عنوان مقاله [English]
In this study, the “MPI-ESM-LR” model output from phase 5 of the Coupled Model Intercomparison Project (CMIP5) is used to assess the response of the North Atlantic (NA) and Mediterranian storm tracks to climate change. Historical scenario is used for the past and RCP8.5 scenario is used as the projection for the future period. The conservation of wave activity is used as a diagnostic tool to investigate the eddy activity dynamics. A pair of large centers of divergence-convergence for the horizontal wave activity flux (wave packet) in the NA region forms the signatures of the NA storm track. The NA storm track has a double-branch structure consisting of northern and southern branches. The Mediterranian storm track is identified by a pair of positive/negative centers of wave activity flux in the west/east of the Mediterranian sea. The convergence area extends from the eastern Mediterranian and north-eastern Africa to the Middle-east and western and south-western parts of Iran.
The dynamical analysis of the MPI-ESM-LR results shows that the response of the upper-tropospheirc wave activity, propagation and breaking in the northern and southern branches of the NA storm track to global warming, determines the changes of eddy activity respectively in the northern and southern latitudes in its downstream sectors from Europe to Siberia and from Mediterranean Sea to Southwest Asia. In winter, intensity and number of wave packets decrease in both northern latitudes from the northern branch of the NA storm track to the Scandinavia and Siberia and southern latitudes in the southern branch of the NA storm track, the Mediterranian storm track and the Northern Africa region, while the central branch of wave activity in the middle and eastern NA and its downstream wave packets in the central Europe–Black Sea–Caspian Sea turns out to be the dominant path for the storm activity in the future. Moreover, the eastward flux of wave activity decreases in both the northern and southern latitudes, while it gets stronger in middle latitudes. These results indicate that the double-branch structure of the storm track in the NA and its downstream region in Europe and west Asia will turn to a single-branch pattern at the end of 21st century. Furthermore, the wave breaking and wave packets maxima associated with both the NA and Mediterranian storm tracks and the central branch of wave activity in the Europe–Black Sea will also undergo an eastward shift. Corresponding to that, the tongue of high values of wave activity in the central Mediterranean will also move to the eastern Mediterranian and the tongue of low values of wave activity in the middle-east will disappear. This leads to a considerable increase in penetration of both the Mediterranian and Black Sea wave packets and wave activity to Iran which may result in higher synoptic wave activity in this country in a warming climate.