Transcript Slide 1
Meteorology 10 - Weather and Climate Fall 2008 CHAPTER 7 FOCUS: air circulation patterns on Earth Atmospheric Circulations Chapter 7: Atmospheric Circulations • • • • • Scales of atmospheric motions Eddies - big and small Local wind systems Global winds Global wind patterns and the oceans Scales of Atmospheric Motions Scales of Atmospheric Motions • • • • scales of motion microscale synoptic scale planetary scale • Lots of important weather events occur on microscales, like evaporation of liquid water molecules from the earth’s surface. Eddies - Big and Small Eddies - Big and Small • • • • eddy rotor wind shear turbulence • Wind shear can sometimes be observed by watching the movement of clouds at different altitudes. Local Wind Systems Thermal Circulations • isobars and density • differences • thermal circulations Stepped Art Fig. 7-4, p. 172 Sea and Land Breezes • • • • sea breeze land breeze sea breeze front Florida sea breezes • Sea and land breezes also occur near the shores of large lakes, such as the Great Lakes. Stepped Art Fig. 7-5, p. 174 Seasonally Changing Winds the Monsoon • Monsoon wind system • Asian monsoon • other monsoons Mountain and Valley Breezes • valley breeze • mountain breeze • The nighttime mountain breeze is sometimes called gravity winds or drainage winds, because gravity causes the cold air to ‘drain’ downhill. Katabatic Winds • drainage winds • bora • Katabatic winds are quite fierce in parts of Antarctica, with hurricane-force wind speeds. Chinook (Foehn) Winds • Chinook winds • compressional heating • chinook wall cloud • In Boulder, Colorado, along the eastern flank of the Rocky Mountains, chinook winds are so common that many houses have sliding wooden shutters to protect their windows from windblown debris. Fig. 7-14, p. 180 Santa Ana Winds • Santa Ana wind • compressional heating • wildfires • Many Southern California residents regularly hose down their roofs to prevent fires during Santa Ana wind season. Desert Winds • dust storms • dust devils Global Winds General Circulation of the Atmosphere • cause: unequal heating of the earth’s surface • effect: atmospheric heat transport • Ocean currents also transport heat from the equator to the poles and back. Sun’s energy is not distributed evenly over Earth Tropics more incoming radiation (red) than outgoing radiation (blue) Energy must be transported poleward Stepped Art Fig. 7-29, p. 193 Single-cell Model • basic assumptions • Hadley cell • why the single-cell model is wrong • One of the world’s premier atmospheric science research facilities,the Hadley Centre for Climate Research, is named after George Hadley. Three-cell Model • • • • • • model for a rotating earth Hadley cell doldrums subtropical highs trade winds intertropical convergence zone • Many global circulation terms, • westerlies including ‘trade winds’ and • polar front ‘doldrums’, were named by • polar easterlies mariners who were well acquainted with wind patterns. Fig. 7-21, p. 185 Average Surface Winds and Pressure: The Real World • • • • semipermanent highs and lows Bermuda high & Pacific high Icelandic low & Aleutian low Siberian high • The Bermuda High frequently brings hot, muggy weather to the eastern US. Fig. 7-22a, p. 188 Fig. 7-22b, p. 189 The General Circulation and Precipitation Patterns • major controls • ITCZ, midlatitude storms, polar front • Most of the world’s thunderstorms are found along the ITCZ. Westerly Winds and the Jet Stream • jet streams • subtropical jet stream • polar front jet stream Wind in the upper troposphere: Jet Streams Subtropical Jet - Coriolis turning of Hadley cell Mid-Latitude Jet – results from a steep temperature gradient Global Wind Patterns and the Oceans Winds and Upwelling • upwelling • wind flow parallel to the coastline • Upwelling frequently occurs along the coast of California. El Niño and the Southern Oscillation • • • • El Niño events Southern Oscillation La Niña teleconnections • ENSO is an example of a global-scale weather phenomenon. Fig. 7-32, p. 196 Fig. 7-33, p. 197 Fig. 7-34, p. 197 Other Atmosphere-Ocean Interactions • North Atlantic Oscillation • Arctic Oscillation • Pacific Decadal Oscillation • Other atmosphere-ocean interactions may very well be discovered in the coming years. Jet Streams Jet Streams