Chapter 6 Biogeography: Climate, Biomes, and Terrestrial Biodiversity

Major Themes of the Chapter Different climates occur as a result of currents of air and water flowing over an unevenly heated planet spinning on a tilted axis. Different climates result in different communities of organisms, or biomes. A general climate map can be drawn based on broad patterns of temp. and precipitation

Convection Currents

Hadley Cells Warm, humid air at equator rises. Reaches saturation point and cools (forms clouds) as it moves away from equator. Around 30 o the cool dry air sinks. Adiabatic Heating: Air sinks, which increases pressure. The increase in pressure leads to decrease in volume, ultimately increasing temperature and decreasing pressure, causing the air to rise. Cooling is the opposite

Polar Cells  Cold air at poles descends  Air moves along Earth’s surface to about 60 o, where it warms and rises.  The warm air cools and condenses forming clouds.  Air moves toward pole, where it gets colder and sinks once again

Ferrell Cells Due to being sandwiched between the Hadley and Polar cells

Latent Heat Release Sun energy evaporates water on Earth’s surface and creates water vapor Reverse: Water vapor in air condenses into liquid and gives off heat. Whenever water vapor condenses the air gets warmer and rises

Weather The state of the air at a particular time and place. Caused by the uneven heat distribution. Properties such as temperature, pressure, humidity, precipitation, sunshine, cloud cover and wind direction/speed

Weather Masses of air that are warm or cold, wet or dry, and contain air at high or low pressure constantly move across the land. Weather changes as one air mass replaces or meets another Cold air is heavier than warm air and therefore warm air is pushed upwards. This causes wind Wet air is lighter than dry air and therefore moves above dry air. Why is wet air lighter Video

Fronts The most dramatic changes in weather occur along a front, the boundary between two air masses with different temperatures and densities.

Cold Front Cold air is denser than warm air, so an advancing cold front stays close to the ground. It produces rapidly moving, towering clouds called thunderheads. The overlying mass of warm air is pushed upward, forming large, heavy droplets. When cold fronts pass, they produce high surface winds and thunderstorms.

Warm Front A warm front is the boundary between an advancing warm air mass and the cooler one it’s replacing. As warm air rises, moisture condenses to form layers of clouds. This can bring days of cloudy skies and drizzle.

High Pressure System Contains cool, dense air that descends toward the Earth’s surface and becomes warmer. Fair weather follows as long as the high pressure air mass remains over the area

Low Pressure System Low pressure/low density warm air spirals in and up. As it rises, it cools, condenses and forms clouds. This can produce stormy weather

Weather Extremes Tornadoes: rotating column of air that forms over land Tropical Cyclones: rotating storm system that typically forms over large bodies of warm water. Forming in Atlantic Ocean = Hurricane Forming in Pacific Ocean = Typhoon