The Life Cycle of Northern Hemisphere Upward Wave Coupling between the Troposphere and Stratosphere (Formerly Poster 34)

The composite lifecycle of Northern Hemisphere upward wave coupling between the troposphere and stratosphere is examined. Upward wave coupling events are defined as extreme positive values of the leading principle component of the daily wave-1 meridional heat flux at 30 hPa. The principle component encodes both the temporal and spatial variability of the heat flux, which is concentrated in high latitudes.

During the onset stage of the life cycle a large amplitude westward propagating high-latitude wave-1 anomaly develops and dominates the geopotential height anomaly with a secondary contribution from wave-2. The geopotential height anomalies occur in conjunction with an intensification of the Pacific jet stream. The anomalous zonal winds over the Pacific are partly explained by the geostrophic winds associated with wave-1 and 2 geopotential height anomalies. The results illustrate that the onset of extreme positive heat flux events are dominated by dynamics in the Pacific basin. During the growth stage zonal wind and geopotential height anomalies develop over the Atlantic. The coupling in the Atlantic basin is found to be of the opposite sign to extreme negative heat flux events.

During the mature stage of the life cycle the heat flux reaches its peak amplitude in the strato- sphere and there is a weakening of the stratospheric polar vortex, including a reversal of the zonal- mean zonal wind above 10 hPa. All of the upward wave coupling events involve a reversal of the zonal-mean zonal wind, however there does not exist a robust relationship between either the duration or the peak magnitude of the heat flux pulse and the time-integrated upper stratospheric zonal wind anomalies. The zonal-mean zonal wind and temperature anomalies subsequently migrate down to the surface over a period of several weeks, consistent with previous studies.