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Chapter 6

GG101 Chapter 6 Notes.docx

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Wilfrid Laurier University
James Hamilton

Chapter 6 Notes- Atmospheric and Oceanic Circulations  Air Pressure and Global Winds o Intro o Measurement of Air Pressure o Driving Forces o High and Low pressure areas o General circulation of the atmosphere Mount Pinatubo  Released 15-20M tons of ash, dust and sulfur dioxide into the atmosphere  Technology now permits analysis o Satellites are capable of tracking effects of dust storms, forest fires, industrial haze, warfare, and dispersal of volcanic explosions o Dust from African soil is carried across Atlantic, promoting the toxic algal blooms known as red tides o Global winds are a reason why US, USSR and GB signed Limited Test Ban Treaty Wind Essentials  Atmospheric circulation is generally categorized at three levels: o Primary: consisting of general worldwide circulation o Secondary: migratory high-pressure and low-pressure systems o Tertiary: local winds, temporal weather patterns  Zonal Flows: winds moving east or west along parallels of latitude Air Pressure:  Created by molecules that constitute air  Air pressure is the product of the temperature and density of a mass of air o Torricelli’s experiment (textbook page 145) o Normal air pressure expressed as 101.32Kpa (kilopascale) o Earth’s range is 105-98kpa  Barometer: any instrument measuring air pressure  Aneroid barometer: uses no liquid; uses needle on a dial- as air pressure increases it presses on the chamber, and vice versa, i.e. Aircraft altimeter- measures altitude as air pressure decreases above sea level Wind: Description and measurement  Wind: horizontal motion of air across Earth’s surface o Turbulence adds wind updrafts and downdrafts, also a vertical component o Wind’s two physical properties are speed and direction o Anemometer measures wind speed in kph, mph, or knots o Wind Vane: determines wind direction; the standard measurement Is taken 10m above the ground to reduce the effects of local topography on wind direction  Winds are named for the direction from which they originate o A westerly wind blows eastward o Beaufort wind scale: particularly useful in measuring wind speed (visually) on both land and water; many ships have it- measures calm to hurricanes (0-17)  Global Winds o The patterns in the figure are the result of specific forces at work in the atmosphere: pressure gradient force, friction force, Coriolis force and gravity o Gravitational force: virtually uniform, compresses the atmosphere worldwide, with higher density in lower altitudes o Pressure Gradient: drives air from areas of higher barometric pressure (more dense air) to areas of lower barometric pressure (less) thereby causing winds o Coriolis: deflective force that makes wind travel in a straight path appear to be deflected in relation to Earth’s rotating surface o Friction: drags on the wind as it moves across surfaces- slows down wind  Pressure Gradient Force o Isobar: isoline (a line with constant value) plotted on a weather map to connect points of equal pressure o A pattern of isobars on a weather map provides a portrait of the pressure gradient between an area of higher pressure and one of lower pressure o Steep gradients causes faster air movement from a high-pressure area to a low-pressure one o Coriolis Force: deflects anything that flies or flows across Earth’s surface- wind, an airplane, ocean currents  Earth’s rotational speeds vary by latitude, 0mph at poles to 1041mph at equator  Airplane does not actually deviate from a straight path; instead it appears to do so because we are standing on Earth’s rotating surface beneath the airplane. As a result, airplanes must make constant corrections in flight path to maintain a “straight” heading (due to rotations)  Balances pressure gradient force, resulting in sprialing winds  Geostrophic winds: produces winds that do not flow directly from high to low, but around pressure aras parallel to isobars o Friction force: adds effect of friction to the coriolis and pressure gradient forces on wind movements  Northern Hem winds spiral out from a high pressure area clockwise to form an anticyclone and spiral into a low pressure area to form cyclones Atmospheric Patterns of Motion Primary winds stretch across the face of the planet Secondary winds form within these areas; systems that seasonally migrate to produce changing weather patterns in the regions over which they pass Four broad pressure areas cover the Northern and Southern Hemisphere each: oEquatorial low-pressure trough  Constant hot weather, 12 hour days, low pressure ascending air, wet weather  Heating and convergence forces form intertropical convergence zone (ITCZ)
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