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Weather
What is Weather to You?
What is weather? Describes the current condition of the
atmosphere.
Factors include- temperature, cloud cover,
wind speed & direction, humidity, and air
pressure
What is weather?
• Temperature– Measures how fast air
molecules are moving
– Rapid-warm/slow-cold
– Use a thermometer to
measure
• Atmospheric Pressure
– Air has weight, and the
weight exerts pressure
– When air is heated molecules
move faster and air expands,
making air less dense. This is
why it is moved upward
– Warm rises/cool sinks
– Use a barometer to measure
• Energy Transfer
– Fast moving
molecules transfers
to slow moving,
transfer of energy
when molecules
collide is conduction
– Warm air rising cool
air sinking is
convection (main
way heat is
transferred in
atmosphere)
• Humidity– amount of water
vapor in the
atmosphere
– Warmer more
evaporation occurs
thus more water vapor
– Dew pointtemperature at which
condensation can
occur. when the air is
saturated (holds all the
vapor it can)
condensation can
occur
– Measured with
pshychrometer or
hygrometer
Clouds
Clouds
A cloud is a large collection
of very tiny droplets of water
or ice crystals. The droplets
are so small and light that
they can float in the air.
• Low clouds
–
–
–
–
–
Stratus
Nimbostratus
Cumulonimbus
Stratocumulus
Cumulus
• Middle Clouds
• Altocumulus
• Altostratus
• High and vertical clouds
– Cirrus
– Cirrocumulus
– Cirrostratus
Wind
Wind is the horizontal Measuring Windmovement of air from • Direction is measured by
high to low
wind vane.
pressures.
• An ANEMOMETER
measures wind speed.
Described by their
The cups catch the wind,
direction and their
turning a dial attached
speed. Name tells
to the instrument. The
you where it is
dial shows the wind
coming from.
speed. .
Winds
Trade Winds
• Wind flows outward away
from the subtropical
highs. It encounters the
Coriolis effect.
• we find winds blowing
from east towards the
west.
Coriolis effect
• This force causes the
winds in the Northern
Hemisphere to move
from the east towards
the west below the
subtropical high, and
from the west towards
the east above the
subtropical high.
Westerlies
• Above the subtropical
highs in the Northern
Hemisphere, winds
blow from the west
towards the east.
Sea Breezes
• During the day, land gets heated by the Sun much
quicker than does water. As the land becomes
warmer, it heats the air in the atmosphere above it.
This causes the air to expand, becoming less dense,
and thus creating a low pressure.
Land Breeze
• In the night, land cools down much quicker than does
the waters of the ocean. As the land becomes cooler, so
does the air above it. This results in air becoming more
dense, forming a high pressure, causing winds to blow
outward towards the sea. This is known as a land
breeze.
Animation of sea land breeze
• http://www.classzone.c
om/books/earth_scienc
e/terc/content/visualiza
tions/es1903/es1903pa
ge01.cfm
Air masses
• Air masses move due to wind
• Dry (continental) or moist (maritime) and warm
(tropical) or cool (polar), depending on where it
begins.
• Mass of air that remains over a region for a few days
and takes on the characteristics of the area it occurs
• When air masses of different temperature meet, a
boundary is formed called a front
Air Masses
• A large body of air with similar temperature
and moisture.
• Air masses form over large land or water
masses and are named by where the
form…over land-continental or over watermaritime and also named for where they
originate from-near the tropic-tropical and
from near the poles-polar
• Dry (continental)- comes from land masses
• Humid (maritime)- comes from water
• Warm (tropical)- warm air coming up from the
equator
• Cold (polar)- cool air coming down from the poles
• Pg 598 in book
Description of air masses:
– Continental polar (cP)- cool and dry
• Continental arctic-type of continental polar mass that is much
colder-forms in the arctic circle
– Continental tropical (cT)- warm (hot) and
dry
– Maritime polar (mP)- humid (wet) and cold;
unstable
– Maritime tropical (mT)- humid (wet) and
warm; unstable
cP
continental polar
cold, dry, stable
cT
continental tropical
hot, dry, stable air aloft-unstable surface air
mP
maritime polar
cool, moist, and unstable
mT
maritime tropical
warm, moist, usually unstable
Fronts
• Cold– Cold air pushes under
warm air pushing it up,
– Cumulus &
cumulonimbus brings
– narrow band of
precipitation can occur
(short period of heavy
precip.)
– cold air in (temp drops)
• Warm– less dense (warm) slides
up and over cold air;
– high cirrus clouds first
and then stratus
– Long periods of slow
precip.
– Warm air in Temperature
rises
Fronts
• Cold-
• Warm-
• Cold fronts move faster than
• The weather activity in a warm
warm fronts.
front generally happens before
the front passes through an
• The weather activity in a cold
area.
front is often violent and
happens directly at the front.
• In a warm front the cloud
formation is very low often
• Cold fronts have sudden gusty
creating situations of poor
winds high in the air creating
visibility.
turbulence .
• Shown on a weather map by a • Shown on a weather map by a
red line with half circles
blue line with triangles
pointing the direction in which
pointing the direction in which
the warm air (front) is moving.
the cool air (front) is moving.
Fronts
• Cold– pushes under warm air
pushing it up,
– Cumulus &
cumulonimbus brings
– narrow band of
precipitation can occur
(short period of heavy
precip.)
– cold air in (temp drops)
• Warm– less dense (warm) slides
up and over cold air;
– high cirrus clouds first
and then stratus
– Long periods of slow
precip.
– Temperature rises
Fronts
• Stationary
• Occluded
– Warm air & cold air -When a warm front is trapped by
(between) two cold fronts.
meet and neither
-Shown on a weather map by a
advances
purple line with alternating
triangles and half circles pointing
– Remains in same
the direction the front is moving.
location for days
-may produce cloudy with precip.
– Cloudiness and
precip. may occur
Fronts
• Stationary
• Occluded
– Warm air & cold air meet When a warm front is trapped
and neither advances
by (between) two cold
– Remains in same location
fronts.
for days
-Shown on a weather map by a
– Cloudiness and precip. may
purple line with alternating
occur
triangles and half circles
pointing the direction the
front is moving.
-may produce cloudy with
precip.
High and low pressure centers
• Moves from high to low
areas
• High pressure areas air
sinks
– Moves from high to low
– Air moves clockwise due to
Coriolis
– Usually dry with few clouds
– High air pressure is
associated with cold
fronts which means
sunny and fair weather.
• Low pressure area- air
rises and cools
– Air circulates in
counterclockwise
– Air reaches dew point
water vapor condenses
forming clouds and
precipitation
– Low pressure is
associated with warm
fronts which means
cloudy, overcast, drizzly,
and possibly rainy
weather.
Cyclones
• Cyclones- swirling center
of low air pressure
• Warm air at the center
rises and air pressure
decreases. Cooler air
blows from areas
nearby.
• Spins counterclockwise
in Northern Hemisphere
Anticyclones
• High pressure centers
• Winds spiral outward
from centers of dry air
• Spin clockwise in
Northern Hemisphere
Winds spiral
inward
towards the
lowpressure
centercounterclockwise
Winds
spiral
outward
from the
highpressure
centerclockwise
cyclone
anticyclone
Cyclones
Anticyclones
• Decreasing air pressure
• Marked as Lows on
weather maps
• Counterclockwise
• Associated with clouds,
wind, and precipitation
• High pressure centers
• Marked as High on
weather maps
• Clockwise
• Associated with dry,
clear weather
Severe Weather
• Thunderstorms- cumulonimbus clouds (along
cold fronts)
– Lightning- energy flow that occurs between areas of
opposite electrical charge
Thunder
– Thunder- what causes?
• Lightning: 5-6 times hotter than sun’s
surface (54,000 degrees Fahrenheit.) -causes air
to expand quickly, then cools quickly and
contracts producing rapid movement of
molecules
–Sound due to expansion and
contraction of the heated air
Thunder Exp.
• EXPLANATION:
• Hitting the bag causes the air inside the bag to
compress so quickly that the pressure breaks the
bag. The air rushes out and pushes the air outside
away from the bag. The air continues to move
forward in a wave. When the moving air reaches
your ear, you hear a sound. Thunder is produced in a
similar way. As lightning strikes, energy is given off
that heat the air through which it passes. This heated
air quickly expands producing energetic waves of air
resulting in a sound called thunder.
•
What color is lightning?
Lightning seems to be clear or a white-yellow
color, but it really depends on the background.
• If your hair stands on end or your skin starts to
tingle, lightning maybe about to strike. Get
down on your hands and knees and keep your
head tucked in. Do not lay flat, because it can
give lightning a better chance of strike you.
What is cloud-to-ground lightning?
• All lightning is dangerous, but cloud-to-ground
lightning is the most dangerous type of lightning.
Most cloud-to-ground lightning strikes come from
the negatively charged bottom of the cloud traveling
to the positively charged ground below.
Cloud-to-ground lightning bolts strike the tall
objects, like trees and buildings. These lightning
strikes can cause fire and property damage. If you're
the tallest object, then lighting can strike you.
• Lightning is the second weather related killed.
Triggered lightning/ "natural" lightning
• goes from ground to cloud,
• while "natural" lightning is cloud to ground.
• Lightning happens
when the negative
charges (electrons)
in the bottom of the
cloud (and your
finger) are attracted
to the positive
charges (protons) in
the ground.
• The accumulation of
electric charges has to
be great enough to
overcome the insulating
properties of air. When
this happens, a stream
of negative charges
pours down towards a
high point where
positive charges have
clustered due to the
pull of the
thunderhead.
• The connection is made
and the protons rush up
to meet the electrons. It
is at that point that we
see lightning. A bolt of
lightning heats the air
along its path causing it
to expand rapidly.
Thunder is the sound
caused by rapidly
expanding air.
• http://science.howstuffworks.com/nature/nat
ural-disasters/lightning.htm
What is intracloud
lightning?
Intracloud lightning is
the most common type
of lightning. This occurs
when there are both
positive and negative
charges within the
same cloud. Usually, the
process takes place
within the cloud and
looks like a bright flash
of light which flickers.
What is intercloud
lightning?
Intercloud lightning is
less common. It's when
a lightning strike occurs
when there are positive
and negative charges
within different clouds
and the strike travels in
the air between them.
What is forked lightning?
Forked lighting appears as
jagged lines of light.
They can have several
branches. Forked
lightning can be seen
shooting from the
clouds to the ground,
from one cloud to
another cloud, or from
a cloud out into the air.
This lightning can strike
up to 10 miles away
from a thunderstorm.
What is heat lightning?
• Heat lightning is a term used to describe
lightning flashes that are too far away from
you to hear the thunder.
• The reason that it is called heat lightning is
that it appears most often on a hot summer
day when the sky is clear overhead.
• Outdoor Lightning Safety:
– Seek shelter indoors or in a car.
– Stay away from single tall objects (such as a tree)
and metal objects (fences, pipes, rails).
– Don't hold golf clubs, fishing poles.
– Remove backpacks with metal frames.
– It is not safe to be riding bicycles, motor scooters,
motorcycles, or golf carts.
– If you are out in the open and cannot get to
shelter, stand in a low spot under a group of trees
(not under a lone tree)
– or crouch down on the balls of your feet—do not
lie flat on the ground. If you are swimming or
boating, get out of the water.
Can you tell how far away?
– If You Can Hear It, Clear It; If You Can See It, Flee
It: This saying means that you should take shelter
if the time between a lightning flash and the
thunder is 30 seconds or less, which means that
the lightning is about 5 miles away. Don't resume
activities until 30 minutes after you hear the last
thunder.
Can you tell how far away a storm is?
Yes, you can use thunder to tell how far away a
storm is. Next time you see a storm, count the
number of seconds between when you see the
lightning and hear the thunder. Take the number
of seconds and divide by 5 and that will tell you
how far away the storm is in miles. For example: If
you counted 10 seconds between the lightning
and the thunder, the lightning is 2 miles away!
Tornadoes
• A tornado is a violent rotating column of air
extending from a thunderstorm to the ground.
• The most violent tornadoes are capable of
tremendous destruction with wind speeds of up to
300 mph.
• They can destroy large buildings, uproot trees and
hurl vehicles hundreds of yards. They can also drive
straw into trees. Damage paths can be in excess of
one mile wide to 50 miles long. In an average year,
1000 tornadoes are reported nationwide.
How do tornadoes form?
• Most tornadoes form from thunderstorms.
• You need warm, moist air from the Gulf of
Mexico and cool, dry air from Canada. When
these two air masses meet, they create
instability in the atmosphere.
•
A change in wind
direction and an
increase in wind
speed with increasing
height creates an
invisible, horizontal
spinning effect in the
lower atmosphere.
Rising air within the
updraft tilts the
rotating air from
horizontal to
vertical. An area of
rotation, 2-6 miles
wide, now extends
through much of the
storm.
What is a hurricane?
• A hurricane is a huge storm!
• It can be up to 600 miles across and have
strong winds spiraling inward and upward at
speeds of 75 to 200 mph.
• Each hurricane usually lasts for over a week,
moving 10-20 miles per hour over the open
ocean.
• Hurricanes gather heat and energy through contact
with warm ocean waters.
• Evaporation from the seawater increases their
power.
• Hurricanes rotate in a counter-clockwise direction
around an "eye" in the Northern Hemisphere and
clockwise direction in the Southern Hemisphere.
• The center of the storm or "eye" is the calmest part.
It has only light winds and fair weather. When they
come onto land, the heavy rain, strong winds and
large waves can damage buildings, trees and cars.
What is the difference between a
hurricane and a typhoon?
• Nothing except geography.
• Tropical storms occur in several of the world's
oceans, and except for their names, they are
essentially the same type of storm.
• In the Atlantic Ocean, Gulf of Mexico, and the
Eastern Pacific Ocean, they are called hurricanes.
• In the Western Pacific Ocean, they are called
typhoons.
• In the Indian Ocean, the Bay of Bengal, and Australia,
these types of storms are called cyclones.
Water Cycle
Atmosphere
• The envelope of gases
that surround the planet.
• a buffer that keeps us
from being peppered by
meteorites,
• a screen against deadly
radiation,
• and the reason radio
waves can be bounced for
long distances around the
planet.
• It is roughly
– 78% nitrogen (N2), (Nitrogen is "fixed" from the
atmosphere by bacteria in the roots of certain
plants-nitrogen cycle)
– 21% oxygen (O2) ,
– with trace amounts of water (H2O), argon (Ar),
carbon dioxide (CO2) and other gases.
– Nowhere else in the solar system can one find an
atmosphere loaded with free oxygen,
Atmosphere
• Levels
–Troposphere–Stratosphere
–Mesosphere
–Thermosphere
–Exosphere
credits
• http://www.nssl.noaa.gov/
• www.weatherwizkids.com