Under Pressure As we know, the air in the atmosphere is made up of a number of gases. These gases press down on the Earth’s surface, exerting a force that we call atmospheric pressure or air pressure. Although we are usually unaware of this pressure, it actually presses down very hard – roughly equivalent to the force of an elephant balancing on a desk! Each layer of air presses down on the layers below, and so the greatest pressure is at ground level where we have the maximum amount of air above. In the stratosphere air pressure decreases until it reaches about zero.

Changes in Air Pressure Changes in air pressure are caused by the difference in air temperature above the earth.  Land masses and areas of water change the temperature of the air above them.  These changes create wind and cause pressure patterns to develop.  The wind moves these pressure patterns that change as they pass over mountains, oceans, and other areas.

The Sun: Heat Energy and the Atmosphere

Radiant energy from the sun is transformed into heat by absorption at the earth’s surface.

The angle of the sun’s rays affect the heating of Earth’s surface. The uneven distribution of heat energy in the atmosphere is the cause of weather.

"Winds blow from high to low!" Changes in air pressure bring changes in the weather and make winds blow. Air usually moves from areas of high pressure to areas of low pressure, and this produces winds. This can be easily remembered with the phrase: "Winds blow from high to low!"

Wind Facts: Winds move from high to low pressure areas. High pressure is associated with cold air, low pressure with warm air. Warm air rises because it is less dense than cold air Both local and global winds are caused by differences in air pressure due to unequal heating of the air.

Air Circulation Pattern When air is heated, it becomes lighter (less dense) than the surrounding air. Therefore, warm air rises. Cool air is heavier (more dense), so it tends to sink. As air rises or falls, the surrounding air rushes in to replace it, causing air to circulate. This circulation, brings about changes in the weather. The heating of Earth's surface depends on the nature of the surface ,

Local Winds Sea Breeze, Land Breeze, and Monsoon Occur on warm sunny days Air over the land heats faster than the air over the cool ocean Warmer air rises Cool air flows in under it to fill the area over the land This air warms and the cycle continues Sea Breeze Occur at night and on cool days Air over water maintains an even temperature Air over land cools faster Cooler air flows from the land out under the warmer ocean air This air warms and the cycle continues

Global Winds

Coriolis Force (effect) The original circulation of air caused by convection is in a north –south direction. But because the earth turns toward the east, all winds veer from this north-south direction. The Coriolis force is caused by the differences in velocity of rotation at different latitudes. At the equator the velocity of rotation is at its maximum (1,000 mi/hr). At the poles the velocity of rotation is at its minimum (0mi/hr). The velocity of rotation gradually decreases from the equator to the poles.

Rotation of the earth, distribution of land and water areas, and the exchange of heat between warm and cold areas causes the circulation patterns of the atmosphere.

Major Wind Systems Trade Winds or Easterlies - An area of calm found at the equator. When warm air from the equator rises, it cools, and flows back toward the equator. It appears to flow to the west because of the Coriolis Effect. Prevailing Westerlies - When air moves toward the poles, it flows from west to east. clouds, rain , or snow may occur when highs and lows overtake one another Polar Easterlies - Air over the poles cools and sinks back down, it eventually returns to the equator.

The Jet Stream The Polar Front at the Tropopause Recall that winds aloft are faster than surface winds

Climate Climate is the general character of the weather that prevails in an area from season to season and from year to year. It can be thought of as the average weather of an area over a long period of time. Factors that combine to produce different climates: latitude altitude Large bodies of water Mountain barriers

AIR MASSES What's the definition? A large body of air with similar characteristics throughout

Air masses are classified based on their and amount of temperature moisture

Air masses get their characteristics based on where they form

The abbreviations used to classify air masses use the following letters: c, m, T, P, and A. For each letter, describe its property: Word Means c m T P A continental dry maritime moist Tropical warm Polar cold Arctic very cold

What would their characteristics be? mT cP warm and moist cold and dry

What type of air mass would form over each area? Please label. cA mP mP cP cT mT mT mT

World Air Mass Source Regions