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Weather Factors Chapter 16 15.1The Air Around You ► Earth's Atmosphere is: A mixture of gases with some suspended solids and liquids. ► Three common solids in atmosphere: ► Ice ► Dust ► Salt ► Gas - from ocean spray Composition of Earth's atmosphere: Nitrogen -78% of atmosphere Oxygen - 21% of atmosphere Trace gases -1% - Carbon Dioxide , Argon, Neon, Helium, Hydrogen, Methane 15.2 Air Pressure ► Air consists of atoms & molecules therefore air has mass Because it has mass it also has Density Density = Mass/Volume Pressure – weight of air pressing down on you is the same as a school bus BUT air is pushing in all directions so it balances out ► Measure by a barometer: Mercury Barometer – liquid mercury Aneroid Barometer – without liquid Altitude or Elevation ►Distance above sea level ►Air Pressure decreases as Altitude Increases thus so does density ►Molecules are spaced out more thus it is more difficult to breath 15.3 Layers of the Atmosphere ►5 layers: ► 1. Troposphere – area closest to the ground, 75%of the gases, dust, ice and liquid water-Weather, Clouds, and smog occur here ► 2. Stratosphere – Ozone layer ► 3. Mesosphere – ► 4. Thermosphere – contains the ionosphere where electrical charged particles are (get AM radio at night when sun goes down, particles quit jumping) ► 5. Exosphere – upper most portion Earth’s Atmosphere and its Energy ► Energy comes from the sun in the form of Electromagnetic Waves Energy Transfer occurs by: ► Radiation – electromagnetic waves, no contact but still feel it, moves from object with a higher temperature to one with a lower temperature ► Conduction – direct contact, fast moving molecules to slow moving molecules ► Convection – density differences, air is warmed, the air molecules move apart which increases the volume of air which reduces its density thus the air raises and causes a circular movement of air called a convection current ► Earth’s Movement of Air surface is curved rather than flat, air equator is heated more than any other place on Earth ► Coriolis Effect – caused by Earth’s rotation, air masses moving south in the Northern Hemisphere are turned westward (because Earth is moving to the east) ► Doldrums Wind Systems – windless zone at the equator ► Trade Winds – 15o North or South of the equator blow to the southwest (NH)/northwest (SH) ► Prevailing Westerlies – 30o and 60o North and South winds blow in the opposite direction as the trade winds SW to NE in NH and in SH NW to SE ► Polar Easterlies – NE to SW near the North Pole and from the SE to the NW in the SH ► Jet Streams – winds near top of troposphere ► Sea and Land Breezes – convection current where land meets the sea (sea/day – land/night) Factors of Weather ► Humidity – amount of water vapor in the air ► (cooler air, slower, condenses – rains ► Hot air, faster, air holds more moisture ► Relative humidity – amount of water vapor in air as a percentage of amount it can hold Saturated air – 100% relative humidity Dew Point – temperature at which it condenses ► Clouds formed when the humid air is cooled to its dew point and condenses ► Fog- is a stratus cloud close to the ground ► Precipitation – occurs when water droplets reach .2 mm http://www.schoolship.org/training-manual/page10.gif ► Air Weather Patterns mass – large body of air that has the same properties as the surface over which it develops ► Fronts – boundary between 2 air masses as they collide ► Warm Front – warm air mass slides under cold air mass (less dense) High cirrus clouds, ► Cold Front – cold air invades cold, cumulus clouds and rain ► Stationary Front – pressure differences and it doesn’t move lights winds and rains ► Occluded Front – 2 cool air masses forces warm air up, heavy precipitation and wind ► Precipitation from warm air being cooled