Chapter 24 Water in the Atmosphere Section 3 Precipitation Notes 24-4.
Post on 14-Jan-2016
Chapter 24Water in the AtmosphereSection 3PrecipitationNotes 24-4
PrecipitationPrecipitation: any moisture that falls from the air to the earths surfaceLiquid or solidRain:Liquid; between .5 mm and 5 mmDrizzle: smaller drops; close together; fall slowlySnow:Solid; ice particleSnowflakes are just ice particles that combine together
PrecipitationSnow:Colder the temperature the smaller the flakeBigger flakes occur when the temp. is closer to 0CSleet:Solid; clear ice pelletsForms when rain falls through freezing airGlaze ice: rain that freezes on the surface of the earth during an ice storm
PrecipitationHail: solid lumps of iceAlternating clear and cloudy layersClear: passes through a layer of very moist airCloudy: water droplets with air bubblesUsually forms in cumulonimbus cloudsFrom a continuous up and down movement inside the cloudRain is upswept to lower temp. and frozenAs it falls more water is addedFrozen precip. Is swept up again and againEventually it is large and heavy enough to fall out
PrecipitationCauses: Droplets or ice crystals are large enough to fall outAverage cloud droplet: 20 micrometers or 0.00002 mMust increase size 100 times this diameter to fall out of cloudSlightest air movement keeps it suspended
PrecipitationCauses:Coalescence:Differences in the size of cloud dropletsOriginal size depends on the size of the condensation nucleiAs larger droplets move down, they fall into other smaller dropletsThey collide and combineBecoming so large, they fall out of the cloudTropical region rains form this way
PrecipitationCauses:Supercooling:Water droplets with a temp. of less than 0CMay fall as low as -10CWater droplets do NOT freezeFew freezing nuclei: condensation nuclei with a crystalline structure similar to iceMolecules evaporate from water droplets and condense on ice crystalsIncrease in size until they fall out as rain or snowRain and snow in middle and high latitudes form this way
PrecipitationCauses:Cloud Seeding:Freezing nuclei are added to supercooled cloudsSilver-iodide: from planes or burners on groundPowdered dry ice: cools the droplets causing ice crystals to form; from planesMay increase precipitation in some conditions and decrease in othersCould be used to release precip. from clouds before a storm becomes too large.
Measuring PrecipitationRain gauge:Instrument that measures the amount of rainfallOnly measures rain that falls in one spotPrecipitation varies so much it is hard to get an accurate measure of a larger area
Measuring PrecipitationSnow Board:Board that allows for a flat surface from which you can measure the inches of snow10 cm of snow = 1 cm of waterDepending on the water content of the snow
HomeworkSection Reviewp. 4931-4