Interdecadal change in the North Atlantic storm track during boreal summer around the mid-2000s: role of the atmospheric internal processes

Abstract

The first EOF mode (EOF1) of summer storm track activity over the North Atlantic is characterized by a dipole structure, with negative storm track anomalies over the south coast of Greenland extending northeast across Iceland to the Norwegian Sea and positive anomalies over coastal western Europe. This study shows that a significant interdecadal change in the North Atlantic storm track during boreal summer occurred around the mid-2000s. After the mid-2000s, the EOF1 occurs more frequently at its positive phase, which is associated with an interdecadal increase in the geopotential height anomalies around Greenland. On the intra-seasonal timescale, the anticyclonic anomalies around Greenland are crucial for the occurrence of positive EOF1 events via triggering eastward propagating Rossby waves. Therefore, the interdecadal increase in the geopotential height anomalies around Greenland tends to facilitate the occurrence of the positive EOF1 event and is therefore a key driver of the interdecadal change in the summer storm track activity over the North Atlantic. Further analysis indicates that the development of anticyclonic anomalies around Greenland is maintained by the self-interaction among the low- and high-frequency transients themselves. Moreover, the anomalous synoptic eddy activities associated with the change in storm tracks can in turn amplify and maintain the Rossby waves triggered by the anticyclonic anomalies around Greenland in the synoptic-scale eddy feedback process.