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 2nd midterm weighted heavier Slides from Review Sessions are posted on course website: http://meteora.ucsd.edu/~iacob/sio20/

Climate Model vs. Weather Model If we cannot predict weather more than 10 days into the future, why should we believe climate model projections 50-100 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, 2012 - Hard to predict life expectancy of an individual, but much easier to predict life expectancy for a large group

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

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

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

Often, the net result of these two processes is an “Inversion Layer” Inversion Layer ==> Region where temperature increases with height.

Very stable layer

Height

Temperature

Inversion Layer

Inversion Base mixing

The inversion base limits the vertical extent of mixing ==> inversion base acts like a "lid"

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

Surface

mixing

Clicker Question Set Frequency to "AD"

If the Inversion Base is below the LCL, you would expect (A) clouds to form (B) no clouds to form

LCL

Inversion Base

Surface

mixing

Clicker Question Set Frequency to "AD"

If the Inversion Base is below the LCL, you would expect (A) clouds to form (B) no clouds to form

LCL

Inversion Base

Surface

mixing

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

Surface

mixing

Here, inversion base prevents mixing from reaching LCL

==> NO CLOUDS FORMED

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)

LCL

Inversion Base

Surface

mixing

Here, mixing allowed to extend above and beyond LCL

==> CLOUD FORMS between LCL and Inversion Base

cloud

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)

LCL

Surface

mixing

Here, mixing allowed to extend far above LCL ==> Cloud may not form if too much dry air mixed in from above.

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.

Figure from Ryan Kittell, UCLA

Distinct decrease in number of clear days during May and June

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.

Pollutant: Text: “Substance emitted into air in concentrations large

enough to harm people/animals, vegetation or environment”

Pollutant: Text: “Substance emitted into air in concentrations large

enough to harm people/animals, vegetation or environment”

Other: “Perturbation of the normal background state”

Some Natural Polluters: • Forest Fires • Volcanoes • Dust Storms

Some Natural Polluters: • Forest Fires • Volcanoes • Dust Storms • Vegetation

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

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

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

Acid Rain SO2 + H20 = H2SO4 Sulfur dioxide + liquid water = Sulfuric Acid 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

Primary source is fossil fuel power plants

As power plant emissions are increasingly regulated, the amount of acid rainfall has decreased.

Acid rain deposition in the USA from 1983 through 1997. From: Driscoll (2001)

Particulates (Aerosols) Impact Radiation Balance: 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)

By-product of fossil fuel burning

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

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

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

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 NO2 + VOCs + Sunlight ==> Ozone (O3) NO2: Nitrogen Dioxide VOCs: Volatile Organic Compounds This is the dominant pollution in SW USA (LA Smog)

- mainly in summer (more sunlight) - “photochemical” smog

} from car exhaust

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

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

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

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

Height

Temp

~100- 200 ft

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

Temp

~100- 200 ft

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

Pollution

Height

Temp

~100- 200 ft

Height

Temp

~0.5 - 1.0 km

INVERSION LAYER

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

Pollution

Pollution

Salt Lake City

Los Angeles

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