Arab weather - The five-year depressions are known as thermal depressions that usually form in the spring in the northern part of the continent of Africa (in the Sahara), and move parallel to the Mediterranean coast towards the eastern basin of the Mediterranean and the Levant region. However, these depressions disappear when they approach the sea due to the absence of the heating factor, which is the main cause of their occurrence.
Thermal depression is defined as: a depression resulting from the intense heating of the Earth’s surface, which results in a decrease in the density of the air above it, so it rises to the top and the pressure decreases, and the air begins to gather from areas of high pressure towards areas of low pressure, an upward movement is formed but does not exceed the level of 700 hectopascals, because The winds accompanying these depressions are weak.
The Pentagram depressions are active at the beginning of the spring season, between March 21 and May 10, but they can also form before their season.
The Khamsiniyah depressions are formed in the Sahara and North Africa in the spring as a result of the decrease in atmospheric pressure due to the high temperature there compared to the temperature of the Mediterranean water, which becomes cold after the winter season. These depressions push the surface winds laden with dust from the Sahara towards the East.
The Khamasin depressions are usually accompanied by the Khamasin winds, which are mostly southwesterly winds, and are dry and hot, with a temperature of 40 degrees Celsius, coming from the Sahara Desert, loaded with tons of dust and raised dust, and moving at a speed of up to 140 km / hour towards the eastern Mediterranean regions Such as Egypt, the Levant, and the Arabian Peninsula, where temperatures rise rapidly and dusty weather prevails, which reduces visibility.
The winds accompanying the Khamasin depressions are called the Khamseen; Because it is active intermittently over fifty days in the spring, but it rarely blows more than one or two days a week during this period, and this name is used locally in Egypt and the Levant, and it is called in Sudan "the wind or the tribal wind", and in the Arab Gulf and Iraq It is called the "Tuz wind", and although it rarely reaches Europe, they call it the "Al-Sharqi" wind.
When the presence of these pentagonal depressions is accompanied by a depression at the level of 500 hectopascals, a fusion occurs between them and thunderstorms are formed in the cold sector of the surface depression, while in the hot sector dust storms are formed, that is, thunderstorms are formed in the foreground and in the rear, dust storms are formed.
1. Among the damages that may befall humans as a result of dusty weather: chest allergies, lung and bronchial infections, and nasal and throat congestion if a person is exposed to wind and dust, in addition to its impact on vision, eye inflammation and spring conjunctivitis.
2. Damage to plants: leaves rupture and pollen atrophy, and may cause flowers and fruits to fall as a result of the wind, and increase the risk of infection with the red spider.
3. Wind loaded with sand may cause damage to cars: especially if the car is driven against the direction of the wind, which leads to scratches in the paint, windshield and headlight covers, and the car's air filter may become clogged with repeated driving in sandstorms.