Argo Project Status Report B. Owens, D. Roemmich, S. Riser, G. Johnson, S. Garzol Ocean Climate Observation Annual System Review Silver Spring October 27-29, 2010

The status of Argo 440,000 high quality T,S profiles have been collected during in the open ocean excluding marginal seas (619,000 total profiles). Upper right: profiles per 1 o box, Argo has achieved > 3000 active floats, with global coverage. Data are freely available, ~90% within 24 hours via GTS and internet. The northern hemisphere bias is diminished. There is no seasonal bias. Data are being used by at least 14 operational centers, and a broad community of researchers. Over 100 Argo-related research papers were published last year. Delayed-mode processing backlog essentially gone. International partners match the US level of contributions in floats and data management activity. Argo’s broad international participation is unprecedented. Continuous observation of the global ocean is now a reality. U.S. strategy provides half of Argo by integrating six institutional contributions.

The good news and the bad news The bad news : About 25% of CTDs deployed in early 2009 likely have microleak problem; many will fail early. Some* floats not correctable. Druck assembly procedure changed, Kistler pressure sensor used for some floats. Few deployments from May to November Continued low deployments in US floats deployed in FY in FY2010 with target of 420 floats CTD’s recalled; production backlogged until mid-2010 *Truncated negative pressure drift (TNPD) floats. Only 461 floats deployed in 2009 vs. 882 in 2008

Schematic diagram of a vertical section of a Druck pressure sensor vacuum water oil Titanium diaphram in neutral position titanium Metal conductor Glass Around April 2006, Druck increased the strength of the welds that bonded the pressure sensor to the CTD casing. This causes cracks in the glass/metal seal, through which oil leaks from the sealed inner sensor chamber. As oil leaks, the titanium diaphram is deflected downward, causing a negative pressure error.

Druck Pressure Sensor Cracks in glass-metal seals causes oil leakage. Pressure drifts and ultimately pressure sensor fails. Occurrence rate up until Mar 09 Pre-2008~ 3% UW ice floats Jan % (after 14 months) UW + SIO floats Kaharoa Oct % (after 5 months) Both occurrence rate and oil leak rate have increased! floats with microleak problem good floats From S. Riser and D. Swift

The good news: Still have >3100 active floats. Deployment backlog expected to clear in Impact of TNPD floats can be assessed, and data corrected or eliminated from archive. Microleak floats can be identified and data eliminated. Some international partners increasing their programs (Australia, Europe). US floats presently represent 60% of the active array.

Argo coverage in the southern hemisphere. Mean age of array is 2.8 years. Age of floats in South Pacific requires replacement of floats soon. Most floats are either from the US or Australia. Requires dedicated ship time to sustain array. Array replacement in Atlantic by European Argo. The Kaharoa Argo-10 voyage (yellow symbols) is adding 107 floats between 20 o S and 45 o S. This is a US/NZ/Aus joint effort.

Real time data delivery : Over 90% of profiles within 24 hours surfacing transmitted as TESAC messages. Switching to BUFR format will allow QC flags. Improved processing at GDACs to allow near real-time access of netcdf files and Argo system QC test results. Delayed mode quality control: Common techniques developed and shared with all QC operators. - visual inspection and bad data removal. - salinity drift adjustment Backlog reduced; Over 80% of profiles older than 1 year QC’d. Many Argo equivalent floats presently are not scheduled for QC. Identified regional differences from climatology (Example southern hemisphere). - Developed technique to use data from early profiles from floats to provide climatology for older floats. - Need quick access to global CLIVAR repeat hydrography and other high-quality CTD data.

Zonal averages of T, S, and σ θ from Argo (contours), and the Argo- minus-WOA01 differences (colors). Roemmich and Gilson (2008). Argo era has significant salinity changes, particularly in southern mode waters Calibrating to pre-Argo climatology would remove signal. Use early data from Argo floats with no apparent drift as reference data set. Mode water change

Scientific Analyses of Argo Data Heat content changes presented in previous annual reviews, also included in Greg Johnson’s talk later in meeting - Clear signatures of warming once bad data and biases are taken into account Interpretation of salinity changes - A recent analysis by Durack and Wijffels Many other analyses are showing changes in ocean mode water properties and volumes

50 year trends in salinity Durack and Wijffels, J Climate 2010; historical data + Argo Sea Surface Salinity Trend E-P Zonal Sections, by Basin Enhanced water cycle Evaporative regions increasing salinity Regions of precipitation decreased salinity Mode water changes subducted into interior Argo array does not extend to high latitudes to observe salinity changes due ice melt

Summary The microleak problem has had a substantial impact on maintaining the global Argo array and on data quality. A 3000-instrument array has large inertia; problems affecting hundreds of floats are unfortunate, and should be avoided, but can be absorbed. Compare to what happens when a single satellite fails. Detection of these problems requires analyses of instrument performance and of the data set. This is a challenge for the program to maintain. High quality climate data sets require continually improving methodologies and significant attention to delayed mode quality control. Float technologies continue to advance (to be described by Roemmich later in meeting). Argo’s international partnership continues to grow. Excellent progress has been made in demonstrating the central role of Argo in a global observing system and its high value toward societal objectives.