32 Investigating the Link Between Sudden Stratospheric Warming and Tropospheric Blocking in the Northern Hemisphere

Monday, 17 June 2013
Bellevue Ballroom (The Hotel Viking)
Michael Ewens Kelleher, Cornell University, Ithaca, NY

Connecting the synoptic scale tropospheric blocking with the planetary scale sudden stratospheric warming (SSW) is a challenging task that has been approached in a number different ways. Some of these ways include dynamical and statistical methods. This relationship has implications for exchange between the two lowermost layers of the atmosphere in both directions, i.e. tropospheric weather has the potential to influence stratospheric circulation and vice versa.

This study uses the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data (Kalnay et al., 1996) for 1948-2010, to identify blocking events with a wave breaking method derived from Pelly and Hoskins (2003). The times of their onset and breakdown were compared with a list of major SSW events. The blocking events were then sorted into three geographic sectors: Atlantic, Greenland and Pacific then three temporal groups: blocking events preceded by an SSW, blocking events followed by an SSW, and blocking events with no SSW within 10 days of onset or decay. This data was used to address the differences in duration and location, in block evolution and dynamics and of the Aleutian high strength between each blocking category.

The Aleutian high features an increase in strength before blocking in the SSW pre block group, and after block onset in the SSW follows blocking group. The anticyclone is minimal during non-SSW proximal blocking events. A slight longitudinal preference was found for SSW proximal blocking events. The average in the Atlantic and Greenland sectors was to the west of the non-proximal average while in the Pacific sector it was east of the non-proximal average. It was found that SSW proximal blocking events are longer in duration than non-proximal events. This is potentially linked to the duration of wave activity fluxes as is an anomalous wave train absent in non proximal blocks.

Anomalously large heat fluxes that have been found to be associated with major and minor SSW events (Sjoberg and Berner 2012) were also found to be large in magnitude and duration in the SSW proximal blocking events, and minimal in the non proximal blocking events. Transient wave activity fluxes will be examined to further diagnose differences in these events. These results will also be tested using the NCEP Reanalysis II dataset, in addition to minor warmings to increase the sample size of events and determine the degree to which the tropospheric blocking events impact the stratospheric circulation.

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