Surface maxima are referred to as high pressure

Surface winds are the winds that you feel outside near the surface of the Earth. This lesson looks into why winds exist in some locations and not others and also at the driving forces for these winds.

What Is Wind?

Winds are a common feature of all storms, ranging from thunderstorms to hurricanes. However, winds are also common at certain locations, such as by the ocean or in the mountains. So why are winds associated with certain events and locations?At their very basic, winds are moving air masses in response to differential pressure and temperature gradients in the atmosphere.

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In an attempt to lower the overall energy of the system, air molecules will move from areas of high pressure to those of lower pressure. Think of pressure as a pushing force; the high pressure pushes the air away into lower pressure areas. The pressure gradient force, or PGF, is the force that pushes air from high to low pressure in an attempt to equalize the pressure.These differences in pressure create winds throughout the atmosphere. This lesson will be focused on surface winds.

Surface winds are winds near the Earth’s surface that are normally measured at 10 meters above the surface. We’ll look at unique features of surface winds and how they are formed.

Winds and Air Pressure

So we just learned that winds are created by pressure variations in the atmosphere. These pressure fields are shown on weather charts by a series of isobars, or lines of constant pressure. Just like how contours on a topographic map mark areas of equal elevation, isobars on a pressure chart allow the user to follow areas of equal pressure.In these maps, local maxima are referred to as high pressure systems labeled ‘H’ in red, and minima are low pressure systems labeled ‘L’ in blue.

You’ve likely seen these maps and labels if you’ve watched the local news on TV. We care about the pressure systems across the U.S. because they drive the larger weather patterns across the country. However, these differences between higher and lower pressure create winds on a more local scale as well.

The space between isobars on the map will determine how fast the winds blow. Stronger pressure gradients exist in locations where there are larger changes in pressure across a shorter area. On our pressure map, these are locations where the isobars are closely spaced.

The winds have a higher speed at these locations of larger pressure gradients than lower.There are two types of surface winds based on the distance over which they occur. Synoptic winds are winds that occur due to pressure differences over thousands of miles. Local winds are winds that occur on the scale of one to 30 miles. Synoptic winds are ones that would blow across the entire country due to the pressure differences seen on the country-scale pressure map. Local winds are what you experience on the beach where cool air blows from the ocean to the land.You may be familiar with some common local wind patterns, such as winds at the beach.

When the sun rises, the land heats up quicker than the water. The hot air near the land rises and colder air from the ocean rushes in to fill the space. The opposite happens in the evening when the sun begins to set.

The ocean takes longer to cool so the wind rushes back out to the ocean.

Wind Direction

As we’ve learned, the direction of the wind is from areas of high pressure to low pressure. However, winds over long distances won’t move in a straight line.

This is because the rotation of the Earth actually causes the wind to move. Imagine trying to draw a straight line on a rotating tray or turntable. You start drawing from the center out to the edge, however the tray starts to rotate counter-clockwise. Your line would start to veer off to the right.

In the same way, if you tried to draw a straight line on the bottom of the tray while it was spinning, you would find your line was veering to the left.In the Northern Hemisphere, air path is deflected to the right. In the Southern Hemisphere, air path is deflected to the left. This deflection of wind is known as the Coriolis Effect. The Coriolis Effect is not noticeable across short distances but is more noticeable across longer synoptic wind patterns.

Lesson Summary

Winds are created by air molecules moving from areas of high pressure to low pressure. Surface winds are the ones that exist close to the Earth’s surface and are measured at a height of 10 meters above the Earth’s surface. Pressure gradients are mapped on weather charts with isobars that mark locations of equal pressures.

These are the maps you see on local weather forecasts showing high and low pressure systems across the U.S.Winds will move in the direction of high to low pressure but over longer distances can be deflected by the Coriolis Effect. Across shorter distances, like across the beach, winds are much more affected by local pressure variations caused by things such as temperature variations.


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