Search Results

You are looking at 1 - 3 of 3 items for

  • Author or Editor: Brad DeYoung x
  • All content x
Clear All Modify Search
Richard J. Greatbatch, Youyu Lu, Brad DeYoung, and Jimmy C. Larsen

Abstract

A high-resolution, barotropic model of the North Atlantic is used to study the variation of transport through the Straits of Florida on timescales from a few days to seasonal. The model is driven by wind and atmospheric pressure forcing derived from ECMWF twice daily analyses for the years 1985, 1986, 1987, and 1988. The model-computed transports are compared with the cable-derived estimates of daily mean transport. Atmospheric pressure forcing is found to have an insignificant effect on the model results and can be ignored. A visual comparison between the model-computed transport and the cable data shows many similarities. Coherence squared between the two time series has peaks between 0.4 and 0.5 and is significant at the 95% confidence level in the period range from 6 to 100 days, with a drop in coherence near 10 days. The model overestimates the autospectral energy in the period range of 4 to 20 days but underestimates the energy at longer periods. The authors find that remote forcing to the north of the straits does not significantly affect coherence squared and phase between the model-computed transport and the cable data but is necessary to explain the autospectral energy in the model-computed transports at periods greater than 10 days. The most significant failing of the model is its inability to capture 8–10 mo timescale events in the cable data. Interestingly, the World Ocean Circulation Experiment Community Modeling Effort, driven by synoptic wind forcing, does exhibit roughly 8-month timescale events, as seen in the cable data but missed by the barotropic model.

Full access
Tara Howatt, Jaime B. Palter, John Brian Robin Matthews, Brad deYoung, Ralf Bachmayer, and Brian Claus

Abstract

Transport of freshwater from the Labrador Shelf into the interior Labrador Sea has the potential to impact deep convection via its influence on the salinity of surface waters. To examine this transport, the authors deployed two underwater gliders on a mission to traverse the continental shelf break multiple times between 5 July and 22 August 2014, the period when Arctic meltwater has historically peaked in transport down the Labrador Shelf. The field campaign yielded a unique dataset of temperature, salinity, and oxygen across the shelf break to a depth of 1000 m at unprecedented spatial resolution. Two mechanisms of cross-shelf transport were examined: Ekman transport and transport due to mesoscale eddies. Ekman transport is quantified using satellite wind stress and near-surface hydrographic properties, and eddy-induced transport is scaled using a parameterized eddy diffusivity and thickness gradients of layers of uniform potential density, as well as the tracer gradients along those isopycnals. Both the Ekman and eddy terms transport high-oxygen and low-salinity water from the shelf to the Labrador Sea during the field campaign. The influence of the eddy-driven oxygen flux from the shelf to the Labrador Sea on oxygen budgets depends strongly on the size of the region over which this eddy flux converges. The deduced offshore transport of freshwater (4 ± 6 mSv; 1 mSv = 103 m3 s−1) from both Ekman and eddy mechanisms, which is likely at a seasonal maximum during this summertime survey, represents about 3% of the annual-mean freshwater flowing through Hudson and Davis Straits but may be an important component of the total freshwater budget of the interior Labrador Sea.

Full access
M. Susan Lozier, Sheldon Bacon, Amy S. Bower, Stuart A. Cunningham, M. Femke de Jong, Laura de Steur, Brad deYoung, Jürgen Fischer, Stefan F. Gary, Blair J. W. Greenan, Patrick Heimbach, Naomi P. Holliday, Loïc Houpert, Mark E. Inall, William E. Johns, Helen L. Johnson, Johannes Karstensen, Feili Li, Xiaopei Lin, Neill Mackay, David P. Marshall, Herlé Mercier, Paul G. Myers, Robert S. Pickart, Helen R. Pillar, Fiammetta Straneo, Virginie Thierry, Robert A. Weller, Richard G. Williams, Chris Wilson, Jiayan Yang, Jian Zhao, and Jan D. Zika

Abstract

For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.

Full access