The formation of depressions of the khamsin type

A further study has been made of the conditions in spring which produce khamsin conditions in Egypt. Depressions are then formed which travel from west to east to the south of, and roughly parallel to, the north African coast; and, as a rule, while the more vigorous depressions usually originate far to the west of Egypt, shallow depressions form in Egypt or slightly to the west of it. Such depressions are regarded as produced in the manner suggested by Margules—unstable conditions prevailing between intensely heated air to the south and cool air to the north, the moisture of the air playing a non‐essential part. The cold air is due to an anticyclonic distribution in the Mediterranean, while the hot air is drawn northward from the Sudanese low when it suffers large oscillations towards the north. These oscillations are in the main brought about by the travelling depressions, the current bringing the hot air being specially strong when the depressions reach the Red Sea.