Weather 09 10


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Weather 09 10

  1. 1. Weather
  2. 2. Atmosphere <ul><li>Characteristics </li></ul><ul><li>The Earth’s atmosphere is a mixture of gases, dust and water vapor. The atmosphere is divided into layers based on temperature changes. The lowest layer is called the troposphere, it is where weather occurs. The temperature and pressure decreases as the altitude increases. </li></ul>
  3. 3. Atmosphere <ul><li>Heating </li></ul><ul><li>The Earth is heated by the energy from the Sun. </li></ul><ul><li>The amount of solar radiation an area receives is due to the angle the sunlight strikes the surface. Areas near the equator are heated more than the poles. </li></ul>30% reflected 50% reaches surface 20% absorbed by atmosphere Spreads out concentrated
  4. 4. Wind <ul><li>When the air is heated it rises and is replaced by cooler air. </li></ul><ul><li>Three convection cells are formed in the Northern hemisphere. </li></ul><ul><li>The rotation of the Earth causes the winds in the cells to “turn” causing winds to blow in one main direction depending on latitude. </li></ul>
  5. 5. Water Cycle
  6. 6. Humidity <ul><li>Humidity is the amount of water vapor in the air. </li></ul><ul><li>Relative humidity is the ratio of the actual amount of water vapor in the air to the amount of water the air can hold at a specific temperature. </li></ul><ul><li>The warmer the air the more moisture it can hold. </li></ul><ul><li>As warm air rises it cools and the relative humidity increases until it reaches 100%, then clouds will form. Precipitation may occur at this time. </li></ul>
  7. 7. Humidity & Precipitation <ul><li>Humidity is measured using a hygrometer or a sling psychrometer. Relative humidity is always given as a percent (%) </li></ul><ul><li>Precipitation is measured with a rain gauge and a ruler. </li></ul>
  8. 8. Weather, Climate, and Temperature <ul><li>Weather is the condition of the atmosphere at the present time. </li></ul><ul><li>Climate is the overall average temperature and precipitation for a region. </li></ul><ul><li>Thermometers (digital, liquid, or metal coil) are used to measure temperature. </li></ul>
  9. 9. Air Pressure <ul><li>Air pressure is the weight of the atmosphere all around an object. </li></ul><ul><li>When the air pressure increases it means a high pressure system is moving towards you, thus fair weather. </li></ul><ul><li>When the barometer is falling it means a low pressure system is moving in and it will soon rain/snow or be cloudy. </li></ul>
  10. 10. Barometer <ul><li>A digital, dial, or liquid barometer is used to measure air pressure. </li></ul><ul><li>On most barometers you must take two readings to tell if the air pressure is increasing or decreasing. Air pressure is difficult to detect without an instrument. </li></ul>
  11. 11. Wind Speed & Wind Direction <ul><li>Wind Speed is measured with an anemometer, which can be digital or mechanical. </li></ul><ul><li>Wind Direction – the direction the wind is coming from . (measured using: weather vane, windsock) </li></ul>
  12. 12. Weather Maps <ul><li>Weather maps are used to show existing conditions and predict changes. </li></ul>
  13. 13. Fronts <ul><li>Where cold and warm air meet. </li></ul>Warm Front Cold Front
  14. 14. Severe Weather <ul><li>Watch – conditions could produces severe weather </li></ul><ul><li>Warning – severe weather is occurring or is expected to occur </li></ul>
  15. 15. Thunderstorms <ul><li>Warm moist air rises creating a low pressure area. The raising air cools until it reaches the Dew Point (100% R.H.) Warm air weighs less than cold air, moist air weighs less than dry air. </li></ul><ul><li>Thunderstorms have areas of strong updrafts and strong downdrafts. Hail is formed when the tops of the large thunderhead clouds are below freezing. The hail falls, gets coated with water, is caught in the updraft and is refrozen when it reaches the top. </li></ul>
  16. 17. 6 and 1/8 inch hailstone
  17. 18. Largest hailstone in U.S. history: 7 in. diameter
  18. 19. Lightning <ul><li>Lightning is a static discharge from clouds to ground, ground to cloud, or cloud to cloud. </li></ul>
  19. 20. Tornadoes <ul><li>Wind speed to 300 mph </li></ul><ul><li>Occurs in spring/early summer </li></ul><ul><li>Called a funnel cloud if it does not touch the ground. </li></ul><ul><li>Most common in Texas, Kansas, and Oklahoma </li></ul>
  20. 21. Hurricanes <ul><li>Wind speed up to 150 mph </li></ul><ul><li>Occurs in late summer </li></ul><ul><li>Called Typhoons in the Pacific </li></ul><ul><li>Low pressure area 400 miles wide that rotates </li></ul><ul><li>The eye is calm, fastest winds are just outside the eye </li></ul>