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Slide 1 Visualizing Physical Geography by Timothy Foresman & Alan Strahler Chapter 5 Global Atmospheric and Oceanic Circulation ___________________________________ ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 2 ___________________________________ Chapter Overview Atmospheric Pressure Wind Speed and Direction Global Wind and Pressure Patterns Local Winds ___________________________________ ___________________________________ Oceanic Circulation ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 3 Atmospheric Pressure ___________________________________ Atmospheric pressure • Pressure exerted by the atmosphere because of the force of gravity acting on the overlying column of air ___________________________________ Measuring Atmospheric Pressure • Units = inches of mercury (in. Hg) or millibars (mb) • Standard sea level pressure = 1013.2 mb • Cold, clear night pressure > 1013.2 mb • Center of a storm with rising warm air will have a pressure lower than 1013.2 mb Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. ___________________________________ ___________________________________ Slide 4 Atmospheric Pressure ___________________________________ Measuring Atmospheric Pressure • Radiosonde (balloon) is launched twice a day at key locations in United States ___________________________________ • Radiosondes measure: • Pressure • Altitude • GPS location • Temperature • Relative humidity • Wind speed and direction ___________________________________ Would one expect low or higher than standard sea level pressure in a hurricane? ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 5 Atmospheric Pressure Atmospheric Pressure and Altitude ___________________________________ ___________________________________ • Atmospheric Pressure decreases with altitude ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 6 Wind Speed and Direction ___________________________________ Wind • Horizontal movement of air • Renewable resource • Measured with an anemometer ___________________________________ Wind Direction • Identified by the direction from which the wind comes • West wind blows from west to east • Measured with a wind vane Wind speed and direction are determined by 3 factors: pressure gradient, coriolis effect, and friction Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. ___________________________________ ___________________________________ Slide 7 Wind Speed and Direction ___________________________________ Pressure Gradients • Change of atmospheric pressure measured along a line at right angles to the isobars • Pressure gradient goes from high to low pressure ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 8 Wind Speed and Direction ___________________________________ Pressure Gradients • Isobar = line on a map drawn through all points having the same atmospheric pressure • Widely spaced isobars weak gradient and weaker winds • Closely spaced isobars strong PG and stronger winds ___________________________________ ___________________________________ Where would you find the greatest pressure gradient on this map? a. Oklahoma City b. Southwestern Missouri c. Memphis d. Nashville ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 9 Wind Speed and Direction ___________________________________ Pressure Gradients • Unequal heating of the Earth’s surface leads to a pressure gradient and causes wind • Latitude, terrain differences and land cover can cause uneven heating, pressure gradients and wind 1 ___________________________________ 2 ___________________________________ 3 ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 10 Wind Speed and Direction ___________________________________ Pressure Gradients If the island were in the Arctic and covered by glacial ice, would the pressure gradient be the same or different? ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 11 Wind Speed and Direction ___________________________________ The Coriolis Effect (CE) • An effect of the Earth’s rotation that acts like a force to deflect a moving object on the Earth’s surface to the: • Right in the northern hemisphere • Left in the southern hemisphere ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 12 Wind Speed and Direction ___________________________________ The Coriolis Effect (CE) ___________________________________ ___________________________________ • Due to Earth’s rotation, a path from the North Pole to Chicago along 74° W meridian would curve to the right, toward Chicago. Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. ___________________________________ Slide 13 Wind Speed and Direction The Geostrophic Wind • Wind at high levels (upper levels) above the Earth’s surface moving parallel to the isobars, at a right angle to the pressure gradient ___________________________________ ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 14 Wind Speed and Direction The Frictional Force (FF) • Force exerted by the ground surface that is proportional to the wind speed and always acts in the opposite direction to the direction of motion • Greatest closest to the surface ___________________________________ ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 15 Wind Speed and Direction ___________________________________ Cyclone (low pressure) • The PGF, CE, and FF cause the surface wind to spiral, converging inwards towards the low-pressure center ___________________________________ ___________________________________ • As the inward motion converges, it forces the air to rise (uplift) cools adiabatically clouds and precipitation Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. ___________________________________ Slide 16 Wind Speed and Direction ___________________________________ Anticyclone (high pressure) • Upper troposphere winds spins downward (subsidence) and diverges outward at the surface ___________________________________ ___________________________________ • Air warms adiabatically as it sinks inhibiting clouds and precipitation ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 17 Global Wind and Pressure Patterns ___________________________________ Global surface winds on an ideal Earth ___________________________________ ___________________________________ •Surface winds are shown on the disk of the Earth, and the cross section at the right shows winds aloft ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 18 Global Wind and Pressure Patterns ___________________________________ Tropical Circulation • Warm air over the equator rises and form low pressure resulting in the equatorial trough (wet weather) • Trade winds converge at the equator • Air descends near 25 to 30o latitude forming a subtropical high pressure (dry weather) zone Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. ___________________________________ ___________________________________ ___________________________________ Slide 19 Global Wind and Pressure Patterns ___________________________________ Tropical Circulation • Hadley Cell = A lowlatitude atmospheric circulation cell with rising air over the equatorial trough and sinking air over the subtropical highpressure belts. ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 20 Global Wind and Pressure Patterns Intertropical Convergence Zone (ITCZ) • A zone of convergence of air masses along the equatorial trough • Doldrums • ITCZ shifts with the seasons following the zone of highest insolation • Over the ocean it shifts a few degrees between January and July • Over land, the zone shifts 20o to as much as 40o in Asia ___________________________________ ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 21 Global Wind and Pressure Patterns ___________________________________ Tropical Circulation • Monsoon = seasonal reversal of the wind • January = north wind (dry) • July = warm, moist air (wet) ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 22 Global Wind and Pressure Patterns ___________________________________ Considering the direction of the winds compared to the isobars, which statement is most correct? a. Because this area is near the equator, the Coriolis effect has no influence on these winds. b. Because the pressure gradients are great, friction has no influence on these winds. c. Because some of the winds are over the ocean, neither the Coriolis effect nor friction has an influence on these winds. d. Because the alignment of the wind direction is at 45° to the isobars, both the Coriolis effect and friction are important. ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 23 Global Wind and Pressure Patterns ___________________________________ North American Monsoon ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 24 Global Wind and Pressure Patterns ___________________________________ Subtropical High Pressure Cells • Area of high atmospheric pressure centered at about 30° N and 30° S • Stable and dry weather • Trade winds and westerlies • Hawaiian and Azores high • Shift with the seasons • East and west coast differences Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. ___________________________________ ___________________________________ ___________________________________ Slide 25 Global Wind and Pressure Patterns ___________________________________ In the days of sailing ships, which pattern of navigation made the most sense, considering prevailing wind directions? a. United States to Africa to England back to the United States b. United States to England to Africa back to the United States c. United States to England back to the United States d. United States to Africa back to the United States ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 26 Global Wind and Pressure Patterns ___________________________________ Midlatitude Circulation • Westerlies • Between about 30° and 60° latitude • Polar front = boundary between cold polar air masses and warm subtropical air masses ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 27 Global Wind and Pressure Patterns ___________________________________ Midlatitude Circulation • Jet stream = Highspeed airflow in a narrow band within the upper-air westerlies and along certain other global latitude zones at high altitudes • Polar-front jet stream • Shifts equatorward in the winter • Subtropical Jet stream ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 28 Global Wind and Pressure Patterns ___________________________________ What a Geographer Sees • Air travel and Jet Streams ___________________________________ ___________________________________ If an airplane flying in the center of this subtropical jet stream travels east at 1000 km/hr (621 mi/hr), how fast will the same airplane go, with the same fuel expenditure, when it travels west in the jet stream on its return flight? ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 29 Global Wind and Pressure Patterns ___________________________________ Jet stream disturbance • Rossby waves • Baroclinic instability • Zonal flow (west to east) ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 30 Global Wind and Pressure Patterns ___________________________________ Jet stream disturbance • Growth of disturbances in the jet stream ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 31 Global Wind and Pressure Patterns High-Latitude Circulation ___________________________________ ___________________________________ • January and July ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 32 Global Wind and Pressure Patterns ___________________________________ Global Circulation at Higher Altitudes ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 33 Global Wind and Pressure Patterns ___________________________________ Global surface winds on an ideal Earth (Review) ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 34 Global Wind and Pressure Patterns ___________________________________ Global Air Cells: Ferrel, Hadley, or Polar (Review)? ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 35 ___________________________________ Local Winds Daily Cycles of Winds • Daily reversal of the winds as a result of uneven heating • Sea breeze • Land Breeze ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 36 ___________________________________ Local Winds Daily Cycles of Winds •Mountain breeze •Valley Breeze ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 37 ___________________________________ Local Winds Other Topographic Winds • Chinook For north–south mountain ranges in midlatitude regions (30° to 45° latitude), dry regions will be found on the ____ side in the northern hemisphere and on the ____ in the southern hemisphere. a. east; east b. west; west c. east; west d. west; east ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 38 ___________________________________ Local Winds Other Topographic Winds •Santa Ana winds •Wildfires have already begun in some areas, as is apparent from the smoke drifting off the Southern California coast. ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 39 Oceanic Circulation ___________________________________ Ocean Currents • A persistent, dominantly horizontal flow of water controlled by wind patterns • Gyres ___________________________________ ___________________________________ What relationship do you notice with the northern hemisphere ocean current and the pressure type typically located at 30oN ? Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. ___________________________________ Slide 40 Oceanic Circulation ___________________________________ Ocean Circulation and Energy Transport • Warm surface waters in the tropics move poleward • Thermohaline Circulation • Cold and dense in the N. Atlantic, these waters sink, flow equatorward, and eventually upwell to the surface at far distant locations to cool the surrounding regions and complete the circuit ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 41 Oceanic Circulation ___________________________________ Circulation and Energy Transfer • Energy surplus • Energy deficit • In order to maintain the Earth’s energy balance, absorbed solar energy is moved from regions of excess to regions of deficit, carried by ocean currents and atmospheric circulation ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 42 Oceanic Circulation ___________________________________ Cycles in Atmospheric and Oceanic Circulation • El Niño–Southern Oscillation (ENSO) • La Niña ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 43 Oceanic Circulation ___________________________________ Cycles in Atmospheric and Oceanic Circulation • Climate effects of El Niño events ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc. Slide 44 Oceanic Circulation ___________________________________ Cycles in Atmospheric and Oceanic Circulation • North Atlantic Oscillation (NAO) • Pacific Decadal Oscillation (PDO) ___________________________________ ___________________________________ ___________________________________ Visualizing Physical Geography Copyright © 2012 John Wiley & Sons, Inc.
