Air Pressure and Winds

Triple A ProductionsArnold RobertsAllison CouchAmy Jacobs

Air Pressure: The weight of the atmosphere as measured at a point on the earth’s surface.

How do differences in air pressure from place to place affect weather conditions?

Air Pressure

Air is a gaseous substance whose weight affects air pressure.

The air is heavier and the air pressure is higher closer to the earth’s surface

For equal amounts of cold and hot air, the cold air is denser.

A cold morning is characterized by relatively heavy air, but as afternoontemperatures rise, air becomes lighter.

Physical law

A variety of barometers are to record changes in air pressure.

The air pressure at a given locationchanges as the surface heats or cools.Barometers record the drop in atmospheric pressure when the air heats and the rise in pressure as the aircools.

Barometers

Visualize air as two liquids with different densities,like oil and water:The lighter liquid will move to the topas the denser liquid will move to the bottom of the container becoming the same thickness everywhere; in order to attain equilibrium by evening out pressure imbalances resulting from the heating and cooling processes.

The heavier (cold) air moves to locations with light (warm) air .

Air Density

Pressure Gradient Force

Pressure differences existing between areas cause air to blow from an area of high pressure

toward an area of low pressure

Heavy air stays close to the Earth’s surface Winds are produced Warm air is moved in an upward motion

Balancing Pressure Differences

Heavy AirHigh Pressure Zone

Low Pressure Zone

Wind

Warm Air

If distance between high and low are short1. pressure gradient is steep2. wind velocities are great

If gentle air movements occur when zones are far apart

1. the degree of difference is not great

Differences in Pressure Zones

Convection System

The circulatory motion of descending cool air and ascending warm air

Good example of a convectional system.

Daytime: The warmer air over theland rises vertically, and is replaced by cooler air from over the sea.Breeze from sea.

Nighttime: The water is warmer thanthe land, moving the cooler air from over the land to the sea.Breeze from land.

Land and Sea Breezes

Gravitational forces cause the heavy cool air that accumulates over snow in mountainous areas to descend into the lower valley areas.

Valley Breeze: the warm air from the valley movesup the slopes into the mountainous regions. This usually occurs during the day.

Mountain Breezes: the cool air moves down the slopes into the valley , lowering the temperatures in the valley (with the potential of freezing). This usually occurs at night.

Mountain and Valley Breezes

The Coriolis EffectAs winds move from high pressure to low

pressure:winds in the N. Hemisphere tend to travel to the

right,winds in the S. Hemisphere tend to travel to the

left

Coriolis Effect

The skaters in the middle of the circle do not need to move very quickly, while the out most skaters have to move rapidly to maintain this line

The Earth rotates on its axis

Equatorial regions are rotating much faster

Polar regions are rotating much slower

How does this relate?

When together they produce spirals rather then straight lines of wind

The spiral is the basic form of many storms

Coriolis Effect with Pressure Gradient Force

The Frictional Effect

The cause of wind to follow an intermediate path

Movements are slowed due to friction on Earth’s surface

Friction becomes ineffective about 1 mile above the Earth’s surface

Friction causes wind speed to decrease and change direction

Wind

Global Air Circulation

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Equatorial Low Pressure• Areas of low pressure at the equator line

Subtropical High Pressure• Cooled heavier air from the equatorial air

pressure

Northeast Trades and Westerlies (Southwesterlies)• Belts of wind caused by the cooled air

reaching the earths surface

Polar Air Pressure• Subpolar low is ascending air north of the

westerlies• Polar Easterlies connect the Subpolar low

to the Polar high pressure• Has the greatest effect on Jet Streams

Jet Streams• Strongest flows of upper air wind

• 30,000 – 40,0000 feet from the earths surface

• Air travels East to West, in both hemispheres, at 100 – 200 MPH

• Tends to separate cold polar air from warm tropical air

• Movement of the Jet Stream has the greatest effect on monsoon season in Southeast Asia

Monsoons• Monsoon wind changes directions seasonally

• Sothern and Eastern Asia is effected by this phenomena the most