Chapter 7
Weather
A local area’s short-term temperature, precipitation, humidity, wind speed, cloud cover, and other physical conditions of the lower atmosphere as measured over days or hours
Climate
An area’s general pattern of atmospheric or weather conditions measured over long periods of time ranging from decades to thousands of years
Climate varies in different parts of the earth mostly because…
patterns of global air circulation and ocean currents redistribute heat and precipiatation unevenly
Three major factors determine how air circulates in the lower atmosphere (which helps to distribute heat and moisture from the tropics to other parts of the world):
Uneven heating of the earth’s surface by the sun
Rotation of the earth on its axis
Properties of air, water, and land
Cause of prevailing winds
As the earth rotates on its axis, its equator spins faster than its polar regions. As a result, heated air masses rising above the equator and moving north and south to cooler areas are deflected east or west over different parts of the planet’s surface. The atmosphere over these different areas is divided into huge regions called cells, distinguished by direction of air movement. And the differing directions of air movement are called prevailing winds-major surface winds that blow almost continuously and help distribute air, heat, and moisture
Currents
Prevailing winds blowing over the oceans produce mass movements of surface water
Greenhouse effect
Natural warming effect of the troposphere
As the warming intensifies during this century,
climate scientists expect it to alter precipitation patterns, shift areas where we can grow crops, and shift habitats for some types of plants and animals.
Heat is absorbed and released more slowly
by water than by land
Rain shadow effect
Low precipitation on the leeward side of a mountain when prevailing winds flow up and over a high mountain or range of high mountains, creating semiarid and arid conditions on the leeward side of a high mountain
Biomes
Large terrestrial regions characterized by similar climate, soil, plants, and animals, regardless of where they are found in the world
Desert
annual precipitation is low and often scattered unevenly throughout the year. During the day, the sun warms the ground and causes evaporation of moisture from plant leaves and soil. But at night, most of the heat stored in the ground radiates quickly into the atmosphere. Their soils have little vegetation and moisture to help store heat, and the skies above deserts are usually clear.
Tropical deserts
Hot and dry most of the year. They have few plants and a hard, windblown surface strewn with rocks and some sand.
Temperate deserts
Daytime temperatures are high in summer and low in winter and there is more precipitation than in tropical deserts. Temperate desert plants include drought-resistant shrubs and cacti or other succulents adapted to the lack of water and temperature variations.
Cold deserts
Winters are cold, summers are warm or hot, and precipitation is low. Vegetation is sparse, typically.
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