GC 385 EXAM 1 STUDY GUIDE

• Composition - The atmosphere is a mixture of individual gas molecules, microscopically small

suspended particles of solids and liquids (or aerosols), and falling precipitation.

Atmospheric Gases

• Permanent gases

– Form a constant proportion of atmospheric mass.

• Variable gases

– Distribution varies in both space and time.

Chlorofluorocarbons (CFC’s) - destroy ozone. Used in refrigerators and air conditioners, and

the production of plastic foams, and as solvents in electronics.

- Each October a large hole is detected over Antarctica because of lack of air currents, chemically

unique clouds, and the cold stable temp’s.

Methane (CH4) – Greenhouse gas, 1.7 ppm (little), helps heat atmosphere, 1% yearly increase

over the last few decades.

CAUSED- cattle, coal mines, oil wells, gas pipelines, rice cultivation

• AEROSOLS - Small, solid particles and liquid droplets (smaller than rain or cloud

droplets). Range as small as 1 micrometer (1/1,000,000 of a meter). They form by both

natural and human- induced processes.Residence time is a few days to several weeks.

-CAUSED- winder generated dust, volcanoes, sea spray, combustion of fossil fuels.

-EFFECT- visibility, amounts of solar radiation coming in, can lower temps’s as much as 1o c

for a

month.

Structure of the Atmosphere Layers based on electrical characteristics, chemical composition, density, temp. Changes

• DENSITY - (Mass per. Unit of Volume) No distinct layers, tend to decrease density with

height @ sea level.

• TEMPERATURE PROFILE – Troposphere, Stratosphere, Mesosphere, Thermosphere

• TROPOSPHERE Weather occurs here (80% of atmospheric mass), temp. decreases with elevation (-3.6

oF per. 1,000 ft),

Height varies from 3.6 – 10 miles, Thicker in Summer – Thinner in Winter.

• STRATOSPHERE

Very little water vapor, large thunder clouds may occur, contains (19.9% of atmospheric mass),

temp. increases with elevation (28oF

@ 30 mi.), Strong winds can suspend materials for months,

Height varies from 6.6 – 30 Miles

• MESOSPHERE

Temp. decreases with altitude, Height varies from 30 – 53 Miles

• THERMOSPHERE

Temp. increases with height ( may exceed 1,500oc

), Height extends 53 – 75 Miles

CHEMICAL LAYERS: IONOSPHERE Layer with many ‘Ions’ (electrically charged particles), Divided into several layers D, E, and F. Where the

‘Aurora Borealis’ (Northern Lights) & ‘Aurora Australis’ occur, Sun is drawn into Earth’s magnetic field.

- Zone where AM Radio waves reflect @ NIGHT

- F Layer reflects rather an absorbs

EVOLUTION OF THE ATMOSPHERE

- Many scientists believe it started shortly after the Earth formed 4.5 Billion years ago.

- Original gases may have been lost overcoming Earth’s gravity.

- Collisions with Earth knocking gases free.

- Secondary atmosphere formed, replacing early atmosphere.

- Out gassing, produced amounts of water.

- Secondary atmosphere transformed Oceans(water), CO2 removed from water, precipitation of water

vapor.

- Ozone layer formed from diatomic O2, Allowed plants to evolve, Nitrogen formed.

SOLAR RADIATION ENERGY- ability to do work.

- ‘JOULE’ – Standard unit of energy = 0.239 calories

POWER- rate of which energy is released, transferred, or received.

- ‘WATT’ (W)- Unit of power = 1 J per. Second

2 MAJOR FORMS OF ENERGY

KINETIC ENERGY POTENTIAL ENERGY

- Being Used - Stored Energy

- In Motion - May be related to objects position

TRANSFER ENERGY

1.) CONDUCTION- movement of heat through a substance without movement of molecules in

direction of heat transfer.

EXAMPLE: heat going through a metal rod

2.) CONVECTION- transfer of heat by a mixing of a fluid, medium is involved.

EXAMPLE: Radiators in a house

3.) RADIATION- transfer of heat without a median moving through space.

EXAMPLE: heat off a campfire

• Most of earth’s energy is Radiation (one-billionth energy from the sun) • All matter above absolute zero emits radiation.

(Absolute Zero = 0 Activity = -459oF

• Some may be detrimental, Some useful

• Human adapted to radiation (eyes)

Consists of TWO alternating oscillations (fields)

1.) Electrical

2.) Magnetic

- Characterized in terms of “quality” and “quantity”

-Travel @ the speed of light through space

Wavelength – distance between consecutive crests.

-Shorter the wavelength, easier radiation can penetrate.

-Humans see 10-9

u - 1010

u

-Sun peaks @ 0.5u

Amplitude – height of crest of the wavelength.

-Amount of energy carried is directly proportional to the wave amplitude.

LAWS

• Stefan Boltzman Law- relationship in ‘temperature’ & ‘intensity’ of radiation

emitted by blackbodies.

BLACKBODIES - theoretically perfect emitters of radiation. Sun & Earth come close.

I =σT4

I = Intensity of radiation in W (watts) per. m2

σ= Stefan Boltzman Constant (5.67 x 10-8

W/m2/K

4 )

T = Temperature in Kelvin (K)

-As temperature increases, the more intense its radiation.

-So if you doubled the temperature, radiation intensity increases sixteen fold. (4x4=16)

GREYBODIES – emit only a percentage of radiation a blackbody would.

I =εσT4

This formula can be used with most objects occurring in nature.

• Wein’s Law – determines an objects wavelength (λ) of maximum emission. Usually indicates the

peak in a particular wavelength.

Maximum λ = Constant/T

Why We Have Seasons

-Sun emits nearly constant amount of Radiation.

• Perihelion – when Earth is closest to the Sun. (January 3rd

– 91,000,000 mi.)

• Aphelion – when Earth is farthest from Sun (July 3rd

– 94,000,000 mi.)

-Earth’s Axis always points at the same location, North Star (Polaris)

Solstice – ( June 21 & December 21) Sub Solar Point is located at 23.5o North or South.

Equinox- (March 21 & September 21) neither hemisphere oriented toward the sun. Sub solar point is

located on the equator (0 degrees).

SOLAR ANGLES & BEAM DEPLETION

The more direct the solar angles the more

intense heating occurs.

Atmospheric Influences on Insolation

• Absorbed- Results in net gain in heat to atmospheric absorbers and net loss of energy transferred

to the ground surface. Insolation may be absorbed by atmospheric gases, particulates, and droplets.

• Scattered- radiation is reflected off into a number of lesser, weaker beams in a variety of

directions. 3 Major Categories in Scattering

Rayleigh Scattering- Occurs when scattering agents are smaller

than ~1/10th the wavelength of insolation. (Blue Skies)

Mie (“Mee”) Scattering- Caused by suspended aerosols, which

tend to scatter radiation forward. (Grey/Red Skies)

Nonselective Scattering- Caused by water droplets in clouds

that act like miniature lenses. (Grey/White Skies)

• Reflected- Reflection is a redirection of radiation without any absorption. We see the results of

reflectance all the time when we see colors.

ALBEDO – the percent of reflectance……

light colors = high Albedo (Snow, Clouds)

dark colors = lower Albedo

• Transmitted- At best the Atmosphere will let 80% of insolotion reach the ground.

• Laminar Boundary- thin lay a few meters thin, that conducts air near the earths surface.

• Atmospheric Window- bands which range between 8 and 12 microns and are at the peak of

radiation intensity for the planet.

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• Conduction- warms a thin layer of air near the ground surface, known as the laminar boundary

layer, which may be only a few millimeters thick.

• Convection- is the process by which heat is transferred by the movement of a fluid, which can be

either liquid or gas.

1.) FREE CONVECTION – (Expanding Air) Occurs when localized heating of a parcel of air causes

the parcel to expand and become less dense than the surrounding air (warm air is less dense than

cold air).

2.) FORCED CONVECTION – (Horizontally) occurs when horizontally moving air encounters

surface features, which creates turbulence eddies.

Sensible Heat- heat we can feel or sense, hence the name.

Latent Heat- energy required to change the phase of a substance.

LATENT HEAT of FUSION- Energy needed to change ice to liquid water.

LATENT HEAT of EVAPORATION- Energy needed to change liquid water to water vapor.

• Latitudes from 38o North & South to the Poles get a

Net Loss in Radiation.

• Latitudes from 38o North & South to the Equator get a

Net Gain in Radiation.

ISOTHERM’s SUMMER & WINTER

SUMMER- Isotherms tend to go towards the poles over land

During Summer because the land is warmer than the water.

WINTER- Isotherms tend to go towards the equator over land

During Winter because the land is cooler than the water.

Influences On Temperature

• Latitude- Low latitude areas experience very little range of sun angles or changes in length of day,

which results in fairly constant insolation levels. Away from the tropics, the variations may be

tremendous, resulting in drastic seasonal changes.

• Altitude- The higher you go in the atmosphere the cooler it becomes because the distance from the

surface, which is emanating radiation, increases. There are generally very little daily temperature

fluctuations at high altitudes in the atmosphere. Land at higher elevations will also tend to be cooler,

especially at night (thin atmosphere doesn’t absorb much heat).

• Atmospheric Circulation- Organized global system of wind and pressure that influences the

movement of air masses, which in turn influences things like cloud cover, prevailing winds, and beam

depletion.

• Ocean Currents- Influence conditions along coastal areas. Warm currents moving into higher

latitudes will bring moderating effects to coastal areas that otherwise wouldn’t be so moderate.

• Land/Water Contrasts- Due to many differences, land heats and cools much faster than water.

- The specific heat of water is about 5 times greater than land.

- Insolation penetrates and mixes in water, but can’t in land, which is opaque.

- Evaporation from the surface of a water body will retard heating.

- Convectional currents redistribute energy in water. Doesn’t occur w/land.

Continentality - places that are surrounded by land often display drastic seasonal ranges and extremes of

temperature.

Maritime Effect - places that are near large bodies of water, such as along coasts and on islands, where

seasonal variations are minimized,

Local Impacts

• Slope Aspect- Direction that a slope faces. In the NH, south-facing slopes tend to intersect a great

deal more insolation (angle of incidence is closer to 900 = less beam spreading = energy is more

concentrated).

• Vegetation Cover- The type of vegetation cover will greatly influence the temperature regime of a

particular area. The classic example is the effect of heavy tree canopies.

Atmospheric Pressure

• Pressure- force exerted per. unit area. US uses millibars (mb)

1 mb = 100 pascals (pa)

1 pa = 1 newton (n/m2)

1 kilopascal (Kpa) = 1,000 pa or mb

-1,013 is the Average Sea Level Pressure

-Pressure increases if Density of Atmosphere increases or temperature increases.

-Each gas exerts its own specific amount of pressure. Atmosphere gases always seeking equilibrium.

Vertical and Horizontal Changes in Pressure

• Vertically, pressure decreases as altitude increases because there is less overlying atmospheric mass.

• Horizontally, small differences in surface pressure may be enough to create intensive wind as air

attempts to find an equilibrium between areas of high and low pressure.

Equation of State (Ideal Gas Law)

p = ρRT

p = pressure in pascals

ρ (rho) = density in kg/m3

R = constant = 287 J/kg/K

T = temperature (0K)

Indicates if the air density increases, with no change in temperature, then pressure will increase. If air

temperatures increase, with no change in density, then pressure will increase.

-Close spacing means a rapid change in pressure exists across surface, or a steep pressure gradient.

-Wide spacing between isobars indicates gentle changes in pressure across surface, or a weak pressure

gradient.

Pressure Gradient – exerts a force called ‘PRESSURE GRADIENT FORCE’ which sets air in motion.

Hydrostatic Equilibrium- The vertical pressure gradient force and the force of gravity are about equal

and operate in opposite directions.

CORIOLIS FORCE (EFFECT) • Imaginary deflective force arising from earth’s rotation, necessary to account for

motions measured relative to surface.

-Object curves right in NH

-Object curves left in SH

Air moving on the ground and just above it experience FRICTION

• Free Atmosphere- Air above 1.5 km (1 mile), doesn’t experience much Friction.

• Geostrophic Flow - Winds in the upper atmosphere will become completely deflected by

Coriolis force and flow parallel to the pressure gradient.

• Gradient Flow - In absence of frictional drag, air still flows parallel to the height

contours but is constantly altering direction and undergoing changes in speed.

• Supergeostrophic Flow - Gradient air flow around high pressure systems experiences

higher Coriolis force than pressure gradient force, thus at higher speeds than would occur

with geostrophic flow.

• Subgeostrophic Flow - Gradient air flow around low pressure systems experiences

higher pressure gradient force than Coriolos force, thus at lower speeds than would occur

with geostrophic flow.

• Cyclones - Organized, low pressure systems with enclosed isobars (or height contours). Spin counter clockwise in NH, Spin clockwise in SH

• Anticyclones - Organized, high pressure systems with enclosed isobars (or height contours). Spin clockwise in NH, Spin counter clockwise in SH

• Troughs - equatorward bends in the isobar pattern, which are essentially elongated areas of low

pressure.

• Ridges - poleward bends in the isobar pattern, which are essentially elongated areas of high

pressure.

MOISTURE

Evaporation- Liquid converted to gaseous state. Liquid water converted to water vapor.

Sublimation- From solid to gas. Air temperatures are below freezing, ice to water vapor.

Condensation- Gas converted to liquid. Water vapor converted to liquid water.

Deposition - Gas to solid. Air temperatures below freezing, water vapor converted directly to ice

(example: frost).

-Saturation- limit to the amount of water vapor that can be added to the surrounding atmosphere.

-Vapor Pressure- The measure of vapor pressure is that part of the total atmospheric pressure

that is accounted for due to water vapor.

– Saturation Vapor Pressure - This maximum vapor pressure possible, dependent on one

variable: temperature. Dependent on temperature, higher temperatures mean higher

saturation vapor pressures.

• Absolute Humidity- A measure of the density of water vapor, expressed as the number of grams

of water vapor per m3 of air (i.e. it is mass per unit volume).

• Specific Humidity- Mass of water vapor per mass of air, expressed in grams of water vapor per

kilogram air (g/kg).

- Saturation Specific Humidity - Maximum value of specific humidity.

• Relative Humidity (RH) - A measure of the amount of water vapor in the air compared to the

maximum possible amount that could be there at a given temperature.

- RH = (specific humidity / saturation specific humidity) x 100%

• Dew Point- The temperature at which saturation occurs. Recognizes that for any given parcel of

air (or portion of the atmosphere) there is a point when, at a particular temperature, the amount of

water vapor present is the maximum possible, i.e. saturation conditions.

- High dew point means a great deal of water vapor is present.

- Low dew point means less water vapor is present.

Methods of Achieving Saturation

1.) Adding Water Vapor to the Air-Example: Steam from a tea pot, rain drops evaporating as it falls.

2.) Mixing Cold Air with Warm, Moist Air-Example: Contrails behind jets; Steam (or evaporation)

fog on lakes.

3.) Lowering the Temperature to Dew Point-Many ways to do this; crucial to cloud formation.

Effect of Curvature

• Water droplets are really tiny spheres with considerable curvature.

• The smaller the droplet, the greater the curvature.

• This curvature has an effect on evaporation from cloud droplet surfaces as well as the vapor pressure

needed to reach saturation.

• The smaller the droplet, the higher its saturation vapor pressure will be.

The most important (widespread) mechanism for cloud formation is the lowering of the air

temperature to the dew or frost point.

– Air temperature changes may occur due to two processes:

1.) Diabatic Processes - Energy is added to or removed from a system.

(Follows the Second Law of Thermodynamics (energy moves from areas of high to low temperatures)

2.) Adiabatic Processes- Temperature changes without adding / removing heat.

(Follows First Law of Thermodynamics):

ΔH = p • Δ∞ + Cv • ΔT

H = heat added to system

p = air pressure

Δ∞ = the change in volume (+ for expansion, - for contraction)

Cv = specific heat for air (assuming no changes in volume)

T = the change in temperature

• Dry Adiabatic Lapse Rate (DALR) - Rate at which a rising or falling parcel of unsaturated

air cools or warms. About 1.0 0C / 100 m (5.5

0F / 1000 feet).

o Rising parcels of unsaturated air will cool at this rate.

o Falling parcels of unsaturated air will warm at this rate.

• Saturated Adiabatic Lapse Rate (SALR) - Rate at which saturated parcel of air cools at is

the Saturated (or Wet) Adiabatic Lapse Rate (SALR), which about 0.5 0C / 100 m (3.3

0F / 1000 ft)

• Environmental Lapse Rate (ELR) - Vertical Changes in Temperature Through Still Air. It is highly variable but a global average is about 0.65

0C / 100 m (or 6.5

0C / km

FORMS of CONDENSATION • DEW - Liquid condensation on a surface. Most likely to form on clear, windless nights (no cloud

cover to hold heat in, lack of wind to mix warm air from above).

– At night, the ground surface may cool due to loss of longwave radiation (i.e. diabatically)

– Air in contact with surface cools by conduction, reaching dew point, allowing condensation

to form on ground surface.

• FROST - Coating of very small ice crystals when air adjacent to surface becomes saturated at

temperatures below 0 0C. Formation process is similar to that of dew, except temperature conditions

are below 0 0C. Water vapor is transformed directly into ice, without going through the liquid phase

(deposition).

• FROZEN DEW - Coating of ice that occurs when a layer of dew freezes as temperatures drop

below 0 0C. This also called “black ice” when it forms on road surfaces.

• FOG - Cloud whose base is at or near ground level. Air adjacent to the surface containing

suspended water droplets, usually formed by diabatic processes (but not in all cases).

TYPES

- Evaporation (or Steam) Fogs - Cold, dry air mixes with a thin layer of warm,

moist air over a water surface. Common to see this in the fall or early winter over

inland lakes before they have frozen over.

- Radiation(or Ground) Fog - Develops during night usually when ground

surface loses radiation, cooling adjacent air to dew point. Most likely to form on

cloudless nights, with light wind (5 km/hr or 3 mph), rather than still air.

Water

FOG

(Warm)

Evaporation Fog (winter)

Radiation Fog

FOGConduction

- Advection Fog - As horizontally-moving air passes over cooler surface, it

transfers some of its heat downward, causing it to cool diabatically.

- Upslope (or Orographic) Fog - Forms as air is forced upward, thereby

allowing it to expand and cool to the dew point, which results in condensation.

Mechanisms That Lift Air

• Orographic Lifting (or Uplifting) - Air flowing towards a hill or mountain will be deflected

around and over the barrier.

• Frontal Lifting - The displacement of one air mass over another. Warm air is forced to rise, which

causes saturation and condensation, resulting in cloud formation.

• Convergence - Wind from all directions will converge (horizontally) at a low pressure cell. The

converging air will then move upward (vertically), which results in rising air and adiabatic cooling.

Water

Warm, moist air

FOG

FOG

Mountain

• Localized Convection - Localized heating of ground surface causes adjacent air parcels to heat,

expand, and rise.

Static Stability and the ELR

– Statically Unstable Air

• Will continue to rise if given an initial push upward.

– Statically Stable Air

• Air will resist upward displacement and sinks back to its original

position when the attempts at lifting cease.

– Statically Neutral Air

• Will neither rise on its own following lifting or sink back, but will stay

at the height to which it is displaced.

Positive Buoyancy - When a parcel of air is less dense than the surrounding air.

Negative Buoyancy - Air that is denser than its surroundings, it will sink if not subject to

continued lifting forces.

– Absolutely Unstable Air - If an air parcel is rising at the DALR (1.0 0C/100m) and the

ELR is > DALR (say at 1.5 0C/100m), then the parcel will cool more slowly than the

surrounding air, which makes it positively buoyant.

“DRY AIR COOLS FASTER THAN WET AIR,

BECAUSE IT IS RELEASING LATENT HEAT”

- Absolutely Stable Air - Saturated or not, a lifted air parcel will sink back down

whenever the ELR is < parcel’s SALR.

3 factors can bring about changes in ELR:

a. 1.) Heating or Cooling of the Lower Atmosphere.

Cooling occurs at night, heating during the day.

b. 2.) Advection of Cold and Warm Air at Different Levels.

Advected air may bring winds of different directions at different elevations having air

temperatures that vary greatly.

c. 3.) Advection of an Air Mass with a Different ELR.

A new air mass may have a different ELR.

Inversion Causes

• Radiation Inversion

– Caused by cooling of the ground surface, which cools the adjacent air,

resulting in an inversion.

• Frontal Inversion

– May occur aloft where two air mass meet along a front, resulting in an

inversion.

• Subsidence Inversion

– Result from sinking air, which is warmed and compressed during descent.

– As it is compressed the top layer actually travels farther than the bottom,

which causes a greater temperature increase, resulting in an inversion.

Cloud Types

• Based on height and form:

– High Clouds

• Occur above 6000 m (19,000 feet).

• Composed of ice crystals primarily.

– Middle Clouds

• Between 2000 and 6000 m (6000-19,000 ft).

• Usually composed of liquid water.

– Low Clouds

• Bases are below 2000 m (6000 ft).

• Composed of liquid droplets usually.

– Clouds of Extensive Vertical Development

• Cumuliform clouds that have substantial vertical development.

• Occur when air is absolutely unstable or conditionally unstable.

• Strong Updrafts possible (>50m/s, 100 mph)

• Water vapor contents are high (1 g/cm3)

– Unusual Clouds

• Do not fit the height categories.

High Clouds

• Cirrus (Ci)

– Wispy aggregations of ice crystals (up to 8 mm/0.3 in long), averaging ~1.5 km (1 mile) thick,

w/low water vapor content.

– Fall streaks and “Mare’s Tails” may occur.

• Cirrostratus (Cs)

– Also composed of ice crystals but at lower concentrations and more horizontally extensive,

i.e. layered;

– create halos due to refraction of light from sun and moon.

• Cirrocumulus (Cc)

– Ice crystal arranged into long rows of individual, puffy clouds;

– occur due to wind shear (wind speed and/or direction changes with height);

– sometimes called “Mackerel Sky” because they resemble fish scales in shape.

Middle Clouds

• Altostratus (As)

– Creates a continuous layered covering, scattering much sunlight;

– no shadows;

– sun appears as a bright spot rather than a halo

• Altocumulus (Ac)

– Layered clouds that form long bands or contain a series of puffy clouds arranged in rows

(like cirrocumulus but larger usually).

Low Clouds

• Stratus (St)

– Layered structure;

– 0.5 to 1 km (0.3 to 0.5 miles) thick;

– form where extensive areas of stable air are lifted (1000s of km2).

• Stratocumulus (Sc)

– Low, layered cloud having superimposed rows or cells of vertical development;

– colors vary due to differences in thickness.

• Nimbostratus (Ns)

– Low, layered cloud that yields light precipitation (basically stratus clouds with

precipitation)...

Clouds of Extensive Vertical Development

• Cumulus (two types)

– Cumulis humilis or fair-weather cumulus consist of single plumes, which yield no

precipitation.

– Cumulus congestus are more intensely developed with multiple towers, each having several

cells of development.

• Cumulonimbus

– The most violent of all clouds, and the producer of the most intense thunderstorms.

– May span almost entire troposphere in height.

– Distinguished by an anvil at top of cloud (composed of ice; high winds in stratosphere give it

the unique appearance).

Unusual Clouds • Lenticular

– Lens-shaped clouds that form downwind from mountains.

• Banner

– Individual clouds immediately above isolated mountain peaks.

• Mammatus

– Downdrafts from cumulonimbus clouds create downward hanging projections below the

cloud base.

• Nacreous

– Super-cooled droplets or ice crystals in the stratosphere, usually only seen at twilight in the

winter at high latitudes.

• Notilucent

– Similar to nacreous but located in the mesosphere.

– Often illuminated after sunset or before sunrise.