CHAPTER 2 Focus Points
2.1 The Four Seasons
Cause of seasons: The tilt of Earth’s axis causes the subsolar point to migrate between the Tropic of Cancer and the Tropic of Capricorn, causing seasons.
Solar altitude: The solar altitude determines the intensity of sunlight.
Equinox day length: On the equinoxes, all locations on Earth experience 12 hours of day and 12 hours of night.
Solstice day length: On the June solstice, day length increases northward and decreases southward. The reverse is true for the December solstice.
2.2 Temperature and Heat
Heat transfer: Heat is transferred through conduction, convection, and radiation.
Heat: In conduction, heat always travels from objects of higher temperature to objects of lower temperature.
2.3 Surface Temperature Patterns
Average annual temperature: The average annual temperature decreases at higher elevations and at higher latitudes.
Annual temperature range: The annual temperature range increases at high latitudes and interior continental locations.
Ocean currents: Warm ocean currents from low latitudes raise the average annual temperature and reduce the annual temperature range.
Midlatitude coastal patterns: At midlatitude locations, the west coasts of continents have maritime climates, and the east coasts of continents have continental climates.
2.4 The Sun’s Radiant Energy
Electromagnetic radiation: Electromagnetic radiation is emitted by all objects, and it travels in waves.
The Sun’s emissions: Because of its high temperature, the Sun emits mostly shortwave radiation, most of it in visible wavelengths.
Earth’s emissions: Earth mainly emits longwave infrared radiation because of the planet’s relatively low temperature.
2.5 Earth’s Energy Budget
Insolation: Incoming solar radiation can be transmitted, scattered, reflected, or absorbed.
Albedo: The albedo of Earth as a whole is 30%. Seventy percent of insolation is absorbed.
Absorption: Most absorbed solar radiation is converted to heat and warms Earth’s surface and atmosphere.
Radiative equilibrium temperature: Earth’s radiative equilibrium temperature is a result of the balance between incoming solar and outgoing terrestrial radiation.
Greenhouse effect: The greenhouse effect warms the atmosphere.
Global heat engine: There is a net surplus of heat between 37° latitude north and south, and a net deficit of heat at higher latitudes. These heating inequalities drive Earth’s global climate engine.
2.6 Geographic Perspectives: The Rising Solar Economy
The Sun as an energy resource: The Sun provides Earth with enormous amounts of renewable energy.
Approaches to capturing sunlight: Capturing sunlight and converting it to electricity can be done by decentralized and centralized means.
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