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The Argo Float Program

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July 1, 2004 through June 30, 2005

Dr. Brechner Owens
Woods Hole Oceanographic Institution, Woods Hole, MA 02543

Program Manager: Dr. Steve Piotrowicz, NOAA/OAR

Related NOAA Strategic Plan Goal:
Goal 2. Understand climate variability and change to enhance society’s ability to plan and respond.

Project Background
The goal of the Argo float program is to have 3000 profiling floats reporting profiles of temperature and salinity on a 10-day cycle covering the global ocean. The program expects to reach this goal in October 2007. Once this coverage has been achieved the further objective is to sustain this array indefinitely. The US is expected to provide half the array and the WHOI component of the Argo float program that has been funded through CICOR represents approximately 15% of the array. The duration of present grant is 5 years, starting in July 2006.

The Argo float program was designed to provide data for a number of different usages. These range from real-time analyses by operational centers to high precision analyses by climate scientists to investigate decadal climate signals. This breadth has placed an extraordinary demand on both the performance of the instruments and on the infrastructure to process the data so that the data is distributed in a timely manner to real-time users and subjected to stringent quality control to provide a high-quality data set that will exponentially increase coverage and quantity of data available to construct ocean climatologies.

This grant covers WHOI’s contribution to phase III of the Argo float program. The activities carried out in the final year of this grant include manufacturing of floats for the Argo array, quality-control of the data, and contributions scientific management of the Argo Float program. Further analyses of the data from an array of over 200 floats from the northern North Atlantic are being carried out to investigate the seasonally varying heat and salt content for the region as a demonstration of the types of analyses that can also be applied to the Argo float array.

Over the period from 1 July, 2006 to 30 June, 2007 a total of 137 floats have been manufactured and deployed, primarily in the Atlantic Ocean. Our coordination with AOML to deploy these floats primarily from VOS cruises has developed so that we can anticipate cruises and make deliveries on a timely basis, but there continue to be occasional problems. As compared to the deployments in other oceans, the relatively small size of the Atlantic requires that we only deploy 6-8 floats per VOS cruise and these cruises change on short notice which requires quick responses to these changes or that float leave the lab only to return later since the cruise has been canceled. This means that the time per float spent organizing for its delivery is higher than is the case when a cruise involves 30 or more floats as is the case in the Pacific and Indian Oceans. We have also arranged to deploy floats from research cruises on the R.V. Ron Brown in both the Atlantic and Pacific Oceans. We have also arranged, through Raytheon Polr Services to deploy floats from the R.V. Oden in the Southern Ocean. An additional 10 floats have been loaded on the R.V. Nathaniel Palmer, but their deployment has been delayed due to a recent fire in the biological lab of the ship.

We have now developed a SOLO float that uses the Iridium Short Burst Data (SBD) communications system for data communications and GPS for positioning. Three floats were deployed in the Arctic Ocean under separate funding. A second-generation version was first deployed in October 2006. We are also working with the newest version of Iridium transmitter that is smaller and much lower power, but has a reduced message length. With this new transmitter, we are able to incorporate a continuous profile of dissolved oxygen with the same battery pack presently used for floats equipped with an Argos transmitter. This float has been deployed off Bermuda and is working well. These floats also use an antenna designed at WHOI that costs only slightly more than an Argos antenna. Using this version of the hardware and SBD communications minimizes the additional costs for Iridium compared to Argos equipped floats so that the additional costs give added lifetimes of the float and represent a net savings.

During the present year, an analysis of Argo float data identified that the WHOI FSI equipped floats had data that had a significantly cold bias. After extensive examination of the problem, it was determined that the error occurred because the FSI CTD was carrying out the bin averaging from the bottom of the profile, rather than from the sea surface downward. This error caused the pressure values to be incorrectly reported in the netcdf files. For approximately half of these floats, there is engineering data that will allow the data to be corrected unambiguously. For the other fraction, a least-squares procedure combined with a visual inspection has been developed to best estimate the pressures. This procedure will increase the pressure uncertainty to order 10 dbars. In the process of carefully screening the pressure data from the WHOI floats, a smaller error was found in the way that pressure was reported for the floats equipped with an SBE CTD. Procedures have been developed to correct all these incorrect pressures. At this time, the FSI CTD data that can be corrected unambiguously and the SBE CTD data have been corrected and the files at the global data centers corrected. WHOI is now working through the FSI data that requires manual inspection.

Owens has continued to work with A. Wong (U of Washington) to improve the procedures for calibration of the conductivity sensors against historical CTD data. We have implemented a piece-wise linear fitting procedure that chooses the statistically simplest model of the drift. This new procedure has been evaluated by the Argo community and has been accepted as the method to carry out the calibration of conductivity sensors.

Owens has continued to spend some time involved with the International Argo Steering Team and the Argo Advisory panel. This has included a meeting in Paris in March 2007.

In summary, the WHOI contribution to the Argo Float Program has continued significantly accelerated and improved the performance of the floats. Improvements in both the communications system and the calibration procedures have been implemented. A significant error in the data reported from these floats has been identified and the procedures to correct the data have been developed and implemented.

Last updated: August 19, 2008

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