Ibrahim, Mostafa M. (Departement of astronomy and meteorology, Al Azhar university, Cairo, Egypt)
A synoptic situation where interaction between a middle wave and a tropical disturbance occurs over Africa is studied. It is shown that the invasion of cold air south of 30N is a necessary trigger action for such interaction.
In this case a southerly thermal wind component is developed due to air masses temperature differences. the developed wind component causes a change in the direction of the subtropical jet from westerly to south-west.
This causes advection of moist air from the inter-tropical convergence zone, where deep convection cells existy, towards the north-east. As a result a tongue of inactive medium and high cloud band is formed. As the trough of polar frontal system comes in phase with the cloud band axis, rapid developement of the cloud band connecting the middle and tropical system occur.