Partitioning between resolved wave forcing and unresolved gravity wave forcing to the quasi-biennial oscillation as revealed with a coupled chemistry-climate model

Abstract

The quasi-biennial oscillation (QBO) in the equatorial stratosphere is simulated with general circulation models that include full stratospheric chemistry. One model treats ozone as an interactive species between radiation and chemistry, while the other treats it as a non-interactive species. The dynamical module employs T42 truncation and 68 layers with vertical spacing of about 500 m in the stratosphere. A non-orographic gravity wave drag scheme and the weakening of the horizontal diffusion are also introduced. QBOs of about 27 and 31 months periods are reproduced by the two models. Resolved wave and unresolved gravity wave forcings are found to be of similar magnitude, but their temporal behaviors have different phase relations to zonal-mean zonal wind. The resolved waves exert eastward forcing mainly in the westward-wind phase, while the unresolved gravity waves deposit eastward momentum mostly in the eastward-wind phase. Similar temporal partitioning can be seen in the westward acceleration period. Copyright 2005 by the American Geophysical Union.