Meteorology

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Meteorology

• meteorology study of atmosphere
• 1. weather present state of atmosphere and
  describes current conditions
• a. caused by interaction of air, water, and
  solar energy
• b. variation can take place over minutes,
  hours, days,
• weeks, or months
• 2. climate average of all weather
• conditions of area over
• long period of time

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• energy balance on Earth
• 1. Earth radiates back to space about as much
  energy as it receives over a years time
• 2. sun feels hotter in afternoon due to rays
  striking Earth more directly
• 3. morning and evening rays strike Earth at lower
  angle and energy is spread over larger area
• 4. solar radiation reaching poles is less intense
• 5. tropics and other places maintain fairly
  constant average temperatures due to heat being
  redistributed around the world
• 6. continual motion of air and water reallocate
  heat energy among surface, oceans, and atmosphere

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• air mass large body of air that has same
  properties as region over which it develops
• 1. source region area over which an air mass
  forms
• 2. originate in parts of world where winds are
  light
• 3. can be several thousand kilometers in diameter
  and several kilometers deep
• 4. temperature determined by whether it comes
  from tropics or polar regions
• 5. humidity determined by whether it comes from
  land or sea

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• 6. classified according to source region
• a. c continental (dry)
• b. m maritime (moist)
• c. P polar (cool) high latitudes
• d. T tropical (warm) low latitudes
• e. A arctic
• 7. weather maps use two symbols together to
  describe temperature and humidity
• Ex mT warm moist

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• 8. five major types affect weather in United
  States
• a. mT maritime tropical
• 1) forms over warm waters of Gulf of
  Mexico and tropical North Atlantic Ocean
• 2) holds warm, moist air
• 3) comes into U.S. from Pacific and
  Atlantic oceans and Gulf of Mexico
• 4) summer hot, humid weather,
  thunderstorms, hurricanes
• 5) winter mild, often cloudy weather

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• b. mP maritime polar
• 1) come from cold ocean water (North Pacific
  Ocean)
• 2) holds cold, moist air
• 3) forms over Pacific Ocean in winter and
  summer as well as North Atlantic in summer
• 4) winter rain and snow to Pacific Coast
  summer cool, foggy weather
• 5) maritime polar Atlantic form over North
  Atlantic Ocean
• a) winter cold, cloudy weather and
  precipitation
• b) summer cool weather
• with low clouds and fog
• 6) can produce heavy snow
• and cold temperatures

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• c. cT continental tropical
• 1) form over the deserts of south-western
  U.S. and Mexico
• 2) flow over North America only
• in the summer
• 3) brings in clear, dry and very hot weather
• 4) produces a warm, dry climate
• d. cP continental polar (Canadian)
• 1) forms over interior of Canada and Alaska
  covered by ice
• and snow
• 2) move southeastward across
• Canada and into northern U.S.A.
• 3) brings in cold, dry air (summer)
• 4) during winter can produce
• extremely cold temperatures

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• e. A arctic air
• 1) basically same as continental polar air
  mass, but much colder
• 2) brings most frigid outbreaks of winter
• 3) usually associated with very high pressure
  systems
• 4) develops over latitudes above 60oN in ice
  and snow covered regions of Siberia and Arctic
  Basin
• 5) during winter this region receives almost
  no solar
• radiation but continues to radiate heat
  out to space
• causing it to be very cold area

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• 9. air mass modification occurs when air mass
  starts to gain some of characteristics
  of new surface beneath it
• a. usually an exchange of heat or moisture
  with surface over which air mass travels
• b. modified some as move away from source
  region
• c. eventually modified to have same
  characteristics as new surface it moves over

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• WEATHER SYSTEMS
• Factors responsible for air movement
• 1. Earths surface is curved rather than flat
• a. causes uneven heating in areas around
  world
• b. equator heated more than any other place
  causing air to have low density and rise
• c. poles are cooler so air is more dense and
  sinks and moves along the surface

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• 2. Coriolis effect apparent deflection of
  objects (air) moving across earths surface
• a. caused by an apparent force that results
  from earths
• eastward rotation (to the right)
• b. objects in Northern Hemisphere moving
  south would be
• turned west (deflected right)
• air movement northeast to southwest
• c. objects in Southern Hemisphere are
  deflected to the left
• air movement southeast to
• northwest
• d. combines with global wind systems
• that transport colder air to warmer
• areas and warmer air to colder
• areas

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• 3. convection cells looping pattern of flowing
  air
• a. North and Southern hemisphere each have
  three
• b. form by air rising and sinking at various
  latitudes
• across surface

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• WIND SYSTEMS
• Victor Starr (American meteorologist) designed
  model of major wind systems which suggested that
  major wind patterns were controlled by
  combination of unequal heating and Earths
  rotation
• winds formed by the movement of air from one
  place to another
• 1. caused by differences in temperature and
  pressure
• 2. named for direction from which they blow
  (flow)
• Global winds
• 1. doldrums windless zone at equator (0o
  latitude)
• a. receives much of suns energy
• b. warm air rises producing low pressure area
• c. cooler high pressure air warmed so
• rapidly that winds formed dont reach area
• d. any winds that form are very weak

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• 2. trade winds winds that move from north or
  south toward equator
• a. occur usually at 30oN and 30oS latitudes
• 1) air sink, warms, and moves toward
  equator in westerly direction
• 2) when air reaches equator, it will rise
  again and move back toward 30o latitude where it
  sinks and process starts over
• 3) Northeast trade winds in Northern
  Hemisphere, blow from NE to SW
• 4) Southeast trade winds in Southern
  Hemisphere, blow from SE to NW
• c. 30oN and S latitudes are also called horse
  latitudes
• 1) at times winds become calm stranding ships
  for days or weeks
• 2) those carrying horses began throwing them
• overboard when food supply ran out
• d. convergence
• 1) wind from both hemispheres move together
• from two different directions
• 2) air converges, is forced upward, and
  creates
• area of low pressure
• 3) ITCZ (intertropical convergenence zone)
  large area near
• equator where convergence occurs

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• 3. prevailing westerlies
• a. located between 30o to 60o latitudes
  (north and south)
• 1) circulation pattern opposite of trade
  winds
• 2) surface winds move toward poles in
  generally easterly direction
• b. responsible for movement of weather across
  United
• States and Canada
• c. Northern Hemisphere blow SW to NE
• Southern Hemisphere blow NW to SE
• d. are often particularly strong winds

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• 4. polar easterlies cold, dense, horizontal air
  currents
• a. occurs at the 90o latitudes forcing air up
  at 60o latitudes
• b. have weak winds but provide large amounts
  of energy to
• westerlies
• 1) strongest where flow off Antarctica
• 2) polar front form where easterlies
  meet westerlies producing stormy area
• 3) characterized by cold air
• c. causes changes in weather across United
  States
• d. subpolar lows belt of low air pressure
  at about 60oN and 60oS
• latitude
• e. Northern Hemisphere blow
• NE to SW
• Southern Hemisphere blow
• SE to NW

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• jet streams narrow belts of fast, high
  altitude, westerly winds
• 1. located in upper troposphere and lower
  stratosphere
• 2. strong, high speed, high pressure air
• 3. flow from west to east
• 4. two in each hemisphere
• a. polar jet stream
• 1) separates prevailing westerlies from
  polar easterlies
• (60o latitude)
• 2) altitude of 10-15 km, 100km wide, 2-3
  km thick
• 3) maximum wind speed 500 km/hr
• 4) winds change speed and direction
• 5) control path of storms and
• effect airline routes

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• b. subtropical jet stream
• 1) separates trade winds from prevailing
  westerlies
• (30o latitude)
• 2) warm equatorial air meets cooler air
  of middle latitudes
• 3) do not change much in speed or
  position
• 5. average wind speed range 60 km/h up to 350
  km/h
• 6. tend to wander up and down as they flow around
  Earth
• 7. wind speed, depth, positions in latitude and
  altitude change from season to season or even day
  to day
• 8. large scale weather systems generally follow
  path of these winds

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• LOCAL WINDS
• 1. breezes gentle winds that extend over
  distances of less than 100 km
• 2. sea breezes flow of air from the sea to the
  land
• a. cool, dense air from over the water flows
  inland and
• forces warm air over land up
• b. forms 3-4 hours after sunrise and peaks in
  early
• afternoon
• c. caused by the water being cooler than land
  during the
• day
• d. surrounding area temperature
• may drop by as much as
• 5oC within an hour

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• 3. land breezes flow of air from the land to
  the sea
• a. cool air from land flows over the warmer
  water and pushes
• warm air over sea up
• b. occurs at night because land loses its
  heat to the
• atmosphere while water retains its heat
• c. starts to form in late evening and peaks
  near sunrise

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• 4. valley breeze flow of air up the
• slopes of mountains
• a. occurs during the day
• b. caused by warm air from valleys
• moving up slope
• 5. mountain breeze flow of air from
• mountain peaks to valley
• a. occurs during the night
• b. mountains cool more quickly
• 6. monsoon seasonal winds
• a. part of the year it blows from
• the land to the ocean ? winter
• usually
• b. part of the year it blows from the
• ocean to the land ? summer usually
• c. summer monsoon causes rainy
• season with warm temperatures and
• huge amounts of rain

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• front boundary formed between two air masses
  that have collided
• 1. area where temperatures and humidities change
• 2. greater the difference between air masses,
  greater the change in weather
• 3. can stretch over thousands of km across
  Earths surface
• 4. interaction between colliding air masses can
  cause dramatic changes in weather

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• Four Types of Fronts
• 1. warm front warm air is pushing ahead and
  displacing colder air
• a. lighter warm air slides over heavier cold
  air
• b. presence of high cirrus clouds
• c. stratus clouds form as front continues
• to move into an area
• d. may produce precipitation over a
• large area (rain, snow, sleet, or
  freezing rain)
• e. weather map symbol

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• 2. cold front cold air is advancing and
  displacing warmer air
• a. heavier, cold air is shoving under warm
  air, pushing it
• upward rapidly
• b. cumulus and cumulonimbus clouds form
• c. produces rain and thunderstorms that can
  be violent
• d. squall line long line of heavy
  thunderstorms just ahead of front
• e. fair, cool weather usually follows
• f. weather map symbol

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• 3. stationary front two air masses collide and
  neither can advance the other
• a. front does not move boundary between air
  masses stalls
• b. pressure differences cause warm front or
  cold front to
• stop moving forward
• c. usually remains for several days
• d. widespread clouds can form on both sides
  of frontal
• boundary
• e. light winds and precipitation may occur
  across entire
• frontal region
• f. weather map symbol

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• 4. occluded fronts created when cold, warm, and
  cool air come in conflict
• a. two cooler air masses merge, forcing warm
  air between
• them to rise
• b. often called occlusions
• c. two types
• 1) cold occlusion cold air is shoving
  under cool air at Earths surface
• 2) warm occlusion cool air rises over
  cold air at the surface
• d. usually see strong winds and heavy
  precipitation
• e. weather map symbol

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• 5. polar front boundary where cold polar air
  meets warmer air of middle latitudes
• a. circle between 40o and 60o latitudes N and
  S
• b. winter - average position is across middle
  of U.S.
• c. summer - north of Great Lakes
• d. wave bend formed in a cold or stationary
  front

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• Pressure Systems
• high pressure form when air is cooled
• 1. air molecules more densely packed
• 2. result of cold, dense air that is sinking and
  spreads outward from centers when reach Earth
• 3. warming of air decreases its relative humidity
  and water vapor is evaporated
• 4. Northern Hemisphere ? rotates clockwise
  Southern Hemisphere counterclockwise
• 5. usually means clear weather
• 6. weather map symbol H

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• low pressure form when air is warmed and rises
• 1. molecules farther apart ? less dense ? rises
• 2. rising air must be replaced by air from
  outside system, so net flow is toward center and
  upward
• 3. forms along fronts where warm air meets cold
  air
• 4. Northern hemisphere counterclockwise
  Southern hemisphere clockwise
• 5. cause most of weather changes across United
  States
• 6. associated with clouds and precipitation
• 7. weather map symbol L

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• 8. wave cyclone specific type of low pressure
  system
• a. main producers of inclement weather in
  middle latitudes
• b. usually begins along stationary front
• c. part of front moves south as cold front
  and another part
• moves north as warm front
• d. sets up counterclockwise circulation
• Air moves from an area of high pressure to one
  of low pressure.

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• GATHERING WEATHER DATA
• thermometer used to measure temperature
• 1. bimetal thermometer bar made of two strips
  of different types of metals
• a. curve when heat
• b. straighten when cooled
• 2. thermograph measures temperature change by
  recording movement of bar
• 3. electrical thermometer
• a. as temperature rises, electric current
  flow increases
• b. current flow translated into temperature
  readings

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• barometer instrument measures atmospheric
  pressure
• 1. mercurial barometer uses mercury to
  determine atmospheric pressure
• a. pressure presses on liquid Hg in well at
  base
• b. squeezes Hg up to certain height in tube
• c. height varies with pressure
• d. expressed by how high Hg rises in tube
• e. standard atmospheric pressure 760 mm
• 1) indicates average atmospheric pressure
  at sea level
• 2) 760 mm or 29.92 inches of Hg
• one atmosphere
• f. millibars(mb)) - used on weather maps
• 1 mb 0.001 standard
• atmospheric pressure

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• 2. aneroid barometer works without liquid
• a. most common type used today
• b. seal metal container from which air has
  been removed
• 1) pressure decreases ? sides bulge out
• 2) pressure increases ? sides bend inward
• c. shown by pointer on a scale
• d. usually marked in mm (inches of Hg) or mb
• e. altimeter barometer used to measure
  altitude above sea level
• 1) lowered pressure reading interpreted
• as increased altitude
• 2) must be corrected for local weather
• conditions to be accurate

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• anemometer used to measure wind speed
• 1. expressed as meters/second, miles/hour, or
  knots
• 2. one knot 1850 m/s
• wind vane used to determine the direction of
  the wind on Earths surface
• points into the wind

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• hygrometers used to measure relative humidity
• 1. psychrometer works on principle that
  evaporation causes cooling
• a. wet bulb thermometer has a water soaked
  wick wrapped around its bulb
• b. other is a dry bulb thermometer
• c. wet bulb usually shows a lower temperature
• d. readings give signs of how dry the air is
• e. difference between wet bulb and dry bulb
  is used to determine RH by using a chart
• f. when both thermometers read the same the
  air is saturated

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• 2. hair hygrometer based on principle that
  human hair stretches when it is humid
• a. one end of a bundle of hair is fixed while
  
• the other is attached to pointer
• b. when air is humid ? stretches when air is
  dry ? shrinks back

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• Measuring Precipitation
• 1. rain gauge measure amount of rainfall
• a. measure in inches
• b. measure only precipitation that falls in
  one spot
• c. represents depth of water that rain would
  leave
• if it did not soak into ground, flow away,
  or evaporate
• d. types vary
• 1) wide mouth funnel over cylindrical
  container
• 2) funnel and small divided bucket
• 3) water caught in large bucket and
  weighed continuously

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• 2. measuring stick measure amount of snowfall
• a. snow is measure by both depth of
  accumulation and
• water content
• b. measured in inches and tenths of an inch
• c. on average, 10 inches of snow equals 1
  inch of rain
• d. dry snows are deeper than equal weights of
  wet snow

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• Automated Surface Observing System (ASOS)
  collects multiple data at regular intervals
• 1. ceilometer measures height of cloud layers
  and estimates amount of sky covered by clouds
• 2. continuously record air pressure, temperature,
  wind speed and direction, runway visibility,
  cloud ceiling, and precipitation intensity
• 3. many units being used at major airports

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• Upper Level Data
• 1. radiosonde balloon borne package of sensors
• for measuring at high altitudes
• a. measure temperature, air pressure, and
  humidity
• b. readings sent back by radio signal to
  ground station that tracks movement of balloon
• c. can determine wind speed and direction by
  tracking how
• fast and in what direction balloon is
  moving

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• 2. weather radar used to locate areas of rain
• a. waves are reflected from precipitation
  particles
• b. screen shows location and shape of
  precipitation areas
• c. also gives a rough idea of how heavy
  precipitation is

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• 3. Doppler radar used to determine movement of
  weather system
• a. provides good estimates of wind speeds in
• precipitation areas
• b. show echoes with more detail
• c. can also show wind direction
• d. echoes and winds show up on color screen
• 1) different echo strengths or wind
  speeds show up as different colors
• 2) makes it easier to spot strong
  thunderstorms and even tornadoes

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• 4. weather satellites observes weather that is
  missing by computer models and local weather
  
• a. observations track clouds but not
  necessarily precipitation
• b. provides continuous pictures of clouds
• c. make it possible to track lows,
  hurricanes, and thunderstorms
• d. can see nearly half of Earths surface
• e. every 30 minutes its television cameras
  take infrared as well as visible pictures

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• WEAHTER ANALYSIS/ FORECASTING
• forecast prediction of future weather
  conditions
• - most are made for periods of a few hours up to
  5 days
• meteorologist person who studies weather
• 1. make measurements of temperature, air
  pressure, winds, humidity, and precipitation
• 2. gather data using radar, computers, and
  instruments attached to balloons
• 3. interpret information from local weather
  observers, balloons, satellites, and weather
  stations around world

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• weather map collection of weather data from
  many collecting stations
• surface weather map essential in following
  rapidly changing weather or in compensating for
  poor computer model forecasts
• 1. data is taken hourly at stations all over the
  world
• 2. United States has about 700 National Weather
  Service stations
• 3. official U.S. weather maps are made every 3
  hours (made at the National Meteorological Center
  in Camp Springs, Maryland)

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• station model symbol that describes local
  weather of collecting station
• 1. where possible direct readings are given
• 2. in other cases, codes are used
• 3. models and codes are determined
• by World Meteorological Organization
• 4. show various measurements
• a. wind direction and speed
• 1) shown by a line attached to circle
• 2) direction line points is from
• which wind is blowing
• 3) small lines at end of the line are
• used to indicated wind speed
• b. cloud cover shown by circle
• c. other data includes atmospheric pressure,
  temperature,
• dew point, types of precipitation, types
  of clouds, and
• change in barometric pressure

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• isopleths lines that connect points of equal or
  constant values
• 1. can represent different weather variables
• 2. isotherm lines that connect locations with
  same temperature on weather map
• - number on end of line indicates temperature at
  all points along line

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• 3. isobars lines that connect locations with
  the same air pressure on a weather map
• a. number at end of line represents air
  pressure at each location on line
• b. can be given in millibars or inches of
  mercury
• c. indicates the locations of highs or lows
• d. if close together ? great pressure
  difference over small area ? strong winds
• e. if spread apart ? less difference ? gentle
  winds

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• TYPES OF FORECASTS
• SHORT-TERM
• 1. daily predict weather conditions for 48
  hour period
• 2. digital forecasting relies on numerical data
  from computer calculations
• a. main method used by modern meteorologists
• b. highly dependent on density of data
  available (more data, more accurate forecast)
• 3. most accurate and detailed forecasts can be
  made for 3 to 5 days
• 4. accuracy decreases with each additional day

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• LONG-TERM
• 1. long-range cover monthly and seasonal
  outlooks
• 2. extended up to 6 to 10 days
• 3. analog forecasts compares current weather
  patterns to patterns that took place in
  past
• a. uses assumption that weather systems
  behave in similar fashion
• b. also look for patterns that are analogous
  to current patterns
• c. to be accurate past event must be similar
  through all levels of atmosphere and over large
  area
• d. used for monthly or seasonal forecasts
• 4. computer model copy of atmosphere in
  computer
• a. contains data on wind, temperature,
  pressure, humidity, clouds, and precipitation
• b. can predict future weather patterns
• 5. now better than human forecasters at
  predicting movements and strengths of highs and
  lows