Nonlinear planetary wave reflection in the troposphere

[1] Forty-four years (1958-2001) of daily data from two re-analysis data sets are used to investigate the occurrence of nonlinear reflection from planetary wave breaking (PWB). PWB is manifested in the large-scale and rapid irreversible overturning of potential vorticity (PV) contours on isentropic surfaces in the upper troposphere. PWB takes place as a midlatitude wave train propagates equatorward toward a region of weak background zonal flow. As breaking occurs wave propagation is no longer possible. Linear theory predicts that wave activity will be absorbed in the wave-breaking region following the event. Our results show that almost a third of all PWB events result in nonlinear reflection rather than absorption. The signature of the reflected wave train arching northward and downstream into midlatitudes is very similar to that of nonlinear reflection seen in a hierarchy of modeling studies.