9.6 Analyzing the Northern Hemisphere Wintertime Tropospheric Circulation Using a Novel Standing-travelling Wave Decomposition

Wednesday, 25 January 2017: 11:45 AM
609 (Washington State Convention Center )
Oliver Watt-Meyer, University of Toronto, Toronto, ON, Canada; and P. J. Kushner

The seminal paper by Wallace and Gutzler on the presence of teleconnections in the Northern Hemisphere winter argued that the oscillations that their work identified were standing wave patterns with fixed nodes and antinodes [Wallace and Gutzler, 1981]. This argument was made on the basis of the fact that there were strong regional variations in the strength of “teleconnectivity” and this suggested that certain regions were typically antinodes of standing oscillations. In this current work, a new spectral decomposition of wave variability into standing and travelling components is used to analyze the presence of teleconnections in the Northern Hemisphere winter. This decomposition is a significant improvement on previous methods because it properly accounts for covariance between the standing and travelling waves, and also because it allows for the straightforward reconstruction of the real space standing and travelling fields [Watt-Meyer and Kushner, 2015]. The decomposition is applied to the 500hPa geopotential height field, and it is shown that standing wave variance is largest in the high-latitude North Pacific and North Atlantic, while eastward travelling variance is greatest in the mid-latitude storm track regions. Furthermore, by computing one-point correlation maps with the daily standing, eastward and westward travelling wavefields, it is explicitly shown that the teleconnections of Wallace and Gutzler are indeed made up of true standing oscillations. Finally, as a specific example of the utility of the decomposition, the relative roles of standing and travelling waves in driving the anomalous amplification of the ridge-trough dipole over North America during the winters of 2013/14 and 2014/15 are demonstrated. The analysis shows that the cold air outbreak over eastern North America of 7 January 2014 was driven by a synoptic wave of extreme large amplitude intensifying a persistent background amplification of the typical ridge-trough structure seen during North American winter.

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