Diurnal Variability Working Group: GHRSST-10 Breakout Session Report Chris Merchant Gary Wick

Contents of breakout Theme 1: Towards Diurnal Variability Analysis Theme 2: Satellite observation developments Theme 3: Potential of ARGO profiling floats in the near surface Theme 4: Collaborative projects and WG business

Salvatore Marullo: 3 hourly SST analysis in trop. Atlantic Foundation estimated at 04:00 UTC Bias correction between SEVIRI and MW observations at foundation time OI done on SEVIRI SST anomalies over a 10 day window for the hour of day

Time de-correlation

Lag (Hours) Correlation

Pierre Le Borgne: Example of data driven analysis of DSST from super-collated polar-orbiter observations

Steinar Eastwood Sub-daily SST variability in the Arctic, WASPARC

Occurrence of DW at moored buoys 73N 15E74N 30E > >

3 month: mean dSST ~14LT SEVIRIAMSRE OI SeafluxEdinburgh

4 years: mean peak dSST AMSR-E Seaflux Edinburgh

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 US: 50% of the array US: funded through 2011 UW:  120 floats/year Globally:  800 floats/year deployed US:  400 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

(T, S, p)  (0.005  C, PSU, 2.5 dbar) SeaBird CTD unit

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 ]

Riser’s 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.

Response 1 At essentially no cost and rapidly, unpumped T observations within top 4 m could be routinely provided from ARGO profilers We see considerable potential in this for addressing near-surface stratification and clarifying foundation SST But there is a process of learning how to use the near- surface observations required, especially with regard to depth uncertainty Recommendation: DVWG communicates to the ARGO steering committee –We see immediate scientific use for such observations –We therefore encourage the routine adoption of near-surface sampling –We offer to work with the ARGO community to learn better how to use these observations

Response 2 Iridium-equipped floats could be programmed to give an enhanced near-surface sampling regime Again, very low cost to this, and could be rapid We think this would greatly accelerate the scientific exploitation of ARGO for near-surface work But what the sampling regime should be requires thought Recommendation DVWG approaches ARGO team to open a discussion about potential enhanced sampling regimes for the near-surface / upper ocean

Response 3 At $2500 per float, near-surface T and S observations could be added using additional sensors, with much less depth uncertainty Some deployment of this technology will happen via Aquarius validation missions Observations support more detailed analysis of near-surface stratification including fresh layers Recommendation DVWG notes the additional scientific potential of the enhanced instrumentation, and is supportive of initiatives to extend this technology

Quote from OceanObs “We strongly recommend that all Argo floats are equipped with a capability to make high vertical resolution measurements of SST in the upper 10m of the ocean surface and that shallow-water Argo floats be developed and deployed. Evidence should be gathered and presented to Argo float manufacturers highlighting the applications and benefit of providing high resolution temperature sensors on all Argo floats for the investigation of SST diurnal variability.”

Chairmanship Group adopted the rotating chairs principle Vice chair for 1 year, will take over as chair at next GHRSST Nominations to Craig by 5 pm today!