371Lecture3 - 1/19/11 Structure of the Atmosphere ...

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Unformatted text preview: 1/19/11 Structure of the Atmosphere GEOG 371 January 20, 2011 The Atmosphere: Structure •  The atmospheric structure changes as the distance from the earth’s surface increases •  The transiDons from one layer (sphere) of the atmosphere to another is termed the “pause” •  The layers are defined by a change in temperature 1 1/19/11 •  Troposphere: Layer closest to the earth’s surface. ( 10 ­15km) Temperature decreases with height and there is rapid verDcal mixing. •  Stratosphere: Extends from the tropopause to the stratopouse (~45 to 55 km) temperature increases with alDtude and verDcal mixing is slow. The reason for this warming is that ozone. •  Mesosphere: Extends to ~80 to 90 km. Air temperature again decreases with height and there is rapid verDcal mixing in this layer. •  Thermosphere: Air temperature increases again in this layer, due to the absorpDon of solar radiaDon by oxygen molecules. Rapid verDcal mixing •  Exosphere: (> 500km) where gas molecule can escape from Earth’s gravitaDonal a[racDon •  Ionosphere : A region of the atmosphere where ions are produced. (usually considered as the thermosphere and exosphere together) •  Troposphere: Layer closest to the earth’s surface. ( 10 ­15km) Temperature decreases with height and there is rapid verBcal mixing. •  Stratosphere: Extends from the tropopause to the stratopouse (~45 to 55 km) temperature increases with alBtude and verBcal mixing is slow. The reason for this warming is that ozone. •  Mesosphere: Extends to ~80 to 90 km. Air temperature again decreases with height and there is rapid verDcal mixing in this layer. •  Thermosphere: Air temperature increases again in this layer, due to the absorpDon of solar radiaDon by oxygen molecules. Rapid verDcal mixing •  Exosphere: (> 500km) where gas molecule can escape from Earth’s gravitaDonal a[racDon •  Ionosphere : A region of the atmosphere where ions are produced. (usually considered as the thermosphere and exosphere together) 2 1/19/11 DayBme and NighKme Boundary Layer Free troposphere Free troposphere Entrainment zone / Inversion layer Entrainment zone / Inversion layer Cloud layer Subcloud layer Altitude Convective mixed layer Boundary layer Residual layer Altitude Boundary layer Nocturnal boundary layer Surface layer Surface layer Daytime temperature Nighttime temperature Figure 3.4 . . Zonally ­Averaged Temperatures January July 100 100 80 160 200 220 60 240 280 40 20 260 210 240 220 200 80 60 260 240 260 40 20 140 220 270 240 210 210 180 200 220 210 200 220 220 0 160 190 AlDtude ( Altitude (km) km) Altitude (km) km) AlDtude ( 180 0 290 -80 -60 -40 -20 0 20 40 60 80 Latitude(deg) 290 -80 -60 -40 -20 0 20 40 60 80 Latitude(deg) Figure 3.5 3 1/19/11 Processes AffecBng Temperature Temperature ProporDonal to kineDc energy of an air molecule traveling at its average speed 4 1 2 kB T = M v a ! 2 ConducDon Transfer of energy from molecule to molecule ConvecDon Transfer of energy by verDcal mass movement of a fluid AdvecDon Transfer of energy by horizontal movement of a fluid RadiaDon Energy transferred in the form of electromagneDc waves Toricelli's Experiment With Mercury Barometer 1643 Evangelista Torricelli records first sustained vacuum and demonstrates that air pressure changes daily. Height of fluid = Air pressure / (fluid density x gravity) 1648 Blaise Pascal and brother ­in ­law Florin Périer demonstrate that air pressure decreases with increasing alDtude at Puy ­de ­Dôme, France. Edgar Fahs Smith CollecDon University of Pennsylvania Library 4 1/19/11 Toricelli's Experiment With Mercury Barometer Example 3.1. How much mercury balances 1000 mb of pressure? h= p 1000 mb 100 kg m#1 s# 2 = " = 0 .752 m = 29.6i nches !g 1 3 558 k g " 9 .8 1 m 1 mb , 3 2 m s Pressure and Density Versus AlBtude 1 mb (above 99.9%) 60 10 mb (above 99%) 40 100 mb (above 90%) 20 AlDtude (km) Altitude (km) 80 Altitude (km) 100 80 AlDtude (km) 100 500 mb (above 50%) 0 0 200 400 600 800 1000 Air pressure (mb) Figure 3.2 60 40 20 0 0 0.4 0.8 1.2 Air density (kg m-3) 5 1/19/11 Robert Boyle (1627 ­1691) Jacques Charles (1746 ­1823) Amedeo Avogadro (1776 ­1856) Edgar Fahs Smith CollecDon, University of Pennsylvania Library John Dalton (1766 ­1844) Edgar Fahs Smith CollecDon, U. Penn. Library 6 1/19/11 EquaBon of State for Dry Air Total atmospheric pressure pa = pd+pv EquaDon of state for dry air pd = NdkBT = ρdR'T Dry ­air gas constant: R'=R*/md =kBA/md (3.11) (3.12) Dry ­air mass density: ρd = Nd md /A Volume Mixing RaBo χq=Nq/Nd= pq/pd (molecules of gas/molecule of dry air) (3.14) 1% = 0.01 = 104 ppmv 1 ppmv = 0.000001 = 0.0001% = 1000 ppbv = 106 pptv 7 1/19/11 8 ...
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