Bài giảng khí hậu học chương 1

G304 – Physical Meteorology and Climatology

Chapter 1
Composition and Structure
of the Atmosphere

By Vu Thanh Hang, Department of Meteorology, HUS


The Atmosphere, Weather and Climate
• The atmosphere: a mixture of gas molecules,
microscopically small suspended particles of solid
and liquid, falling precipitation; a complex fluid
system  generates the chaotic motion  weather
• Weather: state of the current atmosphere in lower
levels with time scales from minutes to hours (shortterm phenomena)
• Climate: long-term patterns of weather with time
scales from months to centuries.


1.1 Thickness of the Atmosphere
• The atmosphere has no distinct upper boundary
• The air becomes less and less dense with
increasing altitude
• At 16km, the air density is only ~10% and at 50km it
is ~1% of that at sea level
• In fact, 99.99997% of the atmosphere below 100km
• However, it can reach to an altitude of 20.000km
according to satellite observations
• Compare with the 6500km radius of Earth

1.2 Composition of the Atmosphere
• A mixture of invisible gases and suspended microscopic
solid particles and water droplets
• Molecules of the gases can be exchanged between the
atmosphere and Earth’s surface by physical processes; also
be produced and destroyed by chemical reactions between
gases
• The gas concentration in the reservoir (atmosphere) will
remain constant so long as the input rate (gas moves from
ground to atmos.) is equal to the output rate (gas moves
from atmos. to ground)  the concentration of the gas exists
in a steady state


1.2 Composition of the Atmosphere (cont.)
• Individual molecules stay in the
atmosphere for only a finite period of
time  residence time
• The residence time is found by
dividing the mass of the substance
in the atmosphere (in kilograms) by
the rate at which the substance
enters and exits the atmosphere (in
kilograms per year)
• Atmospheric gases are often
categorized as being permanent or
variable, depending on whether their
Fig. 1.2 (a) long residence time;
concentration is stable

(b) short residence time


1.2 Composition of the Atmosphere (cont.)
• Permanent gases form a constant
proportion of the atmos. Mass (99.999%)
• Nitrogen (N2):
- has a very long residence time, 42
million years due to the processes that
add and remove nitrogen from the
atmosphere occur very slowly
- has little effect on most meteorological
and climatological processes
• Oxygen (O2):
- is crucial to the existence of virtually all
forms of life
- residence time is about 5000 years


1.2 Composition of the Atmosphere (cont.)
Permanent gases of the atmosphere

Permanent gases occur in a constant proportion throughout the
atmosphere’s lowest 80km  homosphere


1.2 Composition of the Atmosphere (cont.)
• Variable gases are those whose distribution
atmosphere varies in both time and space

in

the

• Despite their relative scarcity, some of these gases affect the
behavior of the atmosphere
• Heterosphere, where lighter gases become increasingly
dominant with increasing altitude.

Variable gases of the atmosphere


1.2 Composition of the Atmosphere (cont.)
• Water vapor:
- decreases rapidly with altitude, is found in the lowest
5km of the atmosphere
- is related to hydrologic cycle
- changes phase into liquid and solid forms at Earth’s
surface and in the atmosphere
- has a very short residence time of only 10 days
- higher in the tropics
- the source of moisture needed to form clouds
- a very effective absorber of energy emitted by Earth’s
surface
- a greenhouse gas


1.2 Composition of the Atmosphere (cont.)

Water cycle

1.2 Composition of the Atmosphere (cont.)

The distribution of
water vapor


1.2 Composition of the Atmosphere (cont.)
• Carbon dioxide:
- is supplied to the atmosphere by plant and animal
respiration, the decay of organic material, volcanic
eruptions, and natural and human-produced combustion
- is removed from the atmosphere by photosynthesis
- a greenhouse gas
- in recent decades, the rate of CO2 input to the
atmosphere has exceeded the rate of removal  a
global increase in concentration
- has a residence time of about 150 years


1.2 Composition of the Atmosphere (cont.)


1.2 Composition of the Atmosphere (cont.)


1.2 Composition of the Atmosphere (cont.)
The data are obtained
from the Mauna Loa

Observatory, with the zigzag line showing the
seasonal cycle in the
growth and decay of
plants

The concentration of CO2 has increased at a rate of ~1.8 ppm
per year, because of anthropogenic combustion and
deforestation of large tracts of woodland.


1.2 Composition of the Atmosphere (cont.)


1.2 Composition of the Atmosphere (cont.)
• Ozone:
- is the form of oxygen in which three O atoms are
joined to form a single molecule
- exists in the upper atmosphere
- is a major component of air pollution, causing irritation
to lungs and eyes and damage to vegetation near
Earth’s surface
- O3 in the upper atmosphere is vital to life on Earth
because it absorbs lethal ultraviolet radiation from the
Sun
- is continually being broken down and re-formed to
yield a relatively constant concentration in the O3 layer


1.2 Composition of the Atmosphere (cont.)

1.2 Composition of the Atmosphere (cont.)
• Aerosols:
- are small solid particles and liquid droplets in the air
(excluding cloud droplets and precipitation)
- are formed by both human and natural processes
- reduce visibility
- play a major role in the formation of cloud droplets
(condensation nuclei)
- have life spans of a few days to several weeks
- are removed effectively by falling precipitation


1.3 Vertical structure of the Atmosphere
• Atmospheric structure refers to the state of the air at different
heights
• The true vertical structure of the atmosphere varies with time
and location due to changing weather conditions and solar
activity
• Standard atmosphere: is an idealized, dry, steady-state
approximation of the atmospheric state as a function of
height
• Devided into 4 layers based on how mean temperature
varies with altitude
• Four layers are: troposphere, stratosphere, mesosphere,
thermosphere


1.3 Vertical structure of the Atmosphere (cont.)
- Troposphere:

0≤H ≤11km
- Stratosphere:
11 ≤H ≤47km
- Mesosphere:
47 ≤H ≤84.9km
- Thermosphere:
84.9km ≤H

Temperature profile of the atmosphere


1.3 Vertical structure of the Atmosphere (cont.)
• The troposphere:
- is the lowest of the four temperature layers
- is where the vast majority of weather events occur
- temperature decreases with height
- vertical mixing and turbulence
- contains 80% of the atmosphere’s mass
- the depth varies from 8km (in polar regions) to 16km
(in tropics)
- the average global temperature is ~15oC near the
ground but only ~-57oC at the top of troposphere (an
average decrease of ~6.5oC/km)
- a transition zone called tropopause


1.3 Vertical structure of the Atmosphere (cont.)
• The stratosphere:
- Little weather occurs
- In the lowest part, the temperature remains relatively

constant up to about 20 km
- From there to the stratopause, the temperature increases
with altitude  the result of UV radiation being absorbed
by ozone
- contains about 19.9% of the total mass of the
atmosphere
- Ozone layer (20-30km) is a zone of increased ozone
concentration
- O3 absorbs the solar energy  warms the stratosphere,
protects life on Earth from lethal effects of UV radiation


1.3 Vertical structure of the Atmosphere (cont.)
• The mesosphere:
- Temperature decreases with altitude.
- The absortion of solar radiation near the base of the
mesosphere provides most of the heat for the layer
• The thermosphere:
- Temperature increases with altitude.
- The atmosphere is so sparse  a gas molecule will
normally move several kilometers before colliding with
another.


1.3 Vertical structure of the Atmosphere (cont.)
• The inosphere:
- based on its electrical properties.
extends
from
the

upper
mesosphere into the thermosphere,
contains
electrically
charged
particles (ions).
- is important for reflecting AM radio
waves back toward Earth and is
responsible for the aurora borealis
and the aurora australis.
An aurora borealis. Subatomic particles
from the Sun are captured by Earth’s
magnetic field, causing an agitation of
molecules & the emission of light with
different colors.