110lectatmosphere

Global Environments:

The Atmosphere

Global Environments:
The Atmosphere

The Atmosphere

Composition

Vertical structure

Heat transfer

Atmospheric moisture

Atmospheric circulation

Weather and climate

Global Environments:
The Atmosphere

The earth’s atmosphere

- is unique

in our solar system
in the universe, as far as we know at this time

a relatively thin, life-giving blanket of air surrounding the earth
influences everything we see and hear
is intimately connected to life as we know it

its presence contributes to the physical characteristics of the earth
which in turn determines scope of life

Global Environments:
The Atmosphere

The earth’s atmosphere

is central in physical geography because of its roles in

Heat transfer throughout the globe
Water vapor transport
Determination of weather and climate

Global Environments:
The Atmosphere

Composition of the atmosphere

Gaseous envelope

Comprised of a mixture of
Various gases
Water vapor and ice crystals
aerosols

tiny suspended particles of solid or liquid

Global Environments:
The Atmosphere

Composition of the atmosphere

a mixture of various gases

two gases make up 99% of the total volume of the atmosphere
nitrogen (N₂) = 78%
oxygen (O₂) = 21%
percentages of these two gases are fairly constant up to about 80km
water vapor (H₂O) concentrations vary greatly
vertically and horizontally

Global Environments:
The Atmosphere

Composition of the atmosphere

a mixture of various gases

carbon dioxide (CO₂)
occupies a small percent of volume of atmosphere

~0.036%

varies vertically and horizontally
has been increasing since industrial revolution

Global Environments:
The Atmosphere

Composition of the atmosphere

a mixture of various gases

others, in small amounts
methane
nitrous oxide
chloroflourocarbons
sulfur dioxide
ozone

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

several atmospheric characteristics vary with changes in altitude

air density and air pressure
temperature
gaseous composition
electrical properties

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air density and air pressure

air density
is determined by the masses of the component atoms and molecules and the amount of space between them

density is a measure of the amount of matter in a given volume

is greatest near earth’s surface

because there are more atoms and molecules in a given volume of air

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air density and air pressure

air pressure or atmospheric pressure

results from the force exerted by constantly moving air molecules as they bump against objects

since air molecules are matter, they occupy space and have mass

pressure at any level in the atmosphere can be measured in terms of

the total mass of air above any point

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air pressure and air density

air pressure or atmospheric pressure

average or standard atmospheric pressure at sea level is ~14.7 pounds/in²

1013.25 mb (millibars)

29.92 in. Hg (inches of mercury)

if more air molecules packed into the same column, air would be more dense & pressure would increase

fewer air molecules would result in lower pressure

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air pressure and air density

air pressure or atmospheric pressure

the number of air molecules present in atmosphere decreases with increases in altitude

density decreases with increased altitude
pressure decreases with increased altitude

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air density and air pressure

initially decrease rapidly with altitude

because air near earth’s surface is compressed

about 10 mb/100 m increase in altitude

decrease more slowly with altitude

1013 mb at 0 km

500 mb at ~ 5.5 km

100 mb at ~17.0 km

50 mb at ~22.0 km

10 mb at ~32.0 km

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

several atmospheric characteristics vary with changes in altitude

air density and air pressure

temperature

gaseous composition
electrical properties

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

has a more complicated vertical profile than density and pressure
which decrease with altitude
is a measure of the "heat" of the air
which is a measure of the average speed of movement of the air molecules

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

normally decreases from earth’s surface up to altitude of ~11 km
because atmosphere is heated primarily from below by the transfer of heat energy from the surface

lapse rate

rate at which air temperature decreases with height
average or standard in lower region of atmosphere is ~6.5°C per 1000 m

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

lapse rate

average or standard in lower region of atmosphere is ~6.5°C per 1000 m increase in altitude or elevation
occasionally, temperature may increase with increases in height in lower region of atmosphere, a condition called a

temperature inversion

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

most common parameter used to define atmospheric layers
troposphere
stratosphere
mesosphere
thermosphere

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

troposphere

from 0 km to ~ 11 km
characterized by air temperature decreasing with height
region in which "weather" occurs
ends at point where temperature stops decreasing with height

a boundary called the tropopause

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

stratosphere

from ~11 km to 20 km

air temperature remains constant with altitude

from ~20 km to ~50 km

air temperature increases with altitude
from ~ - 50°C to ~0°C
resulting in a temperature inversion

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

stratosphere

temperature inversion is attributed to ozone

reaches its maximum concentrations in stratosphere
it absorbs energetic UV solar energy
some of the absorbed energy heats the stratosphere

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

mesosphere

separated from stratosphere by boundary called stratopause

from ~50 km to ~85km
% of N and O about same at this level as at sea level

but there is much less air
atmospheric pressure is ~1 mb at 50 km

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

mesosphere

air temperature decreases with height

partly due to there being so little ozone to absorb solar radiation
molecules of air lose more energy than they are able to absorb

cooling continues up to ~ 85 km

where temperature reaches its lowest average value, ~ - 90°C

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

air temperature

thermosphere

separated from mesosphere by boundary called mesopause

from ~85 km to several hundred km
temperature increases with altitude because oxygen molecules absorb solar radiation
actual temperature varies greatly depending on solar activity

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

exosphere

upper limit of atmosphere
at the top of the thermosphere
at an altitude of ~500 km
some atoms and molecules from this region
escape earth’s gravitational pull
shoot off into space

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

several atmospheric characteristics vary with changes in altitude

air density and air pressure
temperature

gaseous composition

electrical properties

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

gaseous composition

homosphere

region below thermosphere where gaseous composition remains fairly constant

from 0 km to ~85 km
a well-mixed region
~78% N & ~21% O

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

gaseous composition

heterosphere

thermosphere & above (>85km)
not well-mixed

heavier atoms and molecules, such as N & O, tend to settle to bottom of layer
lighter gases, H & He, float to top

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

several atmospheric characteristics vary with changes in altitude

air density and air pressure
temperature
gaseous composition

electrical properties

Global Environments:
The Atmosphere

Vertical structure of the atmosphere

electrical properties

ionosphere

above ~60 km
an electrified region

with fairly high concentrations of ions and free electrons
atoms lose electrons and become positively charged when they can’t absorb all the energy transferred to them by collisions or solar radiation

Global Environments:
The Atmosphere

Heat transfer in the atmosphere

occurs via a process called

convection

transfer of heat by the mass movement of a fluid (such as water and air)

takes place because fluids can move freely and it is possible to set up currents within them

leads to a cycle of heated air rising and cooled air descending

called convective circulation

Global Environments:
The Atmosphere

Heat transfer in the atmosphere

convective circulation

certain areas of earth’s surface absorb more heat from the sun than others areas
result in uneven heating of the air near the earth’s surface

heated air expands and becomes less dense
expanded , less dense air rises and transfers heat energy upward

Global Environments:
The Atmosphere

Heat transfer in the atmosphere

convective circulation

after warmed, expanded, less dense air rises
cooler, heavier, more dense air flows toward surface to replace the rising air
upon closer exposure to the warm surface

the cool air heats up, expands, becomes less dense and rises
and the cycle is repeated

Global Environments:
The Atmosphere

Heat transfer in the atmosphere

convective circulation

this vertical exchange of heat called convection

the rising air "bubbles" (or masses of warmed air) are known as thermals
as the warmed air rises, its temperature eventually decreases and it sinks to surface where it can replace rising air
producing a convective circulation or thermal cell

Global Environments:
The Atmosphere

Heat transfer in the atmosphere

convective circulation

any air that rises will expand and cool
any air that sinks is compressed and warms

wind

refers to the horizontally moving part of the circulation

Global Environments:
The Atmosphere

Atmospheric moisture

several processes and principles interact to determine the manner in which moisture enters, moves about in, and leaves the atmosphere

evaporation of water from surface into atmosphere

transport of water vapor through the atmosphere

precipitation, return of water to surface

Global Environments:
The Atmosphere

Atmospheric moisture

in the lower atmosphere, water exists in all three phases of matter

liquid - water
gas - water vapor
solid - ice

various atmospheric conditions govern the change of water from one phase to another

Global Environments:
The Atmosphere

Atmospheric moisture

water changes phases in the atmosphere

sublimation

changing from solid (ice) to gas (water vapor) phase without passing through the liquid phase

evaporation

changing from liquid to vapor phase

condensation

changing from vapor to liquid phase

Global Environments:
The Atmosphere

Evaporation

process by which water molecules escapes surface & enters atmosphere as water vapor

energy is required for this to
ultimately comes from radiant energy from sun

escaping molecules carry heat with them

evaporation tends to be a cooling process

rate of evaporation if affected by amount of moisture already present in a mass of air

affected by wind, temperature and humidity

Global Environments:
The Atmosphere

Evaporation

rate is affected by amount of moisture in a mass of air

amount of water vapor present in a quantity of air can be specified in several ways

absolute humidity

relative humidity

Global Environments:
The Atmosphere

Evaporation

absolute humidity

most direct measure of air’s moisture content
the weight of water present in a given volume of air
is affected by air temperature

warm air is able to contain more water vapor per unit volume than cool air

Global Environments:
The Atmosphere

Evaporation

relative humidity

ratio of the amount of water actually present in a quantity of air to the amount that could be held by the same air if it were saturated
does not by itself indicate actual moisture content of air
when temperature of moist air changes, so does its relative humidity
temperature at which the relative humidity becomes 100% is called the dew point

Global Environments:
The Atmosphere

Transport

water is transported by the atmosphere in the form of water vapor

Global Environments:
The Atmosphere

Precipitation

water leaves the atmosphere and returns to earth’s surface in the form of precipitation

which can take the form of any of the phases of water
liquid - rain
gas - fog
solid - ice

on average, the amount of water that leaves the atmosphere is equal to the amount that enters the atmosphere

Global Environments:
The Atmosphere

Precipitation

several factors govern the process by which water leaves the atmosphere as precipitation

temperature
humidity
dew point
presence of condensation nuclei

Global Environments:
The Atmosphere

Precipitation

condensation

when moist air is cooled to its dew point
the water vapor contained in the air is no longer in stable equilibrium and it tends to condense

dust particles in the air serve as condensation nuclei

collection centers for water molecules
promoting the growth of water droplets to a size large enough to be stable

Global Environments:
The Atmosphere

Adiabatic processes

combining aspects of vertical structure of atmosphere, heat transfer, moisture content and circulation

adiabatic cooling

adiabatic heating

Global Environments:
The Atmosphere

adiabatic cooling

process by which the temperature of a rising mass of air decreases

air mass heated by earth’s surface, rises
as the warm air mass rises it expands
air pressure decreases with altitude
as it expands, it does work against surrounding atmosphere
expenditure of energy causes temperature to decrease

Global Environments:
The Atmosphere

adiabatic heating

process by which the temperature of a descending mass of air increases

air mass adiabatically cooled, descends
as the cool air mass descends it compresses
air pressure increases with decrease in altitude
as it compresses, surrounding atmosphere does work against it, pushing inward
this input of energy causes temperature to increase

Global Environments:
The Atmosphere

lapse rate

normally, air temp. decreases with altitude

~6.5°C per 1000m increase in altitude

dry adiabatic lapse rate

adiabatic cooling in absence of condensation

~10.0°C per 1000m increase in altitude

moist adiabatic lapse rate

adiabatic cooling in presence of condensation

varies with moisture content of the air

~5.0°C per 1000m