Transcript Weather 2011

Weather
Definition
 The result of the atmosphere trying
to balance temperature and humidity
The State of the
Atmosphere
 Air Pressure
 Wind
 Temperature
 Amount of moisture in the air
Water Vapor
 Water in air is in the form of a gas called
water vapor
 Water is also found in the atmosphere as
clouds and fog
 Estimated total of 14 million tons in the
atmosphere
Evaporation
 Changing of a liquid to a gas
 Most evaporation occurs in oceans
 Water also evaporates over lakes, rivers,
puddles, and wet soil
 Winds carry the water vapor
Transpiration
 Water vapor changing back into liquid
water droplets
 Example: Breathing (seeing your breath)
 Plants give off water vapor through
leaves
Role of Water Vapor
 Humidity: amount of water in the air
Is dependent on temperature
 Increase in temp results in an increase in
humidity
 Decrease in temp results in a decrease in
humidity
 When air is saturated it holds all the water vapor
possible at that temperature
 Figure 12-7 pg. 280
Water Vapor Continued
 Relative Humidity: amount of water vapor
air holds compared to what it can hold at a
specific temperature.
 Capacity is 100%, but usually water vapor
may be 50%
 Humidity increases as temperature
increases
 Humidity and comfort- Figure 12-11 pg. 283
Dew Point
 Temperature of air at which condensation
takes place
 Condensation- process of changing a
gas to a liquid
 This takes place when saturated air is
cooled
Dew Point
 Warm air holds more water vapor
 Cold air holds less water vapor
 Water vapor condenses, changes into
liquid water
 Ground cools faster, so condensation
takes place causing dew
Dew Point
Clouds
 Visible formations of small droplets
of water or tiny crystals of ice.
 Form from condensation in the
atmosphere
 Shape determined by how it formed
Steps to Cloud Formation
1. Air ascends (goes up)
2. Pressure decreases and
temperature increases.
3. Air parcel cools to the dew pt.
temperature.
4. Water condenses around small
particles of dust, salt, and smoke.
Types of Clouds
 Classified:
 Height
 Form
Height Classification
• Cirrus - high clouds, generally don’t
produce precipitation.
• Alto - middle clouds, grayish clouds,
infrequent precipitation.
• Strato - low clouds, uniform layer
covering much of the sky.
Cloud Forms
• Cumulus - puffy, white, cauliflowerlike
• Stratus - sheets or layers
• Cirrus - high, white, thin, feathery
• Fair weather, with storm
approaching
Stratus
Cirrus
Cumulus
Combinations
 Cirrostratus - indicates fair weather with rain in
the forecast
 Altostratus - produces intermittent precipitation.
 Cumulus – fair weather
 Cumulonimbus - heavy precipitation, lightning,
thunder, hail
 dark, dense, billowy
 looks like huge towers with an anvil shape
Cirrostratus
Altostratus
Cumulus
Cumulonimbus
Precipitation
 Conditions in the atmosphere vary from
season to season
 Precipitation is water that falls to Earth
from clouds
 May be a liquid or solid
Precipitation
 Snow – falls when temperatures are
below freezing
 Rain – falls when temps are above
freezing
 Sleet – snow falls through a layer of
warm air, melts and refreezes
 Hail – freezes in layers around a particle
of ice during thunderstorms
Effect of Cloud Cover
 Clear skies - more heat reach’s earth’s
surface leading to warmer temperatures.
 Cloudy skies – sun reflected off clouds so
less sun reaches earth’s surface leading
to cooler temperatures.
Night Cloud Cover
 Clear skies – heat from earth travels
freely back to space resulting in cooler
temperatures.
 Cloudy skies – surface heat is trapped
resulting in warmer temperatures.
Air Mass
 Large body of air that has the same
properties as the surface over which it
develops.
 Consists of the same temperature and
same amount of moisture
 Air masses are dependent on where they
form
Types of Air Masses
 P (polar)-cold
 A (arctic)-coldest
 m (maritime)-moist
 T (tropical)-warm
 E (equatorial)-warmest
 c (continental)-dry
Potential Air Masses
 cA – continental arctic
 cP – continental polar
 cT – continental tropical
 mP – maritime polar
 mT – maritime tropical
Fronts
 Boundary between two masses
 Identifies the leading edge of an
advancing air mass
 Cloudy and stormy
 Travel east to west
 Usually bring changes in weather
Warm Front
 When a warm air mass advances on a
cold air mass




Drizzly precipitation
Cirrus, cirrostratus, altostratus, stratus
After front passes temperatures warm-up
Slow clearing and warmer temperatures
show that front has passed
Warm Front
Cold Front
 When a cold air mass advances on a
warm air mass
 Fast moving, produces thunderstorms,
heavy rain, or snow
 Altocumulus, cumulonimbus
 After front passes temperatures drop
 Gusty winds are formed due to air
pressure differences
Cold Front
Stationary Front
 When neither a cold or warm air mass is
advancing
 Brings very little change in the weather
Occluded Front
 When advancing cold front takes over a
warm front and pushes warm air up.
 Cool temperatures and lots of precipitation
 Cloudy, rainy, or snowy
Front Symbols
Severe Weather
 Thunderstorms with possible: hail, heavy
rain, high winds etc
 Tornadoes
 Hurricanes
 Snow storms
Thunderstorms
 Forms in warm, moist air masses or at
cold fronts
 Atmosphere unstable
 16 million occur each year worldwide
 Results from cumulonimbus clouds
Accompanies T-Storms
 Heavy rainfall – drops collide with others
and grow larger
 Electrically active
 Thunder and lightning superheat,
surrounding air (50,000 degrees F) air
expands producing sound waves
Tornadoes
 Violent whirling wind moving over land
from SW to NE
 Produces by severe thunderstorms
 1% of storms
 Differences in wind direction and speed
create wind shear. When wind shear is
tilted, rotation is produced.
 Can reach speed of 500 km/hr
Tornadoes Continued
 Nearly 800 reported annually
 75% of all occur in the US in the spring
and early summer
 Tornado alley: TX, OK, KS, NE
 Fugi intensity scale: F0 least damage, F5
most damage
Hurricanes
 Large swirling, low pressure system that
forms over tropical oceans
 Wind speeds of at least 119 km/hr
 Stages of development




Tropical disturbance
Tropical depression
Tropical storm
Hurricane
Hurricane Risks
 Storm surge causes 90% of deaths
 Heavy winds and low atmospheric
pressure build up over ocean
 Wall of water 1-8 m high and 65-160 km
long
 Inland flooding
Summary
 Clouds
 Forms and heights
 Air Masses
 Classification
 Fronts
 Cold, warm, stationary, occluded
 Sever Weather
 Tornadoes, hurricanes. thunderstorms, etc.
Sources
 http://www.ucar.edu/learn/index.htm
 http://ww2010.atmos.uiuc.edu/(Gh)/home
.rxml
 http://vathena.arc.nasa.gov/curric/weathe
r/hsweathr/index.html
 http://www.atmos.uiuc.edu/earths_atmos
phere/wind.html
 http://eo.ucar.edu/