Bài giảng khí hậu học chương 1

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 atmosph

Chapter 1

Composition and Structure

of the Atmosphere

G304 – Physical Meteorology and Climatology

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 term phenomena)

(short-• 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

concentration is stable Fig 1.2 (a) long 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

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 in the atmosphere varies in both time and space

• 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

zig-zag 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.)

- 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.)

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

with altitude  the result of UV radiation being absorbed

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

1.4 Evolution of the Atmosphere

• Earth was formed perhaps 4.5 billion years ago

• If an atmosphere formed with Earth, it must have consisted

of the gases most abundant in the early solar system including large amounts of hydrogen and helium

• Today’s atmosphere composed mostly nitrogen & oxygen  where did the original gases go & how were they replaced?

• If molecules move with sufficient speed, known as their

escape velocity, they can overcome gravity and leave the

1.4 Evolution of the Atmosphere (cont.)

• The gases spewed out during volcanic events are predominantly water vapor and carbon dioxide, with lesser amounts of sulfur dioxide, nitrogen, and other gases

• The transformation to an atmosphere high in oxygen depended on the advent of primitive, anaerobic bacteria about 3.5 billion years ago

• These primitive life-forms were the first in a long line of organisms that removed carbon dioxide from the air and replaced it with oxygen

• Ultimately, plant and later animal material sank to the ocean floor, where the organic carbon was locked away in sediments

1.5 Some weather basis

1.5 Some weather basis (cont.)

A surface weather map

1.5 Some weather basis (cont.)

• Wind speed and

direction can be obtained

on weather maps by

looking at the station

models, which contain

symbols and numbers

1.5 Some weather basis (cont.)

• Temperature varies from place to place

• Major changes in temperature often occur due to the presence of fronts, fairly narrow boundary zones separating

relatively warm and cold air

• Cold fronts are shown as a blue line with triangles while warm fronts are depicted by a red line with semicircles

the air