Download Chapter 6: Air-sea interaction

Seasons


Earth’s axis of rotation
tilted with respect to
ecliptic orbit around sun
Tilt responsible for
seasons
 Vernal (spring) equinox
(3/21)
○ sun overhead at equator
○ Equal day/night periods
 Summer solstice
(6/21)
○ sun overhead at Tropic of
Cancer (23.5O N)
○ Longest day of the year
in Northern hemisphere
 Autumnal (fall)
equinox (9/23)
○ sun overhead at equator
○ Equal day/night periods
 Winter solstice
(12/22)
○ sun overhead at Tropic of
Capricorn (23.5O S)
○ Shortest day of the year
in Northern hemisphere
Seasons

Seasonal changes and
day/night cause unequal solar
heating of Earth’s surface


Arctic circle (66.5O N)

latitude receives direct sunlight all
day on summer solstice

no direct sunlight during winter
solstice
Antarctic circle – reverse of above
Uneven solar heating

Angle of incidence of solar
rays per area
 Greater the angle, solar
energy spread over more
area
 Equatorial regions more heat
 Polar regions less heat

Thickness of atmosphere –
absorbs or reflects energy
○ Think about South Florida
compared to Maine
Uneven solar heating

Albedo
 Albus = white
 % incident radiation reflected back into space
 Affected by angle of sun – more angle , more
reflected
 Affected by type of surface
○ Snow/ice reflects more
○ Water surface absorbs more
○ Land absorbs most

Day/night and seasonal cycles affect solar
heating
Physical properties of atmosphere

http://www.ux1.eiu.edu/~cfjps/1400
Atmosphere is
comprised of gases and
dust
 mostly nitrogen (N2)
– 78%
 Oxygen (O2) – 21%
 CO2, water vapor,
ozone (O3) are
variable
Fig. 6.4
Physical properties of atmosphere




Warm air, less
dense (rises)
Cool air, more
dense (sinks)
Moist air, less
dense (rises)
Dry air, more
dense (sinks)
Fig. 6.5
Winds, Wind Belts and Climate
Introductory geography

○
○
○
Equator = 0O latitude
Earth rotates from west to east
Wind direction indicated by direction
winds are blowing from
Movements in atmosphere
Fig. 6.6
Air (wind) always moves from regions of high
pressure to low
 Cool dense air, higher surface pressure
 Warm less dense air, lower surface pressure

Air movements over non-rotating Earth
•
Convection or circulation cell
• Air heated at equator 
warm (less dense) air rises
• Surface air moves in to
replace rising air mass
• Air expands & cools as it
rises
• As it cools, becomes more
dense
• Warm air holds more
moisture than cooler air
• As air cools  moisture
condenses & forms
clouds/precipitation
Fig. 6.7
Air movements over a rotating Earth

Coriolis effect causes deflection in moving
body due to Earth’s rotation to east
 Most pronounced on objects that move long




distances across latitudes
Deflection to right in Northern Hemisphere
Deflection to left in Southern Hemisphere
Maximum Coriolis effect at poles
No Coriolis effect at equator
Movements in air on a rotating Earth

Rotational velocity increases approaching
equator
Fig. 6.9
Global atmospheric circulation


Circulation cells as air changes density
due to:
 Changes in air temperature
 Changes in water vapor content
Circulation cells
 Hadley cells (0o to 30o N and S)
 Ferrel cells (30o to 60o N and S)
 Polar cells (60o to 90o N and S)
6 cells of
windbelts and
boundaries:
 Intertropical
convergence
zone
 Doldrums
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Horse latitudes
Tradewinds
Westerlies
Polar front
Polar easterlies
1. Intertropical convergence zone (boundary)
•
Air warms and rises at equator
•
 low surface pressure
(rising air) poduce light winds
= doldrums
•
Long ago sailing
ships became
stuck here
because of lack
of winds
•
Sink at about 30O N & S latitude
•
2. Horse latitudes (boundary)
– low winds, high pressure
ridge
•
Dry, cool, sinking air
•
Sailors would also get
“stuck” here and would
through horses overboard
to conserve water
•
Winds:
•
3. Tradewinds return
to Equator, deflected
west
•
4. Westerlies move
toward poles,
deflected east
•
Winds converge at 50-60O N & S with polar air
•
•
•
5. Polar Front (boundary) - warm air rises (low
press./clouds)
Upper air splits & cools  sinks near poles
Winds:
•
6. Polar Easterlies – air sinks near poles, moves
from poles toward equator
Global atmospheric circulation
High pressure zones
 Subtropical highs
 Polar highs
 Clear skies
 Low pressure zones
 Equatorial low
 Subpolar lows
 Overcast skies with lots of precipitation

Modifications to idealized 3-cell
model of atmospheric circulation

Winds are more complex in nature due
to…
 Seasonal changes
 Distribution of continents and
ocean
 Differences in heat capacity
between continents and ocean
○ Monsoon winds
Ocean weather and climate patterns

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Weather – conditions of
atmosphere at particular time and
place
Climate – long-term average of
weather
Northern hemisphere winds move
counterclockwise (cyclonic) around
a low pressure region
Southern hemisphere winds move
clockwise (anticyclonic) around a
low pressure region
http://www.wunderground.com/US/Region/US/2xFronts.html
Coastal winds


Caused by solar heating &
different heat capacities
of land and water
Sea breeze
 From ocean to land
 During day, land heats air 
rises  draws cooler ocean
air onto coast

Land breeze
 From land to ocean
 At night, warmer ocean
water rises, draws cooler
land air over coast
Fig. 6.13
Fronts and storms

Air masses

Storms
 Large volumes of air, meet at fronts
 Disturbances with strong winds, precipitation, often
with thunder and lightning
 typically develop at fronts

Warm front

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
contact between moving warm
air mass with cooler air mass
More extensive, lighter rains
Cold front



contact between moving cold
air mass with warmer air
mass
Usually steep front, with
heavier, but briefer, rains
Clear skies follow behind
Tropical cyclones (hurricanes)

Caused by release of energy (latent heat of condensation)
 Low-pressure system breaks off equatorial low-pressure belt
 Surface winds feed moisture into storm
○ As water vapor condenses, heat released warms air
○ Rising warm air draws in more moist air  fueling cyclone
○ Large rotating masses of low pressure with calm “eye” (< 25 mph
winds)
 Strong winds, torrential rain outside eye
Fig. 6.16
Hurricane movement

At low latitudes, affected by trades 
move west

Curve toward right in No. hemisphere  cooler
water, influenced by westerlies
Hurricane Wilma
10/25/2005
http://cimss.ssec.wisc.edu/tropic/archive/montage/atlantic/2005/WILMA-track.gif
Table 6.5
Hurricane destruction
Fast winds
 Flooding from torrential rains
 Storm surge most damaging

 increased water levels from low pressure at eye
 On top of tide, most damaging at high tides
 Storm waves on top of storm surge
Historical examples:
Galveston, TX, 1900
Hurricane Andrew, 1992
Hurricane Mitch, 1998
Hurricane Katrina, 2005
Ocean climate patterns
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Equatorial regions
○ Warm, lots of rain
Tropical regions
○ Warm, less rain, trade winds
○ South Florida is tropical, defined rainy and dry season
Subtropical regions
○ Warm, lots of wind and evaporation, find dessert areas
Temperate regions
○ Strong westerlies
Subpolar regions
○ Cool, winter sea ice, lots of snow
Polar regions
○ Cold, ice
Polar oceans and sea ice

Sea ice or masses of frozen seawater form
in high latitude oceans
 Begins as small needle-like ice crystals
○ Pushes out dissolved salts  dense brine
○ Ice is much lower salinity

Rate of formation depends on temperature
http://static.howstuffworks.com/gif/iceberg-calving.
Polar oceans and icebergs

Icebergs – fragments of
glaciers or shelf ice
Global warming (Climate Change)


Average global temperature increased
Part of warming due to anthropogenic greenhouse
(heat-trapping) gases such as CO2
http://healthandenergy.com/images/carbon%20d
ioxide%201700-2000.jpg
http://earthobservatory.nasa.gov/Library/Global
Warming/Images/temperature_vs_co2_rt.gif
Greenhouse effect




Solar radiation enter
atmosphere
Some of that radiation
is reflected to space
Some of it is reflected
back towards Earth by
trace gases and
particles in the
atmosphere
Elevated levels of
carbon dioxide,
methane, etc can
increase that effect
 Literally “trapping” more
heat in the atmosphere
close to the Earth
Fig. 6.24
Greenhouse gases
Absorb longer wave radiation from Earth
 Many “greenhouse gases”

 Water vapor – most common and important
 Carbon dioxide (CO2)
 Other trace gases: methane, nitrous oxide, ozone,
and chlorofluorocarbons

Current controversy is not whether global
temperatures are increasing, but in the extent of
human impact
 The climate is changing, we cannot deny that
 The last time this happen human population
was not as large, even small changes in
climate can effect agricultural crops, larger
storms hitting populated areas, etc.
 Is it significantly above natural background
change?
 Can we afford to keep our heads in the sand?
Consequences of global warming are
not certain, but can be predicted…



When scientists say “uncertain” it DOES NOT mean that they do not
know what they are talking about
It does not mean that there will not be consequences
It is just difficult to predict the extent of those consequences, the
timing of those consequences, etc.
○ This is the first time we are experiencing these changes with
today’s society
○ The Earth and it’s systems are dynamic – constantly changing
- But when we talk about these changes, we are talking about
thousands, millions of years
- Our society, population boom, building of extensive cites along
coastlines, etc has been very recent
- So, let’s say for a moment that man isn’t making it worse by
putting more carbon dioxide into the atmosphere – changes are
still happening……and we have to be prepared to deal with
them….

Consequences of Climate Change
 Sea level rise
 Contamination of freshwater sources
 Vulnerability of more low-lying areas to storm surges
 Shift in species distribution
 Shifts in climate patterns will affect all living organisms
 Melting ice caps & expanding deserts  threaten wildlife
 Extreme weather patterns
 Heat waves, extreme winters, larger storms in populated
areas
 Droughts will affect productivity and crops
 Changing ocean chemistry
 Ocean water will become more acidic, warmer
 Changes in ocean circulation
 Spread of tropical diseases
Possible Impacts of Climate Change on South
Florida

Possible sea level rise of 15-20 inches by 2060
○ South Florida Water Management plays a delicate
balancing game to ensure that areas in South Florida don’t
flood during rain events (canal system), higher sea level
would make that more difficult – areas would be more
vulnerable to flooding
○ Greater vulnerability to storm surges and erosion
○ Salt water intrusion – fresh water supply for the
population could be threatened
Reducing greenhouse gases
Greater fuel efficiency
 Alternative fuels
 Re-forestation
 Eliminate chlorofluorocarbons
 Reduce CO2 emissions

 Intergovernmental Panel on Climate Change
1988
 Kyoto Protocol 1997
Ocean’s role in reducing CO2

Oceans absorbs CO2
from atmosphere
 CO2 incorporated in
organisms and carbonate
shells (tests)
 Stored as biogenous
calcareous sediments and
fossil fuels
 Ocean is repository or sink
for CO2
 Increases ocean acidity
enough to affect
organisms (corals)
http://www.whoi.edu/science/MCG/cafethorium/website/images/tzex_img1.j
Ocean Literacy Principles
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1c - Throughout the ocean there is one interconnected circulation system powered by wind, tides, the
force of the Earth’s rotation (Coriolis effect), the Sun, and water density differences. The shape of
ocean basins and adjacent land masses influence the path of circulation.
1d - Sea level is the average height of the ocean relative to the land, taking into account the
differences caused by tides. Sea level changes as plate tectonics cause the volume of ocean basins
and the height of the land to change. It changes as ice caps on land melt or grow. It also changes as
sea water expands and contracts when ocean water warms and cools.
3a - The ocean controls weather and climate by dominating the Earth’s energy, water and carbon
systems.
3b - The ocean absorbs much of the solar radiation reaching Earth. The ocean loses heat by
evaporation. This heat loss drives atmospheric circulation when, after it is released into the
atmosphere as water vapor, it condenses and forms rain. Condensation of water evaporated from
warm seas provides the energy for hurricanes and cyclones.
3c - The El Niño Southern Oscillation causes important changes in global weather patterns because it
changes the way heat is released to the atmosphere in the Pacific.
3d - Most rain that falls on land originally evaporated from the tropical ocean.
3f - The ocean has had, and will continue to have, a significant influence on climate change by
absorbing, storing, and moving heat, carbon and water.
3g - Changes in the ocean’s circulation have produced large, abrupt changes in climate during the last
50,000 years.