Harnik N., R, K. Scott, and J. Perlwitz, 2003:  Wave reflection and focusing prior
to the major stratospheric warming of September 2002. Submitted to JAS.

Abstract:

Observations and analysis are presented for the 2002 winter in the
Southern Hemisphere, considering in particular events and conditions
during the early and mid winter that may have contributed to the major
warming in late September.  Various zonal mean flow and wave
quantities are examined, including the location of the zero wind line,
vortex strength, and wave geometry, all of which are shown to have
been anomalous during much of the 2002 winter.  The event that
appeared to set the stage for the major warming occurred as early as
mid May, comprising a large burst of wave flux into the stratosphere
and a strong deceleration of the vortex during its early stage of
development, as well as a deceleration of the zonal winds at low
latitudes.  The resulting low-latitude easterlies in turn contributed
to the poleward focusing of wave activity in the mid and upper
stratosphere during the rest of the winter.  The altered wave geometry
of the 2002 vortex allowed internal reflection of traveling wave 2,
which was consequently observed to be persistent for much of the
winter.  The actual major warming itself is shown to result from
superposition of a stationary wave-1 event with the traveling wave-2.
Conditions contributing to the likelihood of such a superposition include
both the weaker, preconditioned vortex that resulted from the poleward
wave focusing during the winter and the persistence of the traveling
wave 2.