Solar Energy, the Atmosphere and Biomes

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: 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: 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 CO2 in the atmosphere 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

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. Figure 7.7 The rain shadow effect is a reduction of rainfall and loss of moisture from the landscape on the side of a mountain facing away from prevailing surface winds. Warm, moist air in onshore winds loses most of its moisture as rain and snow on the windward slopes of a mountain range. This leads to semiarid and arid conditions on the leeward side of the mountain range and the land beyond. The Mojave Desert in the U.S. state of California and Asia’s Gobi Desert are both produced by this effect. Fig. 7-7, p. 145

Tundra (herbs, lichens, mosses) Elevation Mountain ice and snow Tundra (herbs, lichens, mosses) Coniferous Forest Deciduous Forest Tropical Forest Latitude Tropical Forest Deciduous Forest Coniferous Forest Tundra (herbs, lichens, mosses) Polar ice and snow Figure 7.9 Generalized effects of elevation (left) and latitude (right) on climate and biomes. Parallel changes in vegetation type occur when we travel from the equator to the poles or from lowlands to mountaintops. Question: How might the components of the left diagram change as the earth warms during this century? Explain. Stepped Art Fig. 7-9, p. 147

Properties of Air Density At constant pressure, warm is less dense than cold air Therefore, warm air rises, cold air sinks

Properties of Air Water Vapor Capacity Warm air has a higher capacity for water Specific humidity is a measure of the amount of water vapor in the air Relative humidity is a ratio of the amount of water present to the capacity If RH = 100%, saturation occurs Dew point is the temperature at which saturation occurs

Properties of Air Adiabatic Heating and Cooling As air rises in the atmosphere rises, P ↓, air expands and cools As air sinks toward the surface, P ↑, air volume ↓ and warms

Properties of Air Latent Heat Release As the sun warms surface water, it absorbs and stores energy as it evaporates As water vapor in the atmosphere condenses, it releases this stored (latent) energy

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 (120 - 240 km/hour); little friction

Global Winds 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

Heat released radiates to space Condensation and precipitation LOW PRESSURE HIGH PRESSURE Heat released radiates to space Condensation and precipitation Cool, dry air Falls, is compressed, warms Rises, expands, cools Warm, dry air Hot, wet air Figure 7.4 Energy transfer by convection in the atmosphere. Convection occurs when hot and wet warm air rises, cools, and releases heat and moisture as precipitation (right side). Then the denser cool, dry air sinks, gets warmer, and picks up moisture as it flows across the earth’s surface to begin the cycle again. Flows toward low pressure, picks up moisture and heat HIGH PRESSURE LOW PRESSURE Moist surface warmed by sun Fig. 7-4, p. 143

Global Winds & Biomes

Moist air rises, cools, and releases moisture as rain Polar cap Arctic tundra Evergreen coniferous forest 60° Temperate deciduous forest and grassland Desert 30° Tropical deciduous forest Equator 0° Tropical rain forest Tropical deciduous forest 30° Desert Figure 7.6 Global air circulation, ocean currents, and biomes. Heat and moisture are distributed over the earth’s surface via six giant convection cells (like the one in Figure 7-4) at different latitudes. The resulting uneven distribution of heat and moisture over the planet’s surface leads to the forests, grasslands, and deserts that make up the earth’s terrestrial biomes. Temperate deciduous forest and grassland 60° Polar cap Fig. 7-6, p. 144

Figure 7.8 Natural capital: the earth’s major biomes—the main types of natural vegetation in various undisturbed land areas—result primarily from differences in climate. Each biome contains many ecosystems whose communities have adapted to differences in climate, soil, and other environmental factors. Figure 5 on p. S27 in Supplement 4 shows the major biomes of North America. Human activities have removed or altered much of the natural vegetation in some areas for farming, livestock grazing, lumber and fuelwood, mining, and construction of towns and cities (see Figure 3, pp. S24–S25, and Figure 7, pp. S28–S29, in Supplement 4). See an animation based on this figure at CengageNOW. Question: If you factor out human influences such as farming and urban areas, what kind of biome do you live in? Fig. 7-8, p. 146

Decreasing temperature Decreasing precipitation Cold Polar Tundra Subpolar Temperate Coniferous forest Decreasing temperature Desert Deciduous forest Grassland Tropical Chaparral Hot Figure 7.10 Natural capital: average precipitation and average temperature, acting together as limiting factors over a long time, help to determine the type of desert, grassland, or forest biome in a particular area. Although each actual situation is much more complex, this simplified diagram explains how climate helps to determine the types and amounts of natural vegetation found in an area left undisturbed by human activities. (Used by permission of Macmillan Publishing Company, from Derek Elsom, The Earth, New York: Macmillan, 1992. Copyright © 1992 by Marshall Editions Developments Limited). Desert Wet Rain forest Savanna Dry Tropical seasonal forest Scrubland Decreasing precipitation Fig. 7-10, p. 147

Biomes Tundra Boreal forest Temperate rainforest Temperate seasonal forest Woodland/shrubland Tropical rainforest Subtropical desert

Currents

Figure 7.2 Natural capital: generalized map of the earth’s current climate zones, showing the major contributing ocean currents and drifts and upwelling areas (where currents bring nutrients from the ocean bottom to the surface). Winds play an important role in distributing heat and moisture in the atmosphere, which leads to such climate zones. Winds also cause currents that help distribute heat throughout the world’s oceans. See an animation based on this figure at CengageNOW™. Question: Based on this map what is the general type of climate where you live? Fig. 7-2, p. 142

Thermohaline Circulation Warm, less salty, shallow current Figure 7.5 Connected deep and shallow ocean currents. A connected loop of shallow and deep ocean currents transports warm and cool water to various parts of the earth. This loop, which rises in some areas and falls in others, results when ocean water in the North Atlantic near Iceland is dense enough (because of its salt content and cold temperature) to sink to the ocean bottom, flow southward, and then move eastward to well up in the warmer Pacific. A shallower return current aided by winds then brings warmer, less salty—and thus less dense—water to the Atlantic. This water can cool and sink to begin this extremely slow cycle again. Question: How do you think this loop affects the climates of the coastal areas around it? Cold, salty, deep current Fig. 7-5, p. 143

El Nino Southern Oscillation 3 – 7 year cycle Surface currents in the tropical Pacific reverse direction (trade winds weaken) Warm water moves westward, suppressing the upwelling of nutrients off the coast of S. America Fish populations are hurt Global impact: cooler, wetter conditions in SE US; drier in S Africa, SE Asia

Biomes For your biome PowerPoint: Describe vegetation and animal life Describe general climate; include global location(s) Include a climate diagram (annual temperature & rainfall) 3 – 5 slides; keep it simple!

Categorized by salinity, depth, water flow Aquatic biomes

Streams & Rivers Flowing fresh water Originate from springs or runoff Rapid flow = few producers; rely on terrestrial biomes (leaves) Slow rivers: nutrients settle and provide substrate for plants Rapids: high O2 content

Lakes and Ponds Contain standing water Divided into distinct zones: Littoral Zone: shallow area of soil & water near shore; rooted plants, photosynthesis Limnetic Zone: rooted plants cannot survive; phytoplankton photosynthesize Profundal Zone: deep lakes; low O2 due to decomposers; muddy bottom: benthic zone