Chapter 19: Air Masses

1. Chapter 19: Air Masses

2. What are Air Masses? • Similar Moisture • Can cover a whole continent

3. Fronts: • Leading edge of advancing air mass • Polar FrontFrigid, Arctic air moves South from North Pole (Winter Months) West to East  From Rocky Mountains to Maritimes • Warm Front • Cold Front • Stationary FrontWarm and Cold air boundary remains in one place • Occluded  Cold overuns warm mixing the air

4. Air mass Classifications: • Place of OriginHigh latitudes Arctic/Polar vs. Low Latitudes Tropical • Overland/Water Continent vs. Maritimes • Stable vs. Unstable Air • Stable Air: Lower layers of air are cooler than the air above, therefore no vertical movement of air (convection) takes placescharacterized by calm air, clear skies, and no precipitation.ex. When stable air masses blanket large cities such as Toronto, air quality quickly deteriorates as pollutants from factories and vehicle exhaust are unable to rise into the upper atmo. where they can be dispersed by wind currents. (a.k.a temperature inversion) • Unstable Air: The lower layers of air are warmer than the air above so air can readily risecloudy, wind, and rain.

5. Air Masses in North America Continental Polar (aka Continental Arctic in winter) • Originates in North Pole extends as far south as Floridaaffects food crops • Air mass is very cold, stable and dry. • Cold air is heavier than warm air, so as this air mass moves south it stays in contact with the ground. • Clear, sunny skies and high pressure

6. Maritime Polar • Originate over the ocean in temperate and polar regions and move toward lower lats. • Northern Pacific (Gulf of Alaska) is where it originates • Cool, moist, and unstable therefore moisture in BC coast • Continental arctic is usually kept out by mountain ranges running south, but when it makes it way into coast and comes into contact with maritime polar heavy blizzard conditions occur. • Summer this air mass is cool, but stable therefore few rainy days.

7. Maritime Tropical Originate in lower latitudes and are much warmer and far more stable than Maritime Polar air masses. Locations such as California get little ppt. in winter months. Those the originate in the Gulf of Mexico, are warmer, wetter and far less stable, and generate frequent storms. Continental Tropical North from the desert plateau of central Mexico into the central Great Plains region of North America bringing hot, dry conditions Air mass associated with tornado and hurricane activity (Tornado Alley in the mid United States is where Maritime tropical air meets Continental Polar) This air mass is primarily responsible for hurricane and tornado activity!

9. Animations: • http://www.classzone.com/books/earth_science/terc/content/visualizations/es2001/es2001page01.cfm?chapter_no=visualization • http://www.classzone.com/books/earth_science/terc/content/visualizations/es2002/es2002page01.cfm?chapter_no=visualization

10. Chapter 20: Global Winds • Winds are named for the direction from which they blow, not the direction they are going. • For instance, winds blowing from the Pacific Ocean toward the coast of N.A. are called westerly winds because they blow from West to East. • its Remember: they move from high to low. Good diagram on p. 88 of Sovio Fig. 20.1

11. Because the earth turns on its axis, from west to east, the two main factors in wind direction are: A)rotation of earth on its axis B) Location of High and Low Pressure Air masses. • the winds in the northern hemisphere curve to the right and in the south to the left. • Air flows from an area of high pressure to an area of low pressure. • Continual trade winds, the northeast trades and southeast trades blowing from sub-tropical, high pressure belts to the constant low pressure region at the equator. • At the equator, winds are calmdoldrumsArea of continuous low pressure! (popular provincial question) Look at Fig. 20.2 The rotation of the earth on its axis is responsible for the curving of winds, to the right in the northern hemisphere and left in the southern hemisphereknown as Coriolis Effect. http://www.classzone.com/books/earth_science/terc/content/visualizations/es1904/es1904page01.cfm?chapter_no=visualization http://www.wiley.com/college/strahler/0471480533/animations/ch07_animations/animation2.html http://weather.about.com/od/weathertutorials/tp/coriolisvideos.htm

12. Wind Patterns You also need to know which winds are found along latitudes: • Equatorial : Doldrums = low pressure (constant) I ask why? • 0-30 N/S North East and South East Trades • 30-60 N/S Westerlies (affect B.C.—in the North provincial) • 30 N and S known as Horse Latitudes (High • Pressure) • 60 degrees N/S (Low Pressure—not continuous) • 60-90 N/S Easterlies • 90 N/S High Pressure (Constant) therefore, very little or not precipitation

13. Global Circulation Model Global Atmospheric Circulation

14. Jet Stream A stream of fast-moving, atmospheric air that occurs where the troposphere meets the stratosphere Meanders east at speeds of 300 km an hour located in mid-latitudes they migrate north/south Weather systems in the lower troposphere are greatly influenced by jet streams. (bring cold air either south or northcreating bad weather conditions.

15. Chinook Winds • Are warm winds that blow down the leeward side of mountain ranges especially the eastern slopes of the Rockies. • The sinking air is warmed by compression at a rate of about 1 Celsius per 100 meters. • Bring warm conditions to Calgary, Alb.

16. Land and Sea Breezes. (FIG 20.6)-very popular on the provincial exam! Land warms and cools much faster than water creating temperature and pressure changes between these two locations. During the summer the land heats rapidly after sunrise and air in contact with the ground also warms and expands. As the warm expanded air begins to rise, cool dense air from the ocean flows in to replace itSea Breeze

17. Animation: http://www.classzone.com/books/earth_science/terc/content/visualizations/es1903/es1903page01.cfm?chapter_no=visualization As night approaches the land cools rapidly and is now cooler than the ocean. Air over the warmer ocean begins to rise and the cooler air from the land moves out to replace it resulting in a land breeze. Valley and mountain breezes On hot summer day’s valleys act as wind tunnels generating extremely high winds in mountain passes. As the sun heats the mountain slopes, air begins to rise and is replaced by air rushing up the valley. The narrower the valley the stronger the wind. (opposite at night)

18. Local Wind Systems • Sea Breeze • Sun-heated air over land rises – Low pressure • Cooler air over water sinks – High pressure • Land Breeze • Night air over land cools fast – High pressure • Air over water stays warmer – Low pressure

19. Water Cycle (fig. 21.1) Continual movement of water from the oceans into the atmosphere, and back to earth (into the ocean) again is referred to as the water/hydrologic cycle. Evaporation of water leaves behind salt…therefore only freshwater is involved in the cycle. Most of the water comes from ocean, but we also get evaporation from lakes/rives and transpiration from vegetation. When moist air rises, it cools, and the water vapous condenses to form cloudswinds carry clouds over the continent and some comes down as snow or air. Some infiltrates the ground (remember aquifers!) the rest will runoff into rivers and lakes returns water back to the ocean Thing of three environmental issues that you have heard about that would relate to the water cycle?

20. http://www.sweetwater.org/education/watercycle.swfhttp://epa.gov/climatechange/kids/water_cycle_version2.htmlhttp://www.sweetwater.org/education/watercycle.swfhttp://epa.gov/climatechange/kids/water_cycle_version2.html Infiltration—water below ground remember aquifers Transpiration—evaporation of plants (release of water vapour) aka evapo- transpiratio Condensation—gas to liquid Evaporation—liquid to gas Precipitation—result of condensation the water reaching earth

21. Dew, Frost and clouds Dew Point Humidity amount of water vapour air contains Absolute humidity refers to the amount of water vapour present in a body of air. Relative humudity is the percentage of water vapout in the air 100 % saturated then dew point has been reached and water vapour begins to condense Warmer air can hold more vapour before it saturates Cold air is the oposite…some people say its too cold to snow and that is true because the air can only hold very little water Dew Why is the lawn wet in the morning after a clear night? Ground quickly loses much of the heat it gained during the day and begins to cool the air in contact with it. As air temperature drops, relative humidity continues to increase until 100% saturated. condensationresults in dew (below freezingfrost or ice)

22. FogWhen air close to earth is cooled enough that its dew point is reached, water vapour begins to condense and forms a low lying cloud Radiation Fog Forms during cloudless/windless nights seen in low lying valley bottoms as cooler dense air from the surrounding valley where the air quickly reaches dew point and condensation occurs. most common on land in late fall and winter Advection Fog Is produced as warm moist air cools to its dew point (saturation) while moving over a cold surface (always involves horizontal movements of air) Example—occurs along Pacific coast in the summer. Surface water is cooler than air above-air reaches dew point and fog is formed.

23. Radiation Fog Advection Fog