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Variability of North Atlantic heat transport observed from instrument data (Gulf Stream)
http://www.eurekalert.org/pub_releases/2012-01/agu-ajh011312.php[font face=Times,Times New Roman,Serif][font size=5]Variability of North Atlantic heat transport observed from instrument data[/font]
[font size=3]The Atlantic meridional overturning circulation (AMOC), which transports warm water northward and cold water back southward, redistributes energy throughout the North Atlantic Ocean. Some models predict that AMOC will slow down as Earth's temperatures rise due to anthropogenic warming, which could have serious climate consequences for the Northern Hemisphere. However, the response of AMOC to global warming is uncertain-different models predict different rates of slowdown-and there have been few continuous observations of AMOC heat transport. Two research groups have analyzed almost 10 years of ocean instrument data and compared it to the models' predictions.
Drawing on a decade of observations from the Meridional Overturning Variability Experiment (MOVE), Send et al. report for the first time the detection of strong interannual and decadal shifts in the strength of the AMOC. MOVE comprises moored instruments at three sites spread east-west over a 1,000-kilometer (621- mile) region near the Antilles Islands in the western tropical Atlantic that have been collecting temperature, conductivity, and pressure measurements since 2000. The information allowed the authors to calculate how the southbound stretch of the AMOC varied from January 2000 to June 2009. They find that the cold-water flow rate could vary substantially, ranging between 12 and 30 Sv (1 Sv = 1 million cubic meters per second, or 35 million cubic feet per second) during the study period. Further, they show that the AMOC's flow rate declined by 3 Sv over the 10-year period, corroborating recent modeling efforts. On the basis of the intricacies of their observations, and on the agreement with circulation models, the authors suggest that the decade-long drop in the strength of the AMOC is the product of long-term natural variability and need not be a consequence of recent climate change.
In a separate study, Hobbs and Willis used temperature, salinity, and displacement data measured from floats in the Argo array, combined with sea surface heights measured by satellites, to estimate a continuous time series of Atlantic meridional heat transport from 2002 to 2010 at 41 degrees north latitude. They find the mean heat transport is about 0.5 petawatts. The authors note that this estimate is consistent with previous studies in similar latitudes based on atmospheric flux data but is lower than most hydrographic estimates. Heat transport varies on an annual cycle as well as on shorter time scales, with atmospheric variability explaining most of the short-term variance. Hobbs and Willis note that the period of study was too short to infer any long-term trends, and they emphasize the need for continued monitoring of AMOC.
Send et al. Source: Geophysical Research Letters, doi:10.1029/2011GL049801, 2011
http://dx.doi.org/10.1029/2011GL049801
Title: Observation of decadal change in the Atlantic meridional overturning circulation using 10 years of continuous transport data
Authors: Uwe Send and Matthias Lankhorst: Scripps Institution of Oceanography, La Jolla, California, USA;
Torsten Kanzow: Leibniz Institute of Marine Sciences, Kiel, Germany.
Hobbs and Willis Source: Journal of Geophysical Research-Oceans, doi:10.1029/2011JC007039, 2012
http://dx.doi.org/10.1029/2011JC007039
Title: Midlatitude North Atlantic heat transport: A time series based on satellite and drifter data
Authors: Will R. Hobbs and Joshua K. Willis: NASA Jet Propulsion Laboratory, California, Institute of Technology, Pasadena, California, USA.[/font][/font]
[font size=3]The Atlantic meridional overturning circulation (AMOC), which transports warm water northward and cold water back southward, redistributes energy throughout the North Atlantic Ocean. Some models predict that AMOC will slow down as Earth's temperatures rise due to anthropogenic warming, which could have serious climate consequences for the Northern Hemisphere. However, the response of AMOC to global warming is uncertain-different models predict different rates of slowdown-and there have been few continuous observations of AMOC heat transport. Two research groups have analyzed almost 10 years of ocean instrument data and compared it to the models' predictions.
Drawing on a decade of observations from the Meridional Overturning Variability Experiment (MOVE), Send et al. report for the first time the detection of strong interannual and decadal shifts in the strength of the AMOC. MOVE comprises moored instruments at three sites spread east-west over a 1,000-kilometer (621- mile) region near the Antilles Islands in the western tropical Atlantic that have been collecting temperature, conductivity, and pressure measurements since 2000. The information allowed the authors to calculate how the southbound stretch of the AMOC varied from January 2000 to June 2009. They find that the cold-water flow rate could vary substantially, ranging between 12 and 30 Sv (1 Sv = 1 million cubic meters per second, or 35 million cubic feet per second) during the study period. Further, they show that the AMOC's flow rate declined by 3 Sv over the 10-year period, corroborating recent modeling efforts. On the basis of the intricacies of their observations, and on the agreement with circulation models, the authors suggest that the decade-long drop in the strength of the AMOC is the product of long-term natural variability and need not be a consequence of recent climate change.
In a separate study, Hobbs and Willis used temperature, salinity, and displacement data measured from floats in the Argo array, combined with sea surface heights measured by satellites, to estimate a continuous time series of Atlantic meridional heat transport from 2002 to 2010 at 41 degrees north latitude. They find the mean heat transport is about 0.5 petawatts. The authors note that this estimate is consistent with previous studies in similar latitudes based on atmospheric flux data but is lower than most hydrographic estimates. Heat transport varies on an annual cycle as well as on shorter time scales, with atmospheric variability explaining most of the short-term variance. Hobbs and Willis note that the period of study was too short to infer any long-term trends, and they emphasize the need for continued monitoring of AMOC.
Send et al. Source: Geophysical Research Letters, doi:10.1029/2011GL049801, 2011
http://dx.doi.org/10.1029/2011GL049801
Title: Observation of decadal change in the Atlantic meridional overturning circulation using 10 years of continuous transport data
Authors: Uwe Send and Matthias Lankhorst: Scripps Institution of Oceanography, La Jolla, California, USA;
Torsten Kanzow: Leibniz Institute of Marine Sciences, Kiel, Germany.
Hobbs and Willis Source: Journal of Geophysical Research-Oceans, doi:10.1029/2011JC007039, 2012
http://dx.doi.org/10.1029/2011JC007039
Title: Midlatitude North Atlantic heat transport: A time series based on satellite and drifter data
Authors: Will R. Hobbs and Joshua K. Willis: NASA Jet Propulsion Laboratory, California, Institute of Technology, Pasadena, California, USA.[/font][/font]
