The impact of Greenland on cyclone evolution in the North Atlantic

In order to understand better the role of Greenland's orography in determining the position and strength of the Icelandic low, we have carried out a number of experiments using a numerical weather prediction model. In those experiments, Greenland's orography was modified, and the impact on cyclone developments over the North Atlantic was investigated. We have focused on one fairly characteristic winter case from January 1995, but another one from January 1993 gave qualitatively similar results. We have found evidence that the deepening of baroclinic cyclones near Iceland is hampered by the presence of Greenland's orography. This has been shown to be related to the inability of cold air from the north to cross over Greenland, leading to a distortion of the thermal field associated with the disturbance and a halting of the progression of the cold front. In the January 1995 case, a characteristic secondary cyclone forming between Greenland and Iceland was shown to be entirely orographic, in that it was absent in runs where Greenland's orography was removed. The results are considered in the context of recent theoretical studies of how splitting in stratified flow impinging on high mountains.