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Levitus S.,East-West Center | Antonov J.I.,National Oceanographic Data Center | Boyer T.P.,East-West Center | Baranova O.K.,East-West Center | And 7 more authors.
Geophysical Research Letters | Year: 2012

We provide updated estimates of the change of ocean heat content and the thermosteric component of sea level change of the 0-700 and 0-2000m layers of the World Ocean for 1955-2010. Our estimates are based on historical data not previously available, additional modern data, and bathythermograph data corrected for instrumental biases. We have also used Argo data corrected by the Argo DAC if available and used uncorrected Argo data if no corrections were available at the time we downloaded the Argo data. The heat content of the World Ocean for the 0-2000m layer increased by 24.01.9 × 1022 J (2S.E.) corresponding to a rate of 0.39Wm-2 (per unit area of the World Ocean) and a volume mean warming of 0.09C. This warming corresponds to a rate of 0.27Wm-2 per unit area of earth's surface. The heat content of the World Ocean for the 0-700m layer increased by 16.71.6 × 10 22 J corresponding to a rate of 0.27Wm-2 (per unit area of the World Ocean) and a volume mean warming of 0.18C. The World Ocean accounts for approximately 93% of the warming of the earth system that has occurred since 1955. The 700-2000m ocean layer accounted for approximately one-third of the warming of the 0-2000m layer of the World Ocean. The thermosteric component of sea level trend was 0.54.05mmyr-1 for the 0-2000m layer and 0.41.04mmyr-1 for the 0-700m layer of the World Ocean for 1955-2010. © Copyright 2012 by the American Geophysical Union. Source


Chu P.C.,Naval Postgraduate School, Monterey | Tokmakian R.T.,Naval Postgraduate School, Monterey | Fan C.,Naval Postgraduate School, Monterey | Charles Sun L.,National Oceanographic Data Center
Journal of Atmospheric and Oceanic Technology | Year: 2015

Optimal spectral decomposition (OSD) is applied to ocean data assimilation with variable (temperature, salinity, or velocity) anomalies (relative to background or modeled values) decomposed into generalized Fourier series, such that any anomaly is represented by a linear combination of products of basis functions and corresponding spectral coefficients. It has three steps: 1) determination of the basis functions, 2) optimal mode truncation, and 3) update of the spectral coefficients from innovation (observational increment). The basis functions, depending only on the topography of the ocean basin, are the eigenvectors of the Laplacian operator with the same lateral boundary conditions as the assimilated variable anomalies. The Vapnik-Chervonkis dimension is used to determine the optimal mode truncation. After that, the model field updates due to innovation through solving a set of a linear algebraic equations of the spectral coefficients. The strength and weakness of the OSD method are demonstrated through a twin experiment using the Parallel Ocean Program (POP) model. © 2015 American Meteorological Society. Source


Storto A.,Centro Euro Mediterraneo sui Cambiamenti Climatici | Masina S.,Centro Euro Mediterraneo sui Cambiamenti Climatici | Balmaseda M.,European Center for Medium Range Weather Forecast | Guinehut S.,Collecte Localisation Satellites | And 36 more authors.
Climate Dynamics | Year: 2015

Quantifying the effect of the seawater density changes on sea level variability is of crucial importance for climate change studies, as the sea level cumulative rise can be regarded as both an important climate change indicator and a possible danger for human activities in coastal areas. In this work, as part of the Ocean Reanalysis Intercomparison Project, the global and regional steric sea level changes are estimated and compared from an ensemble of 16 ocean reanalyses and 4 objective analyses. These estimates are initially compared with a satellite-derived (altimetry minus gravimetry) dataset for a short period (2003–2010). The ensemble mean exhibits a significant high correlation at both global and regional scale, and the ensemble of ocean reanalyses outperforms that of objective analyses, in particular in the Southern Ocean. The reanalysis ensemble mean thus represents a valuable tool for further analyses, although large uncertainties remain for the inter-annual trends. Within the extended intercomparison period that spans the altimetry era (1993–2010), we find that the ensemble of reanalyses and objective analyses are in good agreement, and both detect a trend of the global steric sea level of 1.0 and 1.1 ± 0.05 mm/year, respectively. However, the spread among the products of the halosteric component trend exceeds the mean trend itself, questioning the reliability of its estimate. This is related to the scarcity of salinity observations before the Argo era. Furthermore, the impact of deep ocean layers is non-negligible on the steric sea level variability (22 and 12 % for the layers below 700 and 1500 m of depth, respectively), although the small deep ocean trends are not significant with respect to the products spread. © 2015 Springer-Verlag Berlin Heidelberg Source


Cheng L.,CAS Institute of Atmospheric Physics | Abraham J.,Thomas University | Goni G.,National Oceanic and Atmospheric Administration | Boyer T.,National Oceanographic Data Center | And 13 more authors.
Bulletin of the American Meteorological Society | Year: 2016

Expendable bathythermograph (XBT) data were the major component of the ocean temperature profile observations from the late 1960s through the early 2000s, and XBTs still continue to provide critical data to monitor surface and subsurface currents, meridional heat transport, and ocean heat content. Systematic errors have been identified in the XBT data, some of which originate from computing the depth in the profile using a theoretically and experimentally derived fall-rate equation (FRE). After in-depth studies of these biases and discussions held in several workshops dedicated to discussing XBT biases, the XBT science community met at the Fourth XBT Science Workshop and concluded that XBT biases consist of 1) errors in depth values due to the inadequacy of the probe motion description done by standard FRE and 2) independent pure temperature biases. The depth error and temperature bias are temperature dependent and may depend on the data acquisition and recording system. In addition, the depth bias also includes an offset term. Some biases affecting the XBT-derived temperature profiles vary with manufacturer/probe type and have been shown to be time dependent. Best practices for historical XBT data corrections, recommendations for future collection of metadata to accompany XBT data, impact of XBT biases on scientific applications, and challenges encountered are presented in this manuscript. Analysis of XBT data shows that, despite the existence of these biases, historical XBT data without bias corrections are still suitable for many scientific applications, and that bias-corrected data can be used for climate research. ©2016 American Meteorological Society. Source


Boyer T.,National Oceanographic Data Center | Gopalakrishna V.V.,National Institute of Oceanography of India | Reseghetti F.,New Energy Technologies | Naik A.,National Institute of Oceanography of India | And 5 more authors.
Journal of Atmospheric and Oceanic Technology | Year: 2011

Long time series of XBT data in the Bay of Bengal and the Arabian Sea are valuable datasets for exploring and understanding climate variability. However, such studies of interannual and longer-scale variability of temperature require an understanding, and, if possible, a correction of errors introduced by biases in the XBT and expendable conductivity-temperature-depth (XCTD) data. Two cruises in each basin were undertaken in 2008/09 on which series of tests of XBTs and XCTDs dropped simultaneously with CTD casts were performed. The XBT and XCTD depths were corrected by comparison with CTD data using a modification of an existing algorithm. Significant probe-to-probe fall-rate equation (FRE) velocity and deceleration coefficient variability was found within a cruise, as well as cruise-to-cruise variability. A small (~0.01°C) temperature bias was also identified for XBTs on each cruise. No new FRE can be proposed for either the Bay of Bengal or the Arabian Sea for XBTs. For the more consistent XCTD, basin-specific FREs are possible for the Bay of Bengal, but not for the Arabian Sea. The XCTD FRE velocity coefficients are significantly higher than the XCTD manufacturers' FRE coefficient or those from previous tests, possibly resulting from the influence of temperature on XCTD FRE. Mean temperature anomalies versus a long-term mean climatology for XBT data using the present default FRE have a bias (which is positive for three cruises and negative for one cruise) compared to the mean temperature anomalies for CTD data. Some improvement is found when applying newly calculated cruise-specific FREs. This temperature error must be accounted for in any study of temperature change in the regions. © 2011 American Meteorological Society. Source

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