The atmospheric envelope of the Earth
You should know that the Earth is surrounded by a gaseous envelope known as the atmospheric air or the atmospheric envelope which is a gaseous envelope rotating with the Earth around its axis , and it extends about 1000 km above the sea level .
You should know that the atmospheric air causes the pressure on all the living organisms , and the non - living things on the Earth's surface . This pressure is known as the atmospheric pressure .
The atmospheric pressure
You should know that the atmospheric pressure is the weight of the air column of an atmosphere height on a unit area , and it is measured by a unit called a bar or millibar .
1 bar = 1000 millibar ( mb ) . |
The normal atmospheric pressure is the atmospheric pressure at the sea level and it equals 1013.25 mb .
You should know that the atmospheric pressure differs from one place to another according to some effects , And the change of the height from the sea level is one of these effects .
You should notice that 50 % of the mass of the atmospheric air is present in the area between the sea level and 3 km height , and 90 % of the mass of the atmospheric air is present up to 16 km height above the sea level . The density of the air decreases by increasing the elevation above the sea level .
The relation between the altitude above the sea level and the pressure . |
The atmospheric pressure instruments
You should know that the atmospheric pressure is measured by the barometers , One of these baromters is Aneroid which is a type of the barometers that is used to determine the possible day weather .
Anderoid is used to determine the possible day weather . |
The Altimeter is an instrument that used by the pilots in the aeroplanes to measure the elevation from the sea level based on the atmospheric pressure .
The Altimeter is used by the pilots in the aeroplanes . |
The atmospheric pressure maps
There are curved lines that join the points of the equal pressure in the atmospheric pressure maps which is known as Isobar .
There are points of equal pressure that are joined by curved lines known as Isobar . |
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