D. Mitchell
The Influence of Stratospheric Vortex Displacements and Splits on
Surface Climate
A strong link exists between stratospheric variability and
anomalous weather patterns at the Earth's surface. Specifically, during
extreme variability of the Arctic polar vortex termed a "weak vortex
event", anomalies can descend from the upper stratosphere to the
surface on timescales of weeks. Subsequently the outbreak of cold-air
events have been noted in high Northern Latitudes, as well as a
quadrapole pattern in surface temperature over the Atlantic and western
European sectors but it is currently not understood why certain events
descend to the surface while others do not. In this study we compare a
new classification technique of weak vortex events, based on the
distribution of potential vorticity, with that of an existing technique
and demonstrate that the subdivision of such events into vortex
displacements and vortex splits has important implications for
tropospheric weather patterns on weekly-monthly timescales. Using
reanalysis data we find that vortex splitting events are correlated with
surface weather and lead to positive temperature anomalies over eastern
North-America of more than 1.5K, and negative anomalies over Eurasia of
up to -3K. Associated with this is an increase in high-latitude blocking
in both the Atlantic and Pacific sectors and a decrease in European
blocking. The corresponding signals are weaker during displacement
events, although ultimately they are shown to be related to cold-air
outbreaks over North America. Due to the importance of
stratosphere-troposphere coupling for seasonal climate predictability,
identifying the type of stratospheric variability in order to capture
the correct surface response will be necessary.
[BACK]