AST-12 meeting report posted - Argo

afternoon, when surface warm layers were most likely to occur. Comparison of the crosscalibration
measurements showed very small differences between the pumped and nonpumped
measurements (apart from one float where the non-pumped temperatures were
consistently warmer). However, the good agreement was not surprising as in most profiles there
was little or no temperature gradient, so any lag in the non-pumped measurements was
impossible to identify.
For the 2 floats that surfaced during the afternoon, the data showed the existence of nearsurface
temperatures up to 2.5 °C warmer than the uppermost pumped temperature (at
nominally 4 or 5m depth). Although relatively few stratified profiles were observed, the results
show the NST capable Apex floats are able to observe near-surface temperature stratification
that would otherwise remain undetected and so do provide useful additional information.
To better quantify the benefit and accuracy of such near-surface temperature measurements,
more NST capable Apex floats need to be deployed in regions where stratification is most likely
and ‘timed’ to surface during the afternoon when stratification is likely to be strongest. More
such floats are now in the water with 107 NST-capable floats having been deployed in the last 3
years by US, UK, Japan and India. The number is likely to increase over the coming years. It
was planned to continue the analysis, either with a soon to be recruited scientist at the Met
Office or as a summer MSc dissertation project at the University of Reading (with Jon Turton
and Andrea Kaiser-Weiss (GHRSST PO) as supervisors). The AST requested that the NSTcapable
float data, from all countries, should be assembled and made available on a publically
accessible website. AST also requested that an analysis of all the available data should be
reported to ADMT-12, to inform a decision on dissemination of the data via the GDACs.
It was recognised the optimum longer-term approach was to report near-surface data from
Iridium floats. Iridium floats typically record at 2 dbar vertical resolution; given the response of
the T sensor (~½ s) it’s possible to sample every second (~0.1 dbar) but with the resolution of
the P sensor (0.1 dbar) it is probably not worth sampling faster than every 2 s (~0.2 dbar
spacing). Hence with Iridium floats it would be possible to meet the GHRSST ‘goal’ of 50 cm
sampling from 5 to 15m depth and the ‘useful’ sampling of 50 cm for less than 5 m depth, but
unlikely to be possible to achieve the 10 cm ‘goal’ accuracy above 5m. However, the accuracy
of Argo temperature measurements is likely to be better than standard SST measurements from
drifting buoys and Voluntary Observing Ships and although Argo would provide fewer reports
they are of high accuracy with vertical information, so would be complimentary to these other
sources.
Action item 28: J. Turton to coordinate gathering unpumped temperature data from
Argo PIs and work with GHRSST to place data in a public place and advertise it throughout their
community. J. Turton, Y. Chao.
Action item 29: J. Turton and GHRSST to analyze pumped and unpumped
temperatures. Report back by the time of ADMT. J. Turton, Y. Chao
6.5 Argo floats in the ice-zone
S. Wijffels reported on work done by E. Van Wijk and others (see more detailed paper in
appendix) on the prospects for extending Argo into the seasonal and fast ice zone.
Seasonal Ice Zone:
There are several options for floats to operate successfully in the seasonal ice zone:
1. Use Iridium/GPS with an ice-avoidance algorithm (AWI or U. Washington)
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