Perlwitz, J., and N. Harnik, 2003.  Downward coupling between the stratosphere and troposphere: The

relative roles of wave and zonal mean processes.



Wave and zonal mean features of the downward

dynamic coupling between the stratosphere and troposphere are compared

by applying a time-lagged singular values decomposition

analysis to Northern Hemisphere height fields decomposed into zonal

mean and its deviations. It is found that both zonal and wave

components contribute to the downward interaction, with zonal wave 1

(due to reflection) dominating on the short time scale (up to 12 days)

and the zonal mean {\bf (due to wave-mean flow interaction)} dominating on

the longer time scale. It is further shown that the two processes

dominate during different years, depending on the state of the

stratosphere. Winters characterized by a basic state that is

reflective for wave 1 show strong correlations (and covariance) for

wave 1 components when the stratosphere is leading and no relationship

in the zonal mean. On the other hand, winters characterized by a

stratospheric state that does not reflect waves show a strong

correlation only in the zonal mean fields. {\bf This study suggests that

downward reflection of waves (primarily of zonal wavenumber 1) is a

significant component of troposphere/stratosphere dynamics.}