Chapter 4 - Chapter 4 Movement of Water Through the...

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Movement of Water Through the Atmosphere Water is everywhere on Earth—in the oceans, glaciers, rivers, lakes, the air, soil, and in living tissue. All of these “reservoirs” constitute Earth’s hydrosphere. The increasing demands on this finite resource have led scientists to focus on the continuous exchange of water among the oceans, the atmosphere, and the continents. This unending circulation of Earth’s water supply has come to be called the hydrologic cycle (or water cycle). The hydrologic cycle is a gigantic system powered by energy from the Sun in which the atmosphere provides the vital link between the oceans and continents. o Water from the oceans and, to a much lesser extent, from the continents, evaporates into the atmosphere. Winds transport this moisture-laden air, often over great distances. Complex processes of loud formation eventually result in precipitation. The precipitation that falls into the ocean has ended its cycle and is ready to begin another by evaporating again. Once precipitation has fallen on land, a portion of the water soaks into the ground, some of it moving downward, then laterally, and finally seeping into lakes and streams or directly into the ocean. Transpiration is the release of water vapor to the atmosphere by plants. The Earth’s water balance is a quantitative view of the hydrologic cycle. Because the total amount of water vapor in the entire global atmosphere remains about the same, the average annual precipitation over Earth must be equal to the quantity of water evaporated. The hydrologic cycle depicts the continuous movement of water from the oceans to the atmosphere, from the atmosphere to the land, and from the land back to the sea. The movement of water through the cycle holds the key to the distribution of moisture over the surface of our planet and is intricately related to all atmospheric phenomena. Water’s Changes of State Water is the only substance that exists in the atmosphere as a solid, liquid, and gas. In all three states of matter these molecules are in constant motion—the higher the temperature, the more vigorous the movement. The chief difference among liquid water, ice, and water vapor is the arrangement of the water molecules. Ice is composed of water molecules that have low kinetic energies and are held together by mutual molecular attractions. Here the molecules form a tight, orderly network. As a consequence, the water molecules in ice are not free to move relative to each other but rather vibrate about fixes sites. When ice is heated, the molecules oscillate more rapidly. When the rate of molecular movement increases sufficiently, the bonds between some of the water molecules are broken, resulting gin melting. In the liquid state. Water molecules are still tightly packed but are moving fast
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Chapter 4 - Chapter 4 Movement of Water Through the...

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