Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.a11b0087e&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #A11B-0087
Physics
3300 Meteorology And Atmospheric Dynamics, 3319 General Circulation, 3337 Numerical Modeling And Data Assimilation, 3362 Stratosphere/Troposphere Interactions
Scientific paper
The Northern Annular Mode (NAM) is the leading mode of variability in the Northern Hemisphere. The NAM consists of a meridional dipole of the zonal mean zonal wind that extends into the stratosphere during the winter season. During the high index state of the NAM, high latitude westerly winds are stronger than normal leading to a stronger and colder polar vortex. Several studies have shown that the zonal wind anomalies associated with the NAM are forced primarily by planetary waves. Previous work on the propagation of planetary waves revealed that a subtropical heat source is able to generate planetary waves that then propagate toward high latitudes. Thus, it is possible that at least part of the NAM forcing has tropical origins. In this study a simple dry primitive equation AGCM without topography is used to demonstrate that NAM variability can indeed be forced by a subtropical heat source. Both the depth of the heat source and the stratospheric temperature distribution are shown to be critical parameters affecting the propagation of the planetary waves and their interaction with the zonal winds. These results will be contrasted with similar model runs using a midlatitude heat source.
Eichelberger Scott J.
Holton James R.
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