Synoptic features associated with the winter variability of the subtropical jet stream over Africa and the Middle East

Spatial, vertical and temporal variations in the subtropical jet stream over Africa and the Middle East were studied from 1958 to 2016 using NCEP/NCAR reanalysis meteorological data. The results of this study showed that the jet stream was located at a pressure level of 200 hPa more than 87% of the time, and it was located in the meridional zone between 20 degrees N and 35 degrees N in more than 83% of these cases. Additionally, the annual winter distribution of the jet stream illustrated two distinct trends: the first trend ended in 1987 and had a high rate of decrease, and the second trend began in 1988 and had a small rate of increase. Furthermore, synoptically, the study showed that the southern shift of the jet stream intensified the low-pressure systems over Africa and the Mediterranean, in addition to producing favorable conditions for the northward extension of the Red Sea Trough. However, the northward shift was related to the intensified Azores high-pressure system over Africa and the southern Mediterranean. Moreover, the temporal variations of the jet stream indicated that the intensification of the high-pressure system (i.e., the Azores and Siberian highs) tended to decrease the number of jet stream cases at 200 hPa or vertically shifted them downward to 250 hPa.