Variability of Saharan cyclone tracks, II: synoptic study
摘要
Long Saharan cyclone tracks have been classified into five main routes, representing approximately 90% of detected cyclones through the period from 1967–2019. In this synoptic study, approximately 55% of these cyclone tracks, i.e., those satisfying the conditions of the developing stages, are used. For the synoptic study, the composite maps display track ratios of approximately 71%, 64%, 61%, 52%, and 43% from the Northeastern Egypt, Southern Sahara, Eastern Mediterranean, Northern Sahara, and Northern routes, respectively. The synoptic forces accompanying these routes indicate that the Azores high acts as a push system, whereas the Siberian high and northern low and gulf trough systems act as steering systems for Saharan cyclones. The upper level systems integrate with the surface systems by intensifying the surface conditions accompanying the routes but exhibit only a weak relationship with the southern Sahara route. Additionally, the relative positions between high- and low-pressure systems produce a high pressure gradient dipole, forming favorable paths for each cyclone route. Furthermore, the spatial distributions of the routes demonstrate that the regional atmospheric conditions and the relative positions between the synoptic systems produce favorable conditions for Saharan cyclones to pass more frequently into or close to the Mediterranean than over southern Sahara.