Rossby Wave Breaking and Nonlinear Reflection
wave breaking (PWB), or Rossby wave breaking, occurs when large
quasi-stationary waves impinge upon regions of weak zonal flow (usually
subtropics). In doing so potential vorticity contours as irreversibly deformed
about the subtropical tropopause – permitting for
the large scale mixing of air between the subtropics and extratropics.
Occurrences of PWB as they impinge upon the weak winds of the
akin to ocean waves breaking as they impinge upon the shallow waters
shoreline. I recently found
observational evidence for PWB to produce nonlinear reflection polewards. In other
words as a large amplitude equatorward
wave breaks in the subtropics it reflects some of the incipient wave
into the midlatitudes downstream of the
Dr. Gudrun Magnusdottir,
have found evidence for nonlinear reflection following PWB. This
entails that wave activity is reversed and a reflected wave train
emerges poleward and downstream of the breaking region in the days
following the break.
Abatzoglou, J.T., Magnusdottir, G. 2004.
Nonlinear planetary wave reflection in the troposphere. GRL, Vol. 31,
No. 9., doi:10.1029/2004GL019495
A full 46 year climatology of PWB (MATLAB binary w/dates,
location of breaking events)
performed by looking for breaking on multiple isentropic surfaces which
intersect the subtropical tropopause. The seasonal cycle of the
"surf zone" is intricately linked to the subtropical jet.
Connections are also found to the monsoonal circulation over
Asia. We report on links to several climate modes (East Asian
Summer Monsoon, ENSO, NAO). Finally we discuss in more detail
nonlinear reflection and the impact that the background flow has in
permitting for reflection to occur.
Abatzoglou, J.T.; Magnusdottir, G. 2006, Planetary Wave Breaking and Nonlinear Reflection: Seasonal Cycle and Interannual Variability, Journal of Climate, Vol. 19, No. 23, pp 6139-6152
A very interesting connection
reflective and non-reflective events and the intraseasonal NAO was
found by analyzing breaking events during DJFM over the Atlantic
sector. It turns out that non-reflective events lead to a
profound increase in the intraseasonal NAO, while reflective events
lead to its demise and reversal. Eddy-momentum flux arguments are
key in fostering this relationship.
IV. Going back to the original observations of planetary wave breaking by McIntyre and Palmer (1983) we implement our PWB diagnostic techniques to the three-dimensional stratospheric polar vortex. Wave breaking in the stratosphere is observed to occur either in the upper-stratosphere (above 5hPa) or in the middle stratosphere (near 30hPa). The impacts of PWB on the mean flow can be rather impressive. For reflective events, wave activity is focused poleward leading to a wave driving at high latitudes that propagates downward into the upper-troposphere over the period of a few weeks - potentially impacting the NAM/AO.