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Earth Science Chapter 18.1 – Water in the Atmosphere Ag Earth Science – Chapter 18.1 precipitation Any form of water that falls from a cloud latent heat The energy absorbed or released during a change in state evaporation The process of converting a liquid to a gas condensation The change of state from a gas to a liquid sublimation The conversion of a solid directly to a gas without passing through the liquid stage deposition The process by which water vapor is changed directly to a solid without passing through the liquid state humidity A general term referring to water vapor in the air but not to a liquid droplets of fog, cloud, or rain saturated The state of air that contains the maximum quantity of water vapor that it can hold at any given temperature and pressure. relative humidity The ratio of the air’s water-vapor content to its water-vapor capacity dew point The temperature to which air has to be cooled in order to reach saturation hygrometer An instrument designed to measure relative humidity “A Dam Picture” Water in the Atmosphere When it comes to understanding atmospheric processes, water vapor is the most important gas in the atmosphere Precipitation – any form of water that falls from a cloud (rain, sleet, hail, snow, etc..) Water Changes in State Solid to Liquid The process of changing state requires that the energy is transferred in the form of heat Latent heat – “hidden” heat. The energy absorbed or released during a change in state Water Changes in State Liquid to Gas Evaporation – the process of changing a liquid to a gas Condensation – the process where water vapor changes to a liquid Water Changes in State Solid to a Gas Sublimation – conversion of a solid directly to a gas without passing through the liquid state Deposition – conversion of a vapor directly to a solid Humidity Humidity – the amount of water vapor in the air Saturation Saturated - The state of air that contains the maximum quality of water vapor that it can hold at any given temperature and pressure. When saturated, warm air contains more water vapor than saturated cold air Humidity Relative Humidity Relative humidity is a ratio of the air’s actual water-vapor content compared with the amount of air can hold at that temperature and pressure. To summarize, when the water-vapor content of air remains constant, lowering air temperature causes an increase in relative humidity, and raising air temperature causes a decrease in relative humidity. Humidity Dew Point The temperature to which a parcel of air would need to be cooled to reach saturation Humidity Measuring Humidity Hygrometer - A tool that measures humidity Ag Earth Science – Chapter 18.2 dry adiabatic rate The rate of adiabatic cooling or warming in unsaturated air wet adiabatic rate The rate of adiabatic temperature change in saturated air orographic lifting Mountains acting as barriers to the flow of air, forcing the air to ascend front The boundary between two adjoining air masses having contrasting characteristics temperature inversion A layer of limited depth in the atmosphere of limited depth where the temperature increases rather than decreases with height condensation nuclei Tiny bits of particulate matter that serve as surfaces on which water vapors condenses Air Compression and Expansion Adiabatic Temperature Changes When air is allowed to expand, it cools, and when it is compressed, it warms Air Compression and Expansion Expansion and Cooling As you travel from earth’s surface upward through the atmosphere, the atmospheric pressure decreases. Ascending air = cools and Descending air = warms Air Compression and Expansion Expansion and Cooling Dry adiabatic rate – the rate of cooling or heating of dry air (fast) Wet adiabatic rate – The rate of cooling or heating of saturated air (slow) Processes That Lift Air Four mechanisms that can cause air to rise are orographic lifting, frontal wedging, convergence, and localized convective lifting. Processes That Lift Air Orographic Lifting Elevated terrains, such as mountains, that act as barriers to air flow (forcing air to ascend) Processes That Lift Air Frontal Wedging Cooler, denser air acts as a barrier over which the warmer, less dense air rises Front – boundary between two different air masses (example – cold/warm air masses) Processes That Lift Air Convergence The collision of contrasting air masses that causes the air to rise Processes That Lift Air Localized Convective Lifting The process that produces rising thermals (localized) Stability Stable air tends to remain in its original position, while unstable air tends to rise. Air stability is determined by measuring the temperature of the atmosphere at various heights. Stability Air is stable when the temperature decreases gradually with increasing altitude Temperature inversion – air temperature actually increases with height Condensation Condensation happens when water vapor in the air changes to a liquid (fog, dew, clouds) For any form of condensation to occur, the air must be saturated Condensation nuclei - Tiny bits of particulate matter that serve as surfaces on which water vapors condenses Ag Earth Science – Chapter 18.3 cirrus 1 of 3 basic cloud forms. Very high clouds that are thin, delicate icecrystal clouds that have veil-like patches or thin, wispy fibers cumulus 1 of 3 basic cloud forms. They are billowy individual clouds with flat bases. stratus 1 of 3 basic cloud forms. They are sheets or layers that cover much or all of the sky. Bergeron process A theory that relates the formation of precipitation to supercooled clouds, freezing nuclei, and the different saturation levels of ice and liquid water. supercooled water The condition of water droplets that remain in the liquid state at temperatures well below 0 degrees. supersaturated air The condition of air that is more highly concentrated than is normally possible under given temperature and pressure conditions. (Greater than 100% humidity) collision-coalescence process A theory of raindrop formation in warm clouds (above 0 degrees C) in which large cloud droplets collide and join together with smaller droplets to form a raindrop. Types of Clouds Clouds are classified on the basis of their form and height. Types of Clouds: Cirrus (“a curl of hair”) – clouds that are high, white, and thin. Types of Clouds Cumulus (“a pile”) – clouds that consist of rounded individual cloud masses Types of Clouds Stratus (“a layer”) – clouds are best described as sheets or layers that cover much or all the sky Types of Clouds High Clouds Three types of clouds make up the family of high clouds (cirrus, cirrostratus, and cirrocumulus). They are very high altitude and have ice crystals. Not considered precipitation makers. Types of Clouds Middle Clouds Middle range clouds (2000-6000 meters). Appear in rounded masses and are larger and denser than higher clouds. Light drizzle or snow may accompany these clouds. Types of Clouds Low Clouds Three members of the family of low clouds (stratus, stratocumulus, nimbostratus). Most common “rain” clouds as they form a layer across the sky. Fog Fog is defined as a cloud with its base at or very near the ground. Fogs caused by cooling When warm, moist air moves over cold areas, the cooling saturates the air below its dew point. Fog Fogs caused by evaporation When cool air moves over warm water. Evaporation moves into cool air and saturates. How Precipitation Forms For precipitation to form, cloud droplets must grow in volume by roughly one million times. Cold Cloud Precipitation Bergeron Process – physical processes of supercooling and supersaturation take place. How Precipitation Forms Warm Cloud Precipitation Collision-coalescence process – water absorbing particles remove water vapor from the air at relative humidities less than 100 percent forming drops that are quite large. As they move through the cloud, they collide and join together with smaller, slower droplets. Forms of Precipitation The type of precipitation (rain, snow, sleet, and hail) that reaches the Earth’s surface depends on the temperature profile in the lowest few kilometers of the atmosphere.
