11 meeting of the International Argo Steering Team Scripps ...

0.11 dbar with a standard error of 0.27 dbar, meaning Argo floats would have to be shifted 0.11
dbar deeper than CTD profiles which is consistent with a negative pressure offset. Matches
were plotted by launch year and by match year. A positive offset is consistent with a negative
pressure drift in APEX floats. The subset of TPND APEX floats based on the list provided by
CSIRO within the 2,819 matches were pulled out and graphed separately. This only yielded
624 matches, with 456 in the NW Pacific region and only 100 matches were in the Southern
hemisphere. Based on this comparison, more recent CTD data is needed to expand the
possible matches. It was also noted that the pressure offset should perhaps be graphed by the
age of the float to see if there are more positive offsets (consistent with a negative pressure
offset) as the floats age.
Gilson
A feature of some past versions of APEX floats in the Argo program is that they truncate
reported surface pressure if the value is less than -5.0 dbar. Thus a subset of APEX floats,
dubbed Truncated Pressure Negative Drift (TPND), have no recorded correction for known
negative drift. An inter- comparison between SIO SOLO floats, which report and have been
corrected for pressure drift, and the TPND floats was presented. Comparing steric height
(0/800db) from nearby floats, defined by space, time, and climatological steric height, the TPND
offset was estimated to be 1dbar (median value) to 2 dbar (modal value). In contrast, the bias
was not apparent when SIO SOLO floats were similarly compared to newer APEX floats with
the APF9 controller. Identification of individual TPND floats with extreme pressure drift is made
difficult by the small percentage of a TPNDs cycles with a nearby SOLO pair. SIO SOLO floats
are primarily in the southern hemisphere, especially the southern Pacific basin. Thus this local
comparison might differ slightly from a global analysis.
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