Measuring Air Temperature 1. THERMOMETER- liquid in thermometer heats up, expands into tube (moves up) 2. Water freezes 0º C and 32º F Water boils 100º C and 212º F
ISOTHERMS Isotherm- line drawn on a map connecting places with SAME TEMPERATURE ISOBARS Isobar- line drawn on a map connecting places with the SAME PRESSURE
Air Pressure • The weight of the atmosphere per unit area. • Directed equally in all directions.
Measuring Air Pressure • Barometer: the instrument used to measure air pressure. • Two Kinds: • Mercury & Aneroid
Mercury Barometer • An increase in air pressure raises the mercury inside the vacuum. • A decrease in air pressure drops the mercury.
Aneroid Barometer • A tin can with most of the air removed from within. • The can changes shape with changes in pressure.
Units of Pressure • Centimeters or inches for a Mercury Barometer. • Standard sea-level air pressure = 29.92 in, 76 cm. • Millibar: metric unit of pressure. • Standard sea-level air pressure = 1,013.2 millibars.
Temperature Changes Air Pressure • Warm air = Lighter = Rises • Cool air = Heavier = Sinks • Warm air rises and cool air comes in to take its place.
Humidity Changes Air Pressure • The more water vapor, the lower the air pressure. • Water vapor is lighter than the nitrogen and oxygen found in the atmosphere. • Lighter gases above = less pressure pushing down from the atmosphere.
What Makes the Wind Blow? • Wind moves from high pressure to low pressure. • Land heats up the air above. • Lowers the air pressure. • High-pressure cool air comes in to take its place. • The steeper the gradient, the stronger the winds.
Local Winds • Sea Breeze • During the day. • Warm air rises from land. • Cool air from sea takes the warm air’s place.
Local Winds • Land Breeze • During the evening. • Warm air rises from sea. • Cool air from land takes the warm air’s place.