الفهرس 
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Abstract
This research aims at giving a new insight into the Saharan cyclogenesis. The analysis performed in this study is done through the application of Melbourne University Tracking Scheme on NCEP/NCAR Reanalysis dataset for the period 1980-2009. This study includes a clustering of the individual Saharan cyclone tracks, analysis of their seasonal climatologies and their variability. The cyclone identification algorithm detected 562 tracks between 1980 and 2009. The tracking led us to identifying two main initiation regions over the Sahara: south of the Atlas mountains, which covers Algeria, Tunisia, Morocco, Mauritania and northern part of Mali and Niger, as well as Libya and Egypt. Most of the Saharan tracks (75%) start south of the Atlas Mountains.
Cyclones tend to decay mostly over the Sahara itself. Outside the Sahara, the Mediterranean is the primary sink; notable cyclolysis regions in the Mediterranean are the Gulf of Genoa and southern Turkey. Spring is the most active season for Saharan cyclogenesis (with 58%); this is followed by winter (with 20%)and finally by both and autumn (with about 11% percent each).
Eastern and northeastern Mediterranean receives 27% of the Saharan tracks, while western Mediterranean receives only 17%. The maximum Saharan cyclonic activity occurs in April, followed by May and to a lesser extent in March. There is a general decrease in the number of tracks between 1993 and 2009, compared with the period between 1980 and1992.
We performed a comparison between the seasonal climatologies of the cyclone and tracks characteristics between three reanalysis datasets; NCEP/NCAR (NCEP1), NCEP/DOE (NCEP2),and ECMWF (ERA40) for the common period 1980-2001.
Generaly, the track numbers in NCEP1 is greater than either NCEP2 or ERA40. NCEP2 tracks are more than ERA40 in all seasons except in winter.
The cyclogenesis patterns in NCEP and ERA40 show that the center over Libya andEgypt is weaker compared withNCEP1 datasets in both winter and spring. The number of tracks decreases significantly over most of the Sahara in both ERA40 and NCEP2 compared with NCEP1 in spring. In autumn, the NCEP2 track climatology is marked with a shift in the tracks to western Mediterranean.
In autumn, the ERA40 tracks have considerably longer lifetimes than NCEP1 and NCEP2. In winter, deepening is stronger in Both NCEP1, NCEP2, than in ERA40.
Our analysis also extends to studying the connection between the large scale circulation patterns: North Atlantic Oscillation (NAO), East Atlantic/West Russia (EAWR), and Scandinavian (SCAND) on the both Saharan cyclone track and cyclone characteristics in sprig.
A large significant positive increase in cyclogenesis of the Saharan cyclogenesis was found in the positive phase of the SCAND over large areas of eastern and Western Sahara. The track density decreases significantly over western Mediterranean and North Africa in the positive phase of NA, while the number of tracks decreases significantly in the positive phase of EAWR over central Algeria and a small area of the Black Sea. In the positive phase of SCAND the number of tracks increases over eastern Sahara, Arabia, and Algeria.