By examining the winter midlatitude climate following varying recurving TC seasons over 50 years, the role of recurving TCs in the redistribution of energy is laterally approximated. The results suggest that a recurving TC, on average, may weaken the subsequent role of winter baroclinic eddies (and, implicitly, the mean pole-to-equator temperature gradient) by approximately one percent. This reduction of meridional eddy temperature flux implies a decrease in the available potential energy (APE) of the atmosphere, either as a direct or indirect result of the anomalous recurving TCs. Simultaneous with the decrease in APE, the static stability (N) of the midlatitudes is decreased as a consequence of the enhanced recurving TCs. These two competing changes result in a shift in winter extratropical cyclone (XC) existence: Following an active recurving TC season, intense XCs are slightly more frequent (owing to the decrease in N), but weak to moderate XCs are far less frequent (owing to the decrease in APE). It remains to be determined conclusively how the accumulated impacts of the TCs, and/or the resulting large-scale circulation changes, retain memory for months following the TC season.
Speculation is provided based on preliminary analyses of hemispheric snowcover leading up to the start of the winter.
Improved seasonal forecasting of higher latitude winter climate anomalies may be possible when the hemispheric frequency of recurving TCs is anomalous. Unfortunately, with this frequency minimally predictable, some component of winter midlatitude climate may be necessarily unpredictable until the TC season has nearly ended. This study suggests a view wherein TCs may be integral to the variability and forcing of climate, rather than incidental and purely responsive to other forcings, such as ENSO.