Troposphere–Stratosphere Coupling Following Tropospheric Blocking and Extratropical Cyclones

Abstract

Abstract A climatology of the 100- and 250-hPa 45°–75°N zonal-mean meridional eddy heat flux anomaly, hereafter heat flux anomaly, was created to examine its variability following cool-season (i.e., October–April) blocks and extratropical cyclones. The goal is to elucidate the dynamical and environmental differences between synoptic events followed by the most extreme heat flux anomalies. The analysis was conducted with the National Aeronautics and Space Administration’s Modern-Era Retrospective Analysis for Research and Applications, version 2 reanalysis. The results show that, on average, European blocks and west Pacific cyclones are followed by positive heat flux anomalies while west Pacific blocks and Atlantic extratropical cyclones are followed by negative heat flux anomalies. However, there was a large range of the 11-day-average heat flux anomaly following the events. Events in each region were further partitioned by their 100-hPa heat flux anomaly for a temporal and spatial analysis of the top and bottom quartile of events. Top-quartile events exhibited a baroclinic wave structure with height from the troposphere through the stratosphere, whereas bottom-quartile events were associated with a barotropic wave structure with height; these structures are significant at the 5% level. The results suggest that the sign of the heat flux anomaly is not dependent on the location of the synoptic event alone, but that there are common climatological and anomalous wave patterns surrounding the synoptic events that result in positive or negative heat flux anomaly. Regardless of event region, the precursor stratospheric structure is a key indicator in whether an event is followed by positive or negative 100-hPa heat flux anomalies.