This is the chemical compositon of the atmosphere, excluding water vapor. You can see that Nitrogen is dominant, but it is really just a filler, not

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2 This is the chemical compositon of the atmosphere, excluding water vapor. You can see that Nitrogen is dominant, but it is really just a filler, not of great significance in weather and climate. Note the greenhouse gases carbon dioxide being the most important, but also Methane and others. These are generally increased due to human activity such as burning of fossil fuels, land-use practices, etc. 2

3 This is just an easier view of the information from the previous slide. 3

4 Carbon 365 ppm is the current concentration. 150 years ago it was at a more natural level of about 280 ppm. Water vapor is actually far and away the most significant of the greenhouse gases and it varies greatly in concentration from place to place and from time to time. The amount of water vapor in the air depends primarily on two factors: (1) distance from a source of moisture, primarily oceans; and (2) temperature of the air; warmer air holds more water vapor than cooler air. 4

5 Water vapor pressure, in millibars, is a common way of expressing the concentration of this gas in the atmosphere. Here you can see the spatial pattern in the USA, which is mostly a result of distance from the warm waters of the Gulf of Mexico and tropical Atlantic Ocean. So you see why Fargo doesn t receive a lot of snow in the winter? 5

6 Same pattern in the summer much more moisture in the atmosphere because of warmer air temperatures and warmer ocean waters. Also, the flow of air from the Gulf into the USA is stronger in the summer. For us on the west coast, you can see that we don t get nearly as much moisture off the Pacific Ocean. 6

7 Self-explanatory. Do you know what explains the see-saw pattern? 7

8 Methane and Nitrous Oxide are two more greenhouse gases, in concentrations that are affected by human activity. 8

9 The standard graph of average annual global temperatures. You see the warming trend up through the 1940 s; then things sort of leveled out, and then Al Gore was born and temperatures began to increase on average since then, with a clear trend of warming over the last 30 years. 9

10 Some of these images might be links, not sure. Click on them and see. Right now, January and February 2011, there is a wonderful photographic exhibit on the Polar Bears and the World Forestry Center. Earn some brownie points from your instructor Go see it! 10

11 Click on the Time Magazine link here and read the article. 11

12 This is the trend of menthane concentrations in Canada where warming has caused melting of partially-frozen soils, and therefore the release of methane into the atmosphere. 12

13 These layers of the atmosphere are defined by thermal (temperature) characteristics. The Troposphere is characterized by a decrease with temperature with distance about the surface (known as the lapse rate ). It is the layer in which the gases are concentrated, including water vapor of course, and it which most of what we know as weather occurs. So, we don t pay much attention to the higher layers this term. 13

14 Ozone is concentrated in a layer in the stratosphere and is important in that it traps (absorbs) ultraviolet radiation, thereby preventing that stuff from reaching the surface of the earth. Thank goodness for the ozone layer, which was being depleted for many years, but now is rebuilding itself as we have quit using flourocarbons and other substances that were destroying it. Wouldn t it be nice if we were able to be equally successful in reducing the emissions of carbon dioxide and other greenhouse gasses. 14

15 These things exist in the atmosphere due to natural processes of many kinds; but many forms of human activity also add to the aerosol loading of the atmosphere, and have an influence on energy exchanges. 15

16 Who knows? 16

17 A lot of reaserch goes into this question. There is a long study on your Reading list that you can wade through if you are so inclined. It is not mandatory. 17

18 OK, back to the vertical structure of the atmosphere. 18

19 Air density (atmospheric pressure) decreases above the surface. The higher you go, the less dense the air; that is, the lower the atmospheric pressure. This makes sense because pressure is essentially the weight of the overlying air. Good quiz question!!! 19

20 See how pressure decreases with height above the surface. 20

21 Same thing, just showing the relationship between units. If average surface pressure is 1013 millibars (common pressure unit) ; then 500 mb would represent the level at which half of the mass of the atmospehre is above and half below. Us weather/climate types like to talk about the 500 mb level or the 800 mb level or whatever! 21

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23 Complex patterns of air movement near the surface of the earth where a lot of factors come into play pressure gradients, topography, surface conditions, etc. 23

24 More simplified patterns higher in the atmosphere where large-scale pressure gradients dominate, and surface conditions are less significant. Notice that the general pattern of winds is west-to-east; this is always the case in the middle latitudes. For direction of the wind, just think of the wind arrows on the map as arrow with feathers flowing with the wind. The number of feathers indicates the speed of the wind at that point. 24

25 OK, here is the temperature structure. The normal lapse rate prevails on average through the Troposphere. Be sure you have read about this in your online Ritter textbook. 25

26 One of my heroes; died this past summer. Early 70 s too young! 26