The Great Sahara Desert

 Sahara Desert - one of the largest deserts in the world. Sahara stretches across much of North Africa, covering 9,000,000 square kilometers. In fact, the Sahara Desert is 30% of the entire African continent. This - the hottest and hot place in the world with summer temperatures often exceeding 57 degrees Celsius. In the desert drops annual rainfall and very strong sandstorms, raising sand at 1000 meters in height and moving dunes.
Some say that the Sahara desert before the first glacial period was much larger, and some assert that the Sahara desert appeared 4000 years ago. For example, German scientists using computer modeling the Earth's climate, and found that the Sahara became a desert 4000 years ago. 10,000 years ago, the largest desert in the world was covered with grass and low bushes, but then the summer was hotter and the rain almost stopped. Of course, disappeared many ancient civilizations, and all life has left the Sahara. According to scientists from the Potsdam Institute for Climate Research, the transformation of the Sahara desert has become one of the most dramatic climatic events on Earth foreseeable millennia. Why is it so unstable climate? It turns out that the axis tilt of the Earth to the Sun is gradually changing: Approximately 9,000 years ago it was 24.14 degrees, but now - 23.45 degrees. Today, the Earth most closely approaches the Sun in January, ten thousand years ago the same - at the end of July. Subtle changes in Earth's orbit around the Sun, increased interaction with the atmosphere, ocean and land, climate change beyond recognition.

 The climate of the Sahara extraordinaire. Damp factor is the widespread provision Sahara to the north and south of the Tropic of Cancer. This explains the fact that a large part of the desert throughout the year is influenced by northeast trade winds. Additional influence on climate is situated in the north of the Atlas mountain barrier, stretching from west to east and prevents penetration into the wilderness of the main mass of moist Mediterranean air. In the south of the Gulf of Guinea to the Sahara freely summer coming wet mass, which gradually draining the reach of its central parts. The extreme dryness of the air, the huge value of the deficit and humidity, respectively, an exceptionally large volatility characteristic of the whole Sahara. On rainfall in the Sahara can be divided into three zones: northern, central and southern.

 In the northern zone of precipitation in winter and their number does not exceed 200 mm per year. To the south of their number decreases, and in the central zone they fall out occasionally. The average value of less than 20 mm. Sometimes 2-3 years of rainfall does not fall out. However, in such areas may unexpectedly get heavy rains, causing severe flooding. Aridity of the Sahara and the changes in the latitudinal direction, from west to east. On the Atlantic coast of rainfall does not fall, because rare westerly winds cooled passing along the coast of the Canary Current. There are frequent fogs. On the tops of mountain ridges and highlands rainfall increases slightly due to condensation of water vapor. Sahara features a high degree of volatility. Its total annual value changes from 2500 to 5500 mm, which is more than 70 times the amount of precipitation.

 The Sahara is characterized by high, we can say champions of air temperature. The average temperature in the coldest months - January, almost the whole of the Sahara does not fall below 10 ° C. The average July temperature in the central part of the desert is 35 ° C. In many places, Africa recorded a temperature above 50 ° C overnight in the Sahara, the cool, the temperature drops to 10 -15 ° C. On the plains of lowering the temperature rarely reaches minus 5 ° C. In the mountains there are frequent frosts. Very large diurnal amplitude of air temperature - 30 ° C, and at the soil surface - up to 70 ° C. At the beginning of summer in the north of the Sahara blow hot sirocco winds that come from the central part of the desert. Strong winds cause dust and sand storms, wind speed during a storm reaches 50 m / sec. As air masses rise up sand and small stones, which are valid for humans and animals. The storms also occur suddenly as it had come to an end, leaving behind clouds of dust slowly settles dry "fog". Uncommon in the Sahara and tornadoes.

 Sahara desert is composed of one-quarter of volcanic mountains, one quarter of the sand, rocks and gravel-covered plains, and small areas of permanent vegetation. Vegetation includes shrubs, grasses and trees in the highlands and in the oases, situated on the river bed. Some of the plants are well adapted to this climate and grow within three days after a rain, and sow their seeds for two weeks after that. Only a small portion of the Sahara is fertile - these sites are taking water from underground rivers and oases.

 Animals in the Sahara desert are mainly gerbils, rabbits dolgonogami, deer, weasels, baboon, jackal, sand fox, mongoose and desert hedgehogs and more than 300 species of birds.