Chapter 7: Atmospheric Circulations Scales of atmospheric motions Scales of atmospheric motions Eddies - big and small Eddies - big and small Local wind systems Local wind systems Global winds Global winds Global wind patterns and the oceans Global wind patterns and the oceans

Scales of Atmospheric Motions Microscale: meters - kilometers Microscale: meters - kilometers Mesoscale: km – a few hundred km Mesoscale: km – a few hundred km synoptic scale: a few hundred km – a few thousand km synoptic scale: a few hundred km – a few thousand km planetary scale: a few thousand km and larger planetary scale: a few thousand km and larger Q1: what is the scale of atmospheric boundary layer turbulence? a) microscale, b) mesoscale, c) synoptic scale a) microscale, b) mesoscale, c) synoptic scale Q2: what is the scale of weather fronts? a) microscale, b) mesoscale, c) synoptic scale a) microscale, b) mesoscale, c) synoptic scale Q3: what is the scale of lake breeze over the Great Lakes a) microscale, b) mesoscale, c) synoptic scale a) microscale, b) mesoscale, c) synoptic scale

Fig. 7-2, p. 171

Eddies - Big and Small eddy or turbulent eddy: caused by convection (heating or cooling), wind shear (or near surface wind), or waves eddy or turbulent eddy: caused by convection (heating or cooling), wind shear (or near surface wind), or waves Rotor: caused by mountain waves Rotor: caused by mountain waves wind shear: change of wind speed or direction with height

Clear-air turbulence: caused by wind shear; important for aviation Q4: what could cause bumpy aircraft flight in the upper troposphere? a) clear-air turbulence, b) rotor, c) billow clouds Billow clouds: caused by mountain waves in a wind shear zone

Local Wind Systems Thermal Circulations: warm air rises and cool air sinks Warm air leads to H in the air (i,e, pushing isobar up); Air moves from H to L; increases surface pressure (i.e., pushing near-surface isobar up) over cool place; Leads to circulation from cool place to warm place near surface Pay attention to the change of isobars with height

Sea and Land Breezes sea breeze: from sea to land sea breeze: from sea to land land breeze: land to sea land breeze: land to sea sea breeze front: clouds sea breeze front: clouds Florida sea breezes Florida sea breezes Sea and land breezes also occur near the shores of large lakes, such as the Great LakesSea and land breezes also occur near the shores of large lakes, such as the Great Lakes Pay attention to the change of isobars with heightPay attention to the change of isobars with height Q5: which is stronger in general? a) sea breeze, b) land breeze, c) the same

Fig. 7-6, p. 175 Q6: When do you expect to see the thunderstorm in summer in Florida? a) 10am, b) noon, c) 3pm, d) 6pm

A B Q7: given the isobars as left, what is the near-surface wind direction? a) from A to B b) from B to A Q8: During the day, if you stand on beach, what would be the wind direction due to sea breeze? a) from sea to beach b) from land to sea height

Seasonally Changing Winds - the Monsoon Monsoon wind system: change with season Monsoon wind system: change with season India and eastern Asian monsoon India and eastern Asian monsoon Global monsoons Global monsoons Q9: What are the differences and similarities between monsoon and sea/land breeze? A: Monsoon system is much greater in geographic area; changes with season; sea/land breeze changes with diurnal cycle; both due to horizontal temperature difference A: Monsoon system is much greater in geographic area; changes with season; sea/land breeze changes with diurnal cycle; both due to horizontal temperature difference

North American monsoon Q10: Coriolis force is important for monsoon circulation. Is it as important for sea breeze as for monsoon? a) yes b) no Q11: Still, is Coriolis force important for sea breeze? a) yes b) no

Mountain and Valley Breezes valley breeze: daytime; from valley to top valley breeze: daytime; from valley to top mountain breeze: nighttime; from top to valley mountain breeze: nighttime; from top to valley The nighttime mountain breeze is sometimes called gravity winds or drainage winds, because gravity causes the cold air to ‘drain’ downhill.The nighttime mountain breeze is sometimes called gravity winds or drainage winds, because gravity causes the cold air to ‘drain’ downhill. Q12: Which is stronger in general? a) valley breeze, b) mountain breeze, c) the same

Katabatic Winds Strong drainage wind from cold elevated plateau down steep slope Strong drainage wind from cold elevated plateau down steep slope Katabatic winds are quite fierce in parts of Antarctica, with hurricane-force wind speeds.Katabatic winds are quite fierce in parts of Antarctica, with hurricane-force wind speeds. Bora: a cold, gusty northeasterly wind along the AdriaticBora: a cold, gusty northeasterly wind along the Adriatic coast in the former Yugoslavia coast in the former Yugoslavia

Chinook (Foehn) Winds Chinook winds: one type of drainage wind; warm and dry wind down the eastern slope of the Rocky Mountains Chinook winds: one type of drainage wind; warm and dry wind down the eastern slope of the Rocky Mountains It is called a Foehn along the leeward slopes of Alps.It is called a Foehn along the leeward slopes of Alps. Q13: Which wind is weakest in general? a) drainage wind, b) katabatic wind, c) Chinook wind a) drainage wind, b) katabatic wind, c) Chinook wind

Fig. 7-14, p. 180 Chinook wall cloud indicates that chinook is coming

Santa Ana Winds Santa Ana wind: warm, dry wind from the elevated desert plateau down to southern California Santa Ana wind: warm, dry wind from the elevated desert plateau down to southern California compressional heating compressional heating Could have very strong wind Could have very strong wind wildfires wildfires Q14: which wind comes from elevated desert plateau? a) Chinook wind; b) Santa Ana wind; c) Katabatic wind; d) mountain breeze Q15: The drainage wind over the lee side of the Rocky Mountain is a) Chinook wind; b) Santa Ana wind; c) Katabatic wind; d) mountain breeze

Desert Winds dust and sand storms: occurs over arid and semiarid regions dust and sand storms: occurs over arid and semiarid regions dust devils – from surface; dust devils – from surface; usually with a diameter of a few usually with a diameter of a few meters and a height of <100 m meters and a height of <100 m Q16: What is the difference between tornado and dust devil? A: Tornado is larger horizontally and deeper vertically; from cloud base down

General Circulation of the Atmosphere cause: unequal net heating of the earth’s surface and atmosphere cause: unequal net heating of the earth’s surface and atmosphere effect: atmospheric circulation and ocean currents to transport heat from the equator to the poles effect: atmospheric circulation and ocean currents to transport heat from the equator to the poles Fig on p. 43

Single-cell Model basic assumptions: no rotation basic assumptions: no rotation Originally proposed by George Hadley in England in the 18 th Century Originally proposed by George Hadley in England in the 18 th Century Hadley cell Hadley cell Q17: Why is the single-cell model wrong? A: Because single cell does not exist due to earth’s rotation Q17: Why is the single-cell model wrong? A: Because single cell does not exist due to earth’s rotation UK’s Hadley Centre for ClimateUK’s Hadley Centre for Climate Research is named after George Hadley. Research is named after George Hadley.

Three-cell Model model for a rotating earth; realistic over the tropics in winter hemisphere: model for a rotating earth; realistic over the tropics in winter hemisphere: Hadley cell; doldrums; subtropical highs Hadley cell; doldrums; subtropical highs trade winds; intertropical convergence zone (ITCZ) trade winds; intertropical convergence zone (ITCZ) Over mid- and high latitudes: Ferrel cell and polar cell do not play major roles; Over mid- and high latitudes: Ferrel cell and polar cell do not play major roles; westerlies in the upper troposphere; westerlies in the upper troposphere; polar front; polar front; polar near-surface easterlies polar near-surface easterlies Q18: if near-surface wind is southwesterly over NH midlatitudes, what is the direction of upper troposphere wind? a) westerly, b) easterly, c) southerly, d) northerly a) westerly, b) easterly, c) southerly, d) northerly

Fig. 7-21, p. 185

Average Surface Winds and Pressure: The Real World semipermanent highs: Bermuda high & Pacific high semipermanent highs: Bermuda high & Pacific high Pacific high moves north in summer; Pacific high moves north in summer; Bermuda high moves west in summer Bermuda high moves west in summer Semipermanent low: Icelandic low Semipermanent low: Icelandic low it moves north in summer it moves north in summer Siberian high in winter due to very cold air Siberian high in winter due to very cold air Aleutian low in winter due to storm track Aleutian low in winter due to storm track ITCZ stays in the warm hemisphere (e.g., NH in July) ITCZ stays in the warm hemisphere (e.g., NH in July) There are three semipermanent highs in SH There are three semipermanent highs in SH

Fig. 7-22a, p. 188

Fig. 7-22b, p. 189

The General Circulation and Precipitation Patterns Most of the world’s thunderstorms are found along the ITCZ.Most of the world’s thunderstorms are found along the ITCZ. Low rainfall over the subtropical regionsLow rainfall over the subtropical regions Fronts and precipitation over the subpolar lowsFronts and precipitation over the subpolar lows Q19: which is correct? a) desert causes subtropical high; b) subtropical high causes desert

Westerly Winds and the Jet Stream jet streams jet streams subtropical jet stream subtropical jet stream polar front jet stream polar front jet stream Low-level jet stream over the Central plains of the U.S. (within 2 km above surface), bringing moist and warm air to form nighttime thunderstorms

Fig. 7-29, p. 193 Global wind drives ocean current Q20: These ocean circulations are consistent with wind of a) high pressure system; b) low pressure system (warm) Gulf Stream; (warm) Kuroshio Current; (cold) California Current; (cold) Canary Current; Equatorial Current and Counter Current in the Pacific

Winds and Upwelling Upwelling is strongest when wind is parallel to the coastline Upwelling is strongest when wind is parallel to the coastline Q21: Why is ocean coldest in northern California? A: wind is parallel to the coastline; upwelling is strongest; cold deep water is brought to surface

El Niño and the Southern Oscillation Q22: what is the El Niño? A: warming, pressure decrease, and weakened upwelling over the central and eastern Pacific; trade wind weakened as well; (cooling, pressure increase over western Pacific) (cooling, pressure increase over western Pacific) La Niña: opposite La Niña: opposite Q23: What is the Southern Oscillation (SO)? A: oscillation of surface pressure over tropical western and eastern Pacific ENSO: El Nino and SO are closely related ENSO: El Nino and SO are closely related Q24: What is teleconnections? A: local changes affect weather in remote regions. SST animation: SST animation:

Fig. 7-32, p. 196 Thermocline is incorrect in bottom panel

ENSO is an example of a global-scale weather phenomenon.ENSO is an example of a global-scale weather phenomenon. Q25: What is the El Nino effect on winter weather in the U.S.? A: Northwestern U.S. usually has a warmer winter, Southeast usualy has a wetter winter, and often Arizona has a wetter winter El Nino effect

Other Atmosphere-Ocean Interactions North Atlantic Oscillation: based on pressure difference between Bermuda and Iceland North Atlantic Oscillation: based on pressure difference between Bermuda and Iceland Arctic Oscillation: pressure difference between about 45 o N and Arctic Arctic Oscillation: pressure difference between about 45 o N and Arctic Pacific Decadal Oscillation: Pacific surface temperature pattern changes every years Pacific Decadal Oscillation: Pacific surface temperature pattern changes every years

Fig. 7-36, p. 199 Over the tropical Pacific, PDO pattern is not very different from ENSO; Over midlatitude Pacific, PDO pattern is different from ENSO