Transcript File meteorology

Composition
and Structure of Atmosphere
Weather Patterns and Forecasting
Factors Influencing Climate
Severe Weather
Weather vs. Climate
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Weather- constantly changing, refers to the state
of the atmosphere at any given time and place
Climate- based on observations that have been
collected over many years and describes a place
or region
Both measure- air temperature, humidity,
precipitation, air pressure, wind (speed and
direction)
What is the climate of the Las Vegas valley?
 What is the weather today in the Las Vegas valley?
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Composition and Structure of Earth’s
Atmosphere
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A mixture of gases with
some suspended solids
(dust, salt, ice) and
liquids (water droplets in
clouds).
Extends from surface to
outer space – hundreds
of km’s.
Very thin layer around
Earth
Earth Science Reference Table
Major Components
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99% of atmosphere is
2 gases- nitrogen and
oxygen
.93% - Argon
.039% Carbon
Dioxide
Variable Components
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Water vapor- source of
clouds and precipitation
 Absorbs solar energy
Ozone- O3 10-50km
above earth. Absorbs
UV radiation from sun
Dust – fine grained
particles can stay
suspended for some time
Changes in Earth’s Atmosphere
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Earth’s atmosphere
thins as you travel
from Earth until there
are too few gas
molecules to detectthis is space
As gas molecules
decrease air pressure
decreases
Layers of the Atmosphere
Troposphere
Stratosphere
Mesosphere
Thermosphere
Troposphere
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Contains 75% of atmospheric gases, Earth’s
surface – 12 kilometers
Weather, clouds, and smog found here
Temperature Trends
Temp decrease with
altitude in the
Troposphere
- Temp rises in the
Stratosphere
Why?
- Ozone layer occurs in
stratosphere
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Remember Ozone
absorbs UV radiation
Being destroyed by
Clorofluorocarcbons
(CFCs)
Pressure Trends
Gases in the
atmosphere, like all
matter, have mass.
Atmosphere is a sea
of air – the deeper you
are in it, the heavier it
feels (more force
exerted)
Sea level pressure is
1013 mb at STP
Denver pressure is
550 mb (1600 m)
Mt Everest pressure
is 315 mb (8800 m)
Types of heat transfer
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Radiation (no molecules needed)
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Convection (air movement)
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transfer of energy without the involvement of a physical
substance in the transmission.
Allows solar radiation to reach Earth as it travels through
space
transmits heat energy by transporting groups of molecules
from one place to another within a substance
- warmer less dense portions of the medium will rise while
colder more dense areas will sink
Conduction (direct contact)
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Transfer of energy between molecules until an even
temperature is reached
What happens to solar radiation?
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1)
2)
3)
When radiation strikes an object 1 of three things
can happen
Energy is absorbed by the object (temperature
of object increases)
Energy is transmitted by object (temperature of
object does not increase) air and water transmit
some radiation
Energy bounces off object without being
absorbed or transmitted
Weather Patterns and Forecasting
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Sun is the external heat engine for our
planet.
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Three possibilities
1)Reflect to space
 Atmosphere
 Land (Albedo)
2)Absorbed by atmosphere
3)Absorbed by land or
absorbed/transmitted by water surfaces
Albedo of Earth Surfaces
Weather
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The present state of the atmosphere
Describes current conditions
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Air Pressure
Wind
Air Temperature
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Amount of Moisture
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Water Cycle
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Evaporation/transpiration
Condensation
Precipitation
Air Masses
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A large body of air that has the same properties
as the surface over which it develops.
When you witness a change
in the weather from one day to
the next, it is due to the movement of air masses.
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Prevailing Winds across U.S.
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Winds tend to move towards the right due to
the Coriolis effect
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Coriolis effect created by the rotation of the earth
Surface winds across U.S. consist of prevailing
westerlies
Winds blow from southwest to northeast
 These winds are responsible for movement of
weather across the U.S. and Canada
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Fronts
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Boundary between two air masses
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Cold Front
Warm Front
Occluded Front
Stationary Front
Humidity
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Refers to the water vapor content in the atmosphere
Relative Humidity is the ratio of the amount of water vapor in
air to the maximum amount it can hold at that temperature.
(expressed as percentage) *Varies with temperature change
Dew Point
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Temperature at which air is saturated and condensation occurs.
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Point where saturated vapor pressure equals actual vapor pressure
 Point where relative humidity equals 100%
Clouds
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Classified mainly on shape and height
Form when warm air is forced upward, expands, and cools.
 At the dew point, condensation occurs
 Aided by nuclei (dust, salt, smoke…)
Classification of Clouds
Weather Maps
Cloud Cover and Precipitation
Weather Maps
Isobar and Isotherm
Weather Map Symbols
Weather Map
Five Factors Influencing Climate
Factors Influencing Climate
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Climate is an average of the weather over a long
period of time.
Influenced by:
Global wind patterns
Latitude
Topographic Features
Large bodies of water
Mountains
Large cities
Global Wind
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Uneven heating of the latitudes produces major
convection currents.
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Deflect to the right in N.H.
 Coriolis Effect
Topographic Features
Severe Weather
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Tornado
Hurricane
Lightning
Tornado
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Violent, whirling wind that moves in a narrow path over
the land, usually in a direction from southwest to northeast.
Typically form along a front
 Local storm, short duration
 Spin counterclockwise
 Vortex extends from cloud
 Why can we see it?
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Tornado Occurrence
< 1% of all thunderstorms
~ 770 per year
April - June
Tornado Category Scale
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Fujita Scale
Tornado Summary
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Lightning
Damaging Hail
High Winds
Torrential Rain
Hurricane (Typhoon/Cyclone)
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Is a low pressure system that forms over tropical oceans.
The greatest storms on Earth – several 100 miles across!
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Wind speeds > 74 mph
Spin counterclockwise
Average 6-10 per year
“Season” July – September
Produces: Torrential rain, Flooding,
Damaging winds, Storm Surge
Anatomy of a Hurricane
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Warm ocean water with a
minimum temp of 80° F
Minimum ocean depth of 200
m
Converging winds near surface
Humid air rises and condenses
– Latent heat
Condensation is a warming process,
releasing stored heat. This heat
warms the surrounding air, making it
lighter
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Upper atmosphere high pressure
removes rising air in storm
Hurricane Category Scale
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Winds greater than 155 mph have been recorded
 Tropical storms have winds 39-74 mph
Tracking Hurricanes
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Movement
 Storms gets energy
from warm ocean
water
 Loses power when it
moves over land
 Difficult to predict
where it will make
land
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Errors in prediction and
evacuation can be costly!
Lightning
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Polarization of + and – charges within
a storm cloud by frictional charging
and freezing.
+ charges carried to upper portions of
cloud and – portions gravitate to bottom
of clouds.
 Electric field from cloud induces
movement of electrons upon Earth
Buildings, trees and people can experience
a build up of static charge as electrons are
repelled by the cloud’s bottom.
Anatomy of Lightning
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As static charge buildup increases,
the electric field becomes stronger
Ionization of surrounding air
makes it more conductive
Begins with development of a
step leader. Why zigzag?
Induces a strong positive charge on
earth surface. This charge begins
migrating upward (streamer)
through buildings, trees and people
into the air.
When step leader meets streamer, a
complete conductive pathway is
mapped out and lightning begins.
Lightning Rods
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Pointed metal pole which extends upward above
the building, is attached by a copper cable to a
grounding rod buried in the Earth below.
“leaks off” excess
charges in the
atmosphere, thus
reducing the likelihood
of a sudden and
explosive discharge.
Myths about Lightning
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Never strikes the same place twice
Only strikes very tall objects
Does not strike water
Could be used as a power source
Rubber shoes or boots insulate and protect
against a lightning strike
A metal vehicle is safe because of rubber
tires
“Heat lightning” is a strange phenomenon
caused by hot water or occurs after very hot
summer days and poses no threat.
Lightning victims are electrified
Facts about Lightning
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The average flash could light a 100-Watt light bulb for
more than three months
Chances of being struck are estimated to be 1 in
600,000
Temperature of a flash is 5x hotter than sun’s surface
Can travel over and through the Earth’s surface
~20 million cloud to ground lightning strikes occur in the
US per year
~2,000 thunderstorms active throughout the world at any
given time, producing more than 100 flashes/second
~26,400 lightning-induced fires/year in the US
80% of livestock deaths attributed to lightning strikes
Second largest storm killer in the US (#1 floods)
END OF PRESENTATION
Greenhouse Effect
As heat is reflected back into the atmosphere it is absorbed by greenhouse
Gases. More gases in the atmosphere means more heat is absorbed.