ENVS 110atmospheric temperaturesSlide 3earth’s orbit around the sun…tilt of earth’s rotational axisflux again …Slide 7spring and fall equinox(northern) summer solstice(northern) winter solsticedue to the tilt of the earth’s axisif earth’s orbit were circular…elliptical orbitsdaily temperature changesSlide 15daily temperature variationsair temperature – Trinity Collegesimilar effect for seasonal temperaturesrole of moisture – latent heatSlide 20latent heat and air temperaturesmoisture and nighttime coolingSlide 23vertical temperature distributionsSlide 25causes of variability in vertical temperature distributionsSlide 27Slide 28horizontal temperature variationsQuestions:Solar flux at low latitudesextent of the tropicsthe effects of the earth’s surfaceOceans / ContinentsSlide 35ENVS 11009-12-2008atmospheric temperatures•seasonal changes•daily changes•temperature profile of the atmosphere•horizontal temperature distributions•global temperature distributionsearth’s orbit around the sun…tilt of earth’s rotational axis•during northern summer, northern hemisphere is tilted towards the sun•days are longer•sun is higher in the sky•how will this affect the temperatures ?flux again …i n c o m i n g r a d i a t i o ni n c o m i n g r a d i a t i o na r e a i l l u m i n a t e d b yl i g h t b e a mi n c o m i n g s o l a r r a d i a t i o nt r o p i c s : s u n i s h i g h i n t h e s k yp o l a r r e g i o n s : s u n i s c l o s e t o h o r i z o n0 5 0 0 1 0 0 0 1 5 0 0s o l a r f l u x ( W / m2)spring and fall equinoxi n c o m i n g s o l a r r a d i a t i o nt r o p i c s : s u n i s h i g h i n t h e s k yp o l a r r e g i o n s : s u n i s c l o s e t o h o r i z o n0 5 0 0 1 0 0 0 1 5 0 0s o l a r f l u x ( W / m2)r o t a t i o n a l a x i se q u a t o rH a r t f o r d(northern) summer solsticei n c o m i n g s o l a r r a d i a t i o nt r o p i c s : s u n i s h i g h i n t h e s k yp o l a r r e g i o n s : s u n i s c l o s e t o h o r i z o n0 5 0 0 1 0 0 0 1 5 0 0s o l a r f l u x ( W / m2)rotational axisequatorHartford(northern) winter solsticei n c o m i n g s o l a r r a d i a t i o nt r o p i c s : s u n i s h i g h i n t h e s k yp o l a r r e g i o n s : s u n i s c l o s e t o h o r i z o n0 5 0 0 1 0 0 0 1 5 0 0s o l a r f l u x ( W / m2)rotational axisequatorHartforddue to the tilt of the earth’s axis•northern hemisphere experiences higher solar flux during summer monthsand•exposed to sunlight for longer period of time•receives more solar energy → warmer temperaturesif earth’s orbit were circular…•both hemispheres would receive same amount of sunlight per year•but earth’s orbit is ellipticalhttp://www.walter-fendt.de/ph11e/keplerlaw2.htmelliptical orbits•in circular orbits – orbiting velocity of planet does not change•in elliptical orbits it does•how does this influence the amount of sunlight received on the northern and southern hemisphere ?•homework assignment on web site (due on Wednesday)daily temperature changes•Remember – atmosphere is heated by conduction from the ground•Very thin boundary layer heats up first•Warm air expands and slowly rises•Optical properties of air depend on its density → objects close to ground are distorteddaily temperature variations•Sun warms ground•Ground warms atmosphere•Highest air temperatures occur after noon because it takes some time to transfer heat from the ground into overlying air layersair temperature – Trinity Collegesimilar effect for seasonal temperaturesrole of moisture – latent heat•Boiling water stays at 100°C even though burner is left on•Where does all the extra energy go?•Evaporating water – water molecules are ripped apart → “hard work” = latent heat•Water vapor contains large amount of heat because water molecules are separated from each otherENVS 11009-15-2008latent heat and air temperatures•Humid days: large amounts of solar energy are used to evaporate water•Air warms up slowly but contains lots of water vapor (which contains large amounts of latent heat)•Cooler but sticky !moisture and nighttime cooling•Air cools by giving off infrared radiation•Water vapor is a greenhouse gas•Water vapor contains large amounts of latent heat•When air cools water vapor condenses and turns back into droplets of water•Latent heat is released and heats surrounding airJ a n F e b M a r A p r M a y J u n J u l A u g S e p O c t N o v D e c0481 21 62 0D a i l y T e m p e r a t u r e D i f f e r e n c e (C )D e a t h V a l l e y , C AH o u s t o n , T Xvertical temperature distributions•Troposphere is heated from below and cooled from the top•Atmospheric temperature decreases as you go up in elevation•Average temperature gradient: 6.5°C/km (3.5°F/1000 ft)http://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1a.htmlcauses of variability in vertical temperature distributions•Underlying surface:–steeper gradient over continents –Shallower gradient over oceans–Oceans – cooler, moister air–Continents heat up faster, air often drier•Surface elevation–Higher elevation – thinner atmosphere = more rapid heat loss–High temperatures similar , nights much coolerhorizontal temperature variationshttp://www.globalwarmingart.com/images/a/aa/Annual_Average_Temperature_Map.jpgQuestions:•Where is the earth the warmest ?•Where does earth receive most of its solar energy ?•Why ?•Does this explain previous map?Solar flux at low latitudes•Solar flux highest if sun is (almost) directly overhead•Solar flux is highest on a clear day•How long is sun (almost) directly overhead at the equator ?•How long is sun (almost) disectly overhead in the tropics ?extent of the tropicsthe effects of the earth’s surface•Albedo•Heat capacity (specific heat)•Subsurface mixingOceans / ContinentsOceans•Water – high heat capacity•Variable albedo•Mix easily through waves etc.•Large evaporative lossesContinents•Earth / rocks - low heat capacity•Immobile – no mixing, only thin surface layer warms rapidly•Little loss of latent heat