1. Lecture 1.3 – Structure of the Atmosphere

2. Today – we answer the following: How big is that atmosphere? Why is it like a cake? Why is cold in Denver? Why do mountaineers need oxygen?

3. Thickness The atmosphere is a very thin (relatively) layer of gas over the surface of the Earth Earth’s radius ~ 6400km Atmospheric thickness ~ 100km (If you travel 100km horizontally you don’t even get to St. Louis. If you do it vertically you’d be in space!)

4. The Relationship Between Air Pressure and Altitude Pressure decreases as you go up in height. The change is pressure is not constant. The pressure decreases exponentially with increasing height.

5. Air Density and height

6. Pressure & Density Figure 1.7 Gravity pulls gases toward earth's surface, and the whole column of gases exerts a pressure of 1000 hPa at sea level, 1013.25 mb or 29.92 in.Hg.

7. Pressure and Density Decrease with Height © 1998 Wadsworth Publishing Co. -- From Ahrens, Essentials of Meteorology

8. Vertical Pressure Profile Pressure increases at a curved rate proportional to altitude squared, but near the surface a linear estimate of 10 mb per 100 meters works well. Figure 1.8

9. Layers by temperature The atmosphere can be divided into layers based on temperature characteristics. This layering of the atmosphere also represents real physical barriers in that within the layers there is lots of vertical motion and mixing of air. This does not happen between layers.

10. Layers of the atmosphere Troposphere Stratosphere Mesosphere Thermosphere

11. Atmospheric Layers Figure 1.9 8 layers are defined by constant trends in average air temperature (which changes with pressure and radiation), where the outer exosphere is not shown.

12. The Troposphere Where we live (all the time) Contains 80% of the mass of the atmosphere Is between 8-16km (5-10 mi) deep Deeper at the equator than the poles WHERE WEATHER HAPPENS

13. Temperature Structure of the Atmosphere Warming in the stratosphere © 1998 Wadsworth Publishing -- From Essentials of Meteorology, 2nd Ed., by C.D. Ahrens, p. 9.

14. The Stratosphere Contains the ozone layer Where ultra-violet radiation is absorbed –This means that we are protected from harmful high-energy radiation from the sun –This also means that the stratosphere is warmer than the top of the troposphere because it has absorbed that energy

15. Ozone Is a variable gas At the surface –Is caused by chemical reactions between a variety of pollutant gases (such as nitrogen oxides) –Mostly caused by vehicle emissions –Is an irritant

16. Ozone In the stratosphere –Is a beneficial gas that absorbs ultra-violet radiation –Protects us from this harmful radiation –Is broken down by chemical reactions with chlorine containing gases (chlorofluorocarbons – CFCs): Man-made compounds used in aerosol sprays, refrigerators and air-conditioners

17. Summary of Chapter 1 To answer our questions –The atmosphere is pretty big, but on the other hand… –It’s like a cake because it has layers –It’s cold in Denver because the troposphere gets colder as you go up –Mountaineers need oxygen because the air is less dense at altitude and this means there are less oxygen molecules

18. Chapter 1 - Homework Read Chapter 1 of Ahrens From Ahrens, Page 24: Questions for review numbers: 2, 3, 11, 12 Due: Friday September 5 th (at the start of class)