Weather and Climate
Weather: is the mix of events that happen each day in our atmosphere including
temperature, rainfall and humidity. Weather is not the same everywhere.
Climate: in your place on the globe controls the weather where you live. Climate is
the average weather pattern in a place over many years.
Layers of the Atmosphere: 4 main layers (starting closest to the Earth)
• Troposphere, Stratosphere, Mesosphere, and Thermosphere
Troposphere
• Starts at the Earth’s surface, and its thickness depends on latitude.
(Equator-about 18km thick, and at the poles- 8km)
• Earth’s weather occurs in the atmosphere.
• Most of the weight of the atmosphere is found in this sphere.
• Gases: Nitrogen (78%), Oxygen (21%), argon (0.93%), and Carbon Dioxide
(0.03%) (these gases are needed to sustain life).
• Temperature in the troposphere gradually decreases with altitude
(approximately 1 degree Celsius for every 150 meters of elevation). This
constant decrease in temperature is known as Environmental Lapse Rate.
• Top of troposphere is known as the tropopause.
Stratosphere
• 2nd layer in the atmosphere (starting at tropopause, ending at the
stratopause).
• Contains little dust or water vapour in this layer.
• Contains strong steady winds known as Jet Streams
• Temperature increases with elevation (until it reaches the stratopause).
• Ozone layer is found in the Stratosphere
• The ozone absorbs UV radiation, causing the gas particles in the air to heat
up.
• The Ozone layer is essential to life on Earth because it protects living
organisms from harmful levels of UV radiation.
Mesosphere (3rd layer )
• Extends from the stratopause to an altitude of about 90 km.
• Here, temperature decreases with elevation gain.
Thermosphere (4th layer)
• Extends from mesopause to an altitude of about 500km
• Temperature rises in this layer due to nitrogen and oxygen atoms that
absorb gamma and x-rays.
• Atmosphere is thin in this layer, and continues to thin as it reaches the
density of outer space.
Ionosphere
• Exists at heights from 65-500km above Earth.
• The air is highly ionized and it reflects radio waves back to Earth.
What Factors Affect Temperature, Precipitation, Pressure, and Wind?
Temperature:
• Sun- unevenly heats the surface of the Earth. Latitude determines which
parts of the Earth receive the most heat from the sun.
• The more direct the angle of sunlight, the more concentrated the energy.
• For example, the tropics around the equator would receive the greatest
concentration of sunlight.
• Temperature is also affected by seasons.
• Earth rotates on its axis on a tilt of 23.5 degrees.
• As Earth orbits around the sun, its orientation changes. The Northern
Hemisphere is tilted towards the sun during the summer months, bringing it
more direct rays from the sun; therefore, the temperature rises.
Summer Solstice:
• June 21- The Earth is on an axis of 23.5 degrees, and the northern
hemisphere is tilted towards the Sun (bringing more energy). The direct rays
of the Sun are at the Tropic of Cancer 23.5 degrees North.
Winter Solstice:
• December 21- During the winter, the southern hemisphere is tilted towards
the Sun, bringing cooler temperatures to the north and warmer temperatures
to the south. The direct rays of the Sun are at the Tropic of Capricorn 23.5
degrees South.
Pressure and Wind:
• The differences in heating create pressure differences and wind.
• Air Pressure- is simply the weight of the atmosphere pressing down on the
surface of Earth.
• Average air pressure at sea level is 1013.25 mb (millibars).
• When air rises, pressure at the surface decreases, and when air falls, pressure
increases.
• When the sun heats the air, the sir rises, creating a region of low air pressure.
• When air falls, it creates a region of high air pressure.
• Wind is the result of the pressure difference.
• Air moves from high to low pressure.
• Sea Breeze:
• When the wind moves from the ocean to the land.
• During the day, the land is warmer than the ocean. Air rises over the land
creating low pressure, and falls over the ocean creating high pressure.
• Land Breeze:
• This is the opposite process of sea breeze.
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At night, the ocean is warmer than the land (creating a low pressure over the
ocean).
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There is only 1 factor that will alter the direction of the wind on the globe,
The Coriolis Effect.
This effect is influenced from the spinning Earth.
The Earth is always in motion, so winds cannot move in a straight line.
Northern Hemisphere- winds deflected to the right.
Southern Hemisphere- winds deflected to the left.
On a global scale, this creates distinct wind belts.
At the equator the air is constantly rising, creating clam winds known as the
doldrums.
Winds blow out of a high and into a low, but because the Coriolis Effect
deflects the winds to the right, the winds move in a circular pattern.
Highs are called anticyclones and move in a clockwise direction.
Lows are called cyclones and move in a counter-clockwise motion.
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Precipitation:
• Clouds must form in order for precipitation to occur.
• Clouds originate as water vapour in the atmosphere.
• As air rises, it cools and condenses into clouds.
• When clouds get thick enough, they cause rain, snow, or hail to fall (all
different forms of precipitation).
• Cloud formation and precipitation is associated with low pressure centres
because air rises in a low pressure area.
Types of Precipitation: Convectional Precipitation, Orographic/Relief
Precipitation, and Frontal Precipitation
Convectional Precipitation:
• Most common where there is heating at the surface, such as equator and
continental locations in the summer.
• The air above the surface heats, rises, and the heated air cools and condenses
once it has reached a certain altitude. The air condenses into clouds and then
precipitation falls.
Orographic/Relief Precipitation:
• Occurs on the windward side of mountains.
• This is the type of precipitation we experience here in British Columbia.
• Moist air that comes into contact with a mountain is forced to rise over the
physical barrier. As it rises, the air cools and condenses into clouds, and
precipitation follows.
• The lee side of the mountain tends to be quite dry because the air is
descending, and the clouds have released any precipitation.
• This dry are is called the rain shadow.
Frontal Precipitation:
• Occurs when a cold air or warm air mass moves into a region. The air rises,
creating clouds, and causing precipitation.
• When a cold air mass moves into a region of warmer air, it pushes the warm
air up, forming congested cumulus, or even cumulonimbus clouds. The
precipitation is heavy but short lived.
• When a warm air mass moves into a region of cooler air, it slowly rides over
the cooler air. The warm air rises and forms stratoform clouds. Precipitation
is not heavy but can last for days. **Images for stratoform clouds and other
cloud formations can be found on the powerpoint slides posted to the school
website.**
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Remember weather is always changing day by day, hour by hour. Climate is
an average pattern of temperature, precipitation, pressure, and wind.
There are 3 broad classifications for climate: Tropical, Temperate, and Polar
Tropical Region:
• Located around 30 degrees south to 30 degrees north.
• This is the only area on the globe to receive direct rays from the sun, so the
tropics are hot.
• At the equator there is heating and a constant low pressure, so it is calm and
it rains almost everyday.
• Just north or south of the equator, it is still very warm, but not as rainy.
Temperate Climate:
• Located around 30 to 60 degrees north and south.
• This is a mixing zone between the hot air from the tropics and the cold air
from the north.
• As a result, the weather is very changeable, and there are distinct seasons.
• Here the rays from the sun are more direct in the summer and bring warm
temperatures, and rays are more spread out during the winter.
• 2 major divisions in the temperate zone:
• Maritime
• Continental
• Maritime climates are close to the ocean. They tend to have mild
winters, cooler summers, and a lot of precipitation.
• Continental climates experience cold winters and hot summers. They
tend to experience little precipitation, but when it does fall it is
convectional. Precipitation falls during the summer months.
Polar Region:
• Located around 60 to 90 degrees north and south of the equator.
• This area receives little heating from the sun, and experiences cold
temperatures.
• Air descends in this region, creating a high pressure. As a result, the poles
are very dry.
Weather Phenomenon
• There are 7 different heating processes in the atmosphere that cause
weather:
Radiation:
• Is the heat given off by the sun.
• This includes incoming solar radiation or insolation.
• Everything that has a temperature gives off electromagnetic radiation
(light).
• The sun is extremely hot and has a lot of energy to give, so it gives off
shortwave radiation because shortwave radiation contains higher amounts
of energy.
• The earth is much cooler, but still emits radiation. Earth’s radiation is
emitted as longwave because longwave radiation contains a smaller amount
of energy.
• Shortwave and longwave radiation interact with the earth and atmosphere in
different ways.
• Solar energy enters our atmosphere as shortwave radiation in the form of
ultraviolet (UV) rays (the ones that give us sunburn) and visible light. The
sun emits shortwave radiation because it is extremely hot and has a lot of
energy to give off. Once in the Earth’s atmosphere, clouds and the surface
absorb the solar energy.
• The ground heats up and re-emits energy as longwave radiation in the form
of infrared rays. Earth emits longwave radiation because Earth is cooler than
the sun and has less energy available to give off.
• Exposure to ultraviolet (UV) rays from the sun (shortwave radiation) is said
to cause 65% to 90% of melanoma of the skin, which accounts for threefourths of all skin cancer deaths.
Absorption:
• When the atmosphere, land, and water absorb the insolation.
Reflection:
• Is when insolation hits the surface and is then reflected out into space.
• This is called albedo and is measured in the percentage of light reflected.
• Example: snow on a mountain will create a high albedo effect. (often is what
causes those fabulous ski goggle burns)
Conduction:
• Is the movement of heat through contact.
• The lowest portion of the atmosphere receives much heating this way
through contact with the earth.
Evaporation:
• Is the process where water changes from a liquid to a gas.
Convection:
• Is the movement of heat in a liquid or a gas.
• In the atmosphere, this is known as wind.
• Example: Huge convection currents are found in the atmosphere, and
oceans.
• Meteorologists usually use "convection" to refer to up and down motions of
air. Heat gained by the lowest layer of the atmosphere from radiation or
conduction is most often transferred by convection.
• Convective motions in the atmosphere are responsible for the redistribution
of heat from the warm equatorial regions to higher latitudes and from the
surface upward.
Condensation:
• Is when water changes from a gas to a liquid.
• This is frequently achieved by letting the vapour come into contact with a
cold surface. It is the process by which water vapour turns into fine water
droplets to form a cloud.
• Condensation in the atmosphere occurs when the air becomes completely
saturated and is unable to hold any more water vapour.
Climate Controls:
• The climate of any particular place is influenced by a host of interacting
factors. These include:
Latitude: The lower the latitude (close to the equator) the more direct the sun rays
are. Around the equator, the tropics experience hot/warm climates with small
temperature ranges.
• Higher latitudes (closer to the poles) the sun rays are more spread out
(weaker) and this creates cold climates with large temperature ranges.
Elevation/Altitude:
• Climate zones coincide roughly with elevation ranges.
• Remember, the temperature decreases with height in the troposphere.
• The environmental lapse rate= temp drop 1 degree for every 150 m. This is
because the air thins out and looses its ability to conserve heat.
• Areas with higher elevations will experience colder temperatures.
Mountains/Topography:
• Local variations in elevation can cause local variations in climate.
• Mountains act as a barrier to air masses moving around the Earth’s surface.
• When wind or an air mass meet a mountain, it is forced to rise. The air cools,
condenses into clouds, and causing orographic precipitation on the
windward side or the mountain.
• The leeward side of the mountain will be in the rain shadow.
Proximity to Water:
• Sea surface temperatures affect land temperatures.
• The ocean heats and cools more slowly than land.
• Locations near water tend to be wetter and more moderate than continental
locations.
• Climates near water tend to not have extreme fluctuations in temperature.
Ocean Currents:
• Water temperatures indicate transfer of heat energy by currents.
• There are many warm and cool ocean currents circulating throughout the
world, and these have a heating or cooling effect on the places they come into
contact with.
• The moderating effect the Gulf Stream has on the British Isles and
Scandinavia is perhaps the most well known.
Pressure Centers:
• Areas of low pressure (around the equator and mid-latitudes) have a lot of
precipitation.
• Areas of high pressure (poles) have little rainfall.
• Mid-latitudes are very changeable due to seasons (having a high pressure in
the in the summer and a low in the winter).
Wind Direction:
• Winds deliver air masses with specific properties.
• In areas where prevailing wind blows from the ocean to the land, it brings
precipitation.
• Coastal locations can be dry if the wind blows from the land to the ocean.
Aspect:
• This is the direction a slope faces.
• This has an impact on the amount of sunshine or shadow.
• In the Northern Hemisphere, south-facing slopes tend to be drier and have
more sunshine., while north-facing slopes are wetter and experience less sun.
Vegetation:
• Vegetation covers about 20% of our planet.
• Vegetation influences both albedo of the earth and the amount of water
vapor and carbon dioxide in the air.
• Plants process and release water vapor (necessary for cloud formation) and
absorb and emit energy used to drive weather.
• Plants also produce their own micro-weather by controlling the humidity
and temperature immediately surrounding their leaves through
transpiration.
Climate Zones:
• Climates from around the world are divided up into broad climate zones.
• Desert Climates: limited precipitation. Can be hot-weather deserts
(Sahara) or cold-weather deserts (poles).
• Mid-Latitude Climates: have distinct seasons, and differing amounts of
precipitation. Maritime climates are moderate and wet, while continental
climates are more extreme and dryer.
• High-Latitude Climates: extremely cold winters and short, cool summers.
Continental sub-arctic locations experience cold, long winters with very little
precipitation, while marine sub-arctic have wet, windy conditions. True
arctic climates are above 70 degrees latitude (these places have no real
summer).
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Highland Climates: Variations in altitude can result in many climate
conditions on a single mountain.
The weather at times sees out of our control at times, but humans do affect weather.
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Cloud Seeding: weather modification that attempts to influence the amount
or type of precipitation that falls.
This is done through dispersing substances into the air serve as cloud
condensation.
Man-made Lakes: these are often created for hydroelectric dams and can
often cause more evaporation, and lead to more precipitation in the area.
Urban Heat Island: cities generate their own heat and remove water very
quickly (not allowing heat loss through evaporation). As a result cities tend
to be warmer than the surrounding countryside.
Interactions Between Human Activity and the Atmosphere
• Ozone Depletion: the depletion of the ozone layer has been caused by
chlorofluorocarbons (or CFC’s).
• CFC’s are chemicals that are odourless, non-toxic, and non-flammable.
• They are used as propellants in aerosol sprays; as refrigerants in air
conditioners, and fridges. They are also found in insulation and other
packaging.
• When these chemicals are released into the air, they travel up into the upper
atmosphere where the UV rays from the sun break down the CFC’s, releasing
a chlorine atom.
• This chlorine atom steals oxygen atoms from the ozone.
Global Warming:
• Earth’s atmosphere receives its energy from the sun, but the atmosphere is
heated from below as well.
• Greenhouse gases in the atmosphere conserve outgoing long-wave radiation
and maintain a livable temperature on earth.
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Greenhouse gases: carbon dioxide, methane, water vapour,
chlorofluorocarbons, ozone, and nitrous oxide.
If these levels of gases are naturally occurring in the atmosphere, these gases
keep earth from freezing. However, too many greenhouse gases are being
produced.
Burning fossil fuels (for electricity or for running our cars) produce carbon
dioxide. Cutting down trees can also contribute.
These greenhouse gases in the atmosphere hold in more heat and global
warming occurs.
Acid Rain: rain water normally is slightly acidic ], with a pH value of 5.6
• burning fossil fuels is one of the main processes that increase the acid level in
rain water.
• When fossil fuels are burned, sulphur dioxide, nitric oxide, and nitrogen
dioxide are released.
• These sulphates and nitrates can mix with water droplets in clouds to form
sulpheric acid and nitrate acid and then fall to the ground as acid rain.