climate and global change notes 21-1 atmospheric motions circulation scales thermally driven winds...

Climate and Global Change Notes

21-1

Atmospheric Motions

Circulation Scales

Thermally Driven Winds

Global Circulations

Rainfall Versus LatitudeObserved Global Circulation

Three-celled CirculationWind PatternsPressure PatternsRainfall PatternsLand-Water Effect

Global ClimateRelationship to Global

Circulation

Science Concepts

Potential Energy

Coriolis Force

The Earth System (Kump, Kastin & Crane)

• Chap. 4 (pp. 59-65, 79)


21-2

Atmospheric Scales

Object of Space Scale TimeTerminology Study or Size Scale

Macroscale Climate Global YearsSeasons Hemisphere

WeeksNational

Cyclonic Highs & Lows (5000 km) or HurricanesSynoptic

Regional DaysFronts (1000 km)

Mesoscale SquallsThunderstorms

Local HoursConvective Showers (100 km) orCumulus Tornadoes

Terminal(10 km)

MinutesMicroscale Gusts

Eddies Spot Seconds(1 meter)


21-3

Thermally Driven Wind Systems

Examples

• Global circulation

• Midlatitude cyclones

• Monsoons

• Hurricanes

• Land-sea breezes

• Heat island circulations

• Mountain-valley winds


21-4


Global Circulation

http://visibleearth.nasa.gov/Sensors/Terra/

Science quotes of 5th and 6th graders -

Clouds just keep circling the earth around and around. And around. There is not much else to do.


21-5


Hurricanes

• Hurricane Georges battering the Gulf Coast on September 28, 1998


21-6

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.


Hurricanes (Con’t)

• Ocean cooling effectsof hurricanes

• Katrina and Rita, each cooled Gulf temperatures more than 4°C in areas, and the entire Gulf ~1°C

• Hurricanes cool the ocean by > transferring heat to the

atmosphere through evaporation

> upwelling of cold water due to the suction effect of the storm’slow pressure

> cold raindrops that remain on the ocean surface for a time

> shielding the ocean surface from direct sunlight by cloud cover

http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17164


21-7


Sea Breezes


21-8

Global Circulations

Net Radiation vs Latitude

400

300

200

100

0 10N 10S 30S 30N 50S 50N 90S 90N

Latitude

Surplus

Heat Transfer Heat Transfer

Radiation Lost Radiation Received

Deficit Deficit

Radiation Intensity ( W

/ m 2 )


21-9

Global Circulations

What do you think the global distribution of precipitation should look like?


21-10

Global Circulations

Global Rainfall

• 1/00 to 4/06precipitation in mm/day

QuickTime™ and aTIFF (LZW) decompressor


http://earthobservatory.nasa.gov/Observatory/Datasets/rainfall.gpcp.html


21-11

Global Circulations

Average Precipitation (mm/day)

• ‘79 - ‘05 average January, July and Annual precipitation

- Dashed lines are 0°, 30°, 60° north and south latitudes



http://www.gewex.org/GPCP_data_products_9-2006.pdf



January

JulyAnnual

What latitude has the highest annual precipitation?


21-12

Global Circulations

Rainfall vs Latitude

90°N 60°N 30°N 0° 30°S 60°S 90°S

0

-500

500

1000

1500

2000

Latitude

Rainfall Evaporation

Runoff

Millimeters per year


21-13

Global Circulations

Inter-TropicalConvergenceZone


21-14

Global Circulations



Annual Average Cloud Amount

• 1983-2001

http://isccp.giss.nasa.gov/climanal2.html

Zonal Mean

Cloud Amount (%)Total Cloud Amount (%)


21-15

Global Circulations

Simple One-Celled Circulation

• Upward motion at the Equator

• Downward motion at the poles

• Equatorward motion at low levels

• Poleward motion at upper levels of the troposphere



http://rst.gsfc.nasa.gov/Sect14/Sect14_1c.html


21-16

Three-Celled Circulation Surface Winds

• Polar Cell- Polar Easteries

• Mid-latitude Cell- Highly variable- Storms move from west to east- Zone of Westerlies

• Equatorial Cell- Northeast Tradewinds in the

northern hemisphere- Southeast Tradewinds in the

southern hemisphere

Global Circulations



21-17



Global Circulations

Three-Celled Circulation

• Polar Cells- Thermally direct- Downward motion at

the Poles

• Equatorial Cells- Thermally direct- Upward motion at

the Equator

• Mid-latitude cell- Thermally indirect- Downward motion

at 30°- Equatorward motion at

upper levels of the troposphere- Poleward motion at lower levels



21-18

Global Circulations

Three-Celled Circulation

• Temperatures at 500 mb (about 5.5 km or 3.4 miles above sea level)

• Total water vapor above 500 mb to the top of the atmosphere

• Note Northern hemispheremid-latitude systems move eastward

• Note Northern hemispheretropical systems move westward


QuickTime™ and aSorenson Video decompressorare needed to see this picture.

http://airs.jpl.nasa.gov/Data/FeaturedProducts/AIRS_T500.mov

QuickTime™ and aSorenson Video decompressorare needed to see this picture.


21-19

Global Circulations

Three-Celled Circulation Surface WindsThe Nantucket whaleship Essex was sunk by an attacking whale just south of the Equator in the Pacific in 1820 and was the inspiration for the Melville’s Moby Dick.

“Like a skier traversing the face of a mountian, a Nantucket whaleship took an indirect route toward Cape Horn, a course determined by the prevailing winds of the Atlantic Ocean. First, pushed by westerlies, the ship sailed south and east toward Europe and Africa. There she picked up winds called the northeast trades, which took her back across the ocean again, in the direction of South America. After crossing the equator in an often airless region known as the doldrums, she worked her way south and west through the southeast trades into an area of variable winds. Then she encountered the band of westerlies that could make rounding the Horn so difficult.”

In the Heart of the Sea; The Tragedy of the Whaleship Essex - Nathaniel Philbrick (p. 37)


21-20

Global Circulations

Northern Deserts Southern Deserts


It is so hot in some places that the people there have to live in other places.


21-21

Global Circulations

Can we have deserts in the ocean?


21-22

Global Circulations

http://aquarius.gsfc.nasa.gov/overview-sss.html

Ocean Deserts

• Note higher values of salinity north and south of the Equator

• Salinity reflects the total amount of dissolved solids in ocean water

- PSU (practical salinity unit) describes the concentration of dissolved salts in water - 35 ppt means 35 lbs of salt per 1,000 lbs of seawater


21-23

Global Circulations

http://aquarius.gsfc.nasa.gov/science-watercycle.html

Ocean Deserts (Con’t)

• Ocean salinity is increased by evaporation and freezing of seawaterand decreased by precipitation and melting of snow and ice


21-24

Global Circulations

Summary

• Driven by differential or uneven heating between the poles and the equator

• Three circulation cells in each hemisphere. In the Northern hemisphere

- 0° to 30° - zone of “Northeast Trade Winds”- 30° to 60° - zone of “Prevailing Westerlies”- 60° to pole - zone of “Polar Easterlies"

• Both the Polar Easterlies and the Northeast Trades are very consistent,

while the Prevailing Westerlies are characterized by being variable and

highly changeable

• As part of the three-celled circulation pattern

- 0° is characterized by upward motion- 30° is characterized by subsidence- 60° is characterized by upward motion- 90° is characterized by sinking motion


21-25

Global Circulations

Summary (Con’t)

• Three-celled circulation results in

- 0° is wet with heavy precipitation

- 30° is dry with more evaporation than rain

- Zone of Prevailing Westerlies has more precipitation than evaporation

- 90° is dry with little precipitation

• This simple latitudinal pattern is modified by the land and water distributions

- More in the Northern Hemisphere because there is more land in the Northern Hemisphere


21-26

Global Circulations

January Mean Surface Pressure (mb)


21-27

Global Circulations

July Mean Surface Pressure (mb)


21-28

Global Circulations

Semi-Permanent Pressure Systems

Ocean Strength Strength Location Position in Winter in SummerAleutian low 60°- 65° Strong Weaker

Icelandic low 60°- 65° Strong Weaker

Hawaiian or 30°- 35° Weaker StrongerPacific high

Bermuda high 30°- 35° Weaker Stronger

Continental Strength Strength Location in Winter in SummerSiberian high Strong Absent

North American high StrongAbsent

SW U.S. thermal low AbsentStrong

India thermal low Absent Strong


21-29

Atmospheric Motions

Global Circulations (Con’t)

Monsoons

Science Concepts

Seasonal Effects


A monsoon is a French

gentleman.

The Blue Planet (Skinner, Porter & Botkin)• Chap. 13 (p. 303)


21-30

Monsoon

Mumbai (Bombay) Monsoon 2005 Rainfall

• Mumbai (formerly Bombay), India received a record-breaking 942 millimeters

(37.1 inches) of rain in a 24-hour period on Tuesday, July 26, 2005

• India’s previous all-time single-day record (838 mm; 33 in) set in 1912

• Heavy monsoon rain triggered deadly floods, which have claimed more than 500 lives in the country’s western Maharashtra state, with 273 fatalities in Mumbai alone, as of July 28

• Monsoon-related flooding is not unusual in summer when heating landmass generates winds that pull warm, moisture-laden air over the Indian subcontinent



http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16985


21-31

Monsoon

Jan 2003 Temperature (K)

Jul 2003 Temperature (K)


Isotherms and isobars are even more important than their names sound.

http://airs.jpl.nasa.gov/multimedia/products_suite/products_suite_temp.html

263 273 283 293 303

Degrees Kelvin


21-32

Monsoon

Jan Average Pressure (mb)

Jul Average Pressure (mb)


21-33

Monsoon

Monsoon Winds

• Winter (top) winds offshore

• Summer (bottom) winds onshore

http://earthobservatory.nasa.gov/Study/Monsoon/monsoon4.html


21-34

Monsoon

Jan Average Precip (mm/day)

Jul Average Precip (mm/day)


21-35

Monsoon

Tucson Average Daily Surface Dewpoint Temperature (°F)

• 1998- Start date July 3

• 2005- Start date July 18

http://www.wrh.noaa.gov/images/twc/monsoon/1998monsoon.pnghttp://www.wrh.noaa.gov/images/twc/monsoon/2005monsoon.png

climate and global change notes 21-1 atmospheric motions circulation scales thermally driven winds...

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