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  • 1. The Earth's weather system represent complex interactions between the oceans, the land, the sun, and the atmosphere.

2. 3.

  • Weatheris the condition of the atmosphere at a particular time and place. It refers to such conditions of the local atmosphere as
  • temperature,
  • atmospheric pressure,
  • humidity (the amount of water contained in the atmosphere),
  • precipitation (rain, snow, sleet, & hail),
  • wind velocity .

4. Vertical Structure of the Atmosphere General trends with increasing altitude: Air pressure decreases . At any given altitude, the air pressure is caused by the weight of air above.Constituent gases decrease in density . Because air pressure decreases with altitude, the amount of air per unit volume (density) also decreases with altitude.Temperature decreases in the troposphere where weather occurs . Water vapor decreases dramatically 5. Composition of the Atmosphere

  • The gaseous envelope that surrounds the planet.
  • Because air pressure decreases with altitude, the amount of air per unit volume (density) also decreases with altitude.
  • The relative proportions of the gases in the air are essentially constant regardless of altitude.Nitrogen, Oxygen, and argon make up 99.96% of the gases by volume.

6. Greenhouse Effect

  • Carbon dioxide, water vapor, methane, greenhouse gasesandchlorofluorocarbons (CFC's) are some greenhouse gases.
  • .

7. Air Pressure

  • Air pressure decreases with altitude.At any given altitude, the air pressure is caused by the weight of air above.This means that the air near the ground is compressed by the weight of the air above it.
  • As air pressure decreases, air density decreases.

8. Water Vapor in the Atmosphere

  • Water can exist in all 3 states at the normal range of earth temperature and pressure.
  • Whenever matter changes from one state to another, energy is either absorbed or released.
  • From liquid to gas -evaporation- heat energy is absorbed
  • From gas to liquid -condensation- heat energy is released

9. The Hydrologic Cycle Water continuously evaporates from oceans and other water bodies, falls as rain or snow, is transpired by plants, and flows through streams and groundwater back to the oceans. 10. Relative Humidity

  • Air is saturated when evaporation = condensation.Temperature dependent.
  • Saturation vapor pressure of air at any given temperature cannot be exceeded.
  • Relative humidity = the ratio of the vaporpressure in a parcel of air to the saturation vapor pressure at the same temperature.

11. Therefore, relative humidity can be changed by...

  • Changing the water vapor content.
    • Add water, increase relative humidity
    • subtract water, decrease relative humidity
  • Changing the temperature.
    • Increase temperature, decrease relative humidity
    • Decrease temperature, increase relative humidity.

12. Adiabatic Processes

  • Processes that occur without the addition or subtraction of heat from an external source.
  • Because air pressure decreases with increasing altitude, rising air expands and sinking air is compressed.
    • Compressional warming- when air is compressed, the temperature rises.
    • Expansional Cooling- when air expands, the temperature decreases.
  • Theadiabatic lapse rate- the way temperature changes with altitude in rising or falling air (top right).
  • Lifting condensation level= altitude at which the rising parcel reaches saturation temperature and cloud forms (bottom right).

13. Upward movement of air results from:

  • Convergence lifting- when flowing air masses of equal density converge and are forced upward.
  • Convective (Density) lifting- When warm, low-density air rises convectively and displaces cooler, denser air.
  • Orographic lifting- When flowing air is forced upward over a mountain range.
  • Frontal lifting- when two flowing air masses of different density meet.

14. Warm Front (Left):Warm air mass advances rapidly. Cold Front (Right): Cold air mass advances rapidly. 15. Atmospheric Stability

  • Two assumptions:
        • Lifting processes force air upward.
        • Rising air does not mix substantially with the surrounding atmosphere.

Atmospheric stability is a property of air that describes its tendency to remain in its original position or sink (stable) or to rise (unstable) once the initial lifting force ceases. A parcel of air forced to rise will expand and cool adiabatically. 16. Atmospheric Stability Stable air- if an air parcel that is forced aloft cools faster than the surrounding environment.If the lifting forced ceased, the parcel would have the density to sink. High pressure system an area characterized by descending cooler dry air and clear skies. Cloud formation may occur at an altitude where the saturation temperature is reached (LCL), but clouds would be layered without much vertical development - fair weather clouds. 17. Atmospheric Stability Unstable air- if an air parcel that is forced aloft cools slower than the surrounding environment. If the lifting force ceased, the parcel will continue to rise because it is warmer and more buoyant than its surroundings. Low pressure system An area characterized by rising warmer and humid air and cloudy skies. If the air parcel rises to an altitude where the saturation temperature is reached (LCL), clouds with vertical development will form as the buoyant air rises on its own. (thunderstorm clouds). 18. Tornadoes How a Tornado Works - Associated with strong thunderstorms that develop when 3 main atmospheric conditions occur simultaneously in the central US 1) a northerly flow of warm, moist air from the Gulf of Mexico 2) a cold, dry air mass rapidly moving southward from Canada or the Rocky Mountains 3) strong easterly jet stream- These three air masses moving in different directions produce shearing conditions that are give thunderstorm clouds a "spin" - Funnel clouds begin to form, they may (or may not) touch down and develop into a tornado. 19. Tornadoes.

  • Warm moist air tropical air shoots upwardas it meets colder, dryer polar air. As the warm moist air rises, it may meet varying wind directions at different altitudes due to a strong westerly jet stream.If these varying winds are staggered in just the right manner with sufficient speed, they will act on the upward rising air, spinning it like a top.

20. The rotational cell sags below the cloud base to form a distinctive slowly rotating wall cloud.Strong tornadoes form within and then descend from the wall cloud. 21. Tornado Characteristics

  • About 70% of all tornadoes on Earth occur in the central and southern US.
  • One section of the nation is best at producing tornadoes. This area is called "Tornado Alley," (shown on the map).- Northern Texas and Oklahoma
  • Occur mostly in late spring - early summer when conditions are best for tornado formation; but can occur anytime.
  • Can move at speeds up to ~60 mph and have max wind speeds of >300 mph.

22. Tornado "magnitude" measured on the Fujita Scale (F1-F5); based on Damage 23. Wind

  • Wind is a horizontal air movement arising from differences in air pressure.
  • Wind results when air flows from a place of high pressure to one of low pressure.

Isobars - lines connecting places of equal air pressure on a map. 24. Wind

  • The spacing of the isobars indicates the amount of pressure change over a given distance = pressure gradient.
  • Compare to the slope of a hill

25. Coriolis Effect

  • Due to the rotation of the earth on its axis.
  • Deflects all free moving objects to the right of their path in the Northern Hemisphere and to the left in the Southern Hemisphere.
  • Strongest at the poles, nonexistent at the equator.
  • Deflection increases with wind speed.

26. Convergent and Divergent Flow

  • In the Northern Hemisphere
  • Around a low pressure cell, aninward counterclockwise flowdevelops;Centers of low pressure are calledcyclones=convergent flow
  • Around a high pressure cell, anoutward clockwise flowdevelops.Centers of high pressure are calledanticyclones=divergent flow .

27. Vertical Flow Net downward movement of air and fair weather Net upward movement of air, often resulting in cloud formation and precipitation . Low pressure center generally related to unstable conditions and stormy weather 28. Around a surface high air is spiraling outward, which leads to a downward flow of air at the center of the high and convergence aloft. Around a surface low air is spiraling inward, which leads to an upward flow of air at the center and divergence aloft. 29. HURRICANES

  • A hurricane is a massive tropical cyclone with rotary winds that exceed 74mph blowing counterclockwise around a relati