An assessment of the XBT Fall-Rate Equation in the Southern Ocean

An assessment of the XBT Fall-Rate Equation in the Southern Ocean AbstractIn this study, a set of 157 collocated XBT (DB/T7 type) and CTD stations distributed across three different regions of the Southern Ocean is explored using the manufacturer’s fall rate equation (FRE), a classic correction method and new correction methods, as to investigate how the regional environment characteristics may impact probe’s descent and the corresponding depth estimates. Regional coefficients were estimated to all three basins and to the Southern Ocean as a whole. The manufacturer’s FRE proved to perform better in high latitudes than in the rest of the world ocean, overestimating true depth by only 2%. The overall depth bias was positive, further supporting the hypothesis of a regional dependence of the XBT fall-rate on water temperature, which leads to a general overestimation of Ocean Heat Content in the upper layer (~4.79 x 109J/ or ~10%). Pure thermal bias was found to be mostly negative, which is likely to be related to temperature errors. However, the Southern Ocean region is notoriously undersampled when compared to the rest of the world ocean as well as it is associated with strong spatial and temporal variability thus raising the overall uncertainty on that estimate. Moreover, although the manufacturer’s FRE has a satisfying performance in the Southern Ocean, the current community recommended correction method still leads to improved temperature values in those waters. Finally, more studies are needed in order to fully understand the XBT regional bias and its implications for climate studies in the region. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Atmospheric and Oceanic Technology American Meteorological Society

An assessment of the XBT Fall-Rate Equation in the Southern Ocean

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0426
D.O.I.
10.1175/JTECH-D-17-0086.1
Publisher site
See Article on Publisher Site

Abstract

AbstractIn this study, a set of 157 collocated XBT (DB/T7 type) and CTD stations distributed across three different regions of the Southern Ocean is explored using the manufacturer’s fall rate equation (FRE), a classic correction method and new correction methods, as to investigate how the regional environment characteristics may impact probe’s descent and the corresponding depth estimates. Regional coefficients were estimated to all three basins and to the Southern Ocean as a whole. The manufacturer’s FRE proved to perform better in high latitudes than in the rest of the world ocean, overestimating true depth by only 2%. The overall depth bias was positive, further supporting the hypothesis of a regional dependence of the XBT fall-rate on water temperature, which leads to a general overestimation of Ocean Heat Content in the upper layer (~4.79 x 109J/ or ~10%). Pure thermal bias was found to be mostly negative, which is likely to be related to temperature errors. However, the Southern Ocean region is notoriously undersampled when compared to the rest of the world ocean as well as it is associated with strong spatial and temporal variability thus raising the overall uncertainty on that estimate. Moreover, although the manufacturer’s FRE has a satisfying performance in the Southern Ocean, the current community recommended correction method still leads to improved temperature values in those waters. Finally, more studies are needed in order to fully understand the XBT regional bias and its implications for climate studies in the region.

Journal

Journal of Atmospheric and Oceanic TechnologyAmerican Meteorological Society

Published: Feb 28, 2018

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