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McGill University
Atmospheric & Oceanic Sciences
ATOC 181
Daniel Kirshbaum

1 THE EARTH AND ITS ATMOSPHERE The Atmosphereatmosphere the envelope of gases that surround a planet and are held to it by the planets gravitational attraction o 99 of mass is confined to a layer of 025 earths radiuso shields humans from ultraviolet radiation o essential for like HO O CO 222 nearly 150 km separates sunearth yet solar radiation drives the earths weather origin o earth born46 billion years ago o outgassing of lava ashesgases erupt from volcanoes supplying HO CON forming the 222atmosphere bound to earth by gravitational fieldmass o traps heatcauses planet to warmaverage global temperature was probably between 85110 C now 15 Co planet cooledwater vapour condensed to form cloudsrainformation of oceansCO stored in oceansdeposited into sedimentary rocks 2 N begins to dominate 2o life formed2 billion years agophotosynthesis produce O 2 through photochemical reactions O shield form 3o now main atmospheric constituents are N 78 and O 21 22 HO ranges from 04 0 in poles 4 in tropics 2 trace amounts of CO Oother gases 23 aerosol particlesOzone O 3 97 in upper atmosphere where it forms naturallyozone shields earth from ultraviolet radiationlayer being depleted near poles by chlorofluorocarbons CFCs from spray cansrefrigerantsat surface primary ingredient in photochemical smog o irritates eyesthroat damages vegetationCarbon Dioxide CO 2 used by plants for photosynthesis to produce oxygenabsorbs portion of earths outgoing radiationradiates it back to earth greenhouse gasconcentration increasing rapidlyWater Vapour HO2 produced by evaporationsublimationlost by condensationdeposition part of hydrologic cyclecondenses to form clouds stores latent heat released in thunderstormshurricanescritical global circulation factorhighly effective greenhouse gasinitially water vapour produced by volcanoes then evaporation of liquidsublimation of ice contributes to formation of water vapourAirmass the amount of mattermaterial in the ample volume 3 density the concentration of mass massvolume ie kgmmassdensity profiles o both tend to decrease rapidly with height but density may be relatively uniform in wellmixed layers o air density decreased with height because the heavier particles of air descend2 weight the force exerted by the mass due to gravity mass x gravitational acceleration ie kgms 2 pressure the weight of the overlying air column force per unit area PaNewtonsmsdont feel it because it acts in all directions bodys internal pressure adjusts to atmosphere so there is no pressure difference densitypressure profile o decrease with increasing altitude layers of the atmosphere o spheres layers o pauses boundaries between layers o tropospheresurface up to12 kmtemperature decreases with height65Ckmwhere weather occursthunderstorm clouds often reach the tropopause o stratospheretemperature initially isothermal constant then increased with height up to50 kmsite of ozone layermay impact weather over seasonal time scales o mesospheretemperature decreased with height up to80 km o thermospheretemperature increases with height o homosphere well mixed lower atmosphere8 N 21 O 22o heterosphere poorly mixed upper atmosphere o ionsphere electrically charged region with ionsfree electronsplays major role in radiocommunications since it reflects AM signals allowing transmission over large distancesD region absorbs radio waves weakening surface signal much stronger during daytime due to photoionization
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