Chapter 17 Notes - ES 101 PDF

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Summary

Kevin Koch
Moisture, Clouds, and Precipitation...

Description

Water’s Changes of State ● Calorie - The amount of heat required to raise the temperature of 1 gram of water 1°C. ● Latent heat - The energy absorbed or released during a change in state. ○ Stored in liquid water ● Evaporation - The process of converting a liquid to a gas. ○ Latent heat of evaporation ● Condensation - The change of state from a gas to a liquid. ○ Latent heat of condensation ● Sublimation - The conversion of a solid directly to a gas w/o passing through the liquid state. ● Deposition - The process by which water vapor is changed directly to a solid w/o passing through the liquid state.

Water Vapor in the Air ● Humidity - A general term referring to water vapor in the air but not to liquid droplets of fog, cloud, or rain. ● Saturation - The maximum quantity of water vapor that the air can hold at any given temperature and pressure. ● Vapor Pressure - The part of the total atmospheric pressure attributable to water-vapor content. ● Mixing ratio - The mass of water vapor in a unit mass of dry air; commonly expressed as grams of water vapor per kilogram of dry air ○ Mixing ratio = mass of water vapor (grams) / mass of dry air (kilograms) ● Relative humidity - The ratio of the air’s water-vapor content to its water-vapor capacity ● Dew-point temperature - The temperature to which air has to be cooled in order to reach saturation. Also called simply dew point. ● Hygrometer - An instrument designed to measure relative humidity.

● Psychrometer - A device consisting of two thermometers (wet bulb and dry bulb) that is rapidly whirled and, with the use of tables, yields the relative humidity and dew point.

Adiabatic Temperature Changes and Cloud Formation ● Adiabatic Temperature Changes - Cooling or warming of air caused when air is allowed to expand or is compressed, not b/c heat is added or subtracted. ● Parcel - An imaginary volume of air enclosed in a thin elastic cover. Typically it is considered to be a few hundred cubic meters in volume and is assumed to act independently of the surrounding air. ● Dry adiabatic rate - The rate of adiabatic cooling or warming in unsaturated air. The rate of temperature changes by 1°C per 100 meters. ● Lifting condensation level - The height at which rising air that is cooling at the dry adiabatic rate becomes saturated and condensation begins. Also simply called the condensation level. ● Sensible heat - The heat we can feel and measure with a thermometer. ● Wet adiabatic rate - The rate of adiabatic temperature change in saturated air. The wet adiabatic rate of temperature change is variable, but it is always less than the dry adiabatic rate.

Processes That Lift Air ● Orographic lifting - Mountains acting as barriers to the flow of air, forcing the air to ascend. The air cools adiabatically, and clouds and precipitation may result. ● Rainshadow desert - A dry area on the lee side of a mountain range. Many middle-latitude deserts are of this type. ● Fronts - The boundary between two adjoining air masses having contrasting characteristics. ● Frontal lifting - Lifting of air that results when cool air acts as a barrier over which warmer, lighter air arises. Also called frontal wedging.

● Convergence - The condition that exists when the distribution of winds in a given area results in a net horizontal inflow of air into the area. B/c convergence at lower levels is associated with an upward movement of air, areas of convergent winds are regions favorable to cloud formation and precipitation. ● Localized convective lifting - Unequal surface heating that causes localized pockets of air (thermals) to rise b/c of their buoyancy. Also called convective lifting.

Atmospheric Stability ● Stable air - Air that resists vertical displacement. If it is lifted, adiabatic cooling will cause its temperature to be lower than the surrounding environment; if it is allowed to do so, it will sink to its original position. ● Unstable air - Air that does not resist vertical displacement. If it is lifted, its temperature will not cool as rapidly as the surrounding environment, so it will continue to rise on its own. ● Environmental lapse rate - The rate of temperature decreases with increasing height in the troposphere. ● Absolute stability - Refers to air with a lapse rate less than the wet adiabatic rate. ● Absolute instability - Air that has a lapse rate greater than the dry adiabatic rate. ● Conditional instability - Moist air with a lapse rate between the dry and wet adiabatic rates.

Condensation and Cloud Formation ● Cloud condensation nuclei - Microscopic particles that serve as surfaces on which water vapor condenses. ● Hygroscopic nuclei - Condensation nuclei that have a high affinity for water, such as salt particles. ● Clouds - A form of condensation best described as a dense concentration of suspended water droplets or tiny crystals.

● Cirrus - One of three basic cloud forms; also one of the three high cloud types. Cirrus clouds are thin, delicate ice-crystal clouds often appearing as veil-like patches or thin, wispy fibers. ● Stratus - One of three basic cloud forms; also, the name given one of the flow clouds. They are sheets or layers that cover much or all of the sky. ● Cumulus - One of the three basic cloud forms; also the name given of the clouds of vertical development. Cumulus are billowy individual cloud masses that often have flat bases. ● Nimbus - A cloud that is a major producer of precipitation ● High Clouds - A cloud that normally has its base above 6000 meters; the base may be lower in winter and at high-latitude locations. ● Middle Clouds - Cloud that occupy the height range from 2000 to 6000 meters. ● Low Clouds - A cloud that forms below a height of 2000 years. ● Clouds of vertical development - Clouds that have their bases in the low-height range but extend upward into the middle or high altitudes. ● Cirrocumulus - A type of cumulus cloud that forms at a high altitude. Cirrocumulus clouds are thin sheets of white ice-crystal cloud that may give the sky a milky look. ● Cirrostratus - A type of stratus cloud that forms at high altitude. Cirrostratus clouds are thin, delicate, fibrous ice-crystal clouds, such as mares’ tails. ● Altocumulus - A type of cumulus clouds that forms at medium altitude. Altocumulus clouds are white to gray “sheepback” clouds, often composed of separate globules. ● Altostratus - A type of stratus clouds that form at medium altitude. Altostratus clouds are generally thin and may produce light precipitation. ● Stratocumulus - low clouds with scalloped bottoms in parallel rolls. ● Nimbostratus - A solid layer of dark grey cloud that forms at low altitude. Nimbostratus clouds are a major source of precipitation. ● Cumulonimbus - A type of towering cloud of vertical development. Cumulonimbus clouds are associated with heavy rainfall, thunder, lightning, hail, and tornadoes.

Types of Fog ● Fog - A cloud with its base at or very near Earth’s surface. ● Radiation fog - Fog resulting from radiation heat loss by Earth. ● Advection fog - A fog formed when warm, moist air blows over a cool surface. ● Upslope fog - Fog created when air moves up a slope and cools adiabatically. ● Steam fog - Fog having the appearance of steam, produced by evaporation from a warm water surface into the cool air above. ● Frontal (precipitation) fog - Fog formed when rain evaporates as it falls through a layer of cool air.

How Precipitation Forms ● 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 - The condition of water droplets that remain in the liquid state at temperatures well below 0°C (32°F). ● Ice (freezing) nuclei - Solid particles that serve as cores for the formation of ice crystals in the atmosphere. ● Collision--coalescence process - A theory of raindrop formation in warm clouds (above 0°C) in which large cloud droplets (giants) collide and join together with smaller droplets to form a raindrop. Opposite electrical charges may bind the cloud droplets together.

Forms of Precipitation ● Rain - Drops of water that fall from clouds that have a diameter of at least 0.5 millimeter. ● Drizzle - Precipitation from stratus clouds consisting of tiny droplets. ● Mist - A cloud of water droplets suspended in the atmosphere at or near Earth’s surface. ● Snow - A solid form of precipitation produced by sublimation of water vapor.

● Sleet - Frozen or semi frozen rain formed when raindrops freeze as they pass through a layer of cold air. ● Freezing rain (glaze) - A coating of ice on objects formed when supercooled rain freezes on contact. ● Hail - Nearly spherical ice pellets having concentric layers and formed by the successive freezing of layers of water. ● Rime - A thin coating of ice on objects produced when supercooled fog droplets freeze on contact.

Measuring Precipitation

● Standard rain gauge - A gauge that has a diameter of about 20 centimeters and funnels rain into a cylinder that magnifies precipitation amounts by a factor of 10, allowing for accurate measurement of small amounts. ● Tipping-bucket gauge - A recording rain gauge consisting of two compartments (“buckets”), each capable of holding 0.025 centimeter of water. When one compartment fills, it tips, and the other compartment takes its place. ● Weather radar - Instruments that utilize transmitters to send out radio waves at wavelengths that can penetrate clouds, to produce a reflected signal called an echo that can be displayed on a monitor to show the location and intensity of precipitation....