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Air Pressure and Wind Air Pressure and Wind • • • • • • • What Is Air Pressure? Measuring Air Pressure Wind High and Low Pressure Atmospheric Circulation Global Precipitation Patterns El Niño and La Niña Terms • Climate belt – Zone of latitude characterized by certain climate conditions – Tropics – Subtropics – Temperate (mid-latitude) – Subpolar – Polar Earth’s Climate Belts boundaries are approximate POLAR: 75-90 SUBPOLAR: 60-75 TEMPERATE: 35-60 SUBTROPICAL: 25-35 TROPICAL: 0-25 SUBTROPICAL TEMPERATE SUBPOLAR POLAR PSCI 131: Air Pressure & Wind What Is Air Pressure? PSCI 131: Air Pressure & Wind What Is Air Pressure? • Force exerted by air’s weight • Equal in all directions • 14.7 pounds per square inch at sea level PSCI 131: Air Pressure & Wind What Is Air Pressure? • Human body is at equilibrium with surrounding air pressure • So, we don’t feel it unless outside pressure changes quickly Rapid air pressure drop can cause “frothy blood” in the lungs as blood gases expand (pulmonary edema). PSCI 131: Air Pressure & Wind Measuring Air Pressure PSCI 131: Air Pressure & Wind: Measuring Air Pressure Mercury Barometers PSCI 131: Air Pressure & Wind: Measuring Air Pressure Aneroid Barometers Aneroid: “no liquid” PSCI 131: Air Pressure & Wind Wind PSCI 131: Air Pressure & Wind: Wind The Power of Wind • Front-row view of massive tornado • Tornado destroys school PSCI 131: Air Pressure & Wind: Wind Dorothy: new tornado-chase vehicle Article on Dorothy PSCI 131: Air Pressure & Wind: Wind Factors Affecting Wind • Wind moves from higher to lower pressure PSCI 131: Air Pressure & Wind: Wind Factors Affecting Wind • Pressure-gradient force – Difference in pressure between high and low – Greater difference = stronger wind PSCI 131: Air Pressure & Wind: Wind Factors Affecting Wind • Pressure-gradient force PSCI 131: Air Pressure & Wind: Wind Factors Affecting Wind • Coriolis Effect – Apparent deflection of wind – Caused by Earth’s rotation PSCI 131: Air Pressure & Wind: Wind Factors Affecting Wind: Coriolis Effect Non-rotating Earth: Rotating Earth: Coriolis animations PSCI 131: Air Pressure & Wind: Wind Factors Affecting Wind: Surface Friction PSCI 131: Air Pressure & Wind High and Low Pressure PSCI 131: Air Pressure & Wind High and Low Pressure Cells • High – Sinking air – Divergence – Fair weather • Low – Rising air – Convergence – “Foul” weather PSCI 131: Air Pressure & Wind: High and Low Pressure Cyclones & Anticyclones • Winds rotating around high and low pressure cells • Rotation caused by Coriolis Effect CYCLONE ANTICYCLONE PSCI 131: Air Pressure & Wind: High and Low Pressure Cyclones & Anticyclones: Rotation Direction Cyclone Anticyclone Northern Hemisphere CCW CW Southern Hemisphere CW CCW PSCI 131: Air Pressure & Wind: High and Low Pressure Cyclones & Anticyclones: Rotation Direction Two cyclones: which is in the northern hemisphere, and which in the southern? Tropical cyclone news clip with mistake PSCI 131: Air Pressure & Wind: High and Low Pressure High- and Low-Pressure Weather • Low pressure – Condensation, clouds, rain, storms • High pressure – Clear, dry – Possibly hot (adiabatic heating of sinking air) PSCI 131: Air Pressure & Wind: High and Low Pressure High- and Low-Pressure Weather Cyclone Yasi, Australia, 2011. Arrows indicate air movement. Since this is a cyclone in the southern hemisphere, it is rotating clockwise. PSCI 131: Air Pressure & Wind: High and Low Pressure High Pressure: Clear skies, dry air PSCI 131: Air Pressure & Wind Atmospheric Circulation PSCI 131: Air Pressure & Wind: Atmospheric Circulation Heat Energy Transfer • From tropics to poles – Convection cells • Part of heat-balance system • Includes ocean currents, tropical storms, hurricanes PSCI 131: Air Pressure & Wind: Atmospheric Circulation Heat Energy Transfer • Complicated by Earth’s rotation – Coriolis Effect – Frictional drag – Causes breakup of idealized convection cells PSCI 131: Air Pressure & Wind: Atmospheric Circulation Circulation if Earth didn’t rotate: PSCI 131: Air Pressure & Wind: Atmospheric Circulation Circulation on rotating Earth Hadley cells Equatorial low Subtropical high Subpolar low Trade winds Westerlies Polar easterlies PSCI 131: Air Pressure & Wind: Atmospheric Circulation Highlights PSCI 131: Air Pressure & Wind Global Precipitation Patterns
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