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UNIT 2 – Patterns in Weather and
Climate
Chapter 4 - Weather and Climate
Weather
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the state of the atmosphere at any one place or time.
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this includes humidity, temperature, sunshine hours, cloud cover,
visibility, and precipitation (fog, rain, snow, sleet, and frost)
Climate
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the average weather conditions of a region
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recorded average is the result of many years of observations of
weather
Rotating vs. Revolving
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The earth rotates (spins) on its axis which takes 24 hours and results
in day and night
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The earth revolves (orbits) around the sun
which takes 365 days and results in
seasons.
Day & Night
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It is the earth's rotation on its axis that results in night and day.
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As Newfoundland rotates away from the sun it appears that the sun is
setting in the west. In actual fact you are rotating away from the sun
to the east.
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In the morning it appears that the sun rises in the east. In actual fact
you are rotating towards the sun from the west.
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Cloud Cover Affects Daily & Nightly Temperatures
Nightly cloud cover reduces the range of temperature from day to night.
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Clouds reflect heat waves
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Heat below clouds is reflected back to earth.
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Without clouds heat escapes giving colder nights
Lack of cloud cover contributes to temperature patterns in the desert.
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Lack of cloud cover in the day results in high daily temperatures.
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However in the night the lack of cloud cover allows the heat to escape
resulting in cold nightly temperatures
Seasons
Viewing figure 5.2 on page 56 will help you see that two characteristics
of the earth-sun relationship result in the seasons occurring outside the
tropics.
1. The tilt on the earth's axis
2. The revolution of the earth around the sun
These two features of the earth-sun relationship mean that different
latitudes on earth receive different directness of light at different times.
When the sun hits more directly the latitude gets hotter temperatures
and what they call summer.
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Defining Equinox & Solstice
Solstice:
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From Latin for “sun stand still”
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Sun is directly over head @ 12 noon on 23.5⁰ North or South.
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Occurs Dec 21 & June 21
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Longest day of the year & shortest day of the year
Equinox :
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From Latin for equal day & night.
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Sun is directly over head @ 12 noon on the equator.
Occurs Sept. 21 & March 21
Equal length of night and day everywhere on earth
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The Tropics vs. The Poles
Tropics
 Refers to warm equatorial climates.
 Technical Info - located between 23.5 degrees north (Tropic of Cancer)
and 23.5 degrees south (Tropic of Capricorn).
 More direct the sunlight the more intense the heat and the further you
move outside the tropics the more severe the seasons.
 The length of day varies more the further you move from the equator.
 When light hits the earth towards the poles it is on a severe angle which
decreases the intensity of heat. The same light/heat energy is spread
over a greater area. (Figure 4.3).
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Explaining the temperature difference in summer and winter
 There are two reasons for the difference in temperature.
1. More direct sunlight gives greater intensity of heat.
2. Longer summer day light hours means there are more heating hours
and fewer cooling hours.
Greenhouse Effect
 Often misunderstood and mistaken for "Global Warming".
 This is a good thing because it moderates our temperature.
 Planets without atmospheres have an extreme variation in temperature
between day and night.
o While facing the sun, those planets without an atmosphere, get the
full intensity of the sun making it very hot.
o On those planets where there is no atmosphere it gets very cold in
the night due the absence of radiant sun light. Without an
atmosphere these planets have nothing to hold heat in.
 On earth the atmosphere reflects and absorbs almost 50% of radiant
energy. Our atmosphere acts like the glass on a greenhouse keeping in much
of the heat. Consequently, on earth the nights are not as cold.
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Latitude & Temperature are Inversely Proportional
 If we say "the further south one goes the warmer it gets" we would be
wrong. Once we go far enough south to go past the equator the
temperatures would start getting colder again.
 The best way to word it is "as latitude increases temperature
decreases" or “Latitude and Temperature are inversely proportional”.
 Other influential factors are ocean currents, prevailing winds, altitude.
 Look at maps on page 60 - For that reason we do see some places like the
Himalayas north of India that are colder than central Asia .
 Think about graphs that were done in last class showing decreased
temperature with increased latitude. ( # 13 P. 58 )
Why The Poles Are Colder Than The Tropics
 The poles of the earth are colder than the equatorial regions of the
earth because of the earth's spherical shape. (not tilt, revolution or
rotation - that’s seasons)
 light rays reaching earth from the sun are almost exactly parallel.
 When 2 units of light hit the equator it is direct (at 90 to the earth's
surface) and has to heat a small area.
 When 2 units of light hit the polar regions it is less direct (at less than
90 to the earth's surface) and has to heat a larger area.
 The ultimate result is more intense heating at the equator due to more
direct sun. In the noon day sun, that is closer to directly over head, the
suns feels very hot while in the evening the sun, which is at a small angle,
does not feel as hot.
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Refer to figure 4.3 on page 56
Reversal of Seasons by Hemisphere
 The Northern Hemisphere and the Southern Hemisphere have opposite
seasons. This is due to the tilt on the earth's axis and its revolution
around the sun.
 As you can see from the world map below, most of the habitable land is
above the equator. However places like Australia, South Africa and
Argentina do have seasons opposite to us in the northern hemisphere.
 The effect of the earth's tilt can be seen in this figure, where the tilt is
exaggerated. The northern hemisphere is getting direct sunlight and
hence summer while the Australians and all the southern hemisphere are
getting less direct sunlight and hence winter.
 The relationship between Northern and southern hemispheres holds
true for all seasons not just winter and summer.
 Canada's winter = Australia's Summer
 Canada's summer = Australia's Winter
 Canada's Fall = Australia's Spring
 Canada's Spring = Australia's Fall
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Prevailing Winds
Winds Blow From High Pressure to Low Pressure
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The statement is fact. Winds blow from regions of high atmospheric
pressure to areas of low atmospheric pressure. Atmospheric
pressures have local variations but there are world pressure belts
that we will explore.
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Think: Air inside a balloon. If left untied the air will escape the high
pressure of the balloon and create a wind blowing from high pressure
inside the balloon to relatively low pressure outside the balloon.
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Think Exhaling: when you exhale the air leaves your lungs because you
create a high pressure inside your chest cavity and breathe (wind is
created from high pressure inside your chest to a lower pressure
outside your chest.)
It is simply fact. High and low pressures in the earth’s atmosphere are
responsible for wind.
Applying Knowledge of Winds (local winds)
Sea Breezes: Look at figure 4.8 in your text book on page 61.
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In the day time the land heats much faster than the water.
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Consequently the air over the land heats and rises. (remember
convection currents)
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The rising air over the land creates a relatively low pressure. The air
pressure over the water/sea is relatively high.
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Consequently wind blows from the high pressure over the sea to the
low pressure over the land.
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Hence the name sea breeze. the wind is blowing off the sea.
Remember winds are named for where they come from. Easterly winds
come out of the east. Southerly winds are coming out of the south and sea
breezes are coming from the sea.
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Prevailing Winds
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Prevailing Wind: Regular, predictable, normal wind direction. They are
caused by global convection cells in the earth's atmosphere. See
figure 4.10 on page 63 of text to see the global convection cells.
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The global convection cells are created because of the differential
heating of the earth's surface. As the equatorial region heats the air
it rises creating a low pressure at the equator. The air falls to earth
30 North and south creating high pressures. The other lows and
highs can be predicted every 30o of latitude.
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Alternating high and low pressures result from the convection cells. A
Low pressure belt is created at the equator and at 60 N and 60 S
while high pressure belts are created at 30 N and 30 S and at the
poles.
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Prevailing Winds have global patterns because of these global
pressure belts. They follow the laws of physics and blow from the
high pressure belts to the low pressure belts.
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The Coriolis effect explains why the winds are deflected in the
directions indicated on figure 4.11. The Coriolis effect is a law of
physics that states: objects in motion in the northern hemisphere are
deflected to the right while in the southern hemisphere they are
deflected to the left. Therefore winds in the north are deflected
right and the winds in the south are deflected left.
Prevailing Wind Names
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0-30 N = Northeast trade winds
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0-30 S = Southeast trade winds
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30-60 N and 30-60 S = Westerly winds
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60-90 N = North Polar easterlies
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60-90 S = South Polar easterlies
Types of Rain
Relief Rainfall
 Moisture laden air blows off the sea.
 It is forced up by mountains (high relief)
 Air cools at higher altitudes
 Cool air holds less moisture
 Consequently clouds condense and rain falls
 Most rain falls on the windward side of the relief
 Leeward side is often in a dry rain shadow because the moisture has
all been lost.
Frontal Rainfall
 Warm Moisture laden air meets cold air.
 Warm air is less dense & is forced up over the cooler, more dense air
 Warm Moisture laden air cools at higher altitude
 Cool air holds less moisture
 Consequently clouds condense and rain falls.
Convectional Rainfall
 Usually occurs in hot areas like tropics or continental summer
 Sun heats the earth causing large amounts of water to evaporate.
 Hot air rises forming convection currents (hence the name)
 Warm Moisture laden air cools at higher altitude.
 Cool air holds less moisture
 Consequently clouds condense and rain falls.
Handout ‘rainfall_handout.wpd’
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Wind & Precipitation
 Looking at the prevailing wind maps on pages 64 & 65 you can see that
some prevailing winds blow off the ocean and onto the land. This is a
recipe for high precipitation. Especially if the wind is blowing off a warm
ocean like the Indian Ocean or the South Pacific.
 On the other hand, if the wind that a location receives is coming off the
land, then there is very little moisture in it and this is a recipe for low
precipitation.
 Knowing the direction of winds over mountains is also important in
predicting precipitation. The windward side of a mountain is going to
receive the greatest rainfall while the leeward side will find itself in a
rain shadow.
Wind & Temperature
 Looking at the prevailing wind maps on pages 64 & 65 you can see that
some prevailing winds bring warm air from the south toward the
north, for example the westerly winds.
 On the other hand some winds, like the north polar easterlies, bring
cold air from the north toward the south.
 The effect on temperature varies with seasons as well.
o Wind off the land in summer is a recipe for heat. Land heats up
faster than water and therefore the wind blowing over it will
pick up the heat.
o However, in the winter wind off the land is a recipe for cold.
Land also cools down faster than water, so winds blowing over
the frozen cold interior will lose its heat.
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Ocean Currents
Turn to page 60 and see figure 4.7 which shows you many of the major ocean currents.
Ocean currents:
 Permanent or semi-permanent horizontal movement of surface water
(the top 100m)
 It is unusually cold or hot, when compared with the surrounding water
 Caused by and shaped by, prevailing winds, variations in temperature &
hence density of water, & Coriolis force
Cold ocean currents: move water towards the equator.
 For example the Humbolt or Peru Current carries cold water from
Antarctica toward the equator. Can you find it on Page 60?
 Another example is the Labrador Current which carries cold water
from the Arctic Ocean. Can you find it on Page 60?
Warm ocean currents: Move water away from warm equatorial regions.
 For example the Gulf Stream moves warm water from the Gulf of
Mexico northeast toward England. Can you find it on Page 60?
 Another good example is the Japanese current which moves warm
water from Japan northeast towards Vancouver. Can you find it on
Page 60?
Ocean Currents & The Affect on Climate
Affect of cold ocean currents:
 Cools the summer temperature
 Reduces precipitation; cooler air holds less moisture
Affect of warm ocean currents:
 Warms the winter temperature
 Increases precipitation; warmer air holds more moisture
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Practical Examples
 Mary’s Harbour on the coast of Labrador is affected by the Labrador
current which gives Mary's Harbour cool summer temperatures and
surprising little precipitation for a location right on the ocean’s edge.
 Brazilia is a city in Brazil and is affected by the Brazil Current. This
gives Brazilia high precipitation. The precipitation is further increased
by the fact that the southeast trade winds blow off the warm ocean
current onto the land. Brazilia is located within the tropics so the degree
of season is very limited anyway.
 Newfoundland's south coast has ice free ports year long while its north
coast has heavy ice for several months. The difference in latitude is not
enough to explain this difference in ice. Can you explain it with ocean
currents?
Continentality
Defining Temperature Range
 Temperature range = the range between the highest and the lowest
average monthly temperatures of a region.
 Large or high temperature range = extremes of temperature, hot
summer cold winter.
 Small or low temperature range = moderated temperature, warm
summer, cool winter
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page 70, figure 4.18
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Continental vs. Maritime Climates
 As distance from the ocean increases, annual temperature range
increases. Continental climates experience greater extremes of
temperature than coastal climates at the same latitude.
 Look at figure 4.18, page 70 - Ottawa, Ontario would experience a
continental climate and St. John’s would experience a Maritime
climate. Discuss using data from table.
Climate Graphs
 Climograph - a graph of monthly average temperature plotted against
average humidity.
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You will need to understand climate graphs to analyze climate statistics.
Climographs - pages 76 & 77
 The left scale indicates the temperature and it is graphed as a line
 The right scale is for precipitation and is graphed as a bar graph
Monsoons
Monsoon:
 From Arabic for seasonal wind
 A sudden wet season in the tropics
India’s Winter Monsoon:
 Continental Asia cools & high atmospheric pressure results.
 Wind blows southward towards the low over Indian ocean.
 Very little rain or dry season result because the wind is blowing over dry
land and does not pick up water.
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India’s Summer monsoon:
 Continental Asia heats up & Low atmospheric pressure results
 Wind blows northward towards the low over India. Tremendous rains
result because the wind is blowing over the warm Indian Ocean.
Monsoon handout (monsoon_handout.wpd)
Continentality Lab handout
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Elevation & Temperature
Elevation is defined as the height of a region above sea level
Air temperature decreases 2C for every 300m increase in elevation.
The higher up we go the colder it gets; hence snow on mountain tops
 La Paz and Rio de Janeiro have a similar distance from ocean and
similar latitude.
o La Paz is much colder because of higher elevation. La Paz is
nestled in the Andes Mountains.
o Rio de Janeiro is very close to sea level
 La Paz, Bolivia, has an elevation of 3600m. Its coldest month is 9C
 Rio de Janeiro, Brazil, has an elevation of 61m. Its coldest month is
25C
Elevation & Precipitation
Relief has an effect on precipitation mostly as it relates to relief rain.
Consequently it must be accompanied by wind.
Relief Rainfall
 Moisture laden air blows off the sea.
 It is forced up by mountains (high relief)
 Air cools at higher altitudes
 Cool air holds less moisture
 Consequently clouds condense and rain falls
 Most rain falls on the windward side of the relief
Rain Shadow
 The Leeward side of a mountain is often in a dry rain shadow
because the moisture has all been lost.
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Examples
 Many places like Vancouver receive large amounts of rain because they
are on the windward side of the mountain.
 Other places like Edmonton receive very little rain because they are on
the leeward side of a mountain range.
Tropical Climates & Dry Climates
Tropical Climates
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All Tropical Climates have average temperatures over 18C every day due to
low latitude & warm ocean currents & prevailing winds. You will notice on the climate
graphs below that the line indicating temperature is fairly flat right around 20C.
 Viewing figure 5.1 on page 75 of your text you can see that almost all of the
tropical wet and the tropical wet & dry climates are located between the
Tropic of Cancer and the Tropic of Capricorn.
o Tropical Wet sub region ; heavy rain all year due to hot temp &
resulting convectional rain.
o Tropical wet & dry sub region; very heavy summer rain & very dry
winter due to seasonal shift in prevailing winds. (monsoon regions)
Dry Climates
 All Dry climates receive less than 500mm precipitation annually.
o The region has more evaporation than precipitation leaving it in a
water deficit.
o There is little vegetation & it is often windy
o Climate graphs of arid and semi-arid regions are difficult to
distinguish from each other but easy to distinguish from all other
climates because of the low precipitation bars.
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 Arid or desert dry climates occur mostly between 10-30N & 10-30S and
receive 10-250mm rain annually.
 Semi-arid or steppe dry climates are really transition zones between
desert & Forest. They receive 250-500mm rain annually which is often
enough to support grasses but not forests.
Temperate Climates & Polar Climates
Temperate Climates
A review of figure 5.1 on page 75 of your text reveals that temperate mild climates occur in
both hemispheres while the temperate cold climates only occur in the northern Hemisphere.
The distinguishing feature on a climograph is the curved temperature
line.
 Temperate Mild Winter
o Temperature varies with seasons
o Mid Latitudes
o Mild winter
o Summer temperatures vary but winters are warmer than –3C
 Temperate cold Winter
o Temperature varies with seasons
o Mid-high Latitudes
o Cold winters
o Summer temperatures vary but winters are colder than –3C
Polar Climates
 Polar climates are distinguished by their extremely low winter
temperatures and low summer temperatures.
o Tundra: summer temperature never above 10C
o Ice Caps: summer's average monthly temperature is never above 0C
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Highland Climates
 These climates are only characterized by their elevation and decreased
temperature. However, the climates vary with latitude of the mountain,
closeness to the ocean etc.
 Some alpine regions can be like the tundra and the ice cap of a mountain is
like the polar ice caps.
Assign:
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Ques
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Ques
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Ques
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Ques
#1 on page 74
#2 on page 75
#3 on page 77
# 7 on page 82
Climatic Conditions & Human Activities
Positive Influences of Climate
 Good tourist industry in subtropics like Florida
 Sports are affected: golf in summer, skiing in winter, etc
 Religious tradition of Christmas strongly associated with winter
conditions
 Clothes Fashion changes with the season
Negative Influences of Climate
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Transportation is affected
winter tires in temperate zone
snow clearing budgets can be high
School closed during winter storms in temperate zone
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A variety of ways that weather and climate can negatively and positively
influence human activity:
o Hurricanes tornados and tropical storms occur in specific regions on a
regular basis. Protection of property, evacuation plans, family safety
plans, cleanup budgets and Insurance are all impacts of hurricanes.
o Seasonal Activity is affected by climate. Farming, fishing and tourism
are scheduled around the seasons.
Assign Case Studies:
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Hurricane Damage Protection in Florida p. 89
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Tornado Kills 400 in Bangladesh p. 87
Human Impact on Climate
Global Warming
 Global warming is the gradual increase of the earth's average
temperature since the industrial revolution. It is a fact that the earth's
average temperature is increasing. The negative effects associated with
global warming are also factual.
 However, it is important to note that some scientists dispute the fact
that it is due to human activity. Some scientists believe the recent
increase in temperature is a part of the normal rhythm s of change in the
earth's atmosphere.
Global warming vs. Greenhouse effect
 It is also important to draw a distinction between global warming and the
greenhouse effect. The greenhouse effect is a good thing and
moderates our temperatures here on earth. It operates by specific
gasses like carbon dioxide and methane.
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 Global warming is due to the human activity that has increased the level
of these greenhouse gasses and consequently increased the earth's
temperature.
Human Impact on Greenhouse Gasses
It is believed that humans have changed the balance of greenhouse gasses
in the atmosphere in two ways:
1.
2.
Increased carbon dioxide emissions: result from the combustion of
fossil fuels. Coal, Gasoline, Furnace oil, Propane, diesel, and jet fuel
are all examples of fossil fuels we burn and result in carbon dioxide
emissions.
Cutting forests: results in fewer trees. Trees and all plants recycle
carbon dioxide into carbohydrates consequently reducing
atmospheric carbon dioxide. When these trees are removed the level
of carbon dioxide in the atmosphere increases.
Global warming & Climate change
 Obviously global warming results in temperature changes. However
that temperature change affects precipitation as well. In some
areas it increases precipitation and in other areas it reduces
precipitation.