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Pressure Gradient
When sunlight strikes the Earth's surface, it heats the surface unevenly. Warm air rises, creating an area of low pressure, and cooler air descends, creating an area of high pressure. The difference in air pressure is the pressure gradient. This area is plotted on weather charts using isobars mapped between areas of high and low pressure. The greater the difference in air pressure, the greater the wind speed.
Coriolis Force
The Coriolis force affects wind direction. When viewed from space, wind travels in a straight line. However, when viewed from Earth, winds are deflected from their straightforward direction between high and low pressure areas. In the Northern Hemisphere, the Coriolis force drives winds to the right; in the Southern Hemisphere, it drives winds to the left.
Friction
Friction affects air movements near the Earth's surface. As winds encounter surface irregularities, they slow down. The Coriolis force acting on the winds also slows. Because the pressure gradient force remains constant, the wind is driven toward the area of lower air pressure. The winds curve inward toward the center of a low pressure area or spiral outward away from the center of a high pressure area.
Upper Level Winds
Upper level winds generate wind patterns at the Earth's surface. Two upper level wind patterns are Rossby waves and the jet stream. Rossby waves are high-altitude winds that bring cold air south and warm air north. They develop along the jet stream, a corridor of exceptionally strong winds.
Local and Regional Winds
Local winds are small-scale winds that result from differences in temperature and pressure in localized areas. Sea and land breezes are examples of such winds. Along coastal areas, winds blow onshore during the day and offshore during the evening. During the day, the air over the land heats up and rises and the cooler air over the water moves onshore. At night, the pattern is reversed.