On the relation between extremes of midlatitude cyclones and the atmospheric circulation using ERA40

摘要

Analyzing ERA40 data there is evidence that extreme intensified midlatitude cyclones are related to the large-scale atmospheric circulation in winter and to a minor degree for spring and autumn. Regionally different circulation patterns are related to extreme intensified cyclones, e. g., cyclones in northern Europe are linked to a slightly rotated NAO-like pattern whereas for southern Europe a blocking-like pattern over central to northern Europe is observed. In the Pacific a north-south dipole pattern is related to extremes in cyclone intensity. In summer these relationships, however, collapse. In winter, depending on the considered region, changes in the meridional temperature gradient, the land-sea temperature contrast, and to some extent changes in static stability modulate the lower to middle tropospheric baroclinicity, being important in the intensification process.