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Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
Natural Disasters Weather Basics Presentation
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Natural Disasters Weather Basics Presentation

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  • Uplift of Air
    The basic mechanism for raising air temperature occurs at ground level with the heating of the surface by the Sun. Consequently, temperatures generally fall with increasing altitude above the Earth's surface. Such a temperature profile in the lowest 10 km of the atmosphere allows significant uplift of air to take place, generating much of the world's weather.
    When a packet of air near the Earth’s surface is heated, it rises, being lighter than the surrounding air. This type of air uplift is called convection. Whether or not an air packet continues to rise will depend upon how stable the surrounding air is. As convection continues, air pressure begins to fall, and the air packet expands. Such expansion consumes heat energy and results in a fall in temperature. After sufficient cooling the dew point is reached and condensation occurs in the form of clouds. If the atmosphere is fairly stable, convection will be limited. Cumulus clouds often form in such atmospheric conditions. If the atmosphere is particularly unstable, uplift of air will continue to much greater altitudes, and huge towering cumulonimbus clouds may form, generating significant rainfall or hail.
    Uplift of air also occurs along fronts , when huge masses of air come together from different directions and with different temperatures. They cannot mix together immediately owing to their different densities, any more than two liquids like water and oil. Mixing takes time. In the meantime, the lighter, warmer air mass begins to rise above the cooler, denser one. The boundary between the two air masses is called a front. Fronts are accompanied by clouds of all types, and very often by precipitation.
    In addition to convection and frontal uplift there is a third lifting mechanism which produces cloud, and sometimes precipitation on its own, or enhances cloud and precipitation which already exists. This is the necessary lift air must make to surmount large obstacles which obstruct its passage. On an otherwise clear day, lift over hills and mountains may be enough to produce clouds over their tops. As the air descends over the other side, the clouds may dissipate. If the air is fairly humid, considerable precipitation may be generated over hills and mountains. Once past these obstructions, precipitation ceases as the air warms up and condensation returns to its vapor state. On the leeward side of mountain ranges, rain shadows can exist where little precipitation penetrates.
  • Stability of Air
    The stability of air in the atmosphere depends on the temperature of rising air relative to the temperature of the stationary surrounding air that it passes through, which varies from place to place and with changing atmospheric conditions. Air stability determines whether clouds form when air is uplifted, and the type of cloud.
    When a packet of air near the Earth’s surface is heated it rises, being lighter than the surrounding air. Whether or not this air packet continues to rise will depend upon how the temperature in the surrounding air changes with altitude. The rising packet of air will lose heat because it expands as atmospheric pressure falls, and its temperature drops. If the temperature of the surrounding air does not fall as quickly with increasing altitude, the air packet will quickly become colder than the surrounding air, lose its buoyancy, and sink back to its original position. In this case the atmosphere is said to be stable. If the temperature of the surrounding air falls more quickly with increasing altitude, the packet of air will continue to rise. The atmosphere in this circumstance is said to be unstable.
    As uplifted air cools, it condenses excess vapor out as cloud. The more unstable the atmosphere the more prolonged the uplift. Small cumulus clouds are evidence of a fairly stable atmosphere. Large cumulonimbus clouds are evidence of a highly unstable atmosphere, conducive to the formation of thunderstorms. Within depressions, atmospheric pressure is low and there is considerable atmospheric uplift and cooling at altitude, increasing atmospheric instability. Low-pressure systems are usually associated with an abundance of cloud and precipitation. In high-pressure systems or anticyclones, air may be descending, compressing and gaining energy , such that temperature at altitude rises, thereby increasing atmospheric stability. Anticyclones are often associated with cloudless skies.
  • Transcript

    • 1. Weather Basics Chapter 10 Climate and Weather Related to Hazards EXTREME WEATHER PHOTOS
    • 2. Earth Cycles Days: Rotation of the Earth on its axis. Seasons: Tilt of the Earth’s axis with respect to its annual orbit around the sun.
    • 3. Greenhouse Effect Carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons (CFC's) are some greenhouse gases of anthropogenic origin. Left: Greenhouse gases trap heat in the Earth’s atmosphere much as the glass in a greenhouse permits the sun to shine in but prevents most heat from escaping.
    • 4. Weather is 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. Weather
    • 5. 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
    • 6. 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
    • 7. 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.
    • 8. Relative Humidity Saturation vapor pressure = Maximum amount of moisture air can hold •cannot be exceeded. •evaporation = condensation •temperature dependent. Relative Humidity = The percentage of moisture in air relative to the maximum amount it can hold (Saturation Vapor Pressure) under its given temperature and pressure.
    • 9. 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.
    • 10. 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. The adiabatic 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).
    • 11. 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.
    • 12. Warm Front (Left): Warm air mass advances rapidly. Cold Front (Right): Cold air mass advances rapidly.
    • 13. 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.
    • 14. 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.
    • 15. 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).
    • 16. Wind Horizontal differences in air pressure between high and low pressure systems create winds. Wind results when air flows from a place of high pressure to one of low pressure. Magnitude is determined from the spacing of the isobars. Isobars - lines connecting places of equal air pressure on a map (Compare to the slope of a hill). The spacing of the isobars indicates the amount of pressure change over a given distance = pressure gradient.
    • 17. 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. Deflection increases with wind speed. Deflection is strongest at the poles and weakens equator ward.
    • 18. Convergent and Divergent Flow In the Northern Hemisphere •Around a low pressure cell (rising air), an inward counterclockwise flow develops near the ground surface; Centers of low pressure are called cyclones = convergent flow •Around a high pressure cell (sinking air), an outward clockwise flow develops near the ground surface. Centers of high pressure are called anticyclones = divergent flow.
    • 19. Right Hand Rule for Rising or Falling Air in the Northern Hemisphere (Left Hand Rule for the Southern Hemisphere)
    • 20. 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
    • 21. 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.

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