Transcript Ch. 24 Weather

Weather
Chapter 24
Air Masses
• Differences in air pressure are caused by
unequal heating of Earth’s surface.
• Heated equatorial air rises & creates a
low-pressure belt.
• Cold air near the poles sinks & creates a
high-pressure centers.
• Differences in air pressure creates the
wind patterns
How does air move?
• Moves from areas of high pressure to low
pressure.
• Worldwide movement of surface air from
poles toward equator.
• Temperature & pressure differences give
us the wind belts.
Formation of Air Masses
• Air mass = large body of air throughout
which temperature & moisture content are
similar.
• Air masses over frozen polar regions are
cold & dry; air masses formed over
tropical regions are warm & moist.
Types of Air Masses
•
•
•
•
•
•
4 TYPES:
MARITIME (WET)
CONTINENTAL (DRY)
POLAR (COLD)
TROPICAL (WARM)
Can be different
combinations, example
maritime polar - mP
North American Air Masses
Fronts
• When 2 unlike air masses meet, density
differences usually keep the air masses
separate.
• Cool air mass is dense; doesn’t mix with
less-dense air of a warm air mass.
• A boundary --- known as a front --forms between the air masses.
Types of Fronts
• Cold fronts = the front edge of a moving mass
of cold air that pushes beneath a warmer air
mass
Warm Front
• Front edge of advancing warm air mass
that replaces colder air with warmer air
Stationary & Occluded Fronts
• Stationary = a front of air masses that moves
either very slowly or not at all.
• Occluded = forms when a cold air mass overtakes
a warm air mass & lifts the warm air mass off the
ground & over another air mass.
Symbols Used for Fronts
Weather Instruments
• Weather observations are based on a
variety of measurements including:
atmospheric pressure, humidity,
temperature, wind speed, & precipitation.
Instruments Used to Measure LowerAtmospheric conditions
Thermometer =
measures &
indicates
temperature
Barometers =
measures
atmospheric
pressure
Wind vane = used to determine direction of wind
Anemometer = used to
measure wind speed
Instruments Used to Measure UpperAtmospheric Conditions
• Radiosonde = package of instruments
carried by a balloons to measure temp,
dew point, & wind velocity
• Radar = a system that uses reflected radio
waves to determine velocity & location of
objects
• Weather satellites
• Computers
Forecasting Weather
• Data that is collected by weather stations
are transferred onto weather maps.
• Station model = a pattern of meteorological
symbols that represents the weather at a
particular observing station & that is
recorded on a weather map.
Weather Symbols
Plotting Temperature, Pressure, Fronts &
Precipitation
• Lines that connect points of equal
atmospheric pressure are called isobars.
• Closely spaced isobars indicate a rapid
change in pressure & high winds
• Isobars that form closed circles indicate
centers of high or low air pressure.
(Marked with an H or L).
Isobars