Circulation

How has Earth's atmospheric circulation changed during the past?
How will it respond to future anthropogenic forcing?



Last millennium North Atlantic jet stream changes

Variations in the North Atlantic jet stream – currents of strong prevailing westerly winds situated over the mid-latitudes – play an important role in modulating North American and European weather, economics, ecosystems, intercontinental transport, and commerce. A number of studies have suggested increased variability and (or) shifts in the position and intensity of the North Atlantic jet stream across recent decades, possibly due to anthropogenic greenhouse gas-induced temperature increases. However, discerning the long-term significance of these changes has been challenged by a lack of long-term jet-stream observations, which in general are not available prior to the 20th century. This lack of direct observations is further challenged by the fact that climate “proxies” found at Earth’s surface are most often not explicitly sensitive to high-altitude atmospheric changes.

Myself, along with colleagues at the University of Hawaii, Desert Research Institute, and Woods Hole Oceanographic Institution, are attempting to address this limitation. By using a unique compilation of many high-elevation ice core records extracted from across the Greenland Ice Sheet, as well as a new ensemble of last millennium climate model simulations, we’re developing the first ever millennium-length, model-validated statistical reconstruction of the North Atlantic jet stream. Our results are being used to constrain the following questions:

Has the North Atlantic jet changed during periods of natural warming and cooling during the last millennium?
How do these changes compare to modeled future changes under “business-as-usual” scenarios?

Reconstruction of the North Atlantic jet stream (via zonal mean zonal winds at 850 hPa) from Greenland ice cores. From Osman et al. (in revision at PNAS).

Northern Hemisphere atmospheric circulation shifts across the last deglaciation

coming soon!


References

  • Osman, M. et al.: A thirteen-century context for North Atlantic jet stream projections. in revision.