Ch' 12 Meteorology

1
Ch. 12 - Meteorology

• Meteorology the study of the atmosphere
• Meteor is Greek for high in the air.
• Hydormeteors cloud droplets and forms of
  precipitation with water.
• Lithometeors condensation nuclei dust, smoke,
  haze, etc.
• Electrometeors thunder and lightning.
• Weather current state of the atmosphere.
• Climate long-term variations in weather for a
  particular area.
• Usually of 30 years or more.

2

• The Suns radiation does not heat the whole
  surface for its round it relies on the green
  house effect.
• The radiation hits the Earth at angles ranging
  from 0 to 90 degrees.
• The continual motion of air and water reallocates
  heat energy among Earths surface, oceans, and
  atmosphere and brings it into balance.
• At what angle does it heat the Earth the most?
• 90 degrees (direct) ? illustrate
• Some areas around the equator receive close to
  direct radiation at noon all year long.

3

• During what part of the day is it coolest?
• Just before sunrise
• During what part of the day is it hottest?
• 300 to 400 Why?
• Cloudy skies trap the heat clear skies allow it
  to release rapidly
• Which would cause a higher risk of sunburn?
• When is it the warmest time of the year in the
  Northern Hemisphere?
• July 21
• Southern Hemisphere?
• Dec. 21
• What is the coolest time in the N.H.?
• What is the coolest time in the S.H.?
• Illustrate tilt of the Earth

4

• Air Masses - these are huge sections of the lower
  troposphere that have the same kind of weather
  throughout it.
• They usually maintain the same position for days
  or even weeks.
• The weather in an air mass is determined by the
  region it originated in. Cold vs. Warm.
• Warm and dry from continental tropic (cT), warm
  and humid from maritime tropic (mT), cold and dry
  continental polar (cP), cold and humid maritime
  polar (mP), and artic (A).
• Fig. 12.3 (pg. 303) Table 12-1 (pg. 304)

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Weather Systems

• Coriolis effect the air coming from the poles
  moves to the right in the northern hemisphere and
  to the left in the southern hemisphere. This is
  due to the rotation of the Earth.
• Trade winds
• Occurs at 30 North South latitude.
• The air sink, warms and moves toward the equator
  in a westerly direction.
• Causes high pressure
• Prevailing westerlies
• Between 30 60 north and south latitude in
  circulation pattern opposite that of the trade
  winds.
• Blowing from the west to the east
• Responsible for movement of weather across the
  U.S.

6

• Polar easterlies
• Between 60 the poles.
• Similar to the trade winds
• Jet Streams narrow bands of fast,
  high-altitude, westerly winds.
• They strongly influence the temperature and
  pressure on either side of the jet stream.
• This causes wind.
• Polar jets stream Subtropical jet stream fig.
  12-6.
• The deeper it dips or the steeper it rises the
  more influence it has on temperature changes.

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Fronts

• Front is a boundary of different air masses.
• They have different densities due to different
  temperatures, pressure, and humidity.
• They can bring big changes in weather.
• 1. Cold Fronts cold, dense air displaces warm
  air up. As the warm air rises it cools and
  condenses clouds, showers, and sometimes
  thunderstorms.
• 2. Warm Front warm air displaces cold air. The
  warm air develops a gradual frontal slope unlike
  a cold front extensive cloudiness and
  precipitation.
• 3. Stationary Front neither air mass advances
  the other. The boundary stalls seldom have
  extensive cloud and heavy precipitation.
• 4. Occluded Front cold air mass moves so
  rapidly that it overtakes a warm front. The cold
  air wedges the warm air upward. Precipitation is
  common on both sides of the front.

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Pressure System

• Rising air is associated with low pressure and
  sinking air is associated with high pressure.
• High Pressure air sinks and spreads away from the
  center. The deflection of the air to the right
  caused by the Coriolis effect makes the overall
  circulation around a high pressure center move
  clockwise in the northern hemisphere and
  counter-clockwise in the southern hemisphere.
• Cold air masses are associated with high
  pressure.
• Low Pressure air rises and must be replaced by
  air from outside the system so it flows inward.
  The air in a low pressure system turns
  counter-clockwise in the northern hemisphere.

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• It is hard for clouds to form when air sinks.
  Thus, high-pressure systems are usually
  associated with fair weather, while low-pressure
  systems are associated with clouds and
  precipitation.
• A wave cyclone usually begins along a stationary
  front. Some imbalance in temperature, pressure,
  or density causes part of the front to move south
  as the cold front and another part of the front
  to move north as a warm front. This causes a
  counterclockwise rotation.

10
Gathering Weather Data

• A thermometer is the most common weather
  instrument used by meteorologist.
• What measures air pressure?
• Barometer
• At sea level the air pressure is 760 mm or 30 in.
• As air pressure goes up the Hg is forced up in
  its measuring column (mercury barometer)
• An aneroid barometer contains a vacuum inside a
  metal chamber in which the chamber contracts or
  expands with changes in air pressure.

11

• Anemometers are used to measure wind speeds.
• A hygrometer is used to measure relative
  humidity.
• Ceilometers may be used to measure the height of
  cloud layers and amount of cloud cover.
• Data must be gathered at the same time at many
  different location. Why?
• Our Project Globe weather station needs to be
  taken at International time at solar noon, so all
  the data collected internationally has
  consistency.

12

• National weather stations use a radiosonde
  (weather balloon), which has temperature, air
  pressure, and humidity sensors that send back
  readings to the ground station. Tracking the
  balloon in the upper-level provides accurate
  snapshots of atmospheric conditions.
• Doppler Radar wave frequencies change speed
  (energy) as rain winds caused by a thunderstorm
  moves towards or away from the radar station.
• Accurate wind speeds, precipitation, and storm
  intensity can be used by meteorologists.

13
Weather Analysis

• To record weather data for a particular site at a
  particular time a station model is used.
• Fig. 12-15 (pg. 317)
• Isopleths are used to plot nationwide or global
  data. The isopleths are lines that connect
  points of equal or constant values.
• Lines of equal pressure isobars (winds)
• Lines of equal temperature isotherms
• Meteorologist use very sophisticated lab
  equipment, computers, models.
• Meteorologists are very accurate compared to
  about 15-20 years ago.

14

• Digital forecasts are highly dependent on the
  density of the data available.
• An analog forecast is also used to compare
  current weather patterns to past patterns.
• Even high-tech computers cannot predict all
  factors that affect the weather.
• Interpreting a Weather Map (pg. 322).