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Most estimates of global oceanic heat content are carried out by integrating temperature from the surface to a fixed depth (e.g. Ishii et al.; Levitus et al.; Polyakov et al. ; Lyman et al. ). While this approach is straight forward, it is vulnerable to the influence of circulation changes and transient phenomena via vertical displacements of the thermocline. The HadGOA approach is to instead carry out the integration from the surface to a fixed isotherm. This method reduces the influence of vertical displacements of the thermocline on the derived analyses.
HadGOA analyses are subsurface thermal diagnostics computed to a number of fixed isotherms and fixed depths at monthly resolution. The data are gridded on a 2-degree grid using the quality-controlled observational data from ENACT/ENSEMBLES
(Enhanced Ocean Data Assimilation and Climate Prediction) for the period 1956-2004. Data products include time series of isotherm depth and heat content anomaly (relative to 1956-2004) and spatial maps of depth/temperature/heat content changes associated with each isotherm. The HadGOA analyses will soon include near real-time updates using Argo data and will be made freely available for use by the climate research community
A time series of global 0-700 m ocean heat content anomalies with uncertainty estimates is available from the download page. This new dataset is based on the latest version of the EN3 dataset.
The figure below shows the difference in the mean observed ocean state for 1985-2004 minus 1961-1980: a) the mean temperature above the 12°C isotherm; and b) the mean depth of the 12°C isotherm. Positive values indicate a warming above the isotherm or deepening of the isotherm in the latter period.
HadGOA poster for NERC RAPID annual meeting, 18th-21st June 2007
A comprehensive list of subsurface ocean observations can be found at: www.marineclimatology.net
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