observed.

If you have an example to share, please comment on this issue. Don't forget to include the float number, a brief description of its programming (cycle length...) and any figures you think might be useful (e.g. Figure 3 & 6 from OWC, Theta/S diagram...).

As I promised during my presentation today I am sharing my presentation with the analysis of the data from the weddell gyre.

tbto_followuppresentaion.pptx
I

[BSHbirgit]

and here is my excel spreadsheet with the floats I looked at .

listoffloatsinweddelgyre_21082023.xlsx

[DebWest]

These are some great examples of the TBTO. Typically, we use a weighted quadratic polynomial curve to visually fit the pcond_factor to the observed TBTO signal. We have found this to be more successful and representative of the curve then to use break points within OWC. We have also found that for really bad cases of TBTO that we need to separate the TBTO section from the rest of the data (ie. create two calseries), because the TBTO affected data skews the OWC results too much.

I recall in the last meeting that we discussed putting together a list of floats and serial numbers affected by TBTO. Have we started that list and where can I find it.

[BSHbirgit]

I have now finished a survey of the entire ocean south of 62 S and have looked for TBTO like signals in all floats in the list. Please have a look the table and lgive me feeback if required.

southern_ocean_final.xlsx

the corresponding figures and the list can also be found on https://drive.google.com/drive/u/0/folders/1FAJRkpbLBQpZYJuquAprv7K_S9LnEWXl