Chapter 19: 1, 6, 7, 8, 10, 11, 15, 16, 29, 20, 21, 27, 42, 46Chapter 20: 1, 2, 7, 13, 14, 16, 19, 20, 34, 37, 40, 41, 42, 43, 47, 48Chapter 21: 1, 2, 3, 7, 10, 12, 13, 14, 16, 19, 20, 21, 27, 29, 30, 32, 34, 38, 39, 44, 45, 46Chapter 22:1, 3, 4, 6, 9, 10, 11, 12, 13, 16, 18, 24, 25, 27, 28, 31, 32, 34, 36, 39, 48

Next quiz: this Friday, 10-20 questions from …

Plus more on Wednesday.

The atmosphereis layered accordingto its temperaturestructure

In some layersthe temperatureincreases with height

In others it decreaseswith height or is constant

Why?

… “pause” is a level

… “sphere” is a layer

Heat transfer processes

• Conduction - Where molecules transfer energy by coming into contact with one another.

• Convection - Where a fluid moves from one place to another, carrying it’s heat energy with it.– In atmospheric science, convection is usually associated

with vertical movement of the fluid (air or water).

– Advection is the horizontal component of the classical meaning of convection.

• Radiation - The transfer of heat by radiation does not require contact between the bodies exchanging heat, nor does it require a fluid between them.

Conduction – Direct Heat Transfer

Conduction of heat energy occurs as warmer molecules transmit vibration, and hence heat, to adjacent cooler molecules.

Warm ground surfaces heat overlying air by conduction.

Heat driven convection

1. Bottom water is warmed

2. It expands an is therefore less dense

3. It rises to the surface and then spreads out

4. Cooler water at the sides descends to fill the void

A convective thunderstorm

Temperature, Density, and Convection

Heating of the Earth’s surface during daytime causes the air to mix

Warmed from Below

Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface does it generate sensible heat to warm the ground and generate longwaveenergy.This heat and energy at the surface then warms the atmosphere from below.

Latent (hidden) Heat:Water phase changes

Moist Convection

A daily occurrence in summer along the high plains --caused by surface heating, rising buoyant plumes, and the release of latent heat in clouds

Electromagnetic Radiation

Radiation travels as waves or photons

Waves do not require molecules to propagate

Rate of energy loss is proportional to the 4th power of temperature

Ways to label radiation

• By its source

– Solar radiation - originating from the sun

– Terrestrial radiation - originating from the earth

• By its proper name

– ultra violet, visible, near infrared, infrared, microwave, etc….

• By its wavelength

– short wave radiation 3 micrometers

– long wave radiation > 3 micrometers

Basic Radiation Laws

• Stefan-Boltzmann law: – (E = T4) (energy flux in Watts/m2)

– As T increases, E increases by a power of 4. If T doubles, E increases by 16 times!

• Wien’s law:– Output wavelength ~ 3000/T

– Wavelength of peak radiation emitted by an object is inversely related to temperature

Solar Spectrum

Solar radiation has peak intensities in the shorter wavelengths, dominant in the region we know as visible, but extends at low intensity into longwave regions.

Shortwave and Longwave Radiation

The hot sun radiates at shorter wavelengths that carry more energy,

Energy absorbed by the cooler earth is then re-radiated at longer wavelengths, as predicted by Wein's law.

The Earth’s Radiation Balance

Incoming Energy = Outgoing Energy

(absorbed sunshine)(area) = (thermal loss)(area)

S(1-a)pr2 = T4 (4 pr2)

The radiative equilibrium temperature

Incoming radiation is balanced by outgoing radiation.

For Earth the equilibrium surface temperature should be -18°C (~0°F) .

But, the Earth’s observed surface temperature is ~ +15°C (~60°F).

Why?Answer: layers

Solar Radiation

30% reflected

50% absorbed by the surface

20% absorbed by the

atmosphere

FAQ 1.3, Figure 1

Greenhouse Effect

Earth's energy balance requires that absorbed solar radiation is emitted to maintain a constant temperature.

Without natural levels of greenhouse gases absorbing and emitting, this surface temperature would be 33°C cooler than the observed temperature.

Greenhouse gas emissions

• Human activities have caused dramatic increases in greenhouse gas concentrations

Scattering: Why is the sky blue?

• Sunlight is scattered by air molecules

• Air molecules are much smaller than the light’s

• Shorter wavelengths (green, blue, violet) scattered more efficiently

• Unless we are looking directly at the sun, we are viewing light scattered by the atmosphere, so the color we see is dominated by short visible wavelengths – blue dominates over violet

because our eyes are more sensitive to blue light

Why are Sunsets Red?• The sun appears fairly white

when it’s high in the sky

• Near the horizon, sunlight must penetrate a much greater atmospheric path– More scattering

• In a clean atmosphere, scattering by gases removes short visible ’s from the line-of-sight– Sun appears

orange/yellow because only longer wavelengths make it through

• When particle concentrations are high, the slightly longer yellow ’s are also scattered- Sun appears red/orange

Weather and Climate

What is the difference?

Time Scales - Terms of Reference• Weather

• The conditions at a specific location at a specific time

– Minutes to weeks - the time period for which a specific event may be forecast

• Diurnal

– The day-night cycle

– 24 hours

– midnight to midday to midnight

• Climate• The average conditions and

their variability (includes extremes)

– Seasonal

– Annual

– Decadal

– Century

– *Age - as in Ice Age

– *Epoch - as in Holocene

– *Period - as in Quaternary

• *Borrowed from Geology

Spatial Terms of Reference• Global - The planet as a whole• Planetary - as in planetary waves

• Hemispheric - eg northern hemisphere

• Zonal- implies East-West

– a latitude band

• eg subtropics 20-30o lat

• Meridional - implies North-South– along a meridion

• Regional– eg - High Plains– - Front Range

• Local– eg - Fort Collins– - DIA

• Synoptic scale– 500 to 3000 Kilometers

• midlatitude cyclones

• Mesoscale– 20 to 200 Kilometers

• Thunderstorms

• Microscale– centimeters to 1 Kilometer

• In-Cloud updraft

Seasons & Sun's Distance

Earth is 5 million kilometers further from the sun in July than in January, indicating that seasonal warmth is controlled by more than solar proximity.

Figure 3.1

Solstice & Equinox

• Earth's tilt of 23.5° and revolution around the sun creates seasonal solar exposure and heating patterns

• At solstice, tilt keeps a polar region with either 24 hours of light or darkness

• At equinox, tilt provides exactly 12 hours of night and 12 hours of day everywhere

Solar intensity, defined as the energy per area, governs Earth's seasonal climate changes

A sunlight beam that strikes at an angle is spread across a greater surface area, and is a less intense heat source than a beam impinging directly.

Seasons & Solar Intensity

Midnight Sun

The region north of the Arctic Circle experiences a period of 24 hour sunlight in summer, where the Earth's surface does not rotate out of solar exposure

Take home message

• Seasons are regulated by the amount of solar energy received at Earth’s surface, which depends upon:

– angle at which sunlight strikes Earth’s surface.

– how long the sun shines per day.

• Seasons are NOT due to the elliptical nature of the earth’s orbit, i.e. changes in distance from the Sun.

Questions to Think About

• Since polar latitudes receive the longest period of sunlight during summer, why aren’t temperatures highest there?

• Why aren’t temperatures highest at the summer solstice?

Temperature Lags

Earth's surface temperature is a balance between incoming solar radiation and outgoing terrestrial radiation.

Peak temperature lags after peak insolation because surface continues to warm until infrared radiation exceeds insolation.

Radiation Budget at the top of the Earth’s Atmosphere

Red Line is incoming radiation

from the sun

Blue Line is outgoing radiation

emitted by the earth

The Job of the Atmosphereis to let the energy out!

“Piles up” in tropics “Escapes” near poles and aloft

The movement of the air (and oceans) allows energy to be transported to its “escape zones!”

What a single cell convection model would look like for a non-rotating earth

• Thermal convection leads to formation of convection cell in each hemisphere

• Energy transported from equator toward poles

• What would prevailing wind direction be over N. America with this flow pattern on a rotating earth?

What’s wrong with the 1-cell model?

Answer: The Earth Spins and ultimately it is not stable.

What is stable?

Climate “Zones”• Circulation features are

tied to regional climate

• Rising air associated with lots of precipitation

Climates of the World• Deep Tropics: hot and wet, with little seasonal variation• Seasonal tropics: hot, with “summer” rain and “winter” dry

(monsoon)• Subtropics: dry and sunny, deserts and savannas, often with a

well-defined rainy season (summer or winter)• Midlatitude temperate zone: warm summers, cold winters,

moisture varies by location but often comes in episodes throughout the year

• Polar regions: very cold, generally very dry, dark in the winter

Other Influences:Ocean currents, “continentality,” vegetation, mountain ranges

(altitude and orographic precipitation)

Orographic = lift due to the presence of mountains

Coriolis Force acts to the right in the Northern Hemisphere

Physics

Coriolis Effect

The Coriolis Effect deflects moving objects to the right in the northern hemisphere and to the left in the southern.

The atmosphere’s water

Water vapor pressure

• Molecules in an air parcel all contribute to pressure

• Each subset of molecules (e.g., N2, O2, H2O) exerts a partial pressure

• The VAPOR PRESSURE, e, is the pressure exerted by water vapor molecules in the air– similar to atmospheric pressure, but due only to the water vapor

molecules

– often expressed in mbar (2-30 mbar common at surface)

Water vapor saturation• Water molecules move

between the liquid and gas phases

• When the rate of water molecules entering the liquid equals the rate leaving the liquid, we have equilibrium– The air is said to be

saturated with water vapor at this point

– Equilibrium does not mean no exchange occurs

Expressing the water vapor pressure

• Relative Humidity (RH) is ratio of actual vapor pressure to saturation vapor pressure

– 100 * e/eS (e = vapor pressure, es = saturation vapor pressure)

– Range: 0-100% (+)

– Air with RH > 100% is supersaturated

• RH can be changed by

– Changes in water vapor content, e

– Changes in temperature, which alter eS

e = vapor pressure; es = saturation vapor pressure

Warm air can hold more water vapor

Dewpoint Temperatures

Dew point temperaturethe temperature at which dew forms, i.e. condensation

• Dewpoint temperature is a measure of the water vapor content of the air

• It is not a measure of temperature!

Condensation

• Condensation is the phase transformation of water vapor to liquid water

• Water does not easily condense without a surface present

–Vegetation, soil, buildings provide surface for dew and frost formation

–Particles act as sites for cloud and fog drop formation

Fogs

• Fogs are clouds in contact with the ground

• Several types of fogs commonly form– Radiation fog

– Advection fog

– Upslope fog

– Evaporation (mixing) fog

Clouds

• Clouds result when air becomes saturated away from the ground

• They can– be thick or thin, large or

small

– contain water drops and/or ice crystals

– form high or low in the troposphere

– even form in the stratosphere (important for the ozone hole!)

• Clouds impact the environment in many ways– Radiative balance, water

cycle, pollutant processing, earth-atmosphere charge balance, etc….

Cloud Classification

• Clouds are categorized by their height, appearance and vertical development

– High Clouds - generally above 16,000 ft at middle latitudes• Main types - Cirrus, Cirrostratus, Cirrocumulus

– Middle Clouds – 7,000-23,000 feet• Main types – Altostratus, Altocumulus

– Low Clouds - below 7,000 ft• Main types – Stratus, stratocumulus, nimbostratus

– Vertically “developed” clouds (via convection)• Main types – Cumulus, Cumulonimbus

Cloud type summary

Cirrus

Altostratus

Alto Stratus Castellanus

Stratus

A Layer of StratocumulusCloud viewed from above

Vertically “developed”

clouds• Cumulus

– Puffy “cotton”

– Flat base, rounded top

– More space between cloud elements than stratocumulus

• Cumulonimbus– Thunderstorm cloud

– Very tall, often reaching tropopause

– Individual or grouped

– Large energy release from water vapor condensation

Cumulonimbus with Pileaus caps

Cumulonimbus Clouds Spawn Tornadoes

Smog over China