Final Exam: Monday March 17 3:00-6:00 pm (here in Center 113) Slides from Review Sessions are posted on course website:

Transcription

1 Final Exam: Monday March 17 3:00-6:00 pm (here in Center 113) 35% of total grade Format will be all multiple choice (~70 questions) Final exam will cover entire course - material since 2 nd midterm weighted heavier Slides from Review Sessions are posted on course website:

2 Climate Model vs. Weather Model If we cannot predict weather more than 10 days into the future, why should we believe climate model projections years from now??? Results from climate models are projections of the statistical behavior of the climate system and NOT predictions of particular events. Analogies: - Seasonal changes: Easy to say that December will be colder than June, but hard to say what the temperature will be on December 15, Hard to predict life expectancy of an individual, but much easier to predict life expectancy for a large group

3 Inversion Layer: Important climate feature in Southern California Plays major role in: - marine stratus clouds (i.e., June gloom) - air pollution throughout the region

4 Marine Stratus Clouds: Low-lying clouds often observed in coastal Southern California during Spring and early Summer Form over the water and wind can advect clouds over adjacent land areas Clouds form when wind mixes moist surface air upwards where relative humidity reaches 100% Lifting Condensation Level (LCL) Height that surface air must rise for relative humidity to reach 100% and clouds begin to form

5 While mixing is going on near surface, also have sinking air from Pacific High. Pacific High nearly constant feature near So. Cal. Sinking air warms due to compression Now have competing processes - Mixing ==> leads to rising air that cools - Pac High ==> leads to sinking air that warms

6 Often, the net result of these two processes is an Inversion Layer Inversion Layer ==> Region where temperature increases with height. Very stable layer Height Inversion Layer mixing Inversion Base Temperature The inversion base limits the vertical extent of mixing ==> inversion base acts like a "lid"

7 The relative location of the LCL and the inversion base determine if clouds will form: Case A: Inversion Base below LCL (typical for very strong High Pressure or very weak mixing) LCL Inversion Base mixing Surface

8 Clicker Question Set Frequency to "AD" If the Inversion Base is below the LCL, you would expect LCL Inversion Base mixing (A) clouds to form Surface (B) no clouds to form

9 Clicker Question Set Frequency to "AD" If the Inversion Base is below the LCL, you would expect LCL Inversion Base mixing (A) clouds to form Surface (B) no clouds to form

10 The relative location of the LCL and the inversion base determine if clouds will form: Case A: Inversion Base below LCL (typical for very strong High Pressure or very weak mixing) LCL Inversion Base mixing Surface Here, inversion base prevents mixing from reaching LCL ==> NO CLOUDS FORMED

11 The relative location of the LCL and the inversion base determine if clouds will form: Case B: Inversion Base above LCL (typical of moderate to strong High Pressure) mixing cloud Inversion Base LCL Surface Here, mixing allowed to extend above and beyond LCL ==> CLOUD FORMS between LCL and Inversion Base

12 The relative location of the LCL and the inversion base determine if clouds will form: Case C: No Inversion Layer (typical of weak High Pressure or even Low Pressure system) mixing LCL Surface Here, mixing allowed to extend far above LCL ==> Cloud may not form if too much dry air mixed in from above.

13 Best chance for marine stratus clouds: - when inversion layer present - and when inversion base ABOVE the LCL This typically happens when strong Pacific High Pressure over Southern California ==> Usually Apr - Sept. During May-Jun, local winds most likely to bring the marine stratus over coastal land.

14 Distinct decrease in number of clear days during May and June Figure from Ryan Kittell, UCLA

15 CATALINA EDDY - prevailing northwesterly wind off of central Calif. - interaction with coastline near Pt. Conception causes strong winds to rotate cyclonically - results in southerly component wind in So. California. Pt Conception L.A. S.D.

16 Pollutant: Text: Substance emitted into air in concentrations large enough to harm people/animals, vegetation or environment

17 Pollutant: Text: Substance emitted into air in concentrations large enough to harm people/animals, vegetation or environment Other: Perturbation of the normal background state

18 Some Natural Polluters: Forest Fires Volcanoes Dust Storms

19 Some Natural Polluters: Forest Fires Volcanoes Dust Storms Vegetation

20 Anthropogenic Sources Industry / Factories Fossil Fuel Power Plants Transportation (planes, trains, cars,...) Heating Units (gas/coal/wood fired stoves, etc.) Fertilizer for Farming and probably many more... Will focus mainly on man-made pollution

21 First Major Air Pollution Problem: - London in winter coal burning for heat SMoke + fog = SMOG Later - Los Angeles summer car exhaust + sunlight called SMOG, but process different than above

22 First Major Air Pollution Problem: - London in winter coal burning for heat SMoke + fog = SMOG Later - Los Angeles summer car exhaust + sunlight called SMOG, but process different than above Usually, air pollution not a problem until certain atmospheric conditions aggravate problem

23 Acid Rain SO 2 + H 2 0 = H 2 SO 4 Sulfur dioxide + liquid water = Sulfuric Acid Primary source is fossil fuel power plants Occurs in clouds (acid rain) and fog (acid fog) Can be a political issue - winds transport pollutants far from source - emissions from one region can end up as acid rain in a different region

24 As power plant emissions are increasingly regulated, the amount of acid rainfall has decreased. Acid rain deposition in the USA from 1983 through From: Driscoll (2001)

25 Particulates (Aerosols) Impact Radiation Balance: By-product of fossil fuel burning 1) Direct Effect - aerosols tend to reflect/scatter sunlight (cooling) 2) Indirect Effect via Clouds - more aerosols = more CCN = more cloud droplets ==> more reflection of solar radiation (cooling)

26 Clicker Question Set Frequency to "AD" With more particulate aerosols, the available cloud water is spread out over many more droplets and as a result the average cloud droplet is smaller. How would you expect high concentrations of aerosols to affect the lifetime of the cloud? (A) shorter cloud lifetime (B) longer cloud lifetime (C) not a factor

27 Clicker Question Set Frequency to "AD" With more particulate aerosols, the available cloud water is spread out over many more droplets and as a result the average cloud droplet is smaller. How would you expect high concentrations of aerosols to affect the lifetime of the cloud? (A) shorter cloud lifetime (B) longer cloud lifetime (C) not a factor

28 Ship Tracks: Pollution (aerosols) from ships enhances cloud formation and allows clouds to last longer

29 Primary Pollutant ==> enters atmosphere directly from source examples: smoke from forest fire, tailpipe emissions Secondary Pollutant ==> forms when primary pollutant reacts with another pollutant or air component example: tropospheric ozone NO 2 + VOCs + Sunlight ==> Ozone (O 3 ) NO 2 : Nitrogen Dioxide VOCs: Volatile Organic Compounds } from car exhaust This is the dominant pollution in SW USA (LA Smog) - mainly in summer (more sunlight) - photochemical smog

30 Role of Weather Wind - a) Will help disperse pollution b) Can also transport to another region Rain - a) Can help remove from atmosphere b) Can also carry (acid rain) Atmospheric Stability

31 Clicker Question Set Frequency to "AD" When would you expect pollution to be more severe? (A) with a stable atmosphere (B) with an unstable atmosphere (C) atmospheric stability not a factor

32 Clicker Question Set Frequency to "AD" When would you expect pollution to be more severe? (A) with a stable atmosphere (B) with an unstable atmosphere (C) atmospheric stability not a factor

33 Role of Weather Wind - a) Will help disperse pollution b) Can also transport to another region Rain - a) Can help remove from atmosphere b) Can also carry (acid rain) Atmospheric Stability: Inversions - Often provide stable conditions that amplify pollution problems

34 RADIATION INVERSION - surface cools at night due to emission of infrared radiation - typically during clear, calm winter night - usually lasts only a few hours Height ~ ft Temp

35 RADIATION INVERSION - surface cools at night due to emission of infrared radiation - typically during clear, calm winter night - usually lasts only a few hours Height ~ ft Pollution Temp

36 RADIATION INVERSION - surface cools at night due to emission of infrared radiation - typically during clear, calm winter night - usually lasts only a few hours SUBSIDENCE INVERSION - strong high pressure overhead - air sinks - compresses and warms - cool mixed layer near surface - typical conditions during summer in coastal Southern California - can last for days-weeks Height Height ~ ft ~ km Pollution INVERSION LAYER Pollution Temp Temp

37 Salt Lake City Los Angeles

38 Typical Summertime conditions in SW USA: - Pacific High (semi-permanent feature) - Relatively low wind speeds ==> prime conditions for Subsidence Inversions Coastal Southern California: - Sea-breeze cool air off ocean -> stable -> maintains inversion throughout the day Why is Los Angeles so Smoggy? - Too many people/cars (obvious) - Surrounded by mountains pollutants cannot escape horizontally