Slide 1Terrestrial planet atmospheresSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39PYTS/ASTR 206 – Terrestrial planet atmospheres1AnnouncementsHW 2Mid-term resultsMid-term went very wellResults87.5 – 100% 1770-87.5% 3762.5-70% 2950-62.5% 19<50% 21PYTS/ASTR 206 – Terrestrial planet atmospheres2PTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected] planet atmospheresPYTS/ASTR 206 – Terrestrial planet atmospheres3In this lecture…In this lecture…Introduction to atmospheresPressure and TemperatureScale heightComparing planetary atmospheresRadiation and atmospheresCloudsGreenhouse effectCirculation Why is Tucson a Desert?What’s El NinoSurface features from the atmosphereSand dunes and how they workEolian erosion‘Atmospheres’ of Moon and MercuryIce in polar cratersPYTS/ASTR 206 – Terrestrial planet atmospheres4What’s the atmosphere?A thin gas layerGas molecules moving around at high-velocitiesHeld down with gravityThe “edge” of the atmosphereThins gradually with altitudeKarman lineBased on aeronautics~100km upIntroductionIntroductionPYTS/ASTR 206 – Terrestrial planet atmospheres5Gravity squeezes the atmosphereHigh pressure at the bottom105 Pascals (Newtons per square meter)~10,000 Kg of mass above each square meterSo why aren’t we squashed flat?The atmosphere is supported by pressurePressure = a * density * temperature‘a’ depends on the type of gasA cold dense atmosphere (e.g. Titan) can have the same pressure as a hot less-dense atmosphere (e.g. Earth)Parcel of airLower pressureHigherpressureWeight of the airThis is “hydrostatic equilibrium”Makes the atmosphere (mostly) stablePYTS/ASTR 206 – Terrestrial planet atmospheres6Pressure drops with heightThe ‘scale height’ measures the thickness of the atmosphereAt the scale height the pressure is 1/e times the surface pressure.e is a special number in math1/e = 37% Earth’s scale height is ~8kmScale height tells you how compact the atmosphere isScale height Elevation Atm. Pressure1 8km 37% =(1/e)12 16km 14% =(1/e)23 24km 5% =(1/e)3PYTS/ASTR 206 – Terrestrial planet atmospheres7Earth’s atmosphere has many sectionsAll our surface features (even the highest mountains) are in the tropospherePYTS/ASTR 206 – Terrestrial planet atmospheres8Here’s a problemWhat’s the atmospheric pressure at the Karman line – 100km elevation100km is 12.5 scale heights (i.e. 100km / 8km) The pressure is (1/e)12.5 Remember 1/e is 0.37 (or 37%).So (0.37)12.5 is 0.000004The atmospheric pressure at 100km (the ‘edge’ of space) is 4 millionths that at sea-levelPYTS/ASTR 206 – Terrestrial planet atmospheres9Different planets have different gases, temperatures and gravitiesIf gravity goes up?If temperature goes up?What if the atmospheric gases were more massive? E.g. CO2 vs. N2PYTS/ASTR 206 – Terrestrial planet atmospheres10Different planets have different gases, temperatures and gravitiesIf gravity goes up?Higher gravity makes the atmosphere more compactSmaller scale heightIf temperature goes up?What if the atmospheric gases were more massive? E.g. CO2 vs. N2PYTS/ASTR 206 – Terrestrial planet atmospheres11Different planets have different gases, temperatures and gravitiesIf gravity goes up?Higher gravity makes the atmosphere more compactSmaller scale heightIf temperature goes up?Higher temperatures makes the atmosphere less compactLarger scale heightWhat if the atmospheric gases were more massive? E.g. CO2 vs. N2PYTS/ASTR 206 – Terrestrial planet atmospheres12Different planets have different gases, temperatures and gravitiesIf gravity goes up?Higher gravity makes the atmosphere more compactSmaller scale heightIf temperature goes up?Higher temperatures makes the atmosphere less compactLarger scale heightWhat if the atmospheric gases were more massive? E.g. CO2 vs. N2 Heavier gases make the atmosphere more compact Smaller scale heightPYTS/ASTR 206 – Terrestrial planet atmospheres13Comparing planetary atmospheresCompositions are very differentTitan95%ZeroZeroZero5% methanePYTS/ASTR 206 – Terrestrial planet atmospheres14Carbon dioxide very common for the inner planetsNot on Titan or other outer solar system bodiesAny guesses why?Not on Earth…Any guesses why?PYTS/ASTR 206 – Terrestrial planet atmospheres15Carbon dioxide very common for the inner planetsNot on Titan or other outer solar system bodiesAny guesses why?Too cold! Carbon dioxide is frozen solid in the outer solar systemNot on Earth…Any guesses why?Carbon dioxide used to dominate Earth’s atmosphereRemoved by plantsPYTS/ASTR 206 – Terrestrial planet atmospheres16Comparing the amounts of atmosphere…Venus, Earth and Mars are hugely differentEarths surface has a pressure of (105 Pa) or 1 bar or 1 atmosphereVenus surface is about 90 barsMars surface is about 0.006 barsPYTS/ASTR 206 – Terrestrial planet atmospheres17Three major effectsReflection from cloudsWater on EarthSulfuric acid on VenusCools the surfaceGreenhouse effectWarms the surfaceCO2 on Earth, Mars and VenusTransports heat to cold areasPolar night on Earth and MarsNight on VenusRadiation and atmospheresRadiation and atmospheresPYTS/ASTR 206 – Terrestrial planet atmospheres18Venus and Earth’s greenhouse effect comparedEarth’s greenhouse boosts surface temperatures by about 33° CVenus’s greenhouse effects has boosted its surface temp. by 400° CResult is that lead melts on the surface of Venus (and so do spacecraft)Venus also has highly reflective clouds If the clouds weren’t there then the surface temperature would be 100s of degrees hotterPYTS/ASTR 206 – Terrestrial planet atmospheres19Air gets heated at the equatorHot air rises and cools offClouds form and lots of rain resultsCirculationCirculationPYTS/ASTR 206 – Terrestrial planet atmospheres20Hadley Cell circulationAir (now dry)
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