Transcript Meteorology Notes

• How do meteorologists study and predict
weather?
• How does the movement of air masses affect
weather?
• How do clouds and rain form?
• Weather = The state of the atmosphere at a
specific time and place
• What is meteorology?
▫ The study of patterns of weather
• What does a meteorologist do?
▫ A specialist who studies processes in the
earth's atmosphere that cause weather
conditions.
• What tools and technology are used in weather
forecasting?
• Thermometers measure air
temperatures.
• Temperature is a measure of how much
heat energy the air molecules possess
• Thermometers work because matter
expands when heated. Most
thermometers are closed glass tubes
containing liquids such as alcohol.
• A barometer measures air pressure.
• There are two types of Barometers:
Mercury and Aneroid.
• Average reading: 29.92 inches
▫ Increasing = sunny
▫ Decreasing = possible storm
• A Mercury Barometer consists of a
glass tube inserted into a dish of
mercury or colored denatured alcohol.
• The surrounding air presses down on
the mercury in the dish and forces
some of the mercury up into the tube.
• The height to which the mercury rises
gives a reading of atmospheric
pressure.
 Used to gather and
measure the amount
of liquid precipitation
over a set period of
time
Most rain gauges
generally measure the
precipitation in
millimeters
• A psychrometer measures the
humidity of the air. One of the two
thermometers has a wick (cloth
cover) which is dipped in water.
• Evaporation of water from the wick
leads to cooling.
• The temperature difference
between the two thermometers gives
the relative humidity of the air
Difference
Air Temp
Humidity (%)
This is an
example
of the
type of
table you
would
use.
• When air moves— “wind”—we feel both its
direction and speed (force.)
• Direction is measured with a “vane”—an
arrow or other shape that points into the wind.
• Speed is measured with an “anemometer.”
The faster the cups spin, the faster the wind.
Anemometer
Vane
• The Forecast Radar
image shows
where area of
precipitation are
expected to be.
• Colors show the
strength and
physical phase of
water
• To measure weather above the surface, the
National Weather Service (NWS) releases weather
balloons with an attached instrument package
called a “radiosonde.”
• Radiosondes contain:
▫ Temperature sensor
▫ Relative humidity sensor
▫ Barometer
▫ Radio transmitter
▫ Battery
▫ Parachute
▫ String to attach to balloon
Weather balloons are launched twice a day
• At 6 a.m. and 6 p.m.
• Ground antennas
receive the radioed
signals as the balloon
rises
• Computers interpret
the signals and send
them to the NWS network
Air rises near
ow Pressure Areas
• Warm, rising air cools; water vapor in the
air condenses to form clouds/precipitation
• Tend to bring cloudy, wet weather
Air sinks near
igh Pressure Areas
• Cool, sinking air warms and dries out.
• Tend to bring fair, dry weather.
Actual winds around highs and lows
• Air masses have different temperatures and
humidity
• Form over water:
▫ Maritime Polar – cool temperature; moist air
▫ Maritime Tropical – warm temperature; moist
air
• Form over land:
▫ Continental Polar – Cool temperature; dry air
▫ Continental Tropical – Warm temperature; dry
air
• Colliding fronts cause
cloud development
and weather changes
Cold Front
Colder
Warmer
Colder
Warmer
Cold air advances
Warm Front
Warm air
advances
Colder
Warmer
Stationary Front
• Occluded Front =
▫ When a fast moving
cold front catches and
overtakes a slower
moving warm front
• Stationary Front =
▫ When cold and warm fronts meet and neither is
strong enough to push the other; front stops
moving
Jet Streams
• Jet Stream
▫ Narrow bands of wind in
the upper atmosphere
▫ The Jet stream always
blows from west to east
across the U.S.