Investigating The Link Between Tropospheric Blocking And Sudden Stratospheric Warming In The Northern Hemisphere
The link between sudden stratospheric warmings (SSWs) and tropospheric blocking events has been heavily investigated, both in the composite sense, as well as individual case studies. The implications of improved SSW forecasting include improved surface weather predictability, as the warmings have long time scale impacts on the troposphere. In this study, the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis (Kalnay et al., 1996), and NASA's Modern Era Retrospective Reanalysis (MERRA) (Rienecker et al., 2011) data sets were used to differentiate blocking events that occur without the presence of any stratospheric warming from those that are linked with warmings, either preceding or following it. This was accomplished through the generation of composites of geopotential height fields, Ertel's potential vorticity on the longitude-time plane and averaged over the polar cap, zonal mean zonal wind diagnosis, and meridional eddy heat flux. It was found that indeed there are several distinguishing features that discriminate blocking events associated with SSWs from those that are not. Firstly, the zonal mean zonal wind appears to link the stratosphere with the troposphere during blocking events associated with SSWs, while no such link appears in the events that are not. The meridional eddy heat flux features large ten-day averaged values in the period before and just after block onset in the SSW associated composites, while it is absent in the non-associated composites. The polar cap PV average also separates the SSW associated events from the non-events, with an anticyclonic anomaly before block onset, and cyclonic anomaly after onset, whereas the non-events feature only a minimal change in tropospheric PV. The tropospheric polar cap PV and meridional eddy heat flux were used as forecast indicators for historical SSW events in both data sets, and presented nominal skill over climatology. A statistical comparison was also performed on the duration of blocking, that indicates that longer duration blocks are more likely associated with SSW events, but this was only statistically significant in the NCEP/NCAR Reanalysis, and was not replicated with the MERRA data set.
Blocking; Sudden stratospheric warming; reanalysis
Colucci, Stephen JohnColucci, Stephen John
Mahowald, Natalie M; Diamessis, Peter J.; Chen, Gang
Ph. D., Atmospheric Science
Doctor of Philosophy
dissertation or thesis