Winds "blow" mainly because of differences in atmospheric pressure.
Pressure gradients develop on a local or a global scale due to the uneven heating of the Earth's surface, thus differences in atmospheric pressure.
Heating and cooling cycles develop daily or annually and can create several common local or regionalthermal circulations.
The basic circulation system that develops is described in the illustrations below.
Pressure gradients develop on a local or a global scale due to the uneven heating of the Earth's surface, thus differences in atmospheric pressure.
Heating and cooling cycles develop daily or annually and can create several common local or regionalthermal circulations.
The basic circulation system that develops is described in the illustrations below.
Cross-section of the atmosphere with uniform horizontal atmospheric pressure.
In this first diagram (Figure 7o-1), there is no horizontal temperature or pressure gradient and therefore no wind. Atmospheric pressure decreases with altitude as depicted by the drawn isobars (1000 to 980 millibars). In the seconddiagram (Figure 7o-2), the potential for solar heating is added which creates contrasting surface areas of temperature and atmospheric pressure. The area to the right receives more solar radiation and the air begins to warm from heat energy transferred from the ground through conduction and convection. The vertical distance between the isobars becomes greater as the air rises. To the far left, less radiation is received because of the presence of cloud, and this area becomes relatively cooler than the area to the right. In the upper atmosphere, a pressure gradient begins to form because of the rising air and upward spreading of the isobars. The air then begins to flow in the upper atmosphere from high pressure to low pressure.
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