Reasons for Seasons (recap)

Transcription

1 Reasons for Seasons (recap) Revolution (around the sun) Rotation (on its axis) Sphericity Axial parallelism Earth s Tilt

2 The Earth s tilt perpendicular to plane of equator Q: do these planes form great circles?

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4 Arctic Circle as viewed from above the plane of the ecliptic 24 hrs day the parallel of the Arctic Circle is set by Earth s tilt 24 hrs night Credit:

5 the circle of illumination divides the earth equally into day and night halves - it forms a great circlenote that 1/2 of earth is always in the light equinox June 21

6 March of the Seasons

7 earthyear.mov

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9 Earth s Modern Atmosphere Chapter 3

10 The atmos- spheres note: relative size of atmosphere not to scale

11 The atmosphere is crucial to life analogous to a cellular membrane, regulating what can enter (such as filtering UV rays) How much atmosphere is there? the total mass of the atmosphere is 5.3x10 18 kg BUT mass ocean = 1.4x10 21 kg & mass Earth = 6x10 24 kg How thick is the atmosphere? The atmosphere is incredibly thin - if Earth were the size of a 12 globe, 99% of its atmosphere would be about as thick as the paint on this globe!

12 Credit: What is air? air is a mixture of nitrogen and oxygen with some trace gases verage density of air is 1.3 kg/m 3

13 Evolution of the Atmosphere the present composition of the atmosphere represents the net sum of many processes (biological and chemical) operating over 100 s of millions of years if Earth were lifeless, its atmospheric composition would be very different (for example, no oxygen)

14 Earth s atmosphere in the distant past *Probable early atmosphere: CH 4, H 2, H 2 O, NH 3 *Early Evolution H 2 is lost H 2 O photochemically disassociates H 2 is lost CH 4 + O 2 CO 2 + H 2 O NH 3 + O 2 N 2 + H 2 O CO 2 reacts to form CaCO 3 *3.5 by: N 2, CO 2, H 2 O (mostly N2) Photosynthesis and oxygen Fe is oxidized, last banded iron *2 by to present: evolution of the modern atmosphere

15 atmospheric oxygen (O 2 ) is produced by photosynthesis light 6CO H 2 O C 6 H 12 O 6 + 6H 2 O + 6O 2 carbon dioxide + light => sugars + oxygen From World Book 2002 World Book, Inc., 233 N. Michigan Avenue, Suite 2000, Chicago, IL All rights reserved. World Book illustration by James Teason phytoplankton in oceans CO 2 Stomata pores on leafs O2 Troughton and Donaldson zajednicki/phytoplankton.jpg

16 most atmospheric nitrogen (N 2 ) is produced by volcanoes

17 atmospheric carbon dioxide (CO 2 ) is produced and released by terrestrial photosynthesis and respiration, as well as air-sea gas exchange atmospheric water vapor (H 2 O) varies tremendously (from <1-4% by volume) and is affected by evaporation and condensation the other relatively abundant gas, argon (Ar), is inert (not reactive) and not involved in biological processes - produced by radioactive decay of 40 K

18 air density decreases with height in the atmosphere because of gravity

19 pressure decreases rapidly with altitude average tropopause elevation elevation where jets typically fly elevation of Mt. Everest ~20% of sea level ~10% of sea level ~30% of sea level Credit:

20 the atmosphere has several layers with distinct properties and functions think of these layers as concentric shells or spheres we can characterize vertical profiles according to three criteria

21 Layers classified by temperature over 99% of the atmosphere is contained in the troposphere and stratosphere Stratosphere Tropopause Troposphere

22 the tropopause elevation (and thus the thickness of the troposphere) varies with latitude the tropical tropopause is twice as high as the polar tropopause because of vigorous surface heating at low latitudes Credit: apter9/graphics/trop_hgt.free.gif

23 Credit: why does T increase with height in the stratosphere? 90% of atmospheric mass ~5x10^18 kg why does T decrease with height in troposphere?