Argo and synthesis products developed and served at the Asia-Pacific Data-Research Center

P. Hacker, N. Maximenko, J. Potemra, K. Lebedev, S. DeCarlo, Y. Shen

Corresponding author: P. Hacker, .

University of Hawaii, International Pacific Research Center, Honolulu, Hawaii, USA

Introduction

The Argo Program, which has developed over the past decade, is now providing some 10,000 vertical profiles of temperature and salinity every month. Since the Argo floats are globally distributed, the float data are now providing unprecedented information on the space/time evolution of the temperature and salinity fields in the upper 2000 meters of the global ocean. To help demonstrate the utility of the Argo data and to encourage its use for research and applications, many data centers and research activities have contributed to the distribution and utilization of Argo data (Freeland et al., 2009 and Pouliquen et al., 2009; OceanObs’09 White Papers).

As a contribution to this effort, in 2006 the Asia-Pacific Data-Research Center (APDRC) within the International Pacific Research Center (IPRC) at the University of Hawaii released its first technical report (Yoshinari, et al., 2006) and database (YoMaHa’05) of velocity estimates at the parking depth and at the sea surface for the global ocean determined from trajectories of the Argo floats. The database was updated and re-released in 2007 (Lebedev et al., 2007). Since May 2008, the APDRC has been releasing monthly updated versions of this database as part of the activities of the Pacific Argo Regional Center (PARC) and the CLIVAR/GSP Velocity Panel of the CLIVAR/ Global Synthesis and Observations Panel. As an example, the utility of the Argo float trajectory data for research purposes has been demonstrated in the Kuroshio Extension region (Chen et al., 2007; Qiu et al. 2008). The APDRC has continued to develop and serve this and other Argo-based and related synthesis products, and plans to continue these research and applications-based activities into the next decade. A primary motivation for this effort is to produce useful, near real-time products for a broad range of users, before all the quality control issues have been fully resolved, in order to both identify problems in the data set and provide early utility to users. This paper provides information on present product development and serving activities as well as some plans and suggestions for future efforts.

As overview, the APDRC is a climate data center that offers a web-based data and product server system, which provides access to a range of in situ, model-based and satellite-based products. Initiated in 2001, a primary motivation has been to provide easy access for the broad user community to the wide range of climate data and products, often underutilized due to lack of easy access. Working closely with our NOAA/PMEL partners, the center has implemented a data server system based on OPeNDAP (Hankin et al. 2009, OceanObs’09 White Paper), a format-neutral data transport protocol, in order to provide binary access to atmospheric, oceanic, and air/sea flux products via client-based software such as GrADS, Matlab, Ferret, and FORTRAN code. The system also includes a range of web-browsing servers including the Live Access Server (LAS), primarily for gridded products, and DAPPER/DChart for both gridded and in situ data.

Argo products, synthesis products and servers

With a robust data server system in place, the APDRC is shifting focus from server infrastructure to the production of value-added products using the new observing-system data such as those collected by Argo and satellite-based programs. To date, the APDRC has developed, and is currently serving, the following global data products based on Argo data from 2001 to the present:

  1. surface and deep velocities from float trajectories;
  2. profile data interpolated onto standard depth levels and isopycnals;
  3. ocean mixed layer, isothermal layer, and barrier layer depths; and
  4. statistics, climatologies, monthly, seasonal and annual averages of all variables.

Products 1-3 are downloadable in ASCII format from the APDRC (Home Page, Projects, Argo Products links) at Product 4 includes velocity parameters (zonal, meridional, and magnitude), profile parameters (potential temperature, salinity, depth, density anomalies, dynamic depth and spiciness), and mixed/barrier layer parameters. Global maps (Figure 1) are available as spatially bin-averaged products (both 1x1 and 3x3 degree bins) and include maps of the number of observations and the standard deviation for each bin. Regions without data are obvious. In addition, gridded/interpolated map products are available for temperature, salinity and absolute dynamic depth on standard levels; similar map products on isopycnals are under development and should be available in the coming year. Product 4 output is available as global maps (pictures), and ASCII and netCDF format files. It can also be accessed via the APDRC Home Page (Data and Server links) for users desiring OPeNDAP, LAS, and DAPPER/DChart access (Figure 2).

A major synthesis product under development is an estimate of the four-dimensional absolute dynamic topography, from which the geostrophic velocity field can be estimated. Absolute dynamic topography is computed using data from Argo floats, drifters, satellite wind and altimetry. The product is based on different ancillary products that could also be useful to some users. The process of developing the absolute dynamic topography involves the following:

  • mean surface dynamic topography, computed from drifter, wind and altimetry data;
  • instantaneous surface dynamic topography, obtained from Mean Dynamic Ocean Topography (MDOT) and AVISO sea level anomaly;
  • absolute dynamic topography at depth, calculated from Argo T/S profiles by integrating surface topography downward; and
  • horizontal gradient of absolute dynamic topography at Argo float parking depths, assessed from float velocities and geostrophy.

The AVISO and MDOT products are now available via the APDRC servers. When ready, the above products will also be available on servers. Absolute dynamic topography at 1000-meter depth from 2003-2007 is already available as images (.png files) and in ASCII format via the APDRC Argo Products page.

The above ADPRC activities were motivated in part from user feedback, which indicated that Argo data were underutilized to some degree because of difficulties in obtaining specific time/space subsets of the data from the Argo data assembly centers (GDACS). Because of the way Argo data are stored at the GDACS, it is neither easy nor straight forward for a general user to obtain, for example, T and S in a specific region (covered by several floats) or at a location over a specific time range. The APDRC efforts help users by creating binned T/S data, which are further interpolated onto a vertical and horizontal grid. Since some users prefer to do their own interpolation, we prepare two different products: one gridded vertically at standard depths and the other gridded horizontally. Argo-derived in situ temperature is used along with salinity to compute potential temperature and potential density. T/S/ is then interpolated to standard depth levels (Levitus, 1982). This product is designed for modelers, who typically want a vertically gridded product to validate their model or to use for assimilation. Another product includes an interpolation in the horizontal , nominally of 1x1 degree resolution. These products are based on 10-daily downloads of the profile and trajectory files from the US GDAC. Mixed layer depth, and barrier layer thickness are produced from the above T/S/ data. The absolute dynamic height and absolute geostrophic velocity products are under development. Additional technical information, including a description of the variational analysis used in the three-dimensional interpolation, and documentation are available at

Future activities and suggestions

The APDRC plans to continue to support Argo product development and PARC activities in the coming decade. A quasi-automated system is now in place that enables 10-daily, near-realtime updates of all products. Any problems in the original data, detected during this project and/or reported by the users of our products, are documented and forwarded to the specific DACs hosting the problematic data. Climatologies and other products will be recomputed when/if the original data are significantly improved by DACs. Periodic updates will also be done as the “delayed mode” Argo data (i.e., more thoroughly quality-controlled) become available.

Future product development at the APDRC will include the combined use of Aquarius sea surface salinity data with Argo data to provide global products on the space/time variability of oceanic salinity fields and regional salinity fronts.

In order to offer increasing utility in the future to the broad user community including applications, management, and the general public (in addition to the traditional research communities), we plan to make products available via Google Earth, Goggle Map and Geospatial Information System (GIS) formats.

Since a variety of Argo products are currently being produced by several centers and by individual researchers, we suggest hosting an “open work space” (either on our website or on the new web-site proposed by IFREMER) for product demonstration, evaluation, and intercomparison, and for comments and discussion. The goal would be to increase product quality and utility. Since there are several groups producing Argo products, perhaps the Argo Steering Team could play a more active role: cataloging, coordinating, assessing, and providing guidance for new products for user groups.

Acknowledgements

IPRC data center activities are supported by grants from JAMSTEC, NASA and NOAA. Our NOAA/PMEL partners have been instrumental in building our server infrastructure.

References

Chen, S., B. Qiu, and P. Hacker, 2007: Profiling float measurements of the recirculation gyre south of the Kuroshio Extension in May-November 2004, J. Geophys. Res., 112, C05023, doi:10.1029/2006JC004005.

Levitus, S., 1982: Climatological Atlas of the World Ocean, NOAA Professional Paper 13, 173 pp.

Lebedev, K.V., H. Yoshinari, N. A. Maximenko, and P. W. Hacker, 2007: YoMaHa'07: Velocity data assessed from trajectories of Argo floats at parking level and at the sea surface, IPRC Tech. Note No.4(2), 16 p.

Qiu, B., S. Chen, P. Hacker, N.G. Hogg, S.R. Jayne and H. Sasaki, 2008. The Kuroshio Extension northern recirculation gyre: profiling float measurements and forcing mechanism. J. Phys. Oceanogr., 38, 1764-1779.

Yoshinari, H., N. A. Maximenko, and P. W. Hacker, 2006: YoMaHa'05: Velocity data assessed from trajectories of Argo floats at parking level and at the sea surface, IPRC Tech. Note No.4, 20 p.

Figure 1. Example plots that can be made from the APDRC Argo products: (a) temperature at 200 m depth in June 2009; (b) 3°x3° bin-averaged salinity at 200 m depth in June 2009; (c) ensemble mean 1° x 1° bin-averaged salinity on σθ = 26.80 isopycnal; (d) deep ensemble mean 1° x 1° bin-averaged velocity in cm/s.

Figure 2. Web-page for OPeNDAP access to Argo products and other data sets (In-situ Observations) at the APDRC: