Global Winds AOSC 200 Tim Canty Class Web Site: http://www.atmos.umd.edu/~tcanty/aosc200 Topics for today: Global Wind Patterns Deserts Jet Stream Monsoons Ocean transport Ocean cycles Lecture 16 Oct 24 2017 1 Global Temperatures What region of the planet is warmest? What happens to the air at this location? 2
Regions of the World Fig 7.24: Essentials of Meteorology 3 Height of tropopause decreases as you get closer to poles Thermal Wind Fig 6-23 Meteorology: Understanding the Atmosphere 4
Hadley Cell This doesn t explain the mid-latitude Westerlies Fig 7.24: Essentials of Meteorology 5 Conceptual Model Polar Cell Ferrel Cell http://www.ux1.eiu.edu/~cfjps/1400/circulation.html 6
Angular Momentum When air moves from the Equator to the Poles, it s rotational radius is also decreasing. So, wind velocity must increase to conserve angular momentum Bottomline: Wind speeds up as it moves away from the equator The faster the wind the stronger the Coriolis force 7 Hadley Cell Fig 7-7 Meteorology: Understanding the Atmosphere 8
The Jet Streams Tropopause height decreases as you move toward Pole Jet Streams form where the fronts meet Wind speeds greater than 100 mph Notice: the fronts are slanted toward the N. Pole 9 The Polar Jet Streams Tropopause height decreases as you move toward Pole Fig 7.35: Essentials of Meteorology 10
The Jet Streams Tropopause height decreases as you move toward Pole Pressure Gradient Force will push the air from south to north, Coriolis forces will move it to the right in the N. Hemisphere. 11 The Jet Streams (strong upper level Westerlies) Fig 7.33: Essentials of Meteorology 12
Force Balance in 3-D When air converges at a surface low pressure system, it can get pushed up and condense What happens when air sinks toward a surface high pressure system? Fig 6-24 Meteorology: Understanding the Atmosphere 13 Force Balance in 3-D The air will warm as it sinks and gets drier This sinking air will also inhibit convection Fig 6-24 Meteorology: Understanding the Atmosphere 14
ITCZ The region where the trade winds meet, near the Equator is called the Intertropical Convergence Zone (ITCZ) Fig 7.27: Essentials of Meteorology 15 Sea-level pressure in Summer Low pressure systems form over land in N.H. summer: Thermal Lows ITCZ has moved northward Similar pattern develops in S.H during summer Fig 7.28: Essentials of Meteorology 16
Sea-level pressure in Winter Low pressure systems form over land in N.H. summer: Thermal Lows ITCZ has moved northward Similar pattern develops in S.H during summer Fig 7.28: Essentials of Meteorology 17 Monsoon Dry Season ITCZ is south, dry surface air flows off of Tibetan plateau Wet Season ITCZ is north, moist surface air flows off of Indian ocean onto land Fig 7.20: Essentials of Meteorology 18
Monsoon Fig 7.21: Essentials of Meteorology 19 Sea-level pressure in Summer N.H. summer: thermal lows over land, high pressure over ocean 20
Ocean Currents Fig 8-6 Meteorology: Understanding the Atmosphere 21 Ocean Currents North Atlantic Gyre driven by trade winds and Westerlies Fig 8-8 Meteorology: Understanding the Atmosphere 22
Ekman Transport Ocean water pushed by wind but is also affect by Coriolis forces Fig 7.39: Essentials of Meteorology 23 Ekman Spiral and Ekman Transport http://www.meted.ucar.edu/fogstrat/ic31/ic313/graphics/comet/ekman.gif 24
Ekman Spiral and Ekman Transport Water off the coast of Southern California is cold and teeming with life Great for fishing!!!! 25 Ocean Currents Fig 8-6 Meteorology: Understanding the Atmosphere 26
Conceptual Model Polar Cell Ferrel Cell http://www.ux1.eiu.edu/~cfjps/1400/circulation.html 27 Normal Conditions
El Niño: warm water sloshes to the east During an El Nino, easterly trade winds weaken and warm water is transported from western pacific to eastern pacific El Niño Warming of Pacific Ocean off coast of South America near Ecuador and Peru. May lead to variations in weather Fig 8-11 Meteorology: Understanding the Atmosphere 30