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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 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
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.
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 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 • 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.
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).