Air Pressure and Winds

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 afternoon temperatures rise, air becomes lighter. Physical law

A variety of barometers are to record changes in air pressure. The air pressure at a given location changes as the surface heats or cools. Barometers record the drop in atmospheric pressure when the air heats and the rise in pressure as the air cools. Barometers

Visualize air as two liquids with different densities, like oil and water: The lighter liquid will move to the top as 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 High Pressure Zone Low Pressure Zone Wind Warm Air

 If distance between high and low are short 1. pressure gradient is steep 2. 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 the land rises vertically, and is replaced by cooler air from over the sea. Breeze from sea. Nighttime: The water is warmer than the 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 moves up 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 Effect As 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 cosscience1.pbworks.com 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