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Unit 4 – 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 (solid, liquid, and vapor).
Weather is the environmental conditions that you experience each day.
Climate may be defined as the average conditions at any given time of the year, and is normally
determined by calculating the mean condition taken over several years.
Measuring Temperature:
A thermometer is used to measure temperature.
Temperature is defined as the measure of the average kinetic energy of a sample of matter. The
atoms and molecules that compose a sample of matter vibrate. They move around and collide
with neighboring particles. The rate of motion of these particles results in their kinetic energy and
is measured as temperature. The higher their kinetic energy, that is the faster they move, the
higher their temperature.
Measuring Relative Humidity:
Humidity is a measure of the amount of moisture (water vapor) in the air. If the humidity is low
it is less likely to rain than when the humidity is high, given the same conditions of temperature
and atmospheric pressure. In general, warm air can hold much more water vapor than can cold
air.
Relative humidity can be measured with a hygrometer. This instrument is made from a material
that changes length in proportion to the amount of moisture present in the air. The material is
connected to a pointing device that changes position depending on the length of the material. A
scale is provided so that the pointing device can be used to read the relative humidity which
ranges from 0% to 100% relative humidity.
Measuring Atmospheric Pressure:
Atmospheric pressure is due to the Earth's gravity. It is a measure of the force exerted on us by
the weight of the air column above us.
The most common way to measure atmospheric pressure is to use an instrument known as the
aneroid barometer. It measures the pressure in kilopascals (kPa = metric unit for pressure).
Measuring Wind Speed and Direction:
The instrument normally used to measure wind speed is known as an anemometer. This device
spins around at different rates depending on the speed of the wind, which is measured in
kilometers per hour (km/h).
The Beaufort Wind Scale may also be used as a measure of wind speed. This scale is based on
the characteristics of smoke exiting from the top of a chimney. Smoke coming from the top of a
chimney can be used to determine wind direction.
Measuring Precipitation:
Precipitation means the amount of moisture that falls to earth from the sky. Precipitation may be
either in liquid or solid form (rain, snow, etc.). The instrument used to measure precipitation is
the rain gauge (snow in cm, rain in mm)
Weather Maps and Symbols
Weather maps make use of standard symbols to indicate weather conditions in various locations.
There is more than one type of weather map. Those found in newspapers and on television are
generally simple versions of the professional map used by a meteorologist.
Read "Interpreting and Creating Weather Maps" p.683-685, 550-551. Look for:
1.
2.
3.
4.
5.
6.
high pressure region (indicated by H)
low pressure region (indicated by L)
wind direction and speed and type of cloud cover
air temperature (oC)
visibility (the distance x100m that one can see)
weather condition (may include rain, freezing rain, snow, thunderstorm, fog, haze, or
dew)
7. dew point (temperature at which moisture will condense on objects)
8. type of low, middle, and high cloud cover
9. isobars (lines representing regions with the same atmospheric pressure)
Atmospheric Layers p. 511
The atmosphere is divided into various horizontal regions or layers, each having it own
characteristics. The atmospheric layers tend to be thicker over the equator than they are
above the poles. 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.
Layers of the Atmosphere
1. Troposphere (weather layer) - 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.
Above the troposphere is the tropopause. Coldest at the top of the layer.
2. Stratosphere- a dry layer located between 12 km and 50 km above the
Earth’s surface. It contains the vast majority of ozone (the ozone layer) of any of the
atmospheric layers. The stratosphere is therefore important to life since it serves to
protect against damage due to excessive exposure to ultraviolet radiation. 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.
3. Mesosphere - the middle layer extends from 50 km to 80 km. This layer has low
concentrations of gases and low temperatures. The top of the mesosphere lies at an
altitude about 80 km above the Earth's surface, with a temperature as low as -70 oC.
4. Thermosphere - The thermosphere absorbs x-rays and other radiation from the sun.
The temperature may reach 30oC. It is in this layer that the northern lights are visible on
clear winter nights. It is located between 80-500 km above the Earth's surface.
5. Exosphere - The exosphere (atmosphere beyond 500 km above the Earth's surface) is
the outermost layer of the atmosphere. The density is so low that it is much like the
vacuum of space. The exosphere is composed mainly of hydrogen gas.
Distribution of Common Gases
In the lowest part of our atmosphere:
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Oxygen makes up about 21% of the total volume
Nitrogen makes up about 78% of the total volume.
This leaves only 1% of the total volume of the atmosphere for water vapour, carbon
dioxide, ozone, the noble elements, carbon monoxide, CFC's, hydrocarbons (like
methane, propane) and some of the other pollutants found in our atmosphere.
In terms of weather, both global and local, the atmosphere carries heat energy originally from the
sun and helps to distribute this energy over the world on a global scale. The atmosphere and the
gases in it are therefore essential, not only to life, but also to weather.
Relationship between Altitude, Temperature and Atmospheric Pressure:
Near the surface the average world-wide temperature is about 15 oC. At an altitude of 11 km the
average temperature is -56.5 oC.
Temperature Gradient - The change in temperature over a distance. The average
change in temperature with altitude (temperature gradient ) is about -6.5 oC/1000m. This
means that for every 1000m climb in altitude, the temperature will drop about 6.5 oC.
This applies to the atmosphere to about 11 km, but is not valid for the layers above the
troposphere.
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.
Activity: Read p510 - 513. Answer questions 2, 4,5, 6, 7 p.513.
Solar Energy and the Water Cycle p.523
The solar energy that enters the Earth's atmosphere may be scattered, absorbed, reflected, or may
pass through the atmosphere to strike the water or land at the surface of the Earth. Albedo plays
an important role in the reflection and absorption of solar radiation. The albedo of the Earth's
surface (water and land) will determine how much of the solar energy that reaches the Earth's
surface is absorbed and how much is reflected back to the atmosphere.
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 remaining 30 % of the Earth's surface is land, and most of the land is
located in the Northern hemisphere.
The Water Cycle - 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. This cycle of water is known as the water cycle and has 4 steps evaporation, condensation, precipitation, and runoff.
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.
Cloud Formation:
There are three ways in which clouds are formed -
1. Convective clouds form 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 when a warm air mass meets a cooler air mass. Since warm air
masses are generally less dense than cooler air masses, the warm air mass tends to move
above the cooler air mass. The rising warm air will cool and water vapor condenses to
form clouds.
3. Orographic clouds form as warm air masses move up the sides of a mountain. As the warm
air rises it expands and cools resulting in the formation of orographic clouds as water vapour
condenses into microscopic droplets of water.
Fog is actually a cloud formed at or near ground level. Fog may be formed as warm air
moves over cold land masses, over snow fields, or cold bodies of water. Fog may also
form as a result of orographic lifting. Air near the ground cools (especially on
clear nights ) and water vapor condenses into fog.
Cloud Classification:
The classification of clouds describes both the form of the cloud and its altitude:
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 are generally flat and long. 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.
To distinguish clouds located at higher altitudes a prefix is added to the basic shape name:
The prefix, alto- is used for medium height clouds (2000-4000 m).
The prefix, cirro- is used for clouds at higher altitudes (4000-7000 m).
The term cirrus is given to the highest clouds (7000-8000 m).
Nimbus or the prefix nimbo- is used to name the darker, rain-holding type of cloud.
(Text: P.533 figure 7 shows 10 types of clouds)
Activity: Read "Clouds and Fog" p.530-534. Answer questions 1-5 on page 534.
Energy Transformations
Temperature is a measure of the kinetic energy of a sample of matter. It is the average
measure of the rate of vibration of the particles in the sample.
Specific heat:
Specific heat capacity is 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.)Water has a much higher specific heat capacity (ability to store heat energy)
than iron. Figure 5 in your text shows the heat capacity of some common substances.
Latent heat of fusion
The amount of heat needed to change a unit mass of a substance from a
solid to a liquid.
Latent heat of vaporization
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.
Energy can be transferred from one place to another in 4 ways:
1. Conduction is the transfer of energy from a sample of matter at higher temperature to
a sample of matter at lower temperature due to the collision between the particles in each
sample. It is important to recognize that conduction can only occur through matter, so the
two samples of matter must be in contact. Heat energy always moves through matter
(called a thermal conductor) from a region of higher temperature (higher kinetic energy)
to a region of lower temperature (lower kinetic energy).
Different materials transfer heat by conduction at different rates. Metals for example
generally have much greater thermal conductivity than glass, sand or soil.
2. Convection is the flow of heat vertically as a result of the movement of matter from a
hot region to a cool region. Convection can only occur in liquids and gases, since
movement of the matter could not be possible in a solid.
3. Advection is very similar to convection. Advection, like convection can only occur in
liquids or gasses. The main difference is that convection transfers heat vertically and
advection transfers heat horizontally.
4. Radiation is the transfer of energy by way of waves. Radiant energy can pass through
the near vacuum of space. Radiant energy can also pass through clear (transparent) solids
such as glass, as well as through liquids and through air. The transfer of energy by
radiation does not involve a medium so there is no collision between particles. The
energy is in the form of waves which travel at the speed of light.
Heat Sink and Heat Source:
A heat source provides energy. A heat sink absorbs energy. The Sun is a heat source
since it is the source of the energy that drives life and weather here on Earth. The Earth
may be considered a heat sink since it absorbs the Sun's energy. Not all of the solar
energy reaching the Earth’s atmosphere actually reaches the land and water. 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 determinehow 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.
Oceans, Currents, and Weather Dynamics
Major Ocean Currents: p.525
The direction of the major ocean currents are similar to the directions of the major winds.
Water, because of its high specific heat capacity, can hold a tremendous amount of
energy absorbed from the Sun. The oceans can serve both as a major heat sink (absorbing
energy from the Sun) as well as a heat source (transferring energy to the atmosphere
above it).
The oceans have an important effect on weather dynamics:
1. Because nearly 70% of the Earth is covered by oceans and because of waters high heat
capacity, the oceans will affect temperatures in a given area.
2. Since there is a large amount of water at the equator, where the sun is most
direct, ocean currents act as conveyer belts to transport energy around the world. The
ocean currents carry cold water from the poles toward the equatorial regions where
sunlight strikes most directly. The heated water is then carried by way of the major ocean
currents toward the poles where the waters of the ocean then serve as a heat source
transferring heat to the atmosphere above. The energy is released to warm the colder air
above and the land nearby.
Causes of the Ocean Currents:
1. Solar heating of the oceans near the equator set up convection currents. Sunlight
striking the water in the equatorial region tends to warm the water causing the water to
become less dense. As the water moves away from the equator it is replaced by more
dense colder water from below.
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.
The Earth's rotation and resulting Coriolis effect tends to rotate waters of the northern
hemisphere in a clockwise direction. At the same time, waters of the southern hemisphere
rotate in a counterclockwise direction.
4. The salt content (salinity) affects ocean currents. As water evaporates, sea water
becomes saltier and sinks, setting up convection currents. This phase change results in the
cooling of the ocean water as the water vapour moves into the atmosphere. Both of these
factors cause the sea water to become more dense and as a result the sea water tends to
sink downward creating deep water ocean currents.
Activity
Read 13.9 "Major Ocean Currents" p. 525-527, questions 1-3, 5 p. 527.
Activity
Based upon your understanding of ocean currents and its influence on the atmosphere above,
explain the difference in climatic conditions in Vancouver, Ottawa, and St. John's.
Activity
Read 15.12 "El Niño and La Niña" p.612 - 615. Questions 1, 2 and 4 p. 615.
Global Wind Patterns
Winds may be classified as global prevailing winds or as local or regional winds. The major
winds of the Earth called the prevailing winds; also known as the trade winds due to their
importance to trade by sailing ship back in the time of the great explorers. Local winds are a
result of geographical features of the land (mountain ranges) or the proximity of land to large
bodies of water, such as a large lake or the ocean. These winds include thermals, sea breezes (or
offshore winds), land breezes (or on-shore winds), and Chinook winds.
Prevailing Winds
Prevailing winds are winds that affect large areas/weather around the world. They mainly
result from the transfer of heat energy from the land and oceans to the atmosphere. The
resulting convection currents and interaction with the Coriolis effect (earth’s rotation)
create major wind currents.
Formation of the Hadley Convection Cells: (see p. 517)
The sun always strikes the Earth in the equatorial region that lies between 23.5o north latitude (the
Tropic of Cancer), and 23.5o south latitude (the Tropic of Capricorn). As a result, the greatest
amount of solar energy is absorbed in the equatorial regions of the Earth, the ocean warms up and
transfers its heat energy and moisture to the air above. This results in the formation of a low
pressure region at the surface. A convection current (known as the equatorial convection
current) of warm, moist air rises to the tropopause. As the moist warm air reaches higher
altitudes, both the pressure and temperature are reduced, causing the air to become cooler and
more dense, often resulting in cloud formation and precipitation. Because moist, warm air
continues to rise from below, the upper air near the tropopause is forced to move toward both
north and south poles.
Once the air reaches the tropopause it tends to cool mainly as a result of radiational energy loss.
As the upper air moves toward the 30o north or 30o south latitude it sinks back down toward the
Earth's surface forming two, massive convection cells (known as the Hadley cells). The
downward moving air is cooler (due to radiational energy loss) and dryer (due to the loss of
moisture by precipitation over the equatorial region) and results in high pressure regions near the
30o latitudes both north and south of the equator. The deserts of the Earth are located near these
30o north and 30o south latitudes.
The Coriolis effect causes a deflection of wind to the right of its direction of motion in
the northern hemisphere and to the left of its direction of motion in the southern
hemisphere.
Major Prevailing Winds:
The prevailing winds are named in terms of the direction from which the wind blows and
not in terms of the direction to which the wind blows. For example: The northeast trade
winds blow from the northeast (toward the southwest).
1. 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. (twist left in the southern hemisphere - southeast trade winds).
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. They generally move in a west to east direction in both hemispheres.
3. Polar Easterlies - near the poles (between 60o and 90o), 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. They
blow in an east to west direction in both hemispheres.
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
Activity:
Read "Prevailing Wind Patterns" p.516-519. Answer questions 1 - 3 p. 519.
Local Air Movements
Regional or local weather patterns are known as thermals, sea breezes and land breezes. These
local weather patterns are far smaller than the prevailing winds and the ocean currents. They all
result from the instability caused by alternating warming and cooling that occurs on a diurnal and
nocturnal basis (day and night) as a result of the Earth's rotation about its axis.
Thermals:
Thermals are caused by the heating of the land by the sun. Land does not have as high a specific
heat capacity as does water so the air above the land becomes heated. As the temperature of the
air rises, it expands and becomes less dense. Rising convection air currents (sometimes called an
updraft) form above the land. In the evening, when the intensity of sunlight diminishes, the
thermal updraft begins to lose its source of driving energy and the local winds die down. This
explains why winds tend to be more calm in the early morning and early evening.
Sea Breezes:
Sea breezes are the result of the difference in the specific heat capacity of water and land. During
the day, land tends to heat up much faster than a large body of water nearby. As a result of the
difference in temperature, a thermal begins to form above the land. The sea air therefore tends to
move in since the air pressure over the sea is higher than over the land.
Land Breezes:
During the night, land cools down much faster than the large body of water nearby. As a result,
the convection cell associated with the sea breeze is essentially reversed. The cool air over the
land becomes more dense and forms a high pressure region. Since the air above the water tends to
be relatively warmer then the cooler air over the land, air begins to move from the land toward
the body of water forming a relatively mild land or off-shore breeze. Because of the higher
stability of water temperature, the night time land breezes are normally much calmer than the day
time sea breezes.
Activity:
Read 14.4 "Regional Weather" p. 553-554. Questions 2,3 p. 555.
Forecasting the Weather
Meteorology - the study of the atmosphere and weather forecasting.
Meteorologist - a person who worsk in the field of meteorology.
Weather System - is the total of all the conditions of temperature, humidity, atmospheric
pressure, wind speed and direction for a relatively large geographical region that moves
over the surface of the region for a period of several days.
Air Mass - is a large body of air in which the temperature and moisture content at a
particular altitude are fairly uniform and stay together for several days at a time. As a
result, air masses pick up the humidity and temperature characteristics from the land or
water over which they form. The prevailing mid-latitude westerlies cause the air masses
to move primarily from west to east.
Six air masses that tend to affect North American weather systems. (diagram p.546):
1. Maritime Polar air mass (2) - cool moist air mass. Usually brings wet,
stormy weather; originate over the oceans
2. Maritime Tropical air mass (2) - warm moist air mass. Brings
Precipitation; originate over the oceans (tropics)
3. Continental Polar air mass - cold dry air mass; originates over the central north;
moves south into Canada.
4. Continental Tropical air mass - warm, dry air mass; originates over Mexico; moves
North into Canada.
Low-Pressure (Cyclonic) Systems:
Low pressure systems (trough) are generally associated with cloudy conditions. A
cyclone is a low-pressure, swirling air mass. They move counterclockwise in the northern
hemisphere and clockwise in the southern hemisphere. A cyclone carries stormy weather.
Low pressure systems are marked using the symbol L on the weather map.
High-Pressure (Anticyclonic) Systems:
High pressure systems (ridge) generally bring clear weather, (marked H on a weather
map). Since this pattern of rotation is opposite the low pressure pattern, the high pressure
pattern is said to be anticyclonic. An anticyclone is a high-pressure, swirling air mass.
They rotate clockwise in the northern hemisphere and counterclockwise in the southern
hemisphere. Anticyclones usually brings clear skies.
Frontal Systems:
A front is the leading edge of a moving air mass, or the boundary that forms between two
air masses that meet. Air masses with different properties (moisture content, temperature,
etc.) don’t blend easily, so a boundary, or front, develops as they meet. Because cold air
is generally more dense than warm air, the warm air mass tends to climb above the cold
air mass. As the warm air mass increases in altitude the air expands leading to cooling
and formation of clouds. Precipitation of some form (rain, snow, etc.) generally results.
Four Types of Fronts (p.547)
1. Warm Front - the leading edge of a warm air mass; moves toward the poles
2. Cold Front - the leading edge of a cold air mass; originates in the polar regions and
moves toward the tropics.
3. Occluded Front - the front that forms when a cold front catches up to and
overtakes a warm front. The warm air is lifted away from the Earth’s surface
and cut off (occluded) from the warm air mass below. This cause a weakening of the
storm system.
4. Stationary Front - an unmoving front between a warm air mass and a cold
air mass. Usually means stable weather until the air mass begins to move.
Activity 11:
Read 14.2 "North American Weather Systems" p. 546 - 549. Answer questions 1,2,6 p.549.
Severe Weather Conditions
Severe weather events include hurricanes, typhoons, tropical cyclones, tornadoes, ice storms,
droughts, floods, hail storms, blizzards, extreme heat, and extreme cold conditions.
Severe weather conditions often have economic, social, and environmental impacts on individuals
and communities as a whole. Think about the impact that severe weather conditions would have
on various occupations such as fish harvesters, pilots, truck drivers, and so on. Severe weather
conditions have wide ranging effects on every aspect of life. When a snowstorm causes the
closure of roads, goods cannot get to communities. This can in turn cause economic problems for
the stores selling these products.
Consider the disaster that occurred in Badger in the spring of 2003. That flood displaced people
from their homes for months. These people were distressed both economically and emotionally as
a result of losing their homes and property. For some, it meant living away from their community
for an extended period of time.
Activity:
1. Read 15.3 "Thunderstorms and Tornadoes" on pages 584-588. Answer questions 1-6
from "Understanding Concepts" on page 588.
2. Read 15.4 "Floods and Droughts" on pages 589-591. Answer questions 1-8 from
"Understanding Concepts" on page 591.
3. Read 15.6 "Hurricanes, Typhoons, and Tropical Cyclones" on pages 594-597.
Answer questions 1-7 from "Understanding Concepts" on page 597.
4. Read 15.7 "Blizzards" on pages 598-599. Answer questions 1-3 from "Understanding
Concepts" on page 599.
Activity :
Choose a severe weather event and analyze how it has affected the people both as individuals and
as a community in terms of economic, social, and environmental conditions.
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Read 15.1 "Weather Records and Events" on pages 580 - 581.
Read 15.8 "Surviving the 1998 Ice Storm" on pages 600 - 603.
Read 15.9 "Extreme Heat and Cold" on pages 604 - 607.
Read 15.10 "Explore an Issue: Winter Shelters for the Homeless" on page 608.
Read 16.9 "Case Study: Monsoons in Bangladesh" on pages 639 - 640.
Satellite Imaging Technology
A major advancement in technology was the weather observation satellite. It gave meteorologists
their first views of the cloud patterns associated with low pressure systems and fronts.
There are 2 types of satellites in orbit:
1. polar-orbiting satellites revolve around the Earth at relatively low altitude (800 km) and scan
a region about 1900 km wide during each orbit which takes about 100 minutes to complete.
2. geosynchronous satellites are positioned at an altitude 35 800 km above the Earth. It circles
the Earth once every 24 hours, the same rate as the Earth revolves around its own axis. Due to its
greater altitude, it is able to capture a much wider image of the continent.
These satellites can be manipulated by computers to produce moving images of weather patterns
and are able to capture images using different wavelengths including infra-red (IR) images,
visible images, and water vapour images. Each type of image can detect weather features not
clearly seen in the other image types so the three imaging technologies complement one another.
Weather Balloons - weather balloons are launched more often daily all across North
America. Onboard instruments collect temperature, pressure, humidity, and ice-crystal
data. This data is relayed to weather stations.
Doppler radar was first used in weather detection in 1942, when radar was used to
follow a thunderstorm and hailstorm. Doppler radar produces a series of microwave
pulses which reflects off small particles of rain, hail, or snow. The data is then collected,
and passed on to a computer for analysis. There are 3 Doppler radar stations in Atlantic
Canada.