Circulation of the atmosphere

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Lecture 4
Circulation of the atmosphere
21 August 2007
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Lecture schedule
Lecture Date Time 1. Introduction to
scientific writing 8/20 900-1020 2. How to
write a scientific paper in English 8/20 1500-16
20 3. Earth structure and plate
tectonics 8/21 900-1100 4. Circulation of the
atmosphere 8/21 1300-1500 5. Water and ocean
structure 8/22 1000-1100 6. Continental
margins and ocean basins 8/22 1300-1500 7.
Sediment 8/23 1000-1200 8. Marine
resources 8/23 1300-1400 9. Circulation of
the ocean 8/24 1100-1230
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The atmosphere and ocean interact.
Atmosphere the volume of gases, water vapor, and
airborne particles that surround Earth
http//www.virtualsciencefair.org/2005/piro5e0/pub
lic_html/atmosphere_layer_pic.gif
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http//sponeil.org/EarthBumpScatter1.jpg
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Exchange of gasses and water between atmosphere
and ocean
Gases
Effect
Ocean
Atmosphere
Ocean
Atmosphere
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Exchange of gasses and water between atmosphere
and ocean
Gases
Effect
Ocean
Atmosphere
Climate
Ocean
Atmosphere
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The great quantities of solar energy that causes
this evaporation are carried from the ocean by
the escaping water vapor.
When water vapor condenses back into liquid water
usually at a distance from where it evaporated
energy is again available to do work.
About 1 meter of water evaporates every year from
the ocean surface .
If the water condenses as precipitation in a cold
climate, heat is given off and temperature is
moderated.
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Exchange of gasses and water between atmosphere
and ocean
Gases
Effect
Ocean
Atmosphere
Climate
Ocean
Sediment Distribution of life Physical
characteristics of water
Atmosphere
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Wind the mass movement of air
Weather the state of the atmosphere at a
specific place and time
Climate the long-term average of weather in an
area
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The atmosphere is composed mainly of nitrogen,
oxygen and water vapor.
78.1
lt1
20.9
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Air is never completely dry

• water vapor can compose up to 4 of volume

Sometimes water vapor is visible.
clouds
fog
But more often is is invisible
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The density of air is affected by its temperature
and water content.
http//resources.yesican-science.ca/lpdd/g08/lp/tr
ansdensity1.gif
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Pressure being equal, warm air can hold more
water vapor than cold air can.
The addition of water vapor to air (making the
air humid) reduces the density of the air

• molecular mass of water (18) lt molecular mass of
  air (about 29)

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Cooler air can hold less water in solution Water
vapor condenses into clouds
Descending air warms as it is compresssed The
clouds evaporate
Air becomes cooler when it expands
If rising and cooling continue, the droplets may
condense into raindrops or snow.
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What powers atmospheric circulation?
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What powers atmospheric circulation?
sunlight
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Heat budget
About ½ of the solar energy is absorbed by
Earths surface
Heat leaves Earth as infrared radiation.

• Over long periods of time, the total incoming
  heat (plus that from earthly sources) equals the
  total heat radiating into the cold of space
• so Earth is in thermal equilibrium

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polar areas receive less radiation per unit area
light filters through more atmosphere
heat is distributed over a smaller area
So tropical latitudes receive more solar energy
than the polar regions
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The solar heating of Earth varies with latitude.
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• Much of this heat is transferred by water
• water vapor
• water currents

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The solar heating of Earth also varies seasonally.
http//www.tiltedearth.org/images/tilted-earth-axi
s.gif
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Northern Hemisphere leans toward the sun in June
Northern Hemisphere leans away from the sun in
December
So, the sun appears higher in the sky in the
summer, but lower in the winter.
http//www.hort.purdue.edu/newcrop/tropical/lectur
e_02/lec_02.html
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Winter
Spring
Summer
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Winter
Spring
Summer
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Mid-latitude heating is strongly affected by
season In Northern Hemisphere, mid-latitudes
receive about 3 times as much solar energy in
June than in December
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Earths uneven solar heating results in
large-scale atmospheric circulation.
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Earths uneven solar heating results in
large-scale atmospheric circulation.
Convection current
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Expected pattern
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Expected pattern
But this is not true pattern.
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Expected pattern
But this is not true pattern.
Why not?
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Expected pattern
But this is not true pattern.
Why not?
Because Earth rotates.
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Any object moving freely across the globe appears
to curve slightly from its initial path.
Coriolis effect
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Buffalo
Quito
http//www.maps-continents.com/maps/north-america-
globe.gif
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43oN
0o

• 1 rotation in 24 hours
• but speeds are different

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The angular velocity of Earth is 15o an hour.
But the linear velocity depends on latitude.
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Buffalo
1260 km/hr
Quito
1668 km/hr
http//www.maps-continents.com/maps/north-america-
globe.gif
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cannon
Buffalo
1260 km/hr
Quito
1668 km/hr
http//www.maps-continents.com/maps/north-america-
globe.gif
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cannon
Buffalo
1260 km/hr
Quito
1668 km/hr
http//www.maps-continents.com/maps/north-america-
globe.gif
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Buffalo
1260 km/hr
Quito
1668 km/hr
http//www.maps-continents.com/maps/north-america-
globe.gif
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Buffalo
1260 km/hr
Quito
1668 km/hr
http//www.maps-continents.com/maps/north-america-
globe.gif
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Buffalo
Quito
http//www.maps-continents.com/maps/north-america-
globe.gif
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Buffalo
Quito
In a sense, the apparent motion of the Coriolis
effect is the difference in expected east-west
position.
http//www.maps-continents.com/maps/north-america-
globe.gif
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• Coriolis deflection
• In Northern Hemisphere
• to right
• In Southern Hemisphere
• to left

Coriolis effect plays an important role in the
movement of air and water
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The Coriolis effect influences the movement of
air in atmospheric circulation cells.
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3 cells
atmospheric circulation cells
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Atmospheric circulation generates large-scale
surface wind patterns.
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westerlies
horse latitudes
trade winds
doldrums
trade winds
http//rst.gsfc.nasa.gov/Sect14/FIG07_006.jpg
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Cell circulation centers on the thermal (not
geographical) equator.
average pattern
geographical equator
There is less ocean surface in Northern
Hemisphere than in Southern Hemisphere, so
thermal equator meteorological equator
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Monsoons are wind patterns that change with the
seasons.
Warm, moist air
http//www.abdn.ac.uk/wpg008/MonsoonCartoon.jpg
The Asian monsoon dominates the climate and
oceanography of East and SE Asia.
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Rain in Bangkok
Monsoon season
http//www.the-backpacking-site.com/countries/thai
land-overview.html
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• Monsoon
• Monsoon is an Arabic word meaning season
• Monsoon winds reverse themselves seasonally.
• Best developed in Western parts of oceans or
  eastern parts of continents, particularly Asia.
• Monsoon is based on differential thermal heating
  and cooling of land areas creating zones of high
  and low pressure over land in different seasons.

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wet monsoon season
Land heats faster than ocean
summer
L
Heating of the great landmass of Asia draws vast
quantities of warm moist air from the Indian
Ocean.
Land cools faster than ocean
H
dry monsoon season
winter
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Cherrapunji, India
average annual rainfall 11.43 m
http//en.wikipedia.org/wiki/ImageCherrapunji.jpg
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Land breezes and sea breezes are small, daily
mini-monsoons.
Land breeze
Sea breeze
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Storms are variations in large-scale atmospheric
circulation.
1970 Bhola (Bangladesh) cyclone
wind speedgt200 km/hr deathsappx. 500,000
http//en.wikipedia.org/wiki/Image1970_Bhola_cycl
one_track.png
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1991 Bangladesh cyclone
wind speedgt250 km/hr deathsappx. 138,000
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cyclone a weather system with a low-pressure
area in the center around which winds blow
counterclockwise in the Northern Hemisphere and
clockwise in the Southern Hemisphere

• cyclones form within or between air masses

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air mass a large mass of air with nearly uniform
temperature, humidity, and density throughout
http//www.weatherquestions.com/What_is_an_air_mas
s.htm
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air mass a large mass of air with nearly uniform
temperature, humidity, and density throughout
front boundary between two air masses of
different density
http//www.weatherquestions.com/What_is_an_air_mas
s.htm
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Energy is required to mix air masses.

• Energy is not always available, a dense air mass
  may slide beneath a lighter air mass
• lifting the lighter one and causing the air to
  expand and cool.

http//www.physicalgeography.net/fundamentals/imag
es/coldfront.GIF
Much turbulence at fronts
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• There are two major types of large storms
• Extratropical cyclones
• Tropical cyclones

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Extratropical cyclones form between two air
masses.
twist

• twist circulates counterclockwise in Northern
  Hemisphere
• embedded in westerly winds, so move eastward
• usually 1,000-2,500 km in diameter, last 2-5 days

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Extratropical cyclone formation areas

30-60oN
30-60oS
http//en.wikipedia.org/wiki/ImageExtratropical_f
ormation_areas.jpg
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http//www.cgd.ucar.edu/research/abstracts/2007/03
march.html
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Extratropical cyclone in northeast Pacific
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Extratropical cyclone near Japan
Typhoon near Japan
http//agora.ex.nii.ac.jp/digital-typhoon/heavy_sn
ow/200401-hokkaido/index.html.en
14 January 2004
11 September 2003
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Tropical cyclones originate in the tropics within
a single air mass
wind speed lt 17 m/sec 17-32 m/sec

• classification
• tropical depression
• tropical storm
• hurricane
• typhoon
• tropical cyclone
• willy-willy

gt 33 m/sec
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From above, tropical cyclones look like circular
spirals
Typhoon Etau 8 August 2003
http//www.eis.noaa.gov/NNVLfolder/etauaug08-0525z
A.jpg
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• energy comes from heat released when moist air
  rises and the water vapor condenses
• form over large bodies of warm water

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Tropical cyclones develop in areas of high
humidity and warm air over a sea surface gt26oC
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Tracks of tropical cyclones
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Tracks of all tropical cyclones that formed
worldwide during 1985-2005
http//en.wikipedia.org/wiki/ImageGlobal_tropical
_cyclone_tracks-edit2.jpg
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Tracks of all tropical cyclones that formed
worldwide during 1985-2005
hurricane
hurricane
typhoon
tropical cyclone
willy-willy
http//en.wikipedia.org/wiki/ImageGlobal_tropical
_cyclone_tracks-edit2.jpg
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Usual typhoon routes near Japan by month.
http//www.outdoorjapan.com/columns/images/sj-21-m
etor-300.jpg
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Typhoon 8 (14 August 2007)
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http//www.nrlmry.navy.mil/port_studies/thh-nc/tha
iland/pattaya/graphics/fig16-11.gif
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The most notable storm near Thailand was Typhoon
Gay.
November 1989
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Damage from Typhoon Gay in November 1989 in the
Thai province Chumphon
http//en.wikipedia.org/wiki/ImageChumphon_typhoo
n_damage_3.jpg
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Three aspects of a tropical cyclone can cause
property damage and injury
1. Wind 2. Rain 3. Storm surge
rise of water associated with a low pressure
system
to 12 m
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The Atlantic hurricane season of 2005 was the
most destructive ever recorded.

• In 2005
• 15 hurricanes

Hurricane Katrina
http//en.wikipedia.org/wiki/ImageHurricane_Katri
na_August_28_2005_NASA.jpg
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Hurricane Katrina was the United States most
costly natural disaster.
Path of Hurricane Katrina
August 2005
http//upload.wikimedia.org/wikipedia/commons/4/46
/Katrina_2005_track.png
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Storm surge height
Gulf Coast
New Orleans
10.4 m
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• 80 below sea level
• levees

New Orleans
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New Orleans
http//katrina.toptensources.com/TopTenSources/Use
rImages/KatrinaHurricane_Katrina_Image1.jpg
http//www.rhombos.de/picture/KatrinaNewOrleansFlo
oded.jpg
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Hurricane Rita struck soon after Katrina.
September 2005
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Hurricane Wilma was the most powerful Atlantic
hurricane ever recorded.
Wind speed295 km/hour!
October 2005
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Why was the 2005 season so devastating?

• during past 35 years, a large increase in very
  powerful storms
• related to global warming?
• human development

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• Hurricane names in the United States
• before 1950, hurricanes in the the U.S. were
  referred to by number
• e.g., hurricane 1, hurricane 2
• starting in 1951, names were used
• during World War II, meteorologists in the
  military started using women's names for the
  storms in the Pacific Ocean
• in 1978, the U.S. Government began also using
  mens names

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Name list for hurricanes in the North Atlantic
2009
2010
2011
2012
2007
2008
Ana Bill Claudette Danny Erika Fred
Grace Henri Ida Joaquin Kate Larry
Mindy Nicholas Odette Peter Rose Sam
Teresa Victor Wanda
Alex Bonnie Colin Danielle Earl
Fiona Gaston Hermine Igor Julia Karl
Lisa Matthew Nicole Otto Paula
Richard Shary Tomas Virginie Walter
Arlene Bret Cindy Don Emily
Franklin Gert Harvey Irene Jose Katia
Lee Maria Nate Ophelia Philippe Rina
Sean Tammy Vince Whitney
Alberto Beryl Chris Debby Ernesto
Florence Gordon Helene Isaac Joyce
Kirk Leslie Michael Nadine Oscar
Patty Rafael Sandy Tony Valerie William
Andrea Barry Chantal Dean Erin
Felix Gabrielle Humberto Ingrid Jerry
Karen Lorenzo Melissa Noel Olga Pablo
Rebekah Sebastien Tanya Van Wendy
Arthur Bertha Cristobal Dolly Edouard
Fay Gustav Hanna Ike Josephine Kyle
Laura Marco Nana Omar Paloma Rene
Sally Teddy Vicky Wilfred
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Key points 1. The atmosphere and ocean interact
with each other. 2. The atmosphere is composed
mainly of nitrogen, oxygen and water vapor. 3.
The atmosphere moves in response to uneven solar
heating and Earths rotation. 4. Atmospheric
circulation generates large-scale surface wind
patterns. 5. Storms are variations in large-scale
atmospheric circulation. 6. The Atlantic
hurricane season of 2005 was the most destructive
ever recorded.
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Lecture schedule
Lecture Date Time 1. Introduction to
scientific writing 8/20 900-1020 2. How to
write a scientific paper in English 8/20 1500-16
20 3. Earth structure and plate
tectonics 8/21 900-1100 4. Circulation of the
atmosphere 8/21 1300-1500 5. Water and ocean
structure 8/22 1000-1100 6. Continental
margins and ocean basins 8/22 1300-1500 7.
Sediment 8/23 1000-1200 8. Marine
resources 8/23 1300-1400 9. Circulation of
the ocean 8/24 1100-1230