Chapter 19: The Atmosphere in Motion 19.1: Air Pressure and Wind 19.2: Factors Affecting Winds 19.3: Global Wind Patterns 19.4: Continental and Local Winds

19.1: Air Pressure and Wind Air Pressure Air Pressure- The weight of the atmosphere as it pushes down upon Earth's surface exerts a force per unit of area called air pressure. Air pressure decreases by about 50% for each 5 km (3 mi) increase in elevation.

19.1: Air Pressure and Wind B. Measuring Air Pressure Mercury B. Measuring Air Pressure A barometer is used to measure air pressure. Two Types: Mercury and Aneroid. P.414 & 415 Air pressure at sea level is 30 in Hg. Or 1013 millibars. If air pressure increases the column rises, if it decreases it falls. Click me Aneroid

19.1: Air Pressure and Wind Why Does Air Pressure Change? Elevation, temperature and Humidity all affect air pressure. This is a result of air molecules being closer or farther apart. Higher elevations mean fewer air molecules. Why? Warmer air causes air molecules to be spaced farther apart and moist air molecules are also spread farther apart. A decrease in air pressure usually indicates the approach of warm, moist air. Isobar-a line that joins points of equal pressure. Answer: Less Gravitational Pull

19.1: Air Pressure and Wind D. What Makes Wind Blow? Air moves from areas of high pressure to areas of low pressure. The greater the difference the quicker it moves. This causes WIND!

19.1: Air Pressure and Wind 2. What creates these differences? 3. Meteorologists use a wind vane to measure direction and an anemometer to measure speed. Answer: Differences in Pressure, Temperature, and Altitude

19.2: Factors Affecting Winds If the earth were perfectly smooth and did not rotate, air would flow straight from high-pressure areas to low pressure areas.

19.2: Factors Affecting Winds The Coriolis Effect It is the tendency of an object moving freely over the Earth's surface to curve away from its path of travel. See page 419. In the Northern Hemisphere objects are deflected to their right and in the Southern Hemisphere the objects are deflected to the left. Coriolis Effect

19.2: Factors Affecting Winds B. Friction The smoother the surface the faster the wind! Jet Stream- Bands of swiftly moving winds formed in the troposphere. Polar Jet Stream- Cool air from polar regions combines with warmer air to the south.

19.3: Global Wind Patterns Factors that affect winds are: Temperature differences between equatorial and polar regions, the rotation of the earth, locations of the continents, the time of year and local topography.

19.3: Global Wind Patterns Effects of Earth's Rotation Three Celled Circulation Model- The Northern and Southern hemispheres each have three circulation cells: one between the equator and 30° lat., the second between 30° and 60° lat., and a third between 60° lat. and the pole. See page 423.

19.3: Global Wind Patterns 2. The circulation cells are caused by alternating bands of high and low pressure. 3. There are weaknesses in the Three-Celled Model. These can be attributed to generalizations about the earth landscape and seasons.

19.3: Global Wind Patterns Description of Wind and Pressure Belts Intertropical Convergence Zone- The air is hot and humid, there is little wind, and rain is common. This area is historically called the doldrums. Horse Latitudes- Found between latitudes of 20°-30°. They are created by dry sinking air, which creates little wind and precipitation.

19.3: Global Wind Patterns 3. Trade Winds- Found between the doldrums and the horse latitudes. They are warm and relatively steady in both direction and speed. 4. Prevailing winds- Blow from the same direction.

19.4: Continental and Local Winds Winds change with the changing of the seasons due to changes in temperatures.

19.4: Continental and Local Winds Effects of Seasons and Continents Air pressure on continents is low in the summer and high in the winter. The opposite is true for the oceans. See page 427. Monsoons-Winds that change direction seasonally. Summer moist moist H H Warm Hot Warm

19.4: Continental and Local Winds Land and Sea Breezes Hot Cooler H L Cool Warm LAND-BREEZE SEA-BREEZE