The Atmosphere, Weather and Climate

Atmosphere,
Weather and
Climate
Section 1: Atmosphere
Atmosphere
Atmosphere: a thin envelope of gases that surrounds
the earth/planet
Between 1650 and 1660 a scientist
named Robert Boyle discovered
that air contains a substance that is
required for life.
He called it “vital air.”
We call it oxygen, or O2
In the 1750’s a scientist named
Joseph Black discovered that
limestone mixed with acid gives
off a substance that quickly
extinguished flames.
He called it “fixed air.”
We call it carbon dioxide,
or CO2
In 1772, Daniel Rutherford preformed
experiments that got rid of vital air and fixed air.
What was left killed living things and extinguished
flames.
He called the substance that
remained “noxious air.”
We call it nitrogen or N2
*
There are 6 major components of air:
1. Nitrogen
2. Oxygen
3. Carbon dioxide
4. Trace Gases
5. Water Vapor
6. Particles
Which one(s) do you think is/are the most
abundant in the air we breath?
Nitrogen - N2
78% of the volume of the atmosphere and the
air we breath
Oxygen - O2
Comprises 21% of volume of the
atmosphere
Another form is called ozone – O3
Ozone - a form of oxygen that has 3 oxygen atoms
instead of the normal 2 atoms
Less stable than O2 (breaks down faster)
Good in stratosphere (a portion of the upper
atmosphere)
absorbs UV radiation
Not good at ground level
a pollutant – irritates the linings of lungs
Carbon Dioxide – CO2
Essential for life – photosynthesis
Burning fuels releases CO2
A greenhouse gas
Trace Gases
Trace: tiny, very small amounts
Includes gases such as:
Argon (Ar), Neon (Ne), Helium (He),
Methane (CH4), Krypton (Kr), and
Hydrogen (H2)
Water Vapor
Water vapor: water in the form of a gas
Invisible (generally, except for clouds)
Very important to weather and climate
Particles/Particulates
Not gases
actual pieces of “things”
in the air
Includes:
dust
smoke
salt
chemicals
sand
*
Why Is The Atmosphere So Important?
1.
2.
3.
4.
5.
*
Contains O2 and other gases required for respiration
Contains CO2, O2 and other gases required for
photosynthesis
Keeps surface of earth warm enough to keep H2O in
liquid form (requirement for life)
Protects us from harmful UV radiation
Protects us from meteoroids
slows them down
burns them up
Properties of Air
1. Mass
2. Density
3. Pressure
Mass
Mass: the amount of matter contained in an object
Anything that consists of gases and particles has mass
If we know that air has mass,
what else might it have that is
related to mass?
Density
Density: the amount of mass in a given volume
Density = mass
volume
g/ml
or
3
g/cm
more molecules = higher density
Pressure
Pressure: pushing force on a surface or
area
Air pressure: the pressure caused by the
weight of a column of air pushing
down on a surface
Why don’t we get crushed by the air pressure?
Because air is pushing in all directions
(up, down, sideways, etc.) - it is balanced
Air pressure changes day to day, hour to hour
Denser air (more molecules) has higher
air pressure
Pressure is measured by a barometer
Barometer: an instrument used to measure air
pressure
There are 2 types of barometers
 Mercury barometer (now called a liquid
barometer)
 Aneroid barometer
Units for both types:
inches of mercury or millibars
1 in ~ 33.87 mb
*
Mercury Barometer
Mercury is a restricted metal
(new ones are not being made anymore)
• water can be used too - hence the alternate
name, liquid barometer
• the tube is a minimum of 84 cm tall
(for accuracy)
• 1 atmosphere = 760 mm
Aneroid Barometer
air-tight metal chamber, usually made of copper and
beryllium, making it sensitive to changes in air
pressure
• an increase in air pressure:
chamber walls go in
(causing a dial to move)
• a decrease in air pressure:
chamber walls bulge out
(causing a dial to move in the
opposite direction)
*
Altitude and Air
As you go farther away from Earth: mass, pressure,
density and temperature changes
Mass
• decreases as you go higher
• still has the same amount of all
of the gases, but the gases are
more widely dispersed, or
spread out as you go higher
Density
• decreases as you go higher in altitude
Density = mass
volume
• if volume stays the same but mass
decreases, then density must also
decreases
Pressure
• decreases with increasing altitude
• the farther you get away from the
earth’s core, the less gravity affects
objects, so pressure decreases
(pressure deals with weight, which is a
function of gravity ).
Temperature
• does not change on a
linear scale
• temperatures do not
steadily increase or
decrease throughout
the atmosphere
• layers of the atmosphere
are categorized by
temperature changes
Layers of the Atmosphere
a.
b.
c.
d.
Troposphere
Stratosphere
Mesosphere
Thermosphere
Troposphere
Tropo = changing
Troposphere: layer of the atmosphere
where the Earth’s weather occurs
• sea level to about 18-20 km high
9 km at poles, 18-20 km at equator
• where we live
• area of most weather occurrence
• conditions are the most variable than all other layers
• contains almost all of the mass of the atmosphere
• temperature steadily decreases as you go higher
• in upper regions of the troposphere,
temperature is around -60C (-76 F)
• on average, for every 1 km increase in altitude
temperature decreases by 6.5C (almost 12 )
Stratosphere
Strato = spread out, layer
Stratosphere: layer of the atmosphere that contains a
large amount of ozone
• found from around 18-20 to 50 km above sea level
• where many airplanes fly
• as altitude increases, temperature
increases
recall ozone is absorbing
UV radiation!
• temperature ranges between
- 60 C to –2 C
Mesosphere
Meso = middle
Mesosphere: the layer of the atmosphere that protects
the earth from meteoroids
• found from 50 – 80 km
above sea level
• as altitude increases,
temperature decreases
• temperature ranges
between -2C to - 80C
(contains fewer ozone
and other gas molecules)
Thermosphere
Thermo = heat
Thermosphere: the outermost layer of the earth’s atmosphere
that contains the ionosphere and exosphere
• found from 80 km to space (blends gradually, no definite edge)
• as altitude increases, temperature increases
• temperature ranges between -90C to +1800C
• temperature increases due
to solar radiation hitting this
layer first and heating up the
molecules found there.
• does not feel hot because there
are not a lot of molecules hitting
you (or the thermometer) even
though they are moving very fast.
Thermosphere
divided into 2 layers:
1. Ionosphere
2. Exosphere
Ionosphere
• lower portion of the thermosphere
• found between
80 km – 400 km
• energy from sun causes gas
molecules to become electrically
charged (called ions)
• radio waves bounce off these ions
and back to Earth’s surface
• the aurora borealis occurs in the
ionosphere
• particles from the sun enter
the ionosphere near the poles
and hit molecules that causes the molecules to glow!
Exosphere
Exo = outer
• upper portion of the thermosphere
• found from about 400 km out to outer space
(thousands of kilometers wide)
• Earth’s satellites for
phone, television
and weather are
located in
this area
Air Quality
Natural sources of air pollution:
1. Forest fires:
dust, smoke, CO2, NO2
2. Soil erosion
3. Sand storms
4. Erupting volcanoes
Air Quality
Man-made sources for air pollution:
1. Farming
2. Construction
3. Burning fossil fuels such as coal, gas, methane and oil which
causes:
Smog: air that is polluted
with particulates from
the burning of fossil fuels
Acid rain: rain that contains
more acid than normal due
to the burning of high-sulfur
fossil fuels, especially coal
4. Cars
5. Man-made fires
6. Gas Stations
Atmosphere,
Weather and
Climate
Section 2: Weather Factors – Wind, Humidity, Precipitation
Weather - Quick Background
The movement of heat in the atmosphere is a major
factor of weather
it can affect temperature, wind, rain
*
Heat comes from the sun in the form of
electromagnetic waves
Most is visible light and infrared radiation (long
wavelength), and a small amount is UV radiation
(short wavelength)
Much of the UV radiation is
absorbed by ozone in stratosphere
Not all reflected sunlight makes
it out into space:
The warm gases make a “blanket”
around the Earth keeping it warm
Incoming sunlight:
• 50% is absorbed by surfaces and becomes heat
• 25% is reflected back into space by clouds
• 20% is absorbed by gases and particles in air
(remember O3)
• 5% reflected back into
space by water
Some things to remember/memorize:
• hot/warmer air rises
• cold/cooler air sinks
• warmer air can hold more moisture than
cooler
Weather Factors
A. Wind
B. Humidity
C. Precipitation
A. Wind
Air is fluid, so it moves from place to place
wind: the horizontal movement of air from a region of high pressure to a
region of low pressure
Remember:
 warm air rises
- if warm air rises, that means that it is less dense
warm air is less dense = warm air has a lower air pressure
 cold air molecules do not move much
- more dense air = higher air pressure
SO . .
Wind is caused by
differences in air pressure
Wind
How do you measure wind?
You measure both direction and speed
To measure direction - use a wind vane
Wind swings the vane so that one end points
into the wind,
Wind vanes indicate where the wind is
coming from
To measure speed - use an anemometer
Think pinwheel on its side
3-4 cups attached to an axel and can spin
freely
A gauge/meter on the axel calculates wind
speed
Wind
Another part of wind is how it feels Wind-chill Factor: a measure of cooling, due to a
combination of wind and temperature.
Wind blowing across skin will “pull” body heat out of you (heat
moves from areas of high heat to areas of lower heat)
The stronger the wind, the faster the wind moves,
the cooler you feel
Great when it is warm out –
cools you off !
Can be deadly when it is already cold
outside.
Local Winds
Form only where large scale winds are weak
Only travel/blow over short distances
Caused by the unequal heating of the Earth’s surface
within a small local area
Local Winds
There are 2 types of local winds:
sea breeze
land breeze
Both occur near large bodies of water
Local Wind - Sea Breeze
Sea breeze: a local wind that blows in from a sea or lake onto the land
(also called lake breeze)
Occurs along the shore of a large body of water
(i.e. sea/ocean, gulf, Great Lakes)
Land heats up faster than water, so the warm air over the land
rises, allowing the cool air over the water to come blowing in
Generally occurs during the daytime.
Local Wind - Land Breeze
Land breeze: a local wind that blows from the land over a sea or lake
Occurs along the shore of a large body of water
Land cools faster than water
(cooler air = higher pressure)
• wind moves from higher pressure to lower pressure
• wind now blows from the land to the water!
Generally occurs at night
Global Winds
Global wind: a wind that blows steadily over a long distance
from a specific direction
Created by the unequal heating of the Earth’s surface
Middle of the day:
Sun hits most directly at Equator, heating
that area a lot!
Sun hits the poles at an angle, spreading out
over a wide area, heating the surface less
Temperature difference between poles and
equator creates a giant convection current
Warm air rises at the equator (lower pressure)
Colder air sinks at the poles (higher pressure)
Difference causes the winds to blow from the Poles to the Equator
Winds do not blow in a straight line from the poles to the
equator because the Earth rotates and is tilted.
The rotation of the Earth causes winds to curve.
This is called the Coriolis Effect.
Global winds in Northern hemisphere
generally blow from east to west
Global winds in the Southern hemisphere
generally blow from west to east
Do not have one large temperature
current.
Warm air will travel a limited distance before
cooling and then sinking.
Global Wind Belts
Earth has a total of six (6) global wind belts:
3 in Northern hemisphere
3 in Southern hemisphere
From poles to the equator, they are named:
(The same name is used in both hemispheres)
( 90˚ to 60˚ N/S)
Polar Easterlies
Polar Front (60˚ N/S)
Prevailing Westerlies
(30˚ N/S to 60˚ N/S)
Horse Latitudes (30˚ N/S)
Tradewinds
(0˚ to 30˚ N/S)
Doldrums (0˚)
Open up your agendas to the world map!
90°
60° N
30° N
0°
30° S
60° S
90°
Polar Easterlies
global wind belt found between 60 N or S
and the Pole
cold air at the Pole sinks and flows
back toward lower latitudes
Coriolis effect twists these winds
in a westerly direction so winds blow
from the east
meets the Prevailing Westerlies around
60 N or S in a region called the polar front
the meeting of the warm and cold air along this
front greatly effects the U.S. weather
*Remember: Air temperature is relative to position on
Earth
Prevailing Westerlies
global wind belt found between 30 N or S and 60 N or S
does not blow directly towards the north due to the
Coriolis Effect
pushes the winds from west to east, therefore blows
or comes from a SW direction
important to U.S. weather
Tradewinds
a global wind belt found between 0° to 30° N/S
named because sailors depended on these winds to get
to trading countries around the world
Warm air rising from the equator,
causing low pressure, cooler air travels
from N/S to the equator, warming, etc.
Blow from the Horse Latitudes (~ 30 N/S) to the
equator from a NE direction due to the Coriolis Effect
2 areas of relative calm or weak winds:
• doldrums (warm air rises)
• horse latitudes (cooler air sinking)
where air is either rising or descending there is little
wind movement (horizontal movement)
Doldrums
an area of calm winds located right around the equator, 0
steady rising of warm air
(creates low pressure)
cooler air rushes in but is quickly warmed by the sun
and rises before it can move too far.
therefore, the wind near the equator is weak.
Horse Latitudes
an area of calm winds located around 30 N or S
upper air stops moving towards poles and sinks
– high pressure (it gets cooler)
Why is it called the “horse” latitudes?
Jet Stream
Recent discovery (1940’s) when WWII jets began
flying higher
located around 10 km above sea level
• high speed winds 200-400 kmph
• very wide (100 km), but shallow (1-2 km)
• move in a slow wavy pattern from W to E
(following Earth’s rotation)
B. Humidity
Recall the water cycle
Humidity: a measure of the amount of water
vapor in the air
Humidity
Generally recorded as “relative humidity”
Relative humidity: percentage of water vapor
actually in the air compared to the maximum amount
of water vapor the air can hold at a given temperature
Ex: 10C air can hold 8g water vapor/m3
If humidity was 8g water vapor, then:
relative humidity = 8g/8g = 100% i.e. saturated
If humidity was 4g water vapor, then:
relative humidity – 4g/8g = 50%
Humidity
Humidity is measured using a psychrometer
Psychrometer: device used to measure relative
humidity
Has 2 thermometers:
a wet bulb and a dry bulb
Wet bulb: cloth covers bulb;
this cloth can be and is moistened
with water
Dry bulb: no covering over
thermometer bulb
Relative humidity is found by comparing the
temperatures of the dry bulb to the wet bulb
The psychrometer is “slung” around
its handle for about 30-45 seconds
• Air blows over both thermometers
• The wet-bulb thermometer is cooled
to a lower temperature than the
dry-bulb due to evaporation of water
from the wet cloth
• If humidity is high –
little evaporation on the cloth occurs,
so the difference between the two thermometers is small
• If humidity is low –
lots of evaporation on the cloth occurs,
causing the wet-bulb thermometer to read a much lower
temperature than the dry-bulb thermometer
Cloud Formation
Clouds form when water vapor condenses to form
liquid water or ice crystals
Condensation requires two (2) conditions:
1. Cooling of the air
Remember - cooler air holds less water vapor
2. Presence of particulate
Surface for condensation to
occur upon
Most particulates are:
salt crystals from oceans
dust from the soil
smoke
bacteria
Clouds are classified
by:
Shape
Altitude
Capability to produce
precipitation
Cloud Classification - Shape
There are three (3) basic shapes:
Cirrus
Cirrus = curl of hair
• Look wispy, feathery, mare’s tail
• Only form in high altitudes (above 6 km)
• Made of ice crystals
Cumulus
Cumulus = heap, mass
• Look like fluffy, rounded piles of cotton
• Form less than 2 km above the ground but can grow
to extend up to 18 km tall!
Stratus
Stratus = spread out
• Flat layers, generally dull, grey color
• Cover a lot, if not all, of the sky
• Low level clouds
Cloud Classification - Altitude
Alto
alto = high
Clouds that form 2-6 km above the ground (middle level
clouds) or above the level that the shape is usually found
Cirro
Clouds that usually form in very high altitudes,
generally above 8 km
Cloud Classification - Moisture
Moisture/Precipitation Ability
Nimbus or nimbo –
Cloud that can produce rain or snow
Naming Clouds
Cloud terms:
cirrus
cumulus
stratus
alto
cirro
nimbus/nimbo
Now lets put these terms into actual cloud names – 10 to be exact
– and what kind of weather may be indicated when you see them!
Cloud Names
Cirrus – wispy, “mare’s tails”
*fair weather
Cirrocumulus – look like rows of cotton balls or fish scales
*storms are probably on the way
Cirrostratus – very thin clouds that cause halos around the sun or moon
*precipitation may follow in 12-24 hours
Altocumulus – slightly higher than normal and more cumulus clouds
*thunderstorms may occur by the late afternoon
Altostratus – spread out clouds higher than normal
*often form ahead of a storm that will produce a steady
rain/snow
Cumulus – cotton balls
*indicates fair weather until they get big enough to become:
Cumulonimbus – huge towering clouds with flat tops
*produce thunderstorms , sometimes violent
Stratocumulus – cumulus clouds in a steady layer
*can indicate a coming storm
Nimbostratus - uniformly grey clouds in a steady layer
*can produce constant drizzling rain/ light snow
Stratus – “cloudy day” cloud; fog
*sometimes can indicate rain/snow
Cloud Type and Altitude
Cirrus
Cirrocumulus
Cirrostratus
Altocumulus
Altostratus
Cumulus
Stratocumulus
Nimbostratus
Stratus
High clouds
5-13 km
Mid-level
clouds 2-7 km
Low clouds
0-2 km
Cumulonimbus
C. Precipitation
There are 5 types of precipitation:
Rain
Sleet
Freezing Rain
Snow
Hail
Liquid water (droplets) or ice crystals
need to be big enough and heavy enough
to fall through the air and touch the
ground to be considered precipitation
cloud droplet = 0.002 mm
Average time from evaporation of a
single water molecule to precipitation is 9 days
Rain
• Most common form of precipitation
• Must be at least 0.5 mm in diameter
Smaller diameter liquid water is called drizzle
Smallest is mist and usually comes from stratus clouds
Sleet
• Rain that has fallen through a layer of air that is
below 0C (below 32F)
Rain drop freezes on its way to the earth’s surface!
• Smaller than 5 mm in diameter
• OR. . . .
Freezing Rain
• Rain that has fallen through cold air that is located
very near to the ground
Not enough time to freeze
in the air (like sleet), but
freezes as soon as it touches
a cold surface
• Also called an ice storm
Snow
• Water vapor that has turned directly into an ice crystal
inside a cloud (recall sublimation)
• Called snowflakes
• Cloud needs to be a
cold cloud, below
0C, for snow to form
Hail
• Round pellets of ice larger than 5 mm in diameter
• Can form inside cumulonimbus clouds during a
thunderstorm
• Requires strong updrafts of vertical wind inside the
cloud to keep “flinging” the ice pellet back into the
cloud, further coating it in ice
The longer a pellet is in the
cloud, the bigger the hail
Atmosphere,
Weather and
Climate
Section 3: Weather Patterns
Weather Patterns
Recall from previous lessons:
• Warmer air rises – less dense
• Cooler air sinks – more dense
• Warm air holds more moisture
than cooler air
Today’s weather can be influenced by the air 1,000 or more kilometers
away!
Air Masses and Fronts
Air mass:
a large body of air that has similar temperature, humidity
and pressure at any given height
large =1,000,000 km2 and 10 km deep!
We will learn:
Types of fronts
Types of air masses
Movement of air masses
Fronts
Front: boundary where air masses meet
Fronts do not readily mix when they meet
There are four main types of fronts:
• Cold front
• Warm front
• Stationary front
• Occluded front
Cold front: rapidly moving cold air mass runs into a slower
moving warm air mass
Colder air moves under the less dense warm air, pushing the
warm air upwards
As the warm air moves upwards,
it cools - the now cooling warm
air reaches its dew point
Dew point: temperature at which water vapor condenses
into droplets of water or ice crystals
• cloud formation
• if there is enough moisture in the warm air then rain,
snow or a thunderstorm may occur
Behind the cold front:
• cooler temperatures, drier air
• clear skies (why?)
• shift in wind
(direction and speed)
On a weather map depicted as:
• blue line with triangles
• triangles point in the
direction the cold front
is moving towards
(why?)
Warm front: a faster moving warm air mass
overtakes a slower moving colder
air mass
less dense, warm air moves over the denser cold air
• if warm air is humid:
warm air slowly rises over the cold air, cools, and
may release its water vapor in the form of light
rain or snow
• if the warm air is dry:
scattered clouds occur
Warm fronts move slowly, which makes it possible
to have rainy or cloudy weather for days
Behind warm front:
Warm, humid or dry weather WHY?
Warm Front
On a weather map:
• red line with half circles
• semicircles point in direction that the warm air
mass/front is moving
*
Stationary front: two air masses, one warm and
one cold, face each other in a “stand off”
• fronts cannot move each other
• water vapor condenses into rain, snow, fog or
clouds where the two air masses meet
• precipitation can fall for days
• very little, if any, wind in
this region
On a weather map:
• blue + red line with blue triangles and red half
circles
• blue points in the direction that the cold front is
trying to move
• red points in the direction that the warm front is
trying to move
Occluded front: warm air mass is caught between
•
•
•
•
two cooler masses, one colder than the other
denser, colder air masses push under the warm air
mass, pushing the warmer air mass up
warm air is cut off from the ground
(occluded= cut off)
temperatures
cool
weather may
turn cloudy with
rain or snow
On a weather map:
• purple line with alternating purple triangles and
hemispheres
• point in the direction that the colder air mass
is moving
Types of Air Masses
So far we have been talking about cold and warm
air masses. We can actually define them a bit
more!
Air masses are classified by two characteristics:
• temperature
(temperature affects air pressure)
• humidity
Words to know:
Tropical: warm air masses that formed in the tropics
(0-30)
Polar: colder air mass formed above 50N or 50 S
Maritime: humid air mass that formed over the
oceans
Continental: dry air mass that has formed over land
Now we can put these 4 words together like we did with the clouds words how many will there be if you can only put one humidity word with one
temperature word?
Maritime Tropical (mT)
Warm, humid air mass formed over the tropical oceans
tropical oceans near the US:
Gulf of Mexico, Southern Atlantic, Southern Pacific
Travel into SE U.S., then get pushed to the N and NE
into Central and Eastern U.S. (nor’easter)
Summer  hot, humid
weather
Winter  heavy snow or
rain
Maritime Polar (mP)
Cool, humid air mass formed over the North
Pacific and North Atlantic oceans in the U.S.
Can effect West Coast much more than East Coast
(why?)
Summer/winter  cooler
temperatures with fog
or rain
Continental Tropical (cT)
Hot, dry air mass formed generally in the summer
over the SW and Northern Mexico
• covers a smaller area
• moves in a NE direction
• brings hot, dry weather
to Arizona, New Mexico,
eastern Texas and the
Great Plains
Continental Polar (cP)
Cold, dry air mass forming over Canada and Alaska
Winter  brings very cold, dry, and clear weather
to North America
Summer  air mass is more mild, but still brings
cooler
temperatures
Movement of Air Masses
Two (2) major means to move air masses:
• Prevailing Westerlies
• major wind belt across the continental
United States
• generally push air masses from W to E
• Jet Stream
• bands of high speed winds starting at
around 10 km above sea level
• generally push air masses from
W to E in an undulating pattern
Weather Technology
Meteorologist: a scientist who studies the causes
of weather and predicts what weather will be
like in certain areas
Old methods of determining weather include:
• Cloud types
• Broken bones
• Barometer readings
Automated weather stations
over 1700 surface stations in U.S.
record:
• temperature
• pressure
• relative humidity
• rainfall
• wind speed/direction
New technologies are used to increase accuracy:
Weather Balloons
Carry instruments into upper troposphere
to the lower stratosphere
Measure: temperature, pressure, humidity
Satellites
• TRIOS-1 launched in 1960 was the first weather satellite
• cameras show:
• Earth’s surface
• clouds (tops of)
• storms
• snow cover
• instruments take readings in:
• temperature
• humidity
• solar radiation
• wind speed/direction
Computer forecasts
• collects large amounts of data
• process data quickly
• each forecast builds upon the
previous forecast
(as new data arrives,
the forecast is updated)
gives forecast for:
12 hours (most accurate)
24 hours
36 hours
5-10 days (least accurate)
*
Reading A Weather Map
• many small weather stations across the U.S. and
the world
• data from weather stations in the US are gathered
and assembled
into weather
maps at the
National
Weather
Service
From data collected, you can make:
Isobars
Isotherms
Weather Station Symbols
Isobars: lines joining stations that have the same
pressure
Listed with just the last three numbers in mb
(millibars)
Isotherms: lines joining stations
that have the same temperature
(F in the U.S.)
Isobars and isotherms never
cross each other –
make wavy circles, ovals in
areas
Surface Temperature Map
Surface Air Pressure Map
Weather Station Symbols
Not all symbols are given every
hour, especially if there is no
change in weather conditions
Also depends on the site you
use; some give all, some give
just a few
C
A
E F G
I
J
Cyclones and Anticyclones
Occur when air masses collide around large surface
features like mountains, the jet stream or even
other air masses
Bends develop, air begins to swirl, forming a:
•
•
•
•
Cyclone
Anticyclone
Tornado
Hurricane
Cyclone
Air swirls counterclockwise, inward and up
• low pressure system
• clouds gather, gets windy
(upward motion of air causes air to come rushing in to fill
the void)
• humid air
Cyclones over water can become:
• Hurricane (Atlantic, Pacific)
• Typhoon (West Pacific)
• Cyclone (Indian Ocean, Southern Hemisphere)
Anticyclone
Air swirls clockwise, outward and down
• high pressure system
• skies clear (air is not moving upward – required for
condensation)
• drier air
• light to no wind
Hurricane
a tropical cyclone with winds of 74 mph or more
that forms over an ocean
(minimum 74 mph, max 157 mph)
Conditions for a hurricane to form:
• warm water
• low pressure area
• sand from Sahara Desert
Hurricane Andrew’s Path (1992)
Hurricane Isabel (2003)
Hurricane Formation
• warm air rises over an ocean forming clouds
(a low pressure area)
• more warm air is pulled into the system
(winds move from high to low pressure areas)
• causing more clouds to form,
pulling more humidity out of
the ocean
(tropical disturbance forms)
• winds spiral inward toward
low pressure area causing a
lowering of pressure, causing
more winds, etc…
“snowball effect”
• hurricanes get their energy from warm ocean currents
• once over land, the hurricane loses its energy source
and loses strength
• damage is due to winds, high waves, severe flooding
and storm surges
a “dome” of ocean water that
sweeps across the coast in a
wide area near where a
hurricane comes onto land
• due to the low pressure and
high winds
Hurricane Ratings
categorized by sustained wind speeds
Saffir – Simpson scale
Category
Wind Speeds
(mph)
Air Pressure
(mb)
Storm Surge
(ft)
1 - minimal
74-95
above 980
3-5
2 - moderate
96-110
979-965
6-8
3 - extensive
111-129
964-945
9-12
4 - extreme
130-156
944-920
13-18
5 - catastrophic
157+
below 920
over 18
Tornados
Tornado: a destructive storm of a rapidly rotating
column of air that is in contact with both
the earth’s surface and a cumulonimbus
cloud
a condensation funnel is
what forms the tornado’s
characteristic shape
can reach speeds of
480 km/h (300 mph)
Conditions for tornado formation:
• warm, humid air mass from Gulf of Mexico
(Maritime tropical)
• cold, dry air mass from Central Canada
(Continental Polar)
• thick cumulonimbus clouds
Tornado Formation:
• warm, moist air is found under cumulonimbus clouds
• cold, dry air comes in and forces the warm, moist air up into
cumulonimbus clouds, forming a low pressure area inside
the cloud
• warm air begins to rotate in the cumulonimbus cloud as it
meets winds blowing in different directions at different
altitudes
• Tornado forms when a part
of the cloud descends to the
earth (in a funnel-shape
condensation tube) due
to the rapidly rotating air
Size of tornado does not always indicate intensity,
very subjective
• depends on how experienced the surveyor is
• “terrible tornado” sounds good on TV but may
not be actual intensity
Fujita Scale
• damage scale invented by Dr. T. Theodore Fujita, at the
University of Chicago (1971)
• tornado damage due to high winds and flying debris
• rating based on damage, swirl patterns on the ground,
radar tracking, photography (if available) and eyewitness
testimony
• how can you estimate rating if
only occurred in a corn field?
• ranged from F0 – F5
• updated in 2007 (EF Scale)
• accounts for plant damage
and differences in
construction techniques
• better technology
EF0: Light damage
• 104-137 kph (65-85 mph)
• few shingles removed
• tree branches broken
(39%)
EF1: Moderate damage
138-177 kph (86-110 mph)
• roofing material peeled off (trusses still in position)
• mobile homes pushed off foundation
• moving autos pushed off roads
(36%)
EF2: Considerable damage
•
•
•
•
•
•
178-217 kph ( 111-135 mph)
trees uprooted
trusses off frame homes
mobile homes demolished
train cars/boxcars overturned
high rise windows broken
(19%)
EF3: Severe damage
•
•
•
•
•
218-266 kph (136-165 mph)
entire trains derailed/overturned
walls and roofs torn from well constructed homes
trees in forests uprooted
heavy cars thrown
(5 %)
EF4: Devastating damage
•
•
•
•
267-322 kph (166-200 mph)
homes leveled
weak foundations broken/blown
cars propelled through air
(1 %)
EF5: Incredible damage
• > 322 kph (> 200 mph)
• steel reinforced concrete
structures damaged
• auto-sized missiles > 100 m
• total destruction
(> 0.1 %)
Hypothesized
F6: Inconceivable damage
?
Tornados
Hurricane
• formed over ocean/sea
• one air mass involved
• lasts for days
• max winds = 157 mph
• damage due to wind
and storm surge
• hundreds of miles wide
• average of 10-15 per year
• days to weeks warning
• can spawn tornadoes
Tornado
formed over land
two air masses involved
lasts for minutes
max winds = 200+ mph
damage due to wind
and flying debris
less than a mile wide
over 1200+ per year
minutes to hours warning
cannot spawn a hurricane
• rating/category based on wind speed
• produce rain, winds
• cyclones (low pressure areas)
Atmosphere,
Weather and
Climate
Section 4: Climate
Climate
the average, year-after-year, conditions of
temperature, precipitation, winds and clouds in
an area
Microclimate –
a small area with climate
conditions different from
that around it
Examples:
riparian area vs.
surrounding desert
irrigated neighborhoods
next to non-irrigated
2 main factors describe climate:
Temperature
Precipitation *
What influences temperature?
1. Latitude
2. Altitude
3. Distance from large bodies of
water
4. Ocean currents
Latitude:
distance from the Equator in degrees
3 main zones:
Tropical
An area that receives direct or almost direct sunlight all year round
• straddles Equator (23.5 N/S)
• almost all of Trade Wind belt
• warm and humid
Polar
An area where the sunlight hits
the surface at an angle (indirectly)
• 66.5 N/S to 90 N/S
• cold
Temperate
An area where the sun is more direct in the summer than the winter
• between tropical and polar
• 23.5 N/S – 66.5 N/S
• Summers warm, winter cold
*
Altitude
the distance above sea level
Supersedes latitude when figuring out temperature
i.e.: can have very cold mountain tops in tropical zone
For every 1km above sea level, temperature drops 6.5 C
Ex: Mount Kilimanjaro
~ 6 km above sea level
6 x 6.5 = 39 C difference
in temperature between
Serengeti Plain and top of
Mt. Kilimanjaro
Distance from large body of water
oceans moderate temperature extremes of nearby land
recall: water heats up/cools off more slowly than land
Wind blowing from oceans to land tends to prevent
extremes
Ex: West Coast vs. Great Plains
West Coast
maritime climate
mild winters,
cool summer
Great Plains
continental climate
cold winters,
warm/hot summer
Ocean Currents
streams of water within the oceans that move in regular patterns
• Cold water flows from the poles towards the equator
• bring cold/cooler air
• can keep some southern latitude countries cold
• East Coast of South America
• West Coast of Africa (southern regions)
• Warm water from the tropics flows towards the poles
• bring warm/warmer air
• can keep some northern latitude
countries warm
• Gulf Stream/North Atlantic Drift:
England, Ireland, Sweden
(mild, humid air)
• (El Niño and La Niña)
Precipitation
What influences precipitation?
1. Wind
2. Mountain Ranges
3. Seasonal Winds
Winds
Amount of water vapor in an air mass –
influences how much precipitation will fall
Amount of water vapor in air masses –
depends on where these winds come from
i.e. Maritime or Continental
In the U.S., most air
masses are moved by
the Westerlies and the
jet stream
Mountain Ranges
Need to be large, cover a big area
Ex: Rockies, Sierra Madres, Cascades
not South Mountain, but it can be a microclimate
Creates what is called a rain shadow:
an area having relatively little precipitation due to the
effect of a large barrier causing the prevailing winds to
lose moisture before reaching the area
Rain Shadow
• winds are forced to rise up and over mountains
(draw diagram)
As air rises, it cools:
• cool air cannot hold as much moisture
• clouds form on the windward side
• precipitation falls before the winds finish going over the
mountains
• winds continue to travel across mountains, but are now drier
• winds descend on downward or
leeward side
• warms up
• soaks up any available moisture
and keeps it!
(warm air holds more moisture)
Seasonal Winds
a change in wind direction between summer and winter
Summer: land generally warmer than water
• caused air to rise
• low pressure to form (over the land)
• more wind comes in from the ocean
• wind moves form an area of high pressure to and area of
low pressure
• increased humidity in the air
• potential increase in precipitation
Winter: land generally cooler than water
• more wind from land to ocean
• drier air
• things in AZ a bit different!!
Seasonal Changes in Climate
• climate conditions are not static
• change with the changing seasons:
summer, winter, fall, spring
What causes seasons?
• seasons change as the
amount of energy from
the sun changes
• due to
• Earth’s tilted axis
Earth’s tilted axis
• at an angle of 23.5
• axis always points in same direction,
no matter where it is in the Earth’s orbit
• tip of axis is pointed at the sun for
part of its orbit (year) and away
in another part of its orbit
• when northern end of axis is tilted
at the sun:
• summer in the Northern hemisphere
winter in the Southern hemisphere
• when southern end of the axis is tilted at the sun:
• winter in the Northern hemisphere
summer in the Southern hemisphere
Short-term climate change
El Niño and La Niña
short term changes in the tropical Pacific Ocean
sea surface temperatures (SST) due to changes in
the currents and trade wind strength
Figure A - normal conditions
Figure B – El Niño conditions
El Niño
short-term change in the Pacific Ocean
where SST are warmer than normal
• generally begins in November/December
• occurs every 2-7 yrs and can last 1-2 yrs
• trade winds weaken –
• do not blow from the east as strong
• warmer water begins to travel west
towards South America
• warmer water causes the surface water temperature off the
coast of South America to rise by as little as 0.5 C or as much
as 3.5 C
• disrupts: nutrient flow, weather
• warmer water = warmer maritime winds
= more precipitation
La Niña
short-term change in the Pacific Ocean where SST are colder than
normal
• opposite of El Niño
• trade winds strengthen, forcing more cold water into tropics and
west across the Pacific Ocean towards the Australia, Indonesia, etc.
• good for nutrient cycle in ocean
brings up nutrients from far below the ocean surface
strong
weak
Climate: Global Warming
• the Earth’s atmosphere holds in heat from the sun
(keeps water in a liquid state)
• different types of molecules/gasses trap or hold heat in the
atmosphere and are called greenhouse gases
any gas found in the atmosphere that can hold heat
• most common greenhouse gases:
• water vapor (H2O)
• methane (CH4)
• carbon dioxide (CO2)
• nitrous oxide (N2O)
• CFCs
Chlorofluorocarbons; man-made chemicals
that trap heat in the atmosphere and break
down ozone
Possible effects of a warmer Earth:
Warmer ocean waters
• increase in hurricane strength
• change of ocean currents
• increased glacier ‘calving’
Increased land temperatures:
• plant crops in new regions
• plant more than one crop per season
in some areas
• reduced crop land
• rising ocean waters due to melting of
glaciers
Climate: Ozone Depletion
In the 1970’s, discovered the ozone
layer over Antarctica was thinning
• more UV radiation was reaching
the Earth’s surface in the area
Cause:
• Increase in amount of CFCs
escaping into the stratosphere
• used in many applications:
• refrigerants, cleaners, aerosols, etc. WHY?
Thinning ozone layer =
• increased eye problems
• increase in number and types of skin cancers
Protection against UV radiation:
• apply sunscreen of at least spf 30
• wear hats, long sleeves and sunglasses
• reduce exposure to midday sun