Download Weather Dynamics

Unit Four:
Weather Systems
Weather Dynamics
Weather dynamics is the study of how the
motion of water and air causes weather
patterns.
 The main components of Earth that affects
weather are the atmosphere, the land
forms, and water in the forms (solid, liquid,
and vapor).
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Web sites to know and love!
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Environment Canada
 http://weatheroffice.ec.gc.ca/canada_e.html
site – Weather basics
http://www.usatoday.com/weather/resources/b
asics/wworks0.htm
 USA Today
Weather vs. Climate
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Weather - is the set of environmental
conditions encountered from one day to
the next.
 Today
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is ….
Climate - is the set of environmental
conditions averaged over many years.
 What
is the climate of St. John’s?
Global Geography
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Longitude - the angle measured east or west
from the 0° line, which passes through
Greenwich, England.
Latitude - the angle measured south or north of
the equator.
Equatorial Region - region located between the
Tropic of Cancer and the Tropic of Capricorn.
Polar Regions - Region north of the Arctic
Circle and the region south of the Antarctic
Circle.
Mid-latitude Regions - Regions between the
tropics and the polar regions.
The following methods of heat
transfer distribute energy around
the Earth.
1. Radiation is the transfer of energy by
waves. Radiation does not require a
medium. Visible light is one form of
radiation that reaches us from the sun via
empty space. Visible light is only one
member of the electromagnetic spectrum.
Some other waves from this spectrum are:
microwaves, X-rays, infrared waves, etc.
2. Conduction is the transfer of energy
through the collision of particles. A frying
pan on a stove element heats up by
conduction. Some materials are better
conductors of heat than others. Metals are
generally better conductors than some
materials such as rock, sand, sand, etc.
3. Convection is the transfer of energy
vertically by movement of particles in a
fluid ( water or atmosphere).
4. Advection is the transfer of energy
horizontally by movement of particles in a
fluid ( water or atmosphere).
The Energy of the Sun
 The
Sun is the Earth’s main source of
electromagnetic radiation. Not all of
the solar energy reaching the Earth’s
atmosphere actually reaches the land
and water. See fig.4 of your text.
 Some solar radiation gets reflected
back into space. How much radiation
that is reflected at any given time is
dependent upon the surface features.
The albedo (percentage of light reflected)
of a material will determine how much
radiation is reflected. Clean snow has a
high albedo whereas black soil has a low
albedo.
 Any material that absorbs energy and
becomes warmer is called a heat sink.
The oceans are good heat sinks whereas
soil and rock are poor heat sinks.
 The heat capacity of a substance will
indicate whether a substance is a good
heat sink or not.

Specific Heat Capacity
the measure of how much heat a
substance requires to increase it’s
temperature one degree.( Or how much
energy it releases as it’s temperature
decreases.)
 Figure 5 in your text shows the heat
capacity of some common substances.
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Types of Heat
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Latent heat of fusion
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Latent heat of vaporization
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The amount of heat needed to change a unit mass of a
substance from a solid to a liquid.
The amount of heat needed to change a unit mass of a
substance from a liquid to a gas.
‘Latent’ means ‘hidden’. When a substance changes
state, the substance either absorbs or releases energy
without changing temperature.
A substance will have its own latent heats of Fusion and
Vaporization constants. Vaporization requires more
energy than Fusion.
Water has latent heat of fusion of 3.3 x 105 J/kg and a
latent heat of vaporization of 2.3 x 106 J/kg
The Atmosphere
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The atmosphere consists of air and moisture
that surrounds the Earth. The common
atmospheric gases are oxygen, nitrogen, carbon
dioxide, and water vapor.
The density of the atmosphere varies with height
above sea level (most dense at sea level).
Altitude is the height (m or km) above sea level.
The atmosphere is thicker above the equator
than it is above the poles. Warmer air takes up
more space because warmer air expands.
Six layers of the Atmosphere
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1. Troposphere - the layer closest to the Earth’s surface.
Altitude of 8 km at the poles and up to 16 km at the
equator. Most of our weather occurs in this layer. The
upper part of this layer is colder than the lower part.
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2. Tropopause – the transition layer between the
troposphere and stratosphere
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3. Stratosphere - a dry layer located between 12 km
and 50 km above the Earth’s surface. This layer contains
high concentrations of ozone. Ozone protects the
Earth from harmful doses of ultraviolet given off by the
sun. The ozone also cause the stratosphere to be
warmer.
Atmosphere (continued)
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4. Mesosphere - the middle layer extends from 50 km to
80 km. This layer has low concentrations of gases and
low temperatures.
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5. Thermosphere - extends from 80 km to 500 km. It is
in this layer that X-rays (from the sun) are absorbed.
This absorption by the few air molecules in this layer
gives the molecules energy producing higher
temperatures. The sun’s radiation cause the particles in
this layer to become electrically charged to produce the
northern and southern lights.
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6. Exosphere - the thin outer part of our atmosphere.
There are very few particles (mainly hydrogen) in this
layer.
Check out this site!
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http://www.mardiros.net/atmosphere/
Gradients
Temperature Gradient - The change in
temperature over a distance. The
troposphere has a temperature gradient of
-60 C per 1000 m (vertical distance)
 Pressure Gradient - is a measure of the
amount the atmosphere pressure changes
across a set distance. A pressure gradient
can be vertical or horizontal. A line graph
or closed lines on a map can indicate a
pressure gradient. To show a high
pressure, lines a bunched together and
vice versa for a low pressure.
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Atmospheric Pressure
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Atmospheric Pressure
 the
pressure the air exerts as gravity pulls it
toward the Earth. Atmospheric pressure is
greatest at sea level where the air molecules
are closer together.
 Atmospheric pressure generally decreases
with altitude but falling/rising air will also affect
atmospheric pressure. Atmospheric pressure
is measured in kilopascals. (See text p.512)
The average atmospheric pressure at sea
level is 100kPa.
Prevailing Winds
A wind is a movement of air in the
atmosphere.
 Prevailing winds are winds that affect large
areas/weather around the world.
 Winds are affected by the Earth’s rotation.
 The apparent change in direction of a
moving mass in a rotating system is called
the Coriolis Effect.
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Major Prevailing Winds
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1. Polar Easterlies - near the poles , the air is cold and
dense. This air sinks and moves toward the equator. The
Earth’s rotation cause this air mass to twist to the right in
the northern hemisphere (left in South) causing the
easterlies.
2. Mid-latitude Westerlies - At 300 latitude, some of the
warm air from the equatorial convection current meets
the cold polar air and a low pressure forms around 600
latitude. The surface air moving north twists to the right
in the northern hemisphere (left in Southern hemisphere)
to form the mid latitude westerlies.
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3. The Trade Winds - the sun heats up
everything at the equator. Hot air rises
leaving behind a low pressure. This rising
air moves northward, cools and becomes
more dense and falls around 300 latitude.
This air moves back towards the equator
(low pressure area) producing the trade
winds. This air movement twist to the right
in the northern hemisphere to form the
northeast trade winds (they twist left in the
southern hemisphere - southeast trade
winds)
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4. Jet Streams - high speed winds in the
upper troposphere near the middle
altitudes. This is due to the different
thickness of the troposphere. Where the
troposphere is thicker (equator) the
atmospheric pressure is greater. The
higher pressure air at the equator will
move northward while twisting.
The Hydrosphere
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The hydrosphere is made up of both
fresh and salt water found on Earth.
Approximately 70% of the Earth’s surface
is water. Only 2.5 % of all water is fresh.
Of this 2.5 % , most of the fresh water on
Earth is frozen in glaciers and in the ice
caps.
The Water Cycle
Review Figure 4 on page 523 of your text.
 Radiant energy from the sun causes water
to evaporate or ice to sublimate.
 Transpiration in plants adds to the
formation of water vapor.
 The water vapor rises , cools, and
condenses into fog, mist, and clouds.
 This precipitation falls to the Earth and the
process repeats.
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Phase Changes of Water
Evaporation - process of changing a
liquid to a vapor.
 Sublimation - process of changing a solid
to a vapor
 Condensation - process of changing a
vapor to a liquid.
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Major Ocean Currents
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The oceans have an important effect on weather
dynamics.
1. The oceans occupy a large portion of the
Earth’s surface. Water’s high heat capacity will
affect temperature changes in a given area.
2. Since there is a large vast of water at the
equator, where the sun is most direct, ocean
currents act as conveyer belts to transport
energy around the world.
The major ocean currents are shown in figure 1
on page 525 of your text. Note that the direction
of the major ocean currents are similar to the
directions of the major winds.
Causes of Ocean Currents
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1. Solar heating of the oceans near the equator
set up convection currents.
2. The continents will redirect water movement
along its edge.
3. Earth’s eastward rotation affects ocean
currents. Currents on the east side of oceans
tend to be fast, those on the west side of oceans
tend to be wider and slower.
4. The salt content affects ocean currents. As
water evaporates, sea water becomes saltier
and sink, setting up convection currents.
Clouds and Fog
Solar energy heats up water causing
evaporation.
 This mixture of water vapor and heated air
rises in the atmosphere.
 As the moist air rises, air pressure and
temperature lowers, causing condensation
to occur.
 If the temperature drops low enough ice
crystals will form.
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Three categories of Clouds
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1. Convective Clouds - formed when air near the
ground absorbs energy from heated surfaces and rises
in the atmosphere. The water vapor cools, condenses,
forming clouds.
2. Frontal Clouds - form where the leading edge, or
front, of a large moving mass of air meets another mass
of air at a different temperature. Warm air contains more
water vapor and will be pushed up by a cold air mass.
The rising warm air will cool and water vapor condenses
to form clouds.
3. Orographic Clouds - form when air moves up a
mountain, expands at the lower pressure, and cools.
Clouds are formed when water vapor in this air cools and
condenses.
Fog
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Fog is actually a cloud at ground level. Air near
the ground cools (especially on clear nights )
and water vapor condenses into fog.
Fog is produced when:
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On clear nights, energy from the Earth’s surface
radiates upward but is not reflected back to Earth by
clouds. The air near the ground cools, allowing water
vapor to condense into fog.
 2. When warm air passes over a snow-covered
ground or moist sea air drifts over a cold current (or
seashore), fog forms.
 3. When warm air rises up the sides of a mountains
during orographic lifting.
Cloud Classification
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Two General Shapes
1. Cumulus clouds - these clouds have a
rounded billowing shape. They tend to grow
vertically, usually indicating unstable weather.
They are usually formed as a result of:
convection currents, orographic lifting, or when a
cold air front moves into a warm air mass.
2. Stratus clouds - these clouds have a
flattened, layered shape. They tend to grow
horizontally and usually indicate stable
conditions. They usually form where the front of
a warm air mass overruns a cold air mass.
Further classification
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According to height:
 alto
- medium height clouds
 cirrus - high-level clouds
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Also: nimbus - rain-holding cloud.
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http://www.srh.weather.gov/jetstream/syno
ptic/precip.htm
What to know for the test!
Notes
 Chapter 13 sections 1, 2, 3, 4, 6, 8, 9, 11,
13.
 Chapter 14 section 2, 4, 5, 6, 9
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Types of Precipitation
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Read Section 14.5 pp. 556-557 and
answer questions 2, 5 & 6.