2 Forms of Water › Water exists in the atmosphere in 3 forms or phases: Gas called water vaporSolid known as iceLiquid› Water changes from one phase to the next when heat energy is absorbed or released
3 Some Vocabulary to Know Latent heat – heat energy that is absorbed or released by a substance during a phase changeEvaporation – Most evaporation takes place in the oceans; water vapor can also enter the atmosphere by evaporation from lakes, streams, ponds, and soil.Sublimation – process in which solid changes directly into a gas
4 Humidity Water vapor in the atmosphere is known as humidity Controlled by rates of condensation & evaporationRate of evaporation is determined by temperature of airHigher temperature, higher evaporation rateRate of condensation is determined by vapor pressureVapor pressure is part of the total atmospheric pressure caused by water vapor
5 Absolute humidity = mass of water vapor (grams) Humidity ContinuedDew point – Temperature at which the condensation rate equals the evaporation rate. Temperatures below dew point, water droplets formAbsolute humidity – mass of water vapor contained in a given volume of airAbsolute humidity = mass of water vapor (grams)Volume of air (cubic meters)Relative humidity – ratio of the actual water vapor content of the air to the amount of water vapor needed to reach saturation.Measure of how close the air is to reaching dew point.
6 Measuring HumidityRelative humidity can be measured by: thin polymer film, a psychrometer, a dew cell, and a hair hygrometer.
7 Clouds & FogClouds are a collection of small water droplets or ice crystals that fall slowly through the air.
9 Cooling Processes That Help Form Clouds Four major processes that cause cooling for clouds to form:1. Adiabatic Cooling – temperature of an air mass decreases as the air mass rises & expands2. Mixing – when 1 body of moist air mixes with another body of moist air of a different temp3. Lifting – forced upward movement of air results in cooling of air& cloud formation4. Advective Cooling – temperature of an air mass decreases as the air mass moves over a cold surface
10 Classification of Clouds CUMULUS CLOUDSCHARACTERISTICS ---PuffyVertical Growing CloudsThickLooks like popcornForm thunderstormsCumulus – piled, heaped
11 STRATUS CLOUDSCHARACTERISTICS --Stratus - Sheet likeLow cloudsLayeredCovers large areas of the skyBlocks the sun“Covers” the earth
12 CIRRUS CLOUDSCHARACTERISTICS --Highest CloudsWispyFeatheryCirrus – curlyMade of ice crystals
13 Produce Hail, Lightning, and Thunder CUMULONIMBUS CLOUDSCHARACTERISTICS --Thunderstorm CloudsProduce Hail, Lightning, and ThunderAnvil shapedCan reach into the stratosphereNimbo - Rain
14 Fog Result of condensation of water vapor in the air. Near the surface of Earth2 types:Radiation fog – results from the loss of heat by radiation; forms from the nightly cooling of Earth; layer of air in contact with the ground becomes chilled below dew point;Advection fog – forms when warm, moist air moves across a cold surface; forms mostly along coasts.
15 Precipitation 4 forms of precipitation: Rain – liquid precipitation Snow – common solid precipitationSleet – forms when rain falls through a layer of freezing air near the groundHail – solid precipitation in the form of lumps of ice
16 Causes of Precipitation Coalescence – formation of a large droplet by the combination of smaller dropletsSupercooling – a condition in which a substance is cooled below its freezing point, condensation point, or sublimation point without going through a change in state
17 Measuring Precipitation Meteorologists use a variety of instrumentsRain gaugeDoppler radar