Argo Floats and Near-Surface Temperature Stephen Riser University of Washington, USA

Canonical Argo mission: m; T, S, p (0.005  C; 0.01 PSU ; 2.5 dbar)  t = 10 days 4-5 years/ profiles 22 Countries UW:  120 floats/year Globally:  800 floats/year deployed

Schematic of a typical Argo mission ( profiles)

 1000 m parking depth [ Service ARGOS; 9 hours surface time; 71 levels] UW float 5086 (WMO )

 UW float 5209 WMO [ GPS fix levels; 7 minutes surface time; 2-way communication, with > 30 possible commands] [520 T, S, p, O 2 samples] The future: Iridium 1000 m parking depth

0-100 m vertically averaged temperature, salinity, and density from Argo floats (5-year mean), and Argo minus WOA01 difference [Roemmich and Gilson, submitted] T S 

(T, S, p)  (0.005  C, PSU, 2.5 dbar) SeaBird CTD unit [ generally measurements collected at depths > 4 meters ]

Results from some recovered Argo floats (Oka, 2005)

Measuring SST (or near- surface T ) from ARGOS floats: 8 points above 4 m Negligible energy cost: this requires 1 extra ARGOS message Data from UW float 6023 (WMO ) in the Indonesian throughflow [ potentially a useful addition to the Argo data stream ] 

surface effects 

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Overall near surface T sampling statistics:  T rms =  C (pumped T minus unpumped T; N = 8) T can be sampled to within a few centimeters of the sea surface; proximity is variable from profile to profile. Caveats: samples very near the surface require manual editing; all data collected so far are from low latitudes.

SeaBird surface temperature/salinity sensor (STS) [  $2300 ]

The data stream from the STS float is designed to allow the STS sensor to be compared and recalibrated to the main SBE41CP CTD unit on each profile, thus insuring the specified accuracy.

An example of typical temperature and salinity profiles from the STS sensors. Note that the measurments continue to be collected until the float breaks the sea surface during its ascent. UW float  N, 165  E 9/25/2008

Near-surface T and S observations from UW float 5131, near Hawaii; data are shown from 0.2, 0.3, 0.4, 0.5 meters below the surface. Temperature Salinity

Offset by 1  C Offset by 0.1 PSU 2.5 day sampling period June 2008 near Hawaii  t  2 hours

Summary and Conclusions  Relatively high-resolution (  10 cm), high accuracy (   C) near- surface T measurements can be made from profiling floats.  Near-surface T measurements can be made using the main float CTD unit, at essentially no extra cost.  The addition of an auxillary near-surface CTD unit allows the collection of both high resolution, high accuracy near-surface T and S.  Tests of these devices are now underway (and going well) and in the future it is possible that nearly all Argo floats will have some type of near-surface T capability.  In addition to T and S, estimates of wind speed and rainfall at 3 hour intervals have been successfully made from profiling floats.

Profiling float end cap with PAL hydrophone added that can be used to make acoustic measurements of wind speed and rainfall, as on UW float 0006 (WMO ) Year-long trajectory of float 0006 in the Bay of Bengal  h 2h2h  Wind speed and rainfall (PAL)… [ h  650 m ]

The wind speed from the float and from QwikScat agree well at speeds below about 10 m/sec.

PAL wind speed and rain rate with the TRMM rain rate estimates added  TRMM WIND RAIN RATE SW monsoon (wet) NE monsoon (dry) SW monsoon (wet)