Objectives

• Differentiate between weather and climate

• Identify the layers of the atmosphere

• Describe the Coriolis Effect and how it relates to weather

• Describe convection and how it relates to weather

What is weather? An Introduction

Weather refers to the temporary state of the atmosphere at a specific time and place.

Can change everyday

Climate is the average weather conditions in an area over a long period of time.

Composition of the Atmosphere Atmosphere- a mixture of gases that surrounds a planet

• The most abundant elements in air are the gases

nitrogen 78% , oxygen 21%, and argon.

• The two most abundant compounds in air are the gases carbon dioxide, CO2, and water vapor, H2O.

• Also carries tiny solid particles, such as dust and pollen.

What is Ozone?

ozone -a gas molecule that is made up of three oxygen atoms

• Ozone in the upper atmosphere forms the ozone layer, which absorbs harmful ultraviolet radiation from the sun.

• Unfortunately, a number of human activities

damage the ozone layer.

Layers of the Atmosphere • atmosphere has distinctive pattern of

temperature changes with increasing altitude

• temperature differences mainly result from how solar energy is absorbed as it moves through the atmosphere

Layers of the Atmosphere • Troposphere

– Closest to earth – Nearly all weather takes place here

• Stratosphere – Most ozone is located here

• Mesosphere – Above stratosphere, extends about 80km

• Thermosphere – Extremely hot temperatures 1000°C

– Hot temp. Cause gas molecules to lose electrons which cause auroras

Layers of the atmosphere

Atmospheric Circulation

• Pressure difference in atmosphere cause movement of air worldwide

– Air moves from high to low pressure

– High pressure regions form where cold air sinks

– Low pressure regions form where warm air rises

Coriolis Effect

• Coriolis Effect- tendency of water and air to follow a curved path rather than a straight path along Earth’s surface

• Due to Earth’s rotation

• Points at Earth’s equator (widest area) travel farther and faster in one day than points at the poles (shortest width)

– Objects in N. Hemisphere deflect to the right

– Objects in S. Hemisphere deflect to the left

Coriolis Effect and Air Movement

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Global Winds

Convection – movement of matter due to differences in density that are caused by temperature variations; can transfer energy as heat – Warm air is less dense and will rise and cold air is

more dense and will sink, creates a cycle called a convection cell

Each hemisphere contains three looping

patterns of flow called convection cells.

Global Winds Continued Each convection cell correlates to an area of Earth’s

surface, called a wind belt, that is characterized by winds that flow in one direction.

• Wind patterns

Trade Winds-wind flows E to W toward equator between 30-0◦ latitude

Westerlies- wind flows W to E between 30-60◦, aided by Coriolis effect

Polar Easterlies-flows E to W between 60-90◦

Objectives

• Identify factors that affect weather.

• Describe types of clouds and cloud formation.

•What are some of the factors that

affect the weather?

1. Air Temperature

Temperature is the measure of the average amount of motion in particles.

2. Wind

a natural movement of air of any velocity; especially : the earth's air or the gas surrounding a planet in natural motion horizontally

3. Humidity

The amount of water vapor present in the air

Relative Humidity -is a measure of the amount of water vapor present in the air compared to the amount needed for saturation at a specific temperature

4. Precipitation

• Water that falls from the clouds

• Air temperature determines the form of precipitation that falls

• 4 main types of Precipitation: Rain, Sleet, Snow and Hail

4 Types of Precipitation

Rain Sleet

Snow Hail

5. Clouds • Masses of small water droplets or tiny ice

crystals that float in the air.

• Three main types are cirrus, cumulus, and stratus.

• Other clouds are a mixture of these three main types.

• Clouds are named for their altitude and shape

Cloud Formation

• 1. rising air cools which makes it reach due point

• 2. a condensation nuclei (ex. Dust) is present For condensation to

happen a solid surface is needed for water to attach

• 3. Condensation Due point turns water

vapor (gas) into water droplets (liquid)

• 4. When the water attaches to the condensation nuclei a cloud forms

a. Cirrus

• Cirro- means “curled” or “feathery”

• Form highest in the sky; are made up of ice crystals; and appear as curls, tufts, or wisps.

• Usually signal the end of clear weather.

b. Cumulus • Cumulo- means “heaped” or “piled”

• Cottony clouds with flat, usually gray bases, and puffy, bright tops.

• Usually signal good weather, but if atmosphere is unstable, can build into towering clouds that produce showers and thunderstorms.

c. Stratus

• Strato- means “layer-like” or “sheet-like.”

• Low-lying, dull-colored clouds that form in layers or sheets.

• Usually bring drizzling rain or light-falling snow.

• Nimbo – Latin for rain

• Two major types:

Nimbostratus- rain clouds

Cumulonimbus- thunderstorm clouds

Nimbus

Other Cloud Types

Cirrocumulus

Cirrostratus

Stratocumulus

Cumulonimbus

Alto- A prefix meaning “middle range of clouds “ and used to describe clouds that lie from 6,500-18,500 ft. (1,980-5,640m).

More Cloud Types

Altocumulus

Altostratus

Nimbostratus

Objectives • 1.)Explain how an air mass

forms

• 2.) List and describe the four main types of air masses

• 3.) Describe the type of weather associated with the four types of air masses on North America

Remember: Air Movement

• Air moves from high pressure to low pressure

• Differences in air pressure are caused by unequal heating of Earth’s surface

– At equator (warmer) the air will rise, creates a low pressure area

– At poles (colder) air sinks and creates high pressure area

– The differences in air pressure creates wind patterns

Worldwide movement of surface air from poles

(high pressure) toward equator (low pressure)

Air Mass

• A large body of air that has uniform temperature and moisture

–If air mass stays in one location for long time acquires properties of the Earth’s surface over which it develops.

Air Mass Terms

• Polar – source regions are cold

• Tropical –source regions are warm

• Continental – form over land

• Maritime – form over ocean

Air Mass Classification

• Classified by source regions

• Continental tropical(cT) – warm and dry

• Continental polar (cP) – cold and dry

• Maritime tropical (mT) – warm and moist

• Maritime polar (mP) – cool and moist

• Continental arctic (cA) – cold and dry

Air Mass Map

Continental Tropical

• Source: warm and dry

• Originate: from northern Mexico, form over tropical Atlantic ocean

• Weather: clear skies, negligible rainfall, hot dry summers (do not form in winter) – Can cause severe drought if remains stagnant for

long time

Air Mass Map

Continental Polar (similar for arctic air mass)

• Source: cold and dry

• Originate: Northern Canada and Alaska, move southward then eastward

• Weather:

– summer: cool, dry

– winter: cold temperatures and high pressure, leads to fog

Air Mass Map

Maritime Tropical • Source: warm and moist

• Originate: subtropical Pacific Ocean, or Gulf of Mexico and Caribbean Sea (tropical Atlantic ocean)

• Weather: – summer: hot, humid can cause thunderstorms

– Winter: mild, cloudy, moderate precipitation can make fog, low clouds

Air Mass Map

Maritime Polar

• Source: cool and moist

• Originate: originates from North Pacific Ocean, or from North Atlantic.

• Weather:

– Winter: rain and snow

– Summer: cool, fog

Air Mass Map

Front Objectives

• 1.)Compare and contrast characteristic weather patterns of cold and warm fronts

• 2.) Describe a stationary and occluded fronts

Fronts

• What is a front?

• It is a boundary between two air masses of different density, moisture, or temperature.

• There are four types of fronts; can you name them?? _____________, ______________

_____________, and ______________

Warm front Cold front

Occluded front Stationary front

Types of Fronts

• Form when two air masses collide with each other

• The type of front that forms determined by how the air masses move in relationship to each other.

Cold Front • Cold air mass overtakes a warm air mass and

pushes beneath the warmer air mass like a wedge

• cold fronts lift the warm moist air ahead of it up and usually the water vapor in the warm air condenses and clouds form

• This leads to short lived precipitation

• Fast moving cold front gives violent thunderstorms or other sever weather

The upper

cut

Cold Front

Precipitation Along a Cold Front

lifting the warm moist air ahead of it

A Closer Examination of the Animation:

Initially, the cold air mass wedges into the warmer air mass ahead

of it, (separated from each other by the cold front). The lighter

warm air is lifted upwards by the denser cold air and if enough

water vapor condenses, clouds develop.

Warm Fronts

• An advancing warm air mass replaces a colder air mass (the cold air mass is retreating)

• The less dense warm air rises over the cold air

• Generally produces precipitation over a large area, usually less sever than cold front because moves slower, last a bit longer

Sleeper

hold

Warm Front

Precipitation Along a Warm Front

warm moist air overriding colder air

A Closer Examination of the Animation:

Initially, a warm air mass (in yellow) nudges against a colder air

mass (in blue) ahead of it, (separated from each other by the

warm front). The lighter warm moist air behind the front is lifted

upward and "overrides" the colder air.

• occluded front -a front that forms when a cold air mass overtakes a warm air mass and lifts the warm air mass completely off the ground and over another air mass

• Occluded

fronts will

produce

precipitation

similar to

warm fronts.

• Involves 3

air masses

Stationary Front

• stationary front -a front of air masses that moves either very slowly or not at all

• Air masses are moving parallel to the front or directly toward each other.

• Weather: several days of overcast, maybe some drizzles, eventually disappears, nothing severe.

Stationary Front

Warm and Cold Front Symbols

• Cold air masses, triangles pointing in direction of movement

• Warm air mass, rounded edge pointing in direction of movement

• Occluded front, same side alternated triangles and rounded circle

• Stationary front alternating red half circles and blue triangles

Polar Front

• Over each of Earth’s polar regions is a dome of cold air that may extend as far as 60° latitude.

• The boundary where this cold polar air meets the tropical air mass of the middle latitudes, especially over the ocean, is called the polar front.

• Waves commonly develop along the polar front.

• A wave is a bend that forms in a cold front or stationary front.