Weather Dynamics

A Closer Look at Earth

Section 13.1

The main components of Earth that influence weather are:◦ the atmosphere◦ land forms◦ water in various forms (solid, liquid, gas)

Earth’s surface area:◦ 70% covered by oceans◦ 30% forms continents

Weather: a set of environmental conditions encountered from day to day.

◦ Today’s weather: sunny with a few clouds, -17 C, wind chill - 30 C, Winds from the West at 37 km/h.

Climate: a set of environmental conditions averaged over many years.

◦ PEI’s climate in February: crisp and clean, temperature ranges from -3 to -11 C.

Weather vs. Climate

Read pages 500-503 and do questions 1-4 & 9 on page 503.

Accuracy of Advanced Weather Forecasts (handout)

Use the following website to do the “Weather Assignment”:

http://www.weatheroffice.gc.ca/canada_e.html

Assignment:

Earth’s Energy Balance

Section 13.2

There are four methods of energy transfer that help to maintain the Earth’s energy balance as well as distribute energy around the world. They all contribute to weather.

1. Radiation: transfer of energy by means of waves.◦ These waves are measured using the electromagnetic spectrum.

2. Conduction: transfer of energy through the collision of particles.

◦ Occurs in metals (steel), rock, sand, soil and water.

3. Convection: vertical transfer of energy by the movement of particles in a fluid (liquid or gas).

4. Advection: horizontal transfer of energy by the movement of particles in a fluid (liquid or gas).

How does Earth receive energy through radiation?The Electromagnetic Spectrum – shows all types

of radiation that can travel through space at the speed of light.

Reflection and Absorption of Energy

Energy from the Sun that reaches the Earth will undergo one of the following:

◦ 27% is reflected off the atmosphere and clouds back into space.

◦ 3 % passes through the atmosphere and bounce off the Earth’s surface and back into the atmosphere.

◦ 20% is absorbed by the atmosphere.

◦ 50% is absorbed by the ground or water at the surface.

The energy that is reflected back off the surfaces of the Earth depends on the albedo of the material.

Albedo: a percentage of light that an object reflects.◦ High albedo - reflects a lot of light (Eg. white snow).◦ Low albedo - reflects very little light (Eg. black soil).

An object which absorbs energy and becomes warmer is called a heat sink.◦ Good heat sinks: oceans and lakes.◦ Poor heat sinks: soil and rocks.

Heat Capacity: how much heat a substance requires to increase its temperature, or how much heat it releases as its temperature decreases.◦ high heat capacity: water (holds a lot of heat).◦ low heat capacity: soil and rocks.

Read pages 504-506 and do questions 1-10 on page 507.

How Much Do You Know? (handout BLM 13.2).

Video Response: Understanding Weather Concepts

Assignments:

The HydrosphereSection 13.8

The Hydrosphere◦ All of Earth’s fresh and salt water.

The Water Cycle Water in our atmosphere is present in 3 states:

liquid, vapour (gas) and solid. The energy from the Sun helps circulate this water and create our weather.

Water is essential for humans. People settle themselves near bodies of water (rivers, lakes, oceans) as they serve as a source of food, drinking water, and transportation. Weather systems near bodies of water affect a large

number of people.

Hydrosphere

Salt water97.5%

Fresh water2.5%

Glaciers and Polar Ice Caps87.3%

Underground Water12.3%

Surface and Atmospheric Water

0.4%

Lakes90%

Atmosphere9%

Rivers1%

Water Distribution in the Hydrosphere

10% of the world’s fresh water supply is located in Canada.

Evaporation◦ changing from liquid to gas.

Sublimation◦ changing directly from solid to a gas.

Condensation◦ changing from gas to liquid.

Transpiration◦ movement of water from plants and bodies to the air.

Precipitation◦ water that falls to the ground (rain, snow, hail, dew,

freezing rain, etc.)

Key Terms

Evaporation

Transpiration

Precipitation

Condensation

Sublimation

Assignment: Read pages 522-524 and do

questions 2, 3 & 4.

Water Cycle Video

Clouds and Fogpages 530-534

The water cycle shows us that energy from the sun and surrounding environment cause water particles to heat up and turn to water vapour.

These particles rise in the less dense air until they reach lower temperatures in higher altitudes and lower pressure.

This is the formation of water droplets that are very small. Only when thousands of these droplets join together does a raindrop form which is carried to earth through precipitation.

Clouds are natures indicators of weather conditions and weather patterns.

Understanding the characteristics of clouds helps to predict the weather.

1. Convective Clouds◦ Are produced when air near the ground absorbs energy from

heated surfaces such as oceans, lakes, asphalt, concrete and dirt.

2. Frontal Clouds◦ Form when a front or large moving air mass meets another air

mass of a different temperature. Warm air masses are usually less dense and contain more water vapour and will rise above the cold air mass. Clouds form due to the moisture cooling and condensing.

3. Orographic CloudsForm when air moves up a mountain, expands at the lower pressure and cools/condenses.

◦ http://www.curriculumbits.com/prodimages/details/geography/rainfall.swf

Cloud Formation is classified into three main categories:

Frontal Clouds

Animation

Fog is a cloud that forms near the ground.

◦ The most common is produced on clear nights when the absence of clouds keeps the energy from the Earth from being reflected or kept near the surface. The air near the ground cools and water vapour turns to fog.

◦ Fog also happens when warm air passes over snow-covered land, when moist sea air drifts over a seashore or a cold current, or when moist air rises up the mountains during the orographic lift.

FOG

A. Clouds are classified using two general shapes:

1. Cumulus Clouds – meaning “heap” which have a billowing rounded shape. They tend to grow vertically and often indicate unstable weather.

They tend to form as a result of:◦ Convection currents◦ Cold air pushing into warm air masses.◦ Orographic lifting

2. Stratus Clouds – meaning “spread out” which have a layered, flat shape. They tend to grow horizontally and often indicate stable weather.

They form when:◦ Warm air takes over a cold air mass.

Section 13.11 Classifying Clouds

B. Clouds are classified by their height (altitude) in the atmosphere.

1. Low-level clouds keep their simple names.◦ Example: Cummulus or Stratus

2. Medium-level clouds start with the prefix alto (which means higher)

◦ Example: Altostratus3. High-level clouds start with the prefix cirrus (which

means curly lock of hair)◦ Example: Cirrostratus

C. Clouds are subclassified by whether or not they hold rain.◦ True rain clouds are called nimbus clouds.

Example: Nimbostratus

Use your textbook to answer the rest of the sheet (handout).

Water Cycle and Clouds Song

There are 10 major classifications of clouds.

cirrus cirro-stratus

Assignment:Questions 1. Describe the three main ways that clouds

form? 2. Why doesn’t rain or snow fall from all clouds?

Read pages 522-524 and answer questions 1, 3, 4, and 5 on page 534.

Handout: *Rain or Shine Quiz/Clouds and Precipitation

North American Weather Systems

Section 14.2

A weather system is a set of temperature, wind, pressure, and moisture conditions for a certain region that moves as a unit for a period of days.

An air mass is a large body of air that has the same temperature and moisture throughout.

1. Maritime Polar◦ These air masses come from the Pacific and Atlantic Ocean and bring:

fog and cooler temperatures in the summer. heavy snow and very cold temperatures in the winter.

2. Continental Polar◦ These air masses come from the North and bring:

cold, dry air in both summer and winter.

3. Maritime Tropical◦ These air masses come from the Pacific and Atlantic Ocean and bring:

warm, moist air in the summer rain or snow in the winter

4. Continental Tropical◦ These air masses come from over Mexico and bring:

hot, dry air in the summer

North America is affected by four major types of air masses:

These air masses help keep the balance of Earth’s energy. Convection and dominant winds move warm air northward, and cold air southward. When these air masses meet, they create interesting and unpredictable weather.

When two air masses meet, the differences in temperature and humidity cause a boundary, or front, to form between them. The weather at a front is usually stormy and unsettled.

Four Kinds of Fronts:Cold Front

◦ forms when a cold air mass moves under a warm air mass◦ violent storms, followed by fair, cool weather.

Warm Front◦ forms when warm air moves up and over a cold air mass◦ rain showers followed by hot, humid weather.

Occluded Front (Cut Off)◦ forms when a fast moving cold air mass catches up with a

slow moving air mass◦ weakens the weather caused by cold or warm fronts.

Stationary Front◦ forms when 2 slow moving air masses collide◦ long periods of rain or other precipitation that lasts for

days.

Assignment: Read pages 546-548

and do questions 1-3.

Section 15.2 Weather in the News

Watch - conditions are present for extreme weather to occur in your area.

Advisory - severe weather, likely to cause local problems and inconveniences, is predicted for your area.

Warning - extreme weather is highly likely to arrive in your area or may already be happening. Take necessary precautions.

Chapter 15 Extreme Weather Events

Thunderstorms and Tornadoes

Section 15.3

http://news.bbc.co.uk/2/hi/5328524.stm

a storm with lightening, thunder, heavy rain, and sometimes hail.

In order for a thunderstorm to occur you need:◦ Moisture to form clouds and precipitation◦ Very strong lifting of air (uplift) to

produce clouds which reach high in the atmosphere.

Thunderstorms form in 3 stages:

Thunderstorm

The sun warms the surface of the Earth and the air. This warm air rises in an updraft. This air will condense into a cumulus cloud, which will continue to grow as long as there is warm air rising below it.

Cummulus Stage

When the cumulus cloud is very large it starts to rain. Also cool air starts to enter the cloud. Because this air is heavier it starts to descend in a downdraft pulling lots of water with it. The updraft and downdraft cause thunder, lightening and heavy rain.

Mature Stage

After a while the downdrafts in the cloud dominates the updrafts stopping water drops from forming. The storm begins to die out with light rain.

Dissipating Stage

* This process normally last about 1 hour.

Lightning occurs when clouds become positively charged at the top and negatively charged at the bottom. The charge builds up until it is strong enough to cause lightning.

To protect yourself:◦ Stay in a car◦ Avoid open areas like fields,

open water, tops of hills.◦ Never stand near or under

a tree, or utility pole

a severe component of a thunderstorm in which a rotating funnel of air extends from the base of a thunderstorm cloud to the ground.

http://esminfo.prenhall.com/science/geoanimations/animations/Tornadoes.html

Tornado

In order for a Tornado to occur you need:◦ Fast rising air in a

thunderstorm sometimes begins spinning, forming a funnel of air and moisture. As more rising air is replaced by cooler air at the surface, the rotation becomes faster and faster. This rising air causes a pressure difference that increases speed.

◦ Because of its shape, the rotating tornado is called a funnel cloud.

◦ At the centre, the wind speeds can be as high as 500 km/h.

The Fujita scale (F-scale) is used to rate the intensity of a tornado based on the damage that it causes.◦ This scale is divided into 6 levels: F0 – F5

To protect yourself:◦ Try to get indoors, preferably in a basement or a

room with no windows.◦ If you are outside, lie down in a ditch (low lying

land) and cover your head.

Read pages 584-588 and do questions 1,2,4,5,6 on page 588.

Assignment:

Hurricanes, Typhoons, and

Tropical CyclonesSection 15.6

http://news.bbc.co.uk/2/hi/science/nature/4588149.stm

Cyclones are low-pressure systems that develop when cold and warm fronts interact.

Depending on where the hurricane happens it may have a different name:

Cyclones Hurricane Typhoon Tropical Cyclone

Where they develop:

- Atlantic Ocean- Caribbean Sea- Gulf of Mexico- Eastern Pacific Ocean

- Western Pacific Ocean- China Sea

- Indian Ocean- Australia

http://www.cbsnews.com/htdocs/natural_disasters/hurricanes/hurricanes101.swfhttp://news.bbc.co.uk/2/hi/science/nature/4588149.stm

Spiral rain bands

Most hurricanes form off of the equator where the ocean is warm, so as air rises it carries moisture with it. As the air rises, it cools and condenses. The rising air turns to the left and begins rotating. The faster the air rises, the faster the surrounding air moves and wind speeds increase.

The centre of the hurricane is calledthe eye. The eye can be 50 km wideand the air is calm, the sky is clear.The border of the eye is the eye wall.At the eye wall the winds are movingfaster and the volume of rainfall isgreatest.

Hurricane wind speeds can reach 300 km/h which are less than atornado, but Hurricanes are muchlarger and can last for days or even weeks.

Hurricane Formation

Storm Surge: a huge amount of sea water piled up by the strong winds and pushed onto shore by a hurricane. The water level may be more than 6 meters higher than normal.

BlizzardsSection 15.7

http://canadaonline.about.com/cs/weather/p/icestorm.htm

A severe snow storm with strong winds (greater than 55 km/h), low temperatures and reduced visibility (less than 0.2 km).

Blizzards develop when a warm air mass filled with moisture moves north and meets a cold Polar air mass.

Blizzards cause whiteout conditions and make travelling by road, water and air dangerous. We may lose electricity and they can cause avalanches in mountain areas.

Blizzard

Humidity –is the amount of water vapor in the air.

Heat wave -a period of more than three days at or above 32 ̊C. Heat waves feel hotter with humidity.

◦ To protect yourself: Drink plenty of fluids to avoid dehydration Eat salty food to retain fluids.

Wind chill factor -is the temperature we feel on our skin. It is caused by the air temperature and wind speed. It is always colder than the air temperature.

◦ To protect yourself: Stay dry Stay out of the cold to prevent frost-bite and hypothermia

Section 15.9Extreme Heat and Cold

Read pages 594-607. Do questions 1,4,7 on page 597. Do questions 1,2,3,5 on page 599. Do questions 1,4,5,6 on page 607.

Video Response: Wonders of Weather Extreme Weather Computer Assignment

Assignments:

El Nino –a shift to warmer than average temperatures in the tropical Pacific Ocean.

Section 15.12El Nino and La Nina

La Nina –a shift to colder than average ocean temperatures in the eastern Pacific