Module 2:HUMIDITY
Objectives
- To study the concept of humidity.
- To understand use of the saturation curve graph.
- Learn about how relative humidity is measured using a sling psychrometer.
SAINT MARY’S UNIVERSITY
GEOG 1200
DEPARTMENT OF GEOGRAPHY
FUNDAMENTALS OF PHYSICAL GEOGRAPHY
Module 2: HUMIDITY
Objectives
1.
To study the concept of humidity.
2.
To understand use of the saturation curve graph.
3.
Learn about how relative humidity is measured using a sling psychrometer.
Section 1: Understanding Humidity
Terminology
Air can hold up to a certain amount of water vapour (water in a gaseous state) but the amount varies depending on the
temperature. Humidity is a general term that refers to the amount of moisture in air. Some other important terms to
know when dealing with moisture in the atmosphere are:
Specific Humidity (SH): the actual quantity of water vapour in the air, in grams per kilogram (g/kg).
Maximum Specific Humidity (MSH): the maximum quantity of water vapour that could be held in the air at a given
temperature (g/kg). If the air is unsaturated, the SH is less than the MSH.
Relative Humidity (RH): the ratio of SH to MSH, expressed as a percentage:
Equation 1:
Specific Humidity
RH (%) = ———————————-Maximum Specific Humidity
x
100
Dew-Point Temperature (DT): the temperature at which air saturation and condensation occur for a given value of
specific humidity. Condensation is the change of water from a gaseous state to a liquid state.
Saturation Curve: a graph (on a separate sheet) showing the relationship between air saturation and temperature.
Once the saturation point is reached, the RH is 100% and no more water vapour can be evaporated into the air.
Example
For reference, an example using the Saturation Curve Graph is given. Follow the example of how to correctly read the
graph.
a.
A sample of air is collected and determined to lie at Point X on the graph.
b.
The air temperature is 30C.
c.
The SH is 10.0g/kg (grams of water vapour per kilogram of air).
d.
What is the MSH?
e.
What is the RH, rounded to the nearest %?
f.
What is the DT?
1
Answers
Air Temperature
(C)
X
30
Specific Humidity
(g / kg)
10
Maximum Spec.
Humidity
(g / kg)
Relative
Humidity
(%)
Dew-Point
Temperature (C)
27.5
36
12.5
2
Section 2: Using the Saturation Curve Graph
•
Recall from the previous section that relative humidity is the ratio between specific humidity and maximum specific
humidity expressed as a percentage.
•
It is possible for the specific humidity to be lower than or equal to, but not higher than, the maximum specific
humidity. A point on the graph can only lie on or below the line.
•
A series of values will be used to demonstrate the relationships between temperature and humidity of air.
•
In this example, the temperature of the air changes, forcing changes in the relative humidity values. A starting
point was selected with an air temperature of 20C and a specific humidity of 10 g / kg.
Air Temperature
(C)
Specific Humidity
(g / kg)
A
20
10
B
13
10
C
0
4
D
10
4
Maximum Spec.
Humidity
(g / kg)
Relative
Humidity
(%)
Dew-Point
Temperature (C)
Use the Saturation Curve Graph to complete the table (above or attached).
Section 3: Measuring Relative Humidity with a Sling Psychrometer
Background
•
A device for measuring relative humidity is called a sling psychrometer.
•
The paragraphs below describe the sling psychrometer and its operation – For the on-line course you will not be
using the instrument, however you will learn about it .
The Sling Psychrometer
•
The sling psychrometer contains two thermometers housed in a plastic casing attached to a handle.
•
The casing is designed to be spun around the handle, vigourously.
•
The upper thermometer is a standard mercury thermometer with a Celcius temperature scale – this is the dry-bulb
thermometer it measures the air temperature.
•
The lower thermometer is similar, except it is covered by a wick at the far end- this is the wet-bulb thermometer. If
the wick is dry, unscrew the plastic cap and add water to the reservoir.
•
The difference between the dry bulb and wet bulb temperatures is called the wet-bulb depression (or depression of
the wet bulb).
How the Sling Psychrometer Works
•
When the psychrometer is spun, evaporation causes the wet-bulb temperature to be lowered.
3
•
The amount of evaporation from the wick is related to the relative humidity (RH). The amount of evaporation is
determined by the amount of water vapour already in the air (the specific humidity) compared to the maximum
amount of water vapour that can be held at that temperature (maximum specific humidity).
•
If the RH is high, there will be relatively little evaporation and the dry and wet bulb temperatures will be close to
each other.
•
If the RH is low, there will be relatively more evaporation and the dry and wet bulb temperatures will be further
apart.
Using the Psychrometer
•
To use, spin the psychrometer vigourously for 30-40 seconds.
•
Read off the two temperatures to the nearest half degree and calculate the wet-bulb depression.
•
On a separate sheet is a chart that will tell you the relative humidity for the air temperature you measure (dry-bulb
temperature) and the corresponding wet-bulb depression.
•
Read the chart down to the dry-bulb temperature you recorded, and across to the wet-bulb depression to obtain
the relative humidity value.
•
For example, if you measured a dry-bulb temperature of 34C and a wet-bulb temperature of 24.5C, the wet-bulb
depression is 9.5C and the relative humidity is 46%. Use the chart to confirm how this value of relative humidity is
obtained.
•
On the chart, if the exact dry-bulb temperature you recorded is missing, you must interpolate between given
values.
Before Moving On
•
It is essential to understand the information provided to this point before moving on. Three points that
frequently require emphasis or clarification are:
o
Dry-bulb temperature on the psychrometer measures the air temperature.
o
Wet-bulb temperature is not the same as wet-bulb depression.
o
Wet bulb depression is the difference between dry-bulb and wet-bulb temperatures. (That is, how much
lower, or “depressed”, is the temperature of the wet-bulb compared to the dry-bulb?)
Section 4: Practice Exercises Using Given Sling Psychrometer Values
Work out the relative humidity assuming the following temperatures were measured off a sling psychrometer:
Dry-Bulb Temperature
(C)
Wet-Bulb Temperature
(C)
30
26
5
2
45
27.5
Wet-Bulb Depression
(C)
Relative Humidity
(%)
4
9.5
4.5
4
Section 5: Relative Humidity Measurements
•
I completed these measures for the class using the sling psychrometer to measure the relative humidity in three
locations on the campus:
1.
In room B205
2.
In the lobby of the Atrium, near the entrance to the library
3.
Outside, well away from any buildings or building entrances
•
Spaces are provided below to about the humidity conditions (using the relative humidity results and the saturation
curve graph).
•
Equation 1 – used to calculate RH when SH and MSH are known – can be rearranged into Equation 1a to calculate
SH, if RH and MSH are known.
Equation 1:
RH = (SH / MSH) x 100
Equation 1a:
SH = (RH / 100) x MSH
Make sure you include appropriate units for all values on p. 4 and 5.
Location 1: In Room B205
Dry-Bulb Temperature
_20.5 C ______________ Wet-Bulb Temperature
16.0 C _______
Location 2: In the lobby of the Atrium
Dry-Bulb Temperature
_19.5 C
Wet-Bulb Temperature
__18.5 C ______________
Location 3: Outside, away from buildings
Dry-Bulb Temperature
6 C ________________
Wet-Bulb Temperature
__2 C ______________
Location 1: In Room B205
Wet-Bulb Depression
Relative Humidity
________________
________________
Maximum specific humidity for this air temperature
________________
Specific humidity (SH = [RH / 100] x MSH)
________________
Dew-point temperature
________________
Location 2: In the Atrium, on the second floor beside the green living wall
Wet-Bulb Depression
Relative Humidity
________________
________________
Maximum specific humidity for this air temperature
________________
Specific humidity (SH = [RH / 100] x MSH)
________________
Dew-point temperature
________________
5
Location 3: Outside, away from buildings
Wet-Bulb Depression
Relative Humidity
________________
________________
Maximum specific humidity for this air temperature
________________
Specific humidity (SH = [RH / 100] x MSH)
________________
Dew-point temperature
________________
For each of the three locations, plot your values of specific humidity vs. air temperature on the Saturation Curve graph.
•
At which location is the relative humidity highest?
________________
•
Which location has the greatest amount of water vapour in the air?
________________
•
Is it possible for the highest relative humidity and the greatest amount of water vapour in the air to have occurred
at different locations?
6
Visualizing Physical Geography
by Timothy Foresman & Alan Strahler
Chapter 3
Air Temperature
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Visualizing Physical Geography
Copyright © 2012 John Wiley & Sons, Inc.
Chapter Overview
Temperature and Heat Flow
Processes
Daily and Annual Cycles of Air
Temperature
© Alberto Garcia/©Corbis
Local Effects on Air Temperature
Guess whether the
World Patterns of Air Temperature eruption of Mt.
Pinatubo had a
cooling or warming
The Temperature Record and
effect?
Global Warming
Visualizing Physical Geography
Copyright © 2012 John Wiley & Sons, Inc.
Temperature and Heat Flow Process
Measuring Temperature
• Temperature = level of internal
motion of atoms and molecules
that make up the matter
• Temperature scales
• Fahrenheit
• Celsius
• Kelvin
What is the freezing and boiling
point of water in oF and oC?
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Temperature and Heat Flow Process
Surface Temperature
•
•
•
•
Air temperature is measured at 1.2 m (4 feet).
Daytime ground temperatures are usually warmer than 1.2 m.
Night ground temperatures tend to be cooler than at 1.2 m.
Ground temperatures are often more extreme than air
temperatures.
Visualizing Physical Geography
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Temperature and Heat Flow Process
Wind Chill and Heat Index
• Wind chill index = the higher the wind speed, the faster
the rate at which heat leaves our bodies, and the colder
we feel.
If the air
temperature is
0o F and the
wind speed is
30 mph, what
is the wind
chill?
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Temperature and Heat Flow Process
Wind Chill and Heat Index
• Heat index:
• Higher levels of humidity raise our perception of heat.
• Humid conditions reduce the amount of evaporative
cooling when we sweat.
If the relative humidity is
85%, at what temperature
should someone
exercising outdoors use
“extreme caution”?
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Temperature and Heat Flow Process
Energy Transfer
• Heat = internal energy transferred from one substance to
another as a result of their temp differences.
• Heat flows by:
• Radiation = all objects emit heat (e.g., SW and LW).
• Conduction = transfer by particles (atoms or molecules).
• Convection = in gases or liquids (e.g., warm air rises).
• Advection = a mass of air moves to a new location,
bringing along its properties (temperature and moisture).
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Temperature and Heat Flow Process
Energy Transfer
• Example:
• Sunlight hits earth via SW
radiation.
• SW is absorbed by ground,
raising its temperature.
• The surface layer radiates
(LW) energy to the air, and
heats the soil below it
through conduction.
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Where is convection
occurring in this image?
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Temperature and Heat Flow Process
Latent Heat
• Sensible heat = flow of heat that results in a temperature
change of an object or its surroundings.
• Latent heat = flow of heat taken or released when a
substance changes states (solid, liquid, or gas) to another.
• Important energy transfer in the atmosphere/ocean:
• Water evaporating into water vapor is a cooling process as
heat is absorbed into the water vapor.
• The latent heat stored in water vapor is released in the
condensation process.
• Hurricanes are fueled by warm water and this process.
Visualizing Physical Geography
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Daily and Annual Cycles of Air
Temperature
Four important controls of air temperature:
• Time of day
• Season
• Surface type (continental
or maritime)
• Latitude
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Other local factors involved in determining temperature (see
the next section) include:
• Elevation
• Land use and urbanization
• Ocean currents
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Daily and Annual Cycles of Air
Temperature
The Daily Cycle of Air Temperature
•Net radiation varies daily:
• Positive after sunrise
• Peaks at noon
• Decreases to negative by
sunset
What time of day would
you expect the high
temperature?
Visualizing Physical Geography
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Daily and Annual Cycles of Air
Temperature
The Daily Cycle of Air Temperature
•Air temperature varies daily:
• Minimum is just after sunrise.
• Rises to a peak in mid-afternoon.
• Even after noon, incoming
radiation is still greater than
outgoing radiation (positive net
radiation); thus, the temperature
continues to increase.
• Temperatures begin to decrease
once net radiation is negative.
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Daily and Annual Cycles of Air
Temperature
Temperatures Close to
the Ground
• Temperatures on the
ground are usually more
extreme than
temperatures at standard
height.
• Soil, surface, and air
temperatures vary
throughout the day.
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Visualizing Physical Geography
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Daily and Annual Cycles of Air
Temperature
Annual Cycles of Insolation and Air Temperature
•Insolation varies by season:
• Day length longest at summer solstice = warmer temp.
• Day length shortest at winter solstice = colder temp.
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Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Daily and Annual Cycles of Air
Temperature
Goddard Institute for Space Studies Surface
Temperature Analysis
• Calculating the Earth’s surface temperature from ground, air,
and satellite measurements is extremely complex.
• http://data.giss.nasa.gov/gistemp/
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Daily and Annual Cycles of Air
Temperature
Land and Water Contrasts
• Specific heat = amount of heat
required to raise the
temperature of a unit mass of a
substance by 1ºC.
• Rock and soil (inland areas)
have low specific heat, which
means less energy is needed to
raise the temperature.
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Water has a much higher
specific heat capacity. An
extensive, deep body of water
heats more slowly and cools
more slowly than inland areas.
Visualizing Physical Geography
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Daily and Annual Cycles of Air
Temperature
Inland climates have more
temperature extremes than
coastal climates:
1. Solar rays heat land
surface, but are distributed
deeper in water.
2. Water has higher heat
capacity than rock and
soil.
3. Water mixes.
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4. Water evaporates,
removing latent heat.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Daily and Annual Cycles of Air
Temperature
Land and Water Contrasts
• Maritime = Coastal regions have smaller daily and annual
temperature ranges.
• Continental = Inland regions have greater daily and annual
temperature ranges.
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Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Daily and Annual Cycles of Air
Temperature
Temperature by Latitude
• Annual cycle of insolation affects→ net radiation, which
affects→ monthly mean air temperature.
• Higher latitudes experience large annual temperature range.
• Equatorial regions experience small annual temp ranges.
Courtesy David H. Miller
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Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Daily and Annual Cycles of Air
Temperature
Temperature by Latitude
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Courtesy David H. Miller
Is the annual temperature range for Manaus, Brazil,
small or large? Explain. In your explanation, describe the
latitude and annual net radiation for Manaus.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Daily and Annual Cycles of Air
Temperature
Temperature by Latitude
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Courtesy David H. Miller
Is the annual temperature range for Yakutsk small or
large? Explain. In your explanation, describe the latitude
and annual net radiation for Yakutsk.
Visualizing Physical Geography
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Daily and Annual Cycles of Air
Temperature
Temperature by Latitude
Although Yakutsk is only 9.5° further north
than Hamburg, the annual temp cycles of
these two cities are quite different. While
summer temp are similar, winter temp at
Yakutsk average –45°C compared to just
about freezing at Hamburg.
Which is the best explanation for this
observation?
a. The elevation is much higher in Yakutsk.
b. The elevation is much higher in
Hamburg.
c. Winds bring air from the Arctic Ocean to
Yakutsk.
d. Winds bring air from the Atlantic Ocean
to Hamburg.
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Local Effects on Air Temperature
Local factors involved in determining temperature:
• Elevation
• Land use and urbanization
• Ocean currents
Microclimates = Local atmospheric zones where the climate
differs from surrounding areas
© Courtesy NASA
© NG Image Collection
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Local Effects on Air Temperature
Effects of Elevation on Temperature
• Temperature decreases with altitude in the troposphere,
then increases above the troposphere.
• Environmental temperature lapse rate = rate at which air
temperature drops with increasing due to pressure drop
and subsequently less carbon dioxide and water vapor to
absorb LW.
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Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
© NG Image Collection
Local Effects on Air Temperature
Effects of Elevation on Temperature
• Temperature Structure of the Atmosphere
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What gas absorbs ultraviolet radiation in the
stratosphere? How does this relate to the
temperature trend?
Visualizing Physical Geography
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Local Effects on Air Temperature
Effects of Elevation on Temperature Variation
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What happens to temperature as one increases in
elevation in the Andes mountains?
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Local Effects on Air Temperature
Effects of Elevation on
Temperature Variation
•Temperature inversion = a
state of the atmosphere in
which air temperature
increases with elevation.
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If you were to plant a frost-sensitive plant/tree, is it best
to plant it on the valley floor or on a hill side?
Visualizing Physical Geography
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Local Effects on Air Temperature
Urban and Rural Environments
• Urban heat island = an area at the center of a city that has a
higher temperature than surrounding regions
• Heat-related fatalities
• Green roofs
© Courtesy NASA
© Courtesy NASA
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
World Patterns of Air Temperature
Air Temperature Maps
• Air temperature maps use
isotherms to show centers of
high and low temperatures.
• Isotherm = line on a map
drawn through all points with
the same temperature.
• Temperature gradient = rate
of temperature change along a
selected line or direction.
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Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
World Patterns of Air Temperature
Air Temperature Patterns around the Globe
Three main factors explaining world isotherm patterns:
1. Latitude affects annual insolation, temperatures, and
seasonal temperature variation
2. Maritime-continental
contrast
3. Elevation
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Data from John E. Oliver
World Patterns of Air Temperature
Air Temperature Patterns around the Globe
Temperature Extremes
1. Hottest = 58oC (136oF) at El Azizia, Libya (~28oN).
2. Coldest = –89°C (–128°F) at Vostok Station, Antarctica
(high elevation near 85oS).
3. Within North America, temperatures range from 57°C
(134°F) in Death Valley, California, to –63°C (–81°F) in
Snag, Yukon, Canada.
Find these locations on physical map. Use at least two
temperature controls to explain the temperature extremes
in Libya and Antarctica.
Visualizing Physical Geography
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World Patterns of Air Temperature
Air Temperature at the Equator and Midlatitudes
Locate regions that show:
1. Temperature decrease with
elevation
2. Seasonal temperature
differences
3. Little to no seasonal
temperature difference
Visualizing Physical Geography
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Data from John E. Oliver
World Patterns of Air Temperature
Air Temperature at the Poles
Data from John E. Oliver
Visualizing Physical Geography
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The Temperature Record and
Global Warming
The Temperature Record
• Satellite technology allows scientists to monitor surface air
temperature and sea surface temperature (SST).
• Direct methods date to mid-19th century.
© Courtesy NASA
© Courtesy NASA
In Figure 3.17b, can you identify:
1. the urban-heat island effect?
2. natural geographic features influencing temp patterns?
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
The Temperature Record and
Global Warming
The Temperature Record
Indirect temperature records
(proxies)
• Tree rings
• Ancient sediment
• Coral reef coring
• Ice cores from glaciers and
polar regions
• Oxygen isotope ratio
Visualizing Physical Geography
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© NG Image Collection
The Temperature Record and
Global Warming
The Temperature
Record
•Cycles of higher and
lower temperatures
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Volcanic activity (SO2)
• Eruption of Mt. Pinatubo
Did the eruption of Mt.
Pinatubo have a cooling
or warming effect?
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Courtesy NASA
The Temperature Record and
Global Warming
Global Warming
•Earth has been getting warmer, especially in the past 50
years.
•Intergovernmental Panel on Climate Change (IPCC)
• 2000 statement:
“Global warming is ‘unequivocal.’ ”
• 2007 statement:
“Climate change is occurring, is caused largely by
human activities, and poses significant risks for—and in
many cases is already affecting—a broad range of
human and natural systems.”
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
The Temperature Record and
Global Warming
Temperature Trends by Latitude
• Small island nations express alarm at rising sea levels.
• Arctic citizens are witnessing a greater rise in temperature.
• Arctic region is warming at 2.5 times the global average.
Courtesy NASA
Temperature averages over the 1951–1980 time period by latitude
Visualizing Physical Geography
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The Temperature Record and
Global Warming
Causes of Global Warming
• IPCC concluded that human activity is very likely the cause
of climatic warming through the increase of the concentration
of greenhouse gases.
• IPCC conclusions are based on computer simulations.
© National Academy of Sciences, U.S.A.
Visualizing Physical Geography
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The Temperature Record and
Global Warming
Air Temperature Trends
•2005 and 2010 are tied as the warmest years on record
since the middle of the 19th century.
•First 10 years of the 21st century are the warmest decade
on record since 1400.
•In the past 30 years, the Earth has warmed by 0.6°C
(1.1°F). In the past century, it has warmed by 0.8°C
(1.4°F).
Visualizing Physical Geography
Copyright © 2012 John Wiley & Sons, Inc.
The Temperature Record and
Global Warming
Consequences of Global Warming
• IPCC has projected that global temperatures will warm between
1.8°C (3.2°F) and 4.0°C (7.2°F) by the year 2100.
• Sea ice will melt.
• Greenland ice sheet will change.
© imagebroker/Alamy
© National Geographic Society
Visualizing Physical Geography
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The Temperature Record and
Global Warming
Consequences of
Global Warming
•Arctic thawing
•Sea-level rise
•Polar sea ice melting
•Habitat loss (coral reefs)
© NG Image Collection
© Courtesy NOAA
© imagebroker/Alamy
© National Snow and Ice Data Center
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Courtesy NASA
The Temperature Record and
Global Warming
Consequences of Global Warming
© Courtesy NASA
© John Wiley & Sons, Inc.
Review Figure 3.20 and answer this question:
Where do you expect to find the largest observed changes in global temperature as a
function of latitude?
a. Tropical regions
b. Subtropical regions
c. Midlatitude regions
d. Polar regions
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The Temperature Record and
Global Warming
Climate Change
• Weather seems to becoming more variable and more extreme:
• Very high 24-hour precipitation—extreme snowstorms,
rainstorms, sleet, and ice storms—have become more
frequent since 1980, with more intense hot and cold weather.
• Seasons affected—early onset of spring and the delay in fall.
• Pine beetle infestations in the Pacific Northwest
• Bleaching of coral reefs in the Indian Ocean
• Could promote the spread of diseases such as malaria
• Shifting climate range boundaries may shift, making some
regions wetter and others drier
• Shifts in agricultural patterns, including desert expansion, could
displace large human populations
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The Temperature Record and
Global Warming
International Response to Global Warming
•1992 Rio de Janeiro Earth Summit
•1997 Kyoto Protocol
•IPCC
•Carbon taxes and cap-and-trade failure or success?
•China, Germany, and Scandinavian countries have reduced
greenhouse gases and supported renewable energy:
• Solar
• Wind
• Geothermal
• Nuclear
Visualizing Physical Geography
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Visualizing Physical Geography
by Timothy Foresman & Alan Strahler
Chapter 4
Atmospheric Moisture and Precipitation
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Visualizing Physical Geography
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Chapter Overview
Water and the Hydrosphere
Humidity
Adiabatic Processes
Clouds and Fog
Precipitation
Human Impacts on Clouds
and Precipitation
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Visualizing Physical Geography
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Water and the Hydrosphere
The Three States of Water
• Solid (ice)
• Liquid (water)
• Gas (water vapor)
• Latent heat is transferred
when water changes states
• Release of energy occurs
when…
• Absorption of energy
occurs when…
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Visualizing Physical Geography
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Water and the Hydrosphere
The Three States of Water
•
•
•
•
•
Evaporation
Freezing
Condensation
Sublimation
Deposition (e.g., Frost)
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On a cold, dry day, snow covering a sidewalk slowly disappears, and there
is no visible melting. Which process is at work?
a. sublimation
b. deposition
c. condensation
d. evaporation?
Visualizing Physical Geography
Copyright © 2012 John Wiley & Sons, Inc.
Water and the Hydrosphere
The Hydrosphere
• The total water realm of the
Earth’s surface, including
the oceans (97.5%) and
freshwater (2.5%).
• Freshwater includes
glaciers (68.7%), ground
water (30%), permafrost
(0.8%), and the surface
waters of the lands and
water held in the
atmosphere make up 0.4%.
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Visualizing Physical Geography
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Water and the Hydrosphere
The Hydrosphere
• Oceans
• Ice sheets and glaciers
• Surface water
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© NG Image Collection
© NG Image Collection
Visualizing Physical Geography
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© NG Image Collection
Water and the Hydrosphere
The Hydrosphere
• The small blue sphere represents the planet’s total water
volume in proportion to the Earth’s size, demonstrating the
limits on this critical resource
© SPL/Photo Researchers
Visualizing Physical Geography
Copyright © 2012 John Wiley & Sons, Inc.
Water and the Hydrosphere
The Hydrologic Cycle
Water moves among the ocean, atmosphere and land
•Evaporation
•Precipitation
•Transpiration
•Evapotranspiration
•Runoff
•Sinks into soil
•Recharge of groundwater
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Water and the Hydrosphere
Humidity
• The amount of water vapor
in the air
• The maximum volume of
water vapor, or humidity, of
a mass of air increases
sharply with rising
temperature
• Air at room temperature
(20°C [68°F]) can hold
about three times as much
water vapor as freezing air
(0°C [32°F])
Visualizing Physical Geography
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Water and the Hydrosphere
Humidity
• The low humidity of
Death Valley in California
creates a warm but
comfortable day for a trek
across the sand
• High-humidity conditions
of a Florida wetland, the
same temperature
reading can be
unbearably hot
© NG Image Collection
Visualizing Physical Geography
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Water and the Hydrosphere
Relative Humidity (RH)
• Compares the amount of water vapor present to the
maximum amount that the air can hold at that
temperature
• Expressed as a percentage
• Air holding ½ its capacity has a RH of 50%
• Can change in two ways:
• Gain or lose moisture
• Change in temperature
Visualizing Physical Geography
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Water and the Hydrosphere
Specific Humidity
• The actual amount of water vapor held by a parcel of
air (g/kg)
• When air cools, capacity is reduced
• When air warms, capacity increases
• Specific humidity and temperature values are high at
low latitudes
• Specific humidity values fall as temperature in high
latitude regions
Visualizing Physical Geography
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Water and the Hydrosphere
Specific Humidity
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Visualizing Physical Geography
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Water and the Hydrosphere
Dew Point
• The temperature at which air with a given humidity will
reach saturation when cooled without changing its
pressure
• Dew
• Frost
What happens as air is cooled below the dew-point
temperature at temperatures above freezing?
Visualizing Physical Geography
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Adiabatic Processes
• As a parcel of air is lifted, atmospheric
pressure becomes lower, and the parcel
expands and cools
• As air cools to the dew point, clouds form
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• As air descends, air is
compressed and warms
• Adiabatic processes =
process in which the
temperature of a parcel
of air changes in
responses to a change
in atmospheric pressure
Visualizing Physical Geography
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Adiabatic Processes
The Dry Adiabatic
Lapse Rate
•The rate at which rising
air cools or descending air
warms when no
condensation is occurring
•10°C per 1000 m
•5.5°F per 1000 ft
© A. N. Strahler
Visualizing Physical Geography
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Adiabatic Processes
The Moist Adiabatic
Lapse Rate
• The rate at which
rising air is cooled by
expansion when
condensation is
occurring; ranges
from:
• 4 to 9°C per 1000
m
• 2.2 to 4.9°F per
1000 ft
Visualizing Physical Geography
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© A. N. Strahler
Adiabatic Processes
Visualizing Physical Geography
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© A. N. Strahler
Adiabatic Processes
© A. N. Strahler
1. Suppose the air parcel shown contained more water vapor. How would
that affect the lifting condensation level?
2. What would be the effect if there were less water vapor in the air parcel?
Visualizing Physical Geography
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Clouds and Fog
Clouds consist of water
droplets, ice crystals, or both
Condensation nucleus = a tiny bit
of solid matter (aerosol) in the
atmosphere, on which water
vapor condenses to form a tiny
water droplet
© NG Image Collection
Visualizing Physical Geography
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Clouds and Fog
Clouds Classification by Height
© A. N. Strahler
Cloud Families: High clouds, middle clouds, low
clouds, clouds of vertical development
Visualizing Physical Geography
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Clouds and Fog
Cirrus Clouds
© NG Image Collection
Cirroform clouds = at the top of the troposphere, these clouds
are high, thin, wispy clouds drawn out into streaks. They are
composed of ice crystals and form when moisture is present
high in the air
Visualizing Physical Geography
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Clouds and Fog
Stratiform Clouds
© NG Image Collection
Stratiform clouds = are blanket-like layers that cover large
areas. A common type is stratus clouds, which often cover the
entire sky. In this photo, high cumulus clouds (left) grade into a
high stratus layer (right).
Visualizing Physical Geography
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Clouds and Fog
Cumulus Clouds
© NG Image Collection
Cumuliform clouds = globular masses of cloud that are
associated with small to large parcels of moist rising air. In this
photo, puffy, fair-weather cumulus clouds drift over a lake.
Visualizing Physical Geography
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Clouds and Fog
Cumulonimbus Clouds
© NG Image Collection
Nimbus clouds = are clouds of any of type that produce
precipitation. An isolated cumulonimbus cell discharges
its water volume as precipitation in this photo.
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Clouds and Fog
Fog
•Radiation fog: formed when
temperature of the air at ground level
falls below dew point
© NG Image Collection
•Advection fog: forms when warm
moist air moves over a cold surface
• Common over oceans (“sea fog”)
• West Coast of US and Canada
Visualizing Physical Geography
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© NG Image Collection
© NG Image Collection
Precipitation
Types of Precipitation
• Rain
• Snow
• Hail
• Ice storm
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© NG Image Collection
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Precipitation
Annual rates of precipitation vary greatly around the
world
Tropical regions
Deserts
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© NG Image Collection
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Wet-dry regions
Equatorial regions
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© NG Image Collection
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Precipitation
• Globally, rainfall ranges
from tropical to desert to
polar
• This profoundly influence
landforms, the biosphere,
and human activities
• Most species have evolved
to survive within narrow
ranges of annual
precipitation
Tropical regions
© NG Image Collection
Deserts
© NG Image Collection
Visualizing Physical Geography
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Precipitation
Precipitation forms in clouds by two different processes:
•Warm Cloud = Collision Coalescence
•Cold Cloud = Ice crystal process
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Warm cloud shown above = Formation of precipitation through
coalescence of water droplets
Visualizing Physical Geography
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Precipitation
© NG Image Collection
© NG Image Collection
© NG Image Collection
Review Figure 4.10 and answer
this question. Which type of cloud
is represented in this figure?
a. cirrus
b. altostratus
c. cumulonimbus
d. cirrostratus
© NG Image Collection
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Precipitation
Cold Cloud = Ice crystal process
Precipitation forms as water vapor evaporates from super
cooled liquid cloud drops. The water vapor is then deposited
on ice crystals, forming snowflakes
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Precipitation
Types of Precipitation
Courtesy NOAA
• Rain and snow
Courtesy NOAA
• Freezing rain
• Measuring Precipitation = U.S. National Weather Service’s
NEXRAD (Next Generation Radar)
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Precipitation
Types of Precipitation
• Hail can form during thunderstorms when there are strong
updrafts
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Precipitation
Atmospheric Lifting
• Air can move upward in four ways: through orographic,
convective, frontal, or convergent lifting
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Precipitation
Atmospheric Lifting
• Orographic precipitation =
Precipitation that is
induced when moist air is
forced vertically over a
mountain barrier
• Convective precipitation =
Precipitation that is
induced when warm, moist
air is heated at the ground
surface, rises, cools, and
condenses to form water
droplets, raindrops, and
eventually rainfall
Visualizing Physical Geography
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Precipitation
Orographic Lifting
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Precipitation
Convective Lifting
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Precipitation
Convective Lifting
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If the environmental lapse rate increased (that is, if it were cooler at higher
altitudes), how would the lifting condensation level change?
a. It would be higher.
b. It would be lower.
c. It would stay the same.
d. It is impossible to determine.
Visualizing Physical Geography
Copyright © 2012 John Wiley & Sons, Inc.
Precipitation
Convergent Lifting
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Visualizing Physical Geography
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Precipitation
Frontal Lifting
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Human Impacts on Clouds and Precipitation
Acid Rain
• Also called acid deposition
• made up of raindrops that
have been chemically
acidified by industrial air
pollutants such as sulfur
dioxide (SO2) and nitric
oxide (NO2)
• Acids have a low pH value,
less than that of distilled
water (pH = 7)
• The lower the pH value,
the more acidic the liquid.
© Illinois State Water Survey
Acidity of rainwater in U.S., 2005
Visualizing Physical Geography
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Human Impacts on Clouds and Precipitation
Effects of Acid Rain
• Acid streams and lakes
affect aquatic life
• Damage to forests
• Damage to soils
© Gerd Ludwig/INSTITUTE
• Damage to buildings
© NG Image Collection
Consider the pattern of acid rain deposition in the
northeastern United States. What is the implication
for international relations?
Visualizing Physical Geography
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Human Impacts on Clouds and Precipitation
Cloud Cover, Precipitation, and Global Warming
Any rise in sea-surface temperature will increase the rate of
evaporation, and an increase in evaporation will raise the
average atmospheric content of water vapor. What effect
will this have on climate?
•Clouds: Longwave warming or shortwave cooling?
•Increased Precipitation?
Visualizing Physical Geography
Copyright © 2012 John Wiley & Sons, Inc.
© NASA Images
Visualizing Physical Geography
by Timothy Foresman & Alan Strahler
Chapter 5
Global Atmospheric and Oceanic Circulation
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Visualizing Physical Geography
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Chapter Overview
Atmospheric Pressure
Wind Speed and Direction
Global Wind and Pressure
Patterns
Local Winds
Oceanic Circulation
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Atmospheric Pressure
• Atmospheric pressure is pressure
exerted by the atmosphere because of
the force of gravity acting on the
overlying column of air.
Measuring Atmospheric Pressure
• Units = inches of mercury (in. Hg) or
millibars (mb).
• Standard sea level pressure = 1013.2 mb.
• Cold, clear night pressure > 1013.2 mb.
• Center of a storm with rising warm air will
have a pressure < 1013.2 mb.
• Barometer is an instrument that measures
atmospheric pressure.
© John Wiley & Sons ,Inc
Visualizing Physical Geography
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Atmospheric Pressure
Measuring Atmospheric Pressure
• Radiosonde (balloon) is launched twice
a day at key locations in United States
• Radiosondes measure:
• Pressure
• Altitude
• GPS location
• Temperature
• Relative humidity
• Wind speed and direction
© NG Image Collection
Would one expect low or higher than standard sea level
pressure in a hurricane?
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Atmospheric Pressure
Atmospheric Pressure and
Altitude
• Air density depends on pressure
and temperature.
• Atmospheric pressure decreases
with altitude.
Visualizing Physical Geography
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Wind Speed and Direction
Wind:
• Horizontal movement of air
• Renewable resource
• Measured with an anemometer
Wind direction:
• Identified by the direction from
which the wind comes
• West wind blows from west to east
• Measured with a wind vane
Courtesy Taylor Instrument Company and
Wards Natural Science Establishment
Wind speed and direction are determined by three factors:
pressure gradient, Coriolis effect, and friction.
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Wind Speed and Direction
Pressure Gradients
• Change of atmospheric pressure measured along a line at
right angles to the isobars.
• Pressure gradient goes from high to low pressure.
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Wind Speed and Direction
Pressure Gradients
• Isobar = line on a map drawn through all points having the
same atmospheric pressure
• Widely spaced isobars → weak gradient and weaker winds.
• Closely spaced isobars → strong PG and stronger winds.
Where would you find the
greatest pressure gradient
on this map?
a. Oklahoma City
b. Southwestern Missouri
c. Memphis
d. Nashville
© John Wiley & Sons, Inc.
Visualizing Physical Geography
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Wind Speed and Direction
Pressure Gradients
• Unequal heating of
the Earth’s surface
leads to a pressure
gradient and causes
wind.
• Latitude, terrain
differences, and land
cover can cause
uneven heating,
pressure gradients
and wind.
1
2
3
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Wind Speed and Direction
Pressure Gradients
If the island were in the
Arctic and covered by
glacial ice, would the
pressure gradient be the
same or different?
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Wind Speed and Direction
The Coriolis Effect (CE)
• An effect of the Earth’s rotation that acts like a force to
deflect a moving object on the Earth’s surface to the:
• Right in the northern hemisphere
• Left in the southern hemisphere
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Wind Speed and Direction
The Coriolis Effect (CE)
© John Wiley & Sons, Inc.
• Due to Earth’s rotation, a path from the North Pole to
Chicago along 74°W meridian would curve to the right,
toward Chicago.
Visualizing Physical Geography
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Wind Speed and Direction
Geostrophic wind is
wind at high levels
(upper levels) above
the Earth’s surface
moving parallel to the
isobars, at a right
angle to the pressure
gradient.
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Wind Speed and Direction
The Frictional Force
(FF)
• Force exerted by the
ground surface that is
proportional to the
wind speed
• Always acts in the
opposite direction to
the direction of motion
• Greatest closest to the
surface
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Wind Speed and Direction
The Frictional Force
A cyclone is a center of low pressure where surface air
converges into a spiral and is uplifted to the upper troposphere.
• The PGF, CE, and FF cause the surface wind to spiral,
converging inward toward the low-pressure center.
© John Wiley & Sons, Inc.
As the inward motion converges, it forces the air to rise
(uplift) → cools adiabatically → clouds and precipitation
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Wind Speed and Direction
The Frictional Force
An anticyclone is a center of high pressure where upper
troposphere winds spins downward (subsidence) and diverges
outward at the surface.
© John Wiley & Sons, Inc.
• Air warms adiabatically as it sinks → inhibiting clouds
and precipitation
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Global Wind and Pressure Patterns
Global surface winds on an ideal Earth (see Figure 5.11):
© John Wiley & Sons, Inc.
•Surface winds are shown on the disk of the Earth, and the
cross section at the right shows winds aloft.
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Global Wind and Pressure Patterns
Tropical Circulation
• Warm air over the equator
rises and forms low
pressure resulting in the
equatorial trough (wet
weather).
• Trade winds converge at
the equator.
• Air descends near 25 to
30o latitude forming a
subtropical high pressure
(dry weather) zone.
Visualizing Physical Geography
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Global Wind and Pressure Patterns
Tropical Circulation
• Hadley cell = A lowlatitude atmospheric
circulation cell with rising
air over the equatorial
trough and sinking air
over the subtropical highpressure belts.
© John Wiley & Sons, Inc.
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Global Wind and Pressure Patterns
Tropical Circulation
Intertropical Convergence Zone (ITCZ):
• A zone of convergence of air
masses along the equatorial trough
• Doldrums
• ITCZ shifts with the seasons
following the zone of highest
insolation:
© John Wiley & Sons, Inc.
• Over the ocean it shifts a few degrees between January
and July.
• Over land, the zone shifts 20o to as much as 40o in Asia.
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Global Wind and Pressure Patterns
Tropical Circulation
• Monsoon = seasonal reversal of
the wind
• January = north wind (dry)
• July = warm, moist air (wet)
© NG Image Collection
© John Wiley & Sons, Inc.
Visualizing Physical Geography
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Global Wind and Pressure Patterns
Considering the direction of the winds compared to the
isobars, which statement is most correct?
a. Because this area is near
the equator, the Coriolis effect
has no influence on these winds.
b. Because the pressure gradients
are great, friction has no
influence on these winds.
© John Wiley & Sons, Inc.
c. Because some of the winds are over the ocean, neither the
Coriolis effect nor friction has an influence on these winds.
d. Because the alignment of the wind direction is at 45°to the
isobars, both the Coriolis effect and friction are important.
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Global Wind and Pressure Patterns
North American monsoon
© Ralph Lauer/Zuma Press/NewsCom
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Global Wind and Pressure Patterns
Subtropical high-pressure cells
• Area of high atmospheric
pressure centered at
about 30° N and 30° S
• Stable and dry weather
• Trade winds and
westerlies
• Hawaiian and Azores high
• Shift with the seasons
• East and west coast
differences
© A. N. Strahler
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Global Wind and Pressure Patterns
In the days of sailing ships, which pattern of navigation made the
most sense, considering prevailing wind directions?
a. United States to Africa to England back to the United States
b. United States to England to Africa back to the United States
c. United States to England back to the United States
d. United States to Africa back to the United States
© A. N. Strahler
Visualizing Physical Geography
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Global Wind and Pressure Patterns
Midlatitude Circulation
• Westerlies
• Between about 30° and 60°
latitude
• Polar front = boundary between cold
polar air masses and warm
subtropical air masses
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Global Wind and Pressure Patterns
Midlatitude Circulation
• Jet stream = high-speed airflow in
a narrow band within the upper-air
westerlies and along certain other
global latitude zones at high
altitudes:
• Polar-front jet stream
• Shifts equatorward in the
winter
• Subtropical jet stream
Visualizing Physical Geography
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© John Wiley & Sons, Inc.
Global Wind and Pressure Patterns
What a Geographer Sees
• Jet Streams and Air Travel
Courtesy NASA
© John Wiley & Sons, Inc.
If an airplane flying in the center of this subtropical jet stream travels
east at 1000 km/hr (621 mi/hr), how fast will the same airplane go,
with the same fuel expenditure, when it travels west in the jet stream
on its return flight?
Visualizing Physical Geography
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Global Wind and Pressure Patterns
Jet stream disturbances
• Rossby waves
• Baroclinic instability
• Zonal flow (west to east)
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© John Wiley & Sons, Inc.
Global Wind and Pressure Patterns
Jet stream disturbances
• Growth of disturbances in the jet stream
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Visualizing Physical Geography
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Global Wind and Pressure Patterns
High-Latitude
Circulation
• January
• July
Courtesy John E. Oliver
Visualizing Physical Geography
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Global Wind and Pressure Patterns
Global Circulation at Higher Altitudes
© John Wiley & Sons, Inc.
Visualizing Physical Geography
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Global Wind and Pressure Patterns
Global surface winds on an ideal Earth (Review)
© John Wiley & Sons, Inc.
Visualizing Physical Geography
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Global Wind and Pressure Patterns
Global air cells: Ferrel, Hadley, or Polar? (Review)
© John Wiley & Sons, Inc.
Visualizing Physical Geography
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Local Winds
Daily Cycles of Winds
• Daily reversal of the winds as a result of uneven heating
• Sea breeze
• Land breeze
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Local Winds
Daily Cycles of Winds
•Mountain breeze
•Valley breeze
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Local Winds
Other Topographic Winds
• Chinook: a dry wind
• Santa Ana winds
For north–south mountain ranges
in midlatitude regions (30° to
45° latitude), dry regions will be
found on the ____ side in the
northern hemisphere and on the
____ in the southern
hemisphere.
a. east; east
b. west; west
c. east; west
d. west; east
Visualizing Physical Geography
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© A. N. Strahler
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Local Winds
Other Topographic Winds
Santa Ana winds can create fire
hazards. In this photo, wildfires
have already begun in some
areas, as is apparent from the
smoke drifting off the Southern
California coast.
Courtesy NOAA
Visualizing Physical Geography
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Oceanic Circulation
Ocean Currents
• A persistent, dominantly
horizontal flow of water
controlled by wind patterns
• Gyres: large circular ocean
movements
© John Wiley & Sons, Inc
What relationship do you notice with the northern hemisphere
ocean current and the pressure type typically located at 30o N?
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Oceanic Circulation
Ocean Currents
Ocean circulation and energy transport:
• Warm surface waters in the tropics move poleward.
• Thermohaline circulation: Cold and dense waters in the N.
Atlantic sink, flow equatorward, and eventually upwell to the
surface at far distant locations to cool surrounding regions
and complete the circuit.
Visualizing Physical Geography
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© NG Maps
Oceanic Circulation
Circulation and Energy Transfer
• Energy surplus
• Energy deficit
• In order to maintain the Earth’s energy balance, absorbed
solar energy is moved from regions of excess to regions of
deficit, carried by ocean currents and atmospheric circulation
© John Wiley & Sons, Inc.
Visualizing Physical Geography
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Oceanic Circulation
Cycles in Atmospheric and Oceanic Circulation
• El Niño–Southern Oscillation (ENSO)
• La Niña
© NG Maps
© NG Maps
Visualizing Physical Geography
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Oceanic Circulation
Cycles in Atmospheric and Oceanic Circulation
• Climate effects of El Niño events
© John Wiley & Sons, Inc.
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Oceanic Circulation
Cycles in Atmospheric and Oceanic Circulation
• North Atlantic Oscillation (NAO)
• Pacific Decadal Oscillation (PDO)
© NG Maps
© NG Maps
Visualizing Physical Geography
Copyright © 2012 John Wiley & Sons, Inc.