In the news Record low temperatures in the Northern Hemisphere.

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1 In the news Record low temperatures in the Northern Hemisphere. - This December was much colder than recent Decembers in the United States and northern Europe. - Coldest December in the UK in 14 years. - End of Global Warming?

2 While some places were colder others were warmer than average. Last year was actually the fifth warmest year on record as far as global temperatures were concerned. The four warmest years were, in ascending order, 2002, 2003, 2005 and The last decade was the warmest on record, followed by the 1990s and then the 1980s, so the world is definitely warming up. Richard Betts BBC news

3 Recap from last class: Weather is the condition of the atmosphere at a particular place and time. The atmospheric parameters include temperature, humidity, precipitation, cloudiness, wind, and barometric pressure Climate is the set of meteorological conditions that prevail in a particular place or region over a long period of time. Climate can vary over broad timescales from years to millennia.

4 Chapter 1 The Earth and Its Atmosphere 30 km 30 km C = 2πr x 10 4 km r 6500 km Ratio: Height/ Length is 30/(4.082 x 10 6 ) 7.35 x height of the atmosphere is extremely small compared with its length air motions are primarily horizontal.

5 air motions are primarily horizontal However, very small vertical motions are very important, e.g., they causing the development/inhibition of clouds.

6 Composition of the atmosphere 1. Permanent gases 2. Variable gases 3. Aerosols

7 1. Permanent gases stable concentration in the atmosphere. N 2 + O 2 = 99% of atmospheric volume below 80 km. They are chemically active. Ar, Ne, He, H2, Xe < 1% and are chemically inert.

8 1. Permanent gases stable concentration in the atmosphere. account for about 99% of the atmospheric mass occur in a constant proportion in the lowest ~80 km of the atmosphere. although individual molecules exchange between the atmosphere and Earth, the total concentration remains the same chemical homogeneity Lowest 80 km is called the Homosphere and is sometimes considered to be the entire atmosphere. The atmosphere above this is called the Heterosphere.

9 1. Permanent gases Nitrogen: N 2 is added and removed from the atmosphere very slowly long residence time** of ~42 million years. N 2 is relatively unimportant for most meteorological and climate processes some gases containing N are important to the Earth s climate such as NO 2. Oxygen: O 2 is crucial to the existence of almost all forms of life currently on the Earth. Its residence time is ~5000 years. ** The residence time of a gas is the average time an individual molecule remains in the atmosphere.

10 2. Variable gases distributions vary both in time and space. account for < 1% of the atmosphere below 80 km. some of these gases impact the behavior of the atmosphere considerably. H 2 O + CO 2 + O 3 = 0.296% of atmospheric volume.

11 Water Vapor (0 to 4%) water vapor varies considerably in both space and time. Continually cycled between atmosphere and Earth by evaporation, condensation and precipitation. (hydrologic cycle) Stores and releases large amounts of heat via evaporation and condensation. Water vapor has a residence time of only 10 days. Water vapor density is greatest at the surface, and decreases rapidly with height. Water vapor is extremely important for clouds Water vapor absorbs radiant energy emitted from the Earth s surface. (Greenhouse gas)

12 Carbon Dioxide (0.036%) (CO 2 ) is supplied to the atmosphere through plant and animal respiration, through decay of organic material, volcanic eruptions, anthropogenic effects such as burning of fossil fuels (coal, oil etc.) and deforestation. It is removed through photosynthesis, the process by which green plants convert light energy to chemical energy. Oxygen is released into the atmosphere as a by-product. CO 2 has a residence time of ~150 yrs. It is an effective absorber of longwave radiation emitted from the Earth s surface. (Greenhouse gas) Its concentration in the atmosphere has increased ~18% since 1958.

13 Ozone (0.01%) (O 3 ) is an unusual molecule made up of 3 Oxygen atoms. It forms when individual O atoms collide with an O 2 molecule. 97% is found in the upper atmosphere or stratosphere (we ll define this a little later). O 3 is vital for absorbing lethal UV radiation from the sun. As it does this, it breaks down into its constituent components O + O 2. Ozone concentrations in the stratosphere have been decreasing due to emission of chlorofluorocarbons (CFCs). Near the surface ozone is a pollutant (photochemical smog), but exists there in extremely small amounts.

14 3. Aerosols are small solid particles or liquid droplets (except water particles) in the air. They are formed by both natural and anthropogenic means. Aerosols typically have residence times of a few days to several weeks. Apart from pollution, aerosols play an important role as condensation nuclei, the core about which water can condense in clouds. Formed from chemical reactions, wind-generated dust, volcanic ejections, sea spray, and combustion (e.g., fine ash) removed from the atmosphere in precipitation.

15 Composition of the atmosphere - recap 1. Permanent gases 2. Variable gases 3. Aerosols

16 Vertical Structure of the atmosphere 1. Density 2. Pressure 3. Temperature

17 mass Density: ρ = volume (kg/m 3 or g/cm 3 ) Initial State ρ ρ Incompressible fluid Initial State ρ ρ Compressible fluid The density of the gases that make up the atmosphere is constantly changing. In addition, the atmosphere is compressible.

18 Near sea level, air density ~ 1.2 kg m -3. Sea-level At Denver CO, (~1.6 km altitude or 1 mile), air density is approximately 85% of that at sea level, or 1.01 kg m 3. Denver, CO

19 Pressure: Can be thought of as weight of air above you. (Note that pressure acts in all directions!) So as elevation increases, pressure decreases. Pressure = force / area Height (km) Higher elevation Less air above Lower pressure Lower elevation More air above Higher pressure

20 A 1 in 2 column of air extending from the surface to the top of the atmosphere weights 14.7 lbs. Pressure near sea level is close to 14.7 lbs/in 2. We use millibars (mb), or hectopascals (hpa) mb = hpa Pressure at any level may be measured in terms of the total mass of air above any point. 1 in 2

21 Density and Pressure Variation Key Points: 1. Both decrease rapidly with height 2. Air is compressible, i.e. its density varies Ahrens

22 Pressure Decreases Exponentially with Height Logarithmic Decrease 1 mb 10 mb 48 km 32 km For each 16 km increase in altitude, pressure drops by factor of mb 16 km 48 km - 1 mb 32 km - 10 mb 16 km mb 0 km mb Ahrens, Fig. 1.5

23 Exponential Variation Logarithmic Decrease For each 5.5 km height increase, pressure drops by factor of km mb 11 km mb 5.5 km mb 0 km mb

24 Equation for Pressure Variation We can Quantify Pressure Change with Height p(at elevation zin km) where z p p MSL = p 10 MSL is elevation in kilometers (km) is pressure in millibars (mb) at elevation z in meters (km) Z /(16km) is pressure (mb) at mean sea level

25 What is Pressure at 2.8 km? (Summit of Mt. Lemmon) Use Equation for Pressure Change: p (at elevation Z in km) = p MSL x 10 -Z/(16 km) Set Z = 2.8 km, p MSL = 1013 mb p (2.8 km) = (1013 mb) x 10 (2.8 km)/(16 km) p (2.8 km) = (1013 mb) x 10 (0.175) p (2.8 km) = (1013 mb) x = 677 mb

26 Pressure and wind Atmospheric pressure impacts every aspect of weather. Air moves from high pressure to low pressure wind Air tends to rise in regions of low pressure and sink in regions of high pressure Pressure Units: mb, hpa, inches Hg, mm Hg Wind Units: m/s, mph, km/h, kts

27 Temperature Stratification Divide into several vertical layers based on electrical, temperature, and chemical (homogeneous/heterogeneous), characteristics. Together with the change in density with height, this gives the atmosphere its structure. Standard atmosphere is calculated based on profiles at 30 latitude.

28 Contains 80% of the atmospheric mass Depth ranges from ~8 km at the poles to ~16 km in the tropics Layer of most interest to this course!!! Tropopause Troposphere The lapse rate is the average decrease in temperature with height ~ 6.5 C/km Rapid decrease in temperature with height Majority of the weather occurs here

29 Contains ~19.9% of the atmospheric mass Temperature increases with height from 20-~50 km (Temperature inversion) Layer of some interest to this course!!! Statopause Stratosphere The ozone layer absorbs much of the incoming solar radiation, warming the stratosphere, and protecting us from harmful UV radiation Isothermal in lowest 10 km Lapse rate is 0 Little weather occurs here

30 Mesosphere Neither of these layers have much interest for the Meteorologist Temperature once again decreases with height Thermosphere Temperature once again increases with height

31 Ionosphere - extends from the upper mesosphere into the thermosphere. Contains large numbers of charged particles called ions. Ions are atoms or molecules that have gained an electron or lost an electron so that they carry a charge. This occurs in the upper atmosphere because the molecules are being constantly bombarded by solar radiation. Important for reflecting AM radio waves back to Earth. Also responsible for the aurora borealis (northern lights) and aurora australis (southern lights).

32 Summary: Divide the atmosphere into several vertical layers based on temperature characteristics. Together with the change in density with height, this gives the atmosphere its structure. Thermosphere Mesosphere Stratosphere Temperature Inversion Stable layer Troposphere

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34 Assignment On 3 x 5 card, 1) write two questions regarding topics you would like me to discuss during the course and 2) Put your name and clicker radio receiver number. Please turn in Thursday Jan 21. FAILURE TO COMPLETE THIS ASSIGNMENT RESULTS IN AN AUTOMATIC ADMINSTATRATIVE DROP!!

35 Potential Activity: Liquid Nitrogen

36 Weather Map

37 Weather Map Symbols Ref:- Appendix B Ahrens Wind direction (from the NW) Wind speed (21-25 miles/hr) * * +22/ 30 Barometric Pressure at sea level ( mb) Pressure change in the last 3 hrs (2.2mb higher than 3hrs ago).

38 Temperature Tends to change gradually in horizontal or vertical directions also changes with time for the same weather system diurnal cycle the only place there are rapid changes in temperature is in the vicinity of fronts Units:- C, F, K

39 Weather Map Symbols Ref:- Appendix C Ahrens Temperature F * * +22/ 30

40 Moisture: Water Vapor Two common ways to express the amount of water vapor in the air - Relative Humidity:- is the amount of water vapor in the air relative to the maximum amount that could be present in the air. Units: % - Dew Point Temperature:- Td > 15 C is humid. Td > 20 C is very uncomfortable and Td < 5 C is dry.

41 Weather Map Symbols Ref:- Appendix C Ahrens 34 * * / 30 Present weather (light snow) Dew point F

42 G1 Springfield, MO Ws=15 kts Wd=N T=20 F Td= 4 F P= W=full cloud cover G2 Kalispell, MT Ws=5 kts Wd=NNE T=16 F Td= 12 F P= W=sky obscured Cts. Full of snowflakes G3 Arcata/Eureka, CA Ws=10 kts Wd=SSE T=57 F Td= 55 F P= W=2 miles visibility Cts rain, heavy at time of observation G4 Ws=5 kts Wd=SE T=34 F Td= 32 F P= W=light fog G5 Ws=15 kts Wd=WNW T=54 F Td= 21 F P= W=clear skies G6 Ws=5 kts Wd=NE T=41 F Td= 28 F P= W=slight rain showers McCall, Idaho Sierra B/Ruidoso, NM Alaska G7 Saranac Lake, NY Ws=5 kts Wd=NNE T= -8 F Td= -17 F P= W=full cloud cover G8 Ontario, Canada Ws=10 kts Wd=NW T= -17 F Td= -27 F P= W=full cloud cover G9 Saskatchewan, Canada Ws=20 kts Wd=SE T= -4 F Td= -9 F P= W=cts snow, light at time of ob.