Pressure Gradient Force (PGF), Coriolis Force Effect and Isobars - اسأل الطيار ask pilot

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## الثلاثاء، 30 يونيو 2020

 Pressure Gradient Force (PGF), Coriolis Force Effect and Isobars

Pressure differences must create a force in order to drive the wind. This force is the pressure gradient force. The force is from higher pressure to lower pressure and is perpendicular to isobars or contours. Whenever a pressure difference develops over an area, the pressure gradient force begins moving the air directly across the isobars.
The closer the spacing of isobars, the stronger is the pressure gradient force. The stronger the pressure gradient force, the stronger is the wind. Thus, closely spaced isobars mean strong winds; widely spaced isobars mean lighter wind. From a pressure analysis, you can get a general idea of wind speed from contour or isobar spacing.

**Coriolis Force Effect
The Coriolis Effect is a result of the conservation of angular momentum. As the aircraft flies, it's angular momentum must be conserved, in the absence of any outside forces. So, as the aircraft moves closer to or further away from the axis of rotation which connects the North and South Poles, the aircraft tends to be deflected off it's path.
The force created by the rotation of the Earth is known as the Coriolis force. This force is not perceptible to humans as they walk around because humans move slowly and travel relatively short distances compared to the size and rotation rate of the Earth. However, the Coriolis force significantly affects motion over large distances, such as an air mass or body of water.
**Isobars
An isobar is a line that connects coordinates with the same air-pressure, they are often pictured as circles around different pressure systems. The isobar also has a specific number displaying the air-pressure in hectopascal. If you have a look at a low-pressure area you can see that the isobars decrease closer to the center.
Isobars are perfect indicators of how the air will move. Since the Pressure Gradient Force will move 90 degrees from the isobars, from high to low pressure, and Coriolis will cause another 90 degree turn, the wind will blow parallel to the isobars, as long as it is not affected by other factors such as friction or terrain.
The distance between the isobars will also decide the velocity of the winds, the narrower the distance between them, the stronger the wind.