Complexities in the climate of the subpolar North Atlantic: a case study from the winter of 2007

As a result of its high topography, Greenland significantly distorts the atmospheric flow affecting local as well as remote weather systems and, via air-sea interaction processes, the coupled climate system. During February and March 2007, a field campaign was carried out to investigate this as part of the international Greenland Flow Distortion Experiment (GFDex). The observational programme occurred during anomalous conditions, relative to the climatological mean, that favoured the formation of barrier flow along the southeastern coast of Greenland and easterly tip jets at Cape Farewell, Greenland's southernmost point, while inhibiting the formation of westerly tip jets in the same region. The North Atlantic Oscillation (NAO) index was positive, indicating a deep Icelandic Low. However, there was a southeastward shift in the low's centre and a more zonally oriented storm track that we propose to be the result of the concurrent positive phase of the East Atlantic (EA) teleconnection. Unlike the usual situation for an NAO positive state, there was also a warming in the lower troposphere over the Labrador Sea that we argue was the result of a relatively weak Canadian Polar Trough over the eastern Canadian Arctic. It is shown that consideration of the strength of the Canadian Polar Trough in conjunction with information on the phases of the NAO and EA provides for a qualitatively better representation of the state of the atmosphere over the subpolar North Atlantic during the winter of 2007, and by inference in general, than is possible via the NAO alone. Copyright (C) 2011 Royal Meteorological Society