عنوان مقاله [English]
نویسندگان [English]چکیده [English]
This paper studies the dynamics of the Mediterranean storm track from the view point of Rossby wave activity and its flux. The evolution of wave activity is related to wave transience and nonconservative effects. In this study, the formulation introduced by Esler and Haynes (1999) has been applyed to compute wave activity. The data used for this study are from December 2004 through February 2005. In order to investigate the flux of the wave activity into and out of the Mediterranean region, first the wave activity and its flux were calculated for each grid point of a grid covering the middle latitudes of the North Atlantic Ocean and the Mediterranean Sea. Next, a two-dimentional rectangular domain at 300 hPa surface as well as a three-dimentional rectangular cubic domain extending from 600 to 200 hPa surfaces was selected on the Mediterranean region, and wave activity and its flux were calculated for their different boundaries. These computations were done at 6-hr intervals for each month (December, January and February) of the winter as well as the periods of the two case studies: case 1 (23/12/2004-01/01/2005) with clear propagation of the wave packets to the western Mediterranean from the North Atlantic storm track, and case 2 (07/01/2005-13/01/2005) with zonal propagation of the wave packets along the central latitude of the North Atlantic storm track.. In addition, to investigate more accurately contributions of the different parts of the domains to wave activity, each of the domains was divided into three smaller subdomains located on the western, central and eastern Mediterranean. Given the importance of the northern boundary in the wave activity flux into the Mediterranean region, the flux of this boundary was studied in more detail. The results indicate that
1. Entrance of the wave activity was observed in the western and northern boundaries of the two- and three-dimentional domains at all the time scales (monthly, seasonally and during the periods of the case studies), while the eastern and southern boundaries showed the exit of wave activity from the Mediterranean region.
2. In all of the cases, except Case Study 1, due to the dominance of the total output flux, the Mediterranean region acted as a source of wave activity. This result might be regarded, at least partly, as the reason for the existence of various cyclogenesis centers in the Mediterranean region.
3. In Case Study region.
4. The wave activity fluxes associated with the subdomains over the western, central and eastern Mediterranean show that the input flux from the eastern boundary of the subdomains west of the Mediterranean was greater than those from the eastern boundaries of the other subdomains. This finding might be one of the possible reasons for the existence of the main cyclogenesis centers in the western part of the Mediterranean. In this case, the western subdomain acted as a source of the wave activity, whereas the central and eastern subdomains played the opposite role.
5. In December 2004, it seemed the wave activity flux in the western Mediterranean was almost independent of the Atlantic storm track, and most of the influx came from the eastern part of the Mediterranean northern boundary. In January 2005, and to a lesser extent in February, the western Mediterranean was affected by the Atlantic storm track and the major influx belonged to the western part of the Mediterranean region.