Solar Energy and the Atmosphere

Earth-Sun Relationships Earth’s Motions Earth has two principal motions—rotation and revolution Earth’s Orientation (tilt) Seasonal changes occur because Earth’s position relative to the sun continually changes as it travels along its orbit

Energy Transfer as Heat Three mechanisms of energy transfer: Conduction is the transfer of heat through matter by molecular activity Convection is the transfer of heat by circulation within a substance. Radiation is the transfer of energy (heat) through space by electromagnetic waves that travel out in all directions

What Happens to Solar Radiation? Scattering: Scattering: – Clouds, dust and gas reflect and bend light rays; light rays are sent out in all directions – Causes sky to appear blue (blue light is more easily bent) – Sunsets appear red because longer wavelengths (red) are able to reach the surface (we are looking through more atmosphere on the horizon)

What Happens to Solar Radiation? Reflection: Reflection: – 20% of solar radiation is absorbed by the atmosphere – 50% is absorbed by the surface – 30% is reflected back into space – Albedo: fraction of solar radiation that is reflected back into space. – Earth’s albedo is 0.3

What Happens to Solar Radiation? Absorption & Infrared Energy: As the surface absorbs radiation, it heats up and releases IR radiation IR radiation is trapped by water vapor and CO 2 in the atmosphere greenhouse effect This process is called the greenhouse effect

What Happens to Solar Radiation? Why Temperatures Vary Factors include: latitude heating of land and water, altitude geographic position cloud cover ocean currents

Fig. 7-7, p. 145 Prevailing winds pick up moisture from an ocean. On the windward side of a mountain range, air rises, cools, and releases moisture. On the leeward side of the mountain range, air descends, warms, and releases little moisture.

Latitude Tropical Forest Deciduous Forest Coniferous Forest Tundra (herbs, lichens, mosses) Polar ice and snow Fig. 7-9, p. 147 Elevation Mountain ice and snow Tundra (herbs, lichens, mosses) Coniferous Forest Deciduous Forest Tropical Forest Stepped Art

Factors Affecting Wind Wind is the result of horizontal differences in air pressure. Air flows from areas of higher pressure to areas of lower pressure The unequal heating of Earth’s surface generates pressure differences Three factors combine to control wind: pressure differences, the Coriolis effect, and friction

Factors Affecting Wind Pressure Differences A pressure gradient is the amount of pressure change occurring over a given distance Isobars are lines on a map that connect places of equal air pressure Closely spaced isobars indicate a steep pressure gradient and high winds

Factors Affecting Wind Coriolis Effect The Coriolis effect describes how Earth’s rotation affects moving objects. In the Northern Hemisphere, all free-moving objects or fluids, including the wind, are deflected to the right of their path of motion. In the Southern Hemisphere, they are deflected to the left

Factors Affecting Wind Friction Friction acts to slow air movement, which changes wind direction Jet streams are fast-moving rivers of air that travel in a west-to-east direction ( km/hour); little friction

Global Winds Convection Cells: Convection Cells: – Warm air rises near the equator – Cooler air from the north replaces it at the surface – The warm air that rose flows northward and downward as it cools – The convection cells are called Hadley Cells

Fig. 7-4, p. 143 Heat released radiates to space Cool, dry air Condensation and precipitation Falls, is compressed, warms Rises, expands, cools Warm, dry air Hot, wet air Flows toward low pressure, picks up moisture and heat HIGH PRESSURE Moist surface warmed by sun LOW PRESSURE HIGH PRESSURE

Global Winds

Fig. 7-6, p. 144 Moist air rises, cools, and releases moisture as rain Polar cap Arctic tundra Evergreen coniferous forest 60° Temperate deciduous forest and grassland 30° Desert Tropical deciduous forest Equator 0° Tropical rain forest 30° Desert 60° Temperate deciduous forest and grassland Tropical deciduous forest Polar cap

Fig. 7-8, p. 146

Fig. 7-10, p. 147 Cold Polar Tundra Subpolar Temperate Coniferous forest Desert Deciduous forest Grassland Chaparral Tropical Hot Desert Wet Rain forest Savanna Tropical seasonal forest Dry Scrubland

Trade Winds Winds that blow out of the east between 0- 30° latitudeWesterlies Winds out of the west; between 30-60° Polar Easterlies Winds out of the east; from 60-90°

Global Winds The Doldrums: Equatorial “Low” Little or no winds “Horse” Latitudes: 30° latitude: sub-tropical high Little or no winds

CURRENTS

Fig. 7-5, p. 143 Warm, less salty, shallow current Cold, salty, deep current

Fig. 7-2, p. 142