Monday, 11 January 2016
The summer of 2010 was characterized by weather and climate extremes such as the western Russia heat wave and the Pakistan floods. In a recent study, it has been shown using a self-organizing map (SOM) analysis of daily June-August 200-hPa geopotential height that the summer of 2010 was dominated by a particular SOM pattern (SOM5) that featured anomalous ridging over Greenland and downstream ridging over eastern Europe and western Russia. In fact, when comparing the periods of 1979-1997 (P1) and 1998-2012 (P2), there has been a dramatic increase in the frequency of occurrence of SOM5 during P2. Furthermore, an examination of sea ice extent and sea surface temperatures during P2 to the west of Greenland in the Baffin and Labrador Seas reveals anomalously low values of sea ice extent in the late winter and spring followed by anomalously warm sea surface temperatures throughout the summer. Therefore, it is hypothesized that the atmosphere is diabatically warmed as a result of these anomalously warm sea surface temperatures which thereby promotes the establishment of the SOM5 pattern. To test this hypothesis, the Geophysical Fluid Dynamics Laboratory (GFDL) spectral dynamical core is employed by perturbing the climatological June-August background flow with heating anomalies to the west of Greenland that correspond to the observed difference in diabatic heating between P2 and P1. The modeled circulation pattern bears a remarkable resemblance to the observed SOM5 pattern, with pattern correlations reaching as high as 0.60. Insomuch as the forcing induced by anomalous sea surface temperatures may be regarded as stationary, this model result provides an explanation as to why SOM5 has been the dominant pattern in recent years, such as during the summer of 2010. Furthermore, this result demonstrates that climate change in the Arctic can induce weather and climate extremes in distant mid-latitude regions.
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