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.