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Deep convection in the Irminger Sea forced by the Greenland tip jet

Abstract

Open-ocean deep convection, one of the processes by which deep waters of the world's oceans are formed, is restricted to a small number of locations (for example, the Mediterranean and Labrador seas). Recently, the southwest Irminger Sea has been suggested as an additional location for open-ocean deep convection. The deep water formed in the Irminger Sea has the characteristic temperature and salinity of the water mass that fills the mid-depth North Atlantic Ocean, which had been believed to be formed entirely in the Labrador basin. Here we show that the most likely cause of the convection in the Irminger Sea is a low-level atmospheric jet known as the Greenland tip jet, which forms periodically in the lee of Cape Farewell, Greenland, and is associated with elevated heat flux and strong wind stress curl. Using a history of tip-jet events derived from meteorological land station data and a regional oceanic numerical model, we demonstrate that deep convection can occur in this region when the North Atlantic Oscillation Index is high, which is consistent with observations. This mechanism of convection in the Irminger Sea differs significantly from those known to operate in the Labrador and Mediterranean seas.

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Figure 1: The Greenland tip jet depicted by the COAMPS weather model and observed by satellite.
Figure 2: A tip-jet event recorded by Greenlandic meteorological land stations.
Figure 3: Triggering of tip-jet events by passing storms.
Figure 4: Tip-jet-forced oceanic convection in a regional numerical model.
Figure 5: Observational support for tip-jet-forced deep convection east of Greenland.

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Acknowledgements

We thank L. Rasmussen for discussions about the meteorology around Greenland. The NSCAT surface winds were derived from the KU2000 retrieval provided by Remote Sensing Systems Inc. Support for this work was provided by the Ocean Sciences Division of the National Science Foundation.

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Correspondence to Robert S. Pickart.

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Pickart, R., Spall, M., Ribergaard, M. et al. Deep convection in the Irminger Sea forced by the Greenland tip jet. Nature 424, 152–156 (2003). https://doi.org/10.1038/nature01729

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