Winter cold of eastern continental boundaries induced by warm ocean waters

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Abstract

In winter, northeastern North America and northeastern Asia are both colder than other regions at similar latitudes. This has been attributed to the effects of stationary weather systems set by elevated terrain (orography)1, and to a lack of maritime influences from the prevailing westerly winds2. However, the differences in extent and orography between the two continents suggest that further mechanisms are involved. Here we show that this anomalous winter cold can result in part from westward radiation of large-scale atmospheric waves—nearly stationary Rossby waves—generated by heating of the atmosphere over warm ocean waters. We demonstrate this mechanism using simulations with an idealized general circulation model3,4,5, with which we show that the extent of the cold region is controlled by properties of Rossby waves, such as their group velocity and its dependence on the planetary rotation rate. Our results show that warm ocean waters contribute to the contrast in mid-latitude winter temperatures between eastern and western continental boundaries not only by warming western boundaries, but also by cooling eastern boundaries.

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Figure 1: Observational data for Northern Hemisphere winter months (December–February), averaged between 1970 and 2009.
Figure 2: Time-averaged fields simulated with the idealized GCM for planetary rotation rates of Ωe, 2 Ωe, 4 Ωe and 8 Ωe.
Figure 3: Extent of upstream cold region as a function of planetary rotation rate.

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Acknowledgements

We thank D. Abbot, I. Eisenman, X. Levine and T. Merlis for comments. This research was supported by the National Oceanic and Atmospheric Administration Climate and Global Change Postdoctoral Fellowship administered by the University Corporation for Atmospheric Research (Y.K.), by a David and Lucile Packard Fellowship (T.S.), and by a grant from the National Science Foundation (AGS-1019211). The simulations were performed on the California Institute of Technology's Division of Geological and Planetary Sciences Dell cluster.

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Y.K. and T.S. designed the study and wrote the paper; Y.K. performed the numerical simulations and data analyses.

Correspondence to Yohai Kaspi.

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Kaspi, Y., Schneider, T. Winter cold of eastern continental boundaries induced by warm ocean waters. Nature 471, 621–624 (2011). https://doi.org/10.1038/nature09924

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