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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.

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Weather

Weather

Chapter 24


Air masses

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

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

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

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

North American Air Masses


Fronts

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

Types of Fronts

  • Cold fronts = the front edge of a moving mass of cold air that pushes beneath a warmer air mass


Warm front

Warm Front

  • Front edge of advancing warm air mass that replaces colder air with warmer air


Stationary occluded fronts

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

Symbols Used for Fronts


Weather instruments

Weather Instruments

  • Weather observations are based on a variety of measurements including: atmospheric pressure, humidity, temperature, wind speed, & precipitation.


Instruments used to measure lower atmospheric conditions

Instruments Used to Measure Lower-Atmospheric conditions

Barometers = measures atmospheric pressure

Thermometer = measures & indicates temperature

Wind vane = used to determine direction of wind

Anemometer = used to

measure wind speed


Instruments used to measure upper atmospheric conditions

Instruments Used to Measure Upper-Atmospheric 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

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

Weather Symbols


Plotting temperature pressure fronts precipitation

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).


Weather

Isobars


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