A contribution to the dynamic climatology of Arabia

Abstract

Maps and transects are presented for January, April, July, and October. The uppertropospheric wind regime is dominated by Westerlies during winter, and the Tropical Easterly Jet in summer; seasonal reversals being related to the meridional gradient in the tropospheric thickness pattern. The relation between the kinematics of flow and the surface climate is most readily apparent during the extreme seasons. In winter, winds from northerly directions prevail over the Arabian Peninsula. Highest speeds are found in the Northeast monsoon flow over the open Arabian Sea. A confluence zone between winds from westerly and northerly directions extends from Ethiopia to the Southern part of the Red Sea, broadly coincident with a band of convergence. Cloudiness and sea surface temperature decrease from the equatorial seas northward. In summer a prominent core of maximum speed is found within the Southwest monsoon over the Western Arabian Sea. Divergence prevails upstream and convergence downstream from this speed maximum. Marked cyclonic vorticity is characteristic for the area to the left of the high speed core, that is along the Southeast coast of Arabia. The concomitant positive curl of wind stress is conducive to oceanic upwelling and cold coastal waters. Concurrently, the increase of surface friction from the open sea to the continent, that is towards the left of the flow core, favors atmospheric subsidence along the Southeast coast of Arabia. The gradient of cloudiness across the coast is also particularly steep in summer. The relative abundance of rainfall along the coasts of the Southern Red Sea seems at least in part to be related to the presence of a confluence zone during much of the year.