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METEORLOGY PART I: Chapters 17&18
CHAPTER 17: Atmosphere
ATMOSPHERE - layer of gases and tiny particles surrounding the earth
WEATHER - general atmospheric conditions at a particular time and place
CLIMATE - general weather conditions over many years
Composition of the Atmosphere

Elements: NITROGEN (N2)
Argon
Carbon Dioxide
All Others
OXYGEN (O2)
ARGON (Ar)

Compounds: CARBON DIOXIDE (CO2)
Oxygen
WATER (H2O)
OZONE (O3)
absorbs harmful UV RAYS (ultraviolet)

Nitrogen
Atmospheric Dust: SOIL
ASH
MICROBES
CRYSTALS
ATMOSPHERIC PRESSURE

Gravity that is PULLING particles TOWARD EARTH

Ratio of:

Measuring Device for Atmospheric Pressure: BAROMETER (p.532)
air weight
.
surface area on which it presses
o Atm.Pressure measured in N/m2.
o 1 Atm = 760 mmHg

Δ Pressure: Higher altitude = FEWER gases = LOWER pressure
Lower altitude = MORE gases = HIGHER pressure

Δ Temperature: Higher altitude = LOWER pressure = LOWER temperature
Lower altitude = HIGHER pressure = HIGHER temperature
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
Atmospheric Layering is caused by TEMPERATURE differences.
MESOSPHERE
ALTITUDE (Miles)
ALTITUDE (Km)
THERMOSPHERE
STRATOSHPERE
MAXIMUM OZONE
TROPOSPHERE
TEMPERATURE
Atmospheric Layers
(1) TROPOSPHERE
 Closest to earth
 Holds the most CO2 and H2O vapor
 All WEATHER changes happen here
 Temperature ↓ as altitude increases.
o Why? FARTHER FROM THE HEAT
ABSORBED BY EARTH
(2) STRATOSPHERE
 From tropopause to 50km in altitude
 Includes the OZONE LAYER (O3)
 Temperature ↑ as altitude increases.
o Why? CLOSER TO O3 LAYER WHICH
ABSORBS UV LIGHT & HEAT
(3) MESOSPHERE
 From stratopause to 80km in altitude
 Coldest layer
 Temperature ↓ as altitude increases.
o Why? FARTHER FROM O3 LAYER
(4) THERMOSPHERE
 From mesopause to outer space
 Temperature ↑as altitude increases.
o Why? OXYGEN AND NITROGEN
ABSORB SHORT-WAVE, HIGHENERGY SOLAR RADIATION

Two layers:
o IONOSPHERE - lower layer.
Holds electrically charged particles.
o EXOSPHERE - upper layer.
Holds light gases (helium/hydrogen).
 No clear boundary between
exosphere and space…
 Air gets thinner and thinner until
you’re in outer space.
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CHAPTER 18: Moisture, Clouds & Precipitation
Atmospheric Moisture
~Section 18.1~
3 forms of water: ICE, LIQUID, or WATER VAPOR (most is in VAPOR form)
Phase Changes: HEAT energy causes an INCREASE in molecular motion.
*Motion causes molecular COLLISIONS and energy transfer.

Evaporation: molecules speed up and change from a LIQUID to WATER VAPOR

Condensation: molecules slow down and change from a GAS to a LIQUID.

Sublimation: SOLIDS change directly to a GAS. (Ex: DRY ICE)

Deposition: GASSES change directly to a SOLID. (Ex: FROST)
Humidity = AMOUNT OF WATER VAPOR IN AIR

SATURATED = air contains all of the water vapor it can hold.

When saturated, WARM air can hold more water vapor than COLD air.

Measuring Devices: HYGROMETER or PSYCHROMETER
Specific Humidity = ACTUAL amount of moisture in the air. (Grams H2O / kg air)
Relative Humidity = percent mass of water vapor compared to mass water vapor at saturation.
Ex: At 200 C, air contains 14.3g H2O / m3 air. Saturation point: 17.1 g/m3

Specific Humidity: 14.3 g/m3

Relative Humidity: 14.3 g/m3 = 84% Relative Humidity
17.1 g/m3
Dew Point = TEMPERATURE to which the air must be cooled to reach saturation.

Depends on Relative Humidity.

When temp. is below Dew Point: CONDENSATION (dew) or DEPOSITION (frost) occur
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Temperature Changes occur in 3 ways:

CONDUCTION: Transfer of heat through
matter by molecular activity.

CONVECTION: transfer of heat by mass
movement or circulation within a substance.

RADIATION: transfer of heat through
matter or a vacuum by electromagnetic waves.
(page483)
Clouds & Fog
~Section 18.2~

ADIABATIC TEMPERATURE CHANGES = when air expands, it COOLS, and when it is
compressed, it WARMS.
o DRY ADIABATIC RATE: applies to unsaturated air.

10°C for every 1000 meters.

Rising air COOLS 10°C every 1000m it rises.

Sinking air WARMS 10°C every 1000m it rises.
o WET ADIABATIC RATE: applies to saturated air.

5-9°C for every 1000 meters.
o The boundary between the dry and wet adiabatic temperature regions is called the
CONDENSATION LEVEL.
o Clouds form above this level, undergoing wet adiabatic changes.

Cloud Formation = from CONDENSATION of water vapor over a large area of air.
 2 requirements:
o Condensation Nuclei = tiny particles of DUST, ICE, and SALT that provide a
SURFACE for condensation.
o Saturation and cooling to the dew point by Convective Cooling

as WARM air rises, it goes to LOWER pressure areas, causing the gas to
EXPAND and COOL.

When it cools, it gets DENSER and sinks, creating a “CONVECTIVE
CURRENT.”
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Cloud Terms
STRATUS = sheetlike or layered
NIMBUS / NIMBO = rain
CUMULUS = piled or heaped
ALTO = middle altitude
CIRRO / CIRRUS = curly, high altitude
WISPY!!!
Cloud Types
~Section 18.3~
Stratus = formed when warm, moist air lies ABOVE cooler air layers.

These are most clouds, and they have little rain.

Form low in the atmosphere.

NIMBOSTRATUS = DARK, LOW RAIN/SNOW CLOUDS

ALTOSTRATUS = MIDDLE ALTITUDE STRATUS CLOUDS
Cumulus = formed when warm, moist air RISES & COOLS.

Puffy, vertical growing clouds with flat bases (where CONDENSATION begins)

Thick, high billowy tops.

ALTOCUMULUS = MIDDLE ALTITUDE CUMULUS CLOUDS

STRATOCUMULUS = LOW COMBINATION CLOUDS (STRATUS & CUMULUS)
Cirrus = ice crystal clouds forming at low TEMPERATURE and high ALTITUDES (above 6 km)

Wispy, feathery clouds

CIRROCUMULUS = RARE ICE CRYSTAL CLOUDS, BEFORE SNOW OR RAIN
Fog = forms near EARTH’S SURFACE

RADIATION (GROUND) FOG = air in contact with earth is cooled below its dew point.

ADVECTION FOG = warm, moist air moves across a cold surface. Common along
COASTLINES.

UPSLOPE FOG = formed by lifting and ADIABATIC cooling.

STEAM FOG = shallow fog layer of cool air over a body of warm water. Common along
INLAND RIVERS & LAKES.
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PRECIPITATION
~18.3~Pages 520-522~
How precipitation forms
Cloud Droplets are very small (~20 micrometers in diameter), so for precipitation to form, cloud
droplets must grow by roughly ONE MILLION TIMES!!!
**Cold Cloud Precipitation: Formed by the BERGERON PROCESS.

When water droplets are SUSPENDED IN AIR,
they do not freeze at 0°C as expected.

Water in liquid form only freezes near a
temperature of - 40°C.
o This is called “SUPERCOOLED” water.
o It readily freezes when it hits a solid object.
o FREEZING NUCLEI (solid material in air)
can cause supercooled water to freeze.
o As water hits freezing nuclei, it becomes
heavier and falls, causing a chain reaction,
allowing the droplet to get bigger as it falls. This forms a SNOWFLAKE.
o When surface temperature is above 4°C, snowflakes melt before impact. So,
summer rainstorms can begin as SNOWSTORMS high in the atmosphere!
**Warm Cloud Precipitation: Formed by the COLLISION-COALESCENCE PROCESS.

As water droplets move throughout a cloud, they COLLIDE and COALESCE (join
together). These droplets get bigger and heavier, and fall in the form of rain.
Types of Precipitation
***The type of precipitation that reaches Earth’s surface is determined
by the temperatures in the lowest few kilometers of the atmosphere.

Rain & Snow

Sleet = small particles of clear-to-translucent ice.

Glaze = A.K.A. “FREEZING RAIN” – rain is supercooled (below 0°C) & become ice when
they impact frozen objects.

Hail = small ice pellets grow as they impact supercooled water droplets as they fall
through a cloud. UPDRAFTS push them back up, so they can gain new ice layers.
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