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The NAO troposphere–stratosphere connection

Ambaum, M. H. P. and Hoskins, B. J. (2002) The NAO troposphere–stratosphere connection. Journal of Climate, 15 (14). pp. 1969-1978. ISSN 1520-0442

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To link to this article DOI: 10.1175/1520-0442(2002)015<1969:TNTSC>2.0.CO;2

Abstract/Summary

Using monthly mean data, daily data, and theoretical arguments, relationships between surface pressure variations associated with the North Atlantic Oscillation (NAO), tropopause height, and the strength of the stratospheric vortex are established. An increase in the NAO index leads to a stronger stratospheric vortex, about 4 days later, as a result of increased equatorward refraction of upward-propagating Rossby waves. At tropopause level the effects of the enhanced NAO index and stratospheric polar vortex are opposite, resulting in a lower tropopause over Iceland and a higher tropopause over the Arctic. The raising of the Arctic tropopause leads to a stretching and spinup of the tropospheric column and is therefore associated with a lowering of the surface pressure near the North Pole. For monthly mean data it is found that a standard deviation increase in the NAO index is associated with a 10% increase in the strength of the stratospheric vortex, as measured by potential vorticity at 500 K. A simple theoretical model predicts that this is associated with about 300-m elevation of the Arctic tropopause, as is observed, and a 5-hPa lowering of the surface pressure at the North Pole. The effects of the spinup of the tropospheric column may project on the NAO pattern so that the stratosphere acts as an integrator of the NAO index.

Item Type:Article
Refereed:Yes
Divisions:Faculty of Science > School of Mathematical and Physical Sciences > Department of Meteorology
ID Code:7701
Publisher:American Meteorological Society

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