Stratosphere influences currents in North Atlantic

Scientists of the University of Utah and the Max Planck Institute for Meteorology (MPI-M) in Hamburg pointed out an up to now unknown correlation between the upper atmosphere and the ocean in their paper published in “Nature Geoscience”.

Thomas Reichler and Junsu Kim of the University of Utah in Salt Lake City, USA, revealed together with Elisa Manzini and Jürgen Kröger of MPI-M in their study that high altitude winds (15 to 30 miles) directly influence the ocean circulation in the North Atlantic. It was known that decadal variations in climate and currents in the North Atlantic occur, but the fact that the stratosphere plays a role in it, is new. The discovery of this correlation has effects on the climate projections for the coming decades, too.

The stratosphere affects the troposphere below it, where weather occurs, and the troposphere in turn affects the ocean below it. Up to now it has not been possible to prove how the direct link works. By using 30-year of meteorological and oceanographic data as well as long simulations performed with climate models, the authors have demonstrated the stratosphere to ocean connection.







This simplified illustration shows the newly discovered influence of stratospheric temperatures and winds (polar vortex) on the ocean circulation in the North Atlantic. Credit: Thomas Reichler, University of Utah.










Striking parallels became obvious in the data from the last 30 years: when the stratosphere over the Arctic, in the polar vortex, warmed up to an unusual degree and strong winds decreased, the ocean currents in the North Atlantic changed as well. These mitigations of the polar vortex were observed in the 1980s and 2000s, but not in the 1990s. In parallel, 12 different ocean-reanalyses implied changes in the Atlantic Meridional Overturning Circulation (AMOC): According to this the AMOC decreased in the 1980s and 2000s, but not in the 1990s. That implies a correlation between the stratospheric circulation and the changes of the ocean current in the North Atlantic.

The results were verified with the help of long-term calculations (4.000 years) with the GFDL model and the Multi-Model Analysis of the Coupled Model Intercomparison Project Phase 5 (CMIP5). The simulations made obvious that variations of the polar vortex cause a reaction of the ocean currents, too. This influence implies for the Atlantic itself that perturbations at the ocean surface penetrate into the deeper ocean and thereby affect how much cold water sinks to greater depths and how much warm water flows from the south via the Gulf Stream.

The study was carried out with the help of the EU project COMBINE, which is coordinated at the MPI-M.


Paper:


T. Reichler, J. Kim, E. Manzini and J. Kröger: A stratospheric connection to Atlantic climate variability. Nature Geoscience, Letters, doi:10.1038/ngeo1586, published online. http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1586.html


Further information:


Initiative “Stratosphere and Climate” at MPI-M:
http://www.mpimet.mpg.de/en/science/the-atmosphere-in-the-earth-system/initiatives/stratosphere-and-climate.html

Thomas Reichler, University of Utah: http://www.inscc.utah.edu/~reichler/

Press release: http://unews.utah.edu/news_releases/stratosphere-targets-deep-sea-to-shape-climate/


Contact:


Dr. Elisa Manzini
Max Planck Institute for Meteorology
Phone: +49 – 40 41173 317
Email: Opens window for sending emailelisa.manzini@we dont want spamzmaw.de

Dr. Jürgen Kröger
Max Planck Institute for Meteorology
Phone: +49 – 40 41173 371
Email: Opens window for sending emailjuergen.kroeger@we dont want spamzmaw.de