Download The Atmosphere

ATMOSPHERE,
WEATHER AND CLIMATE
The Atmosphere:
In this segment we discuss the composition and structure of
the atmosphere, and its influence on earth’s physical systems
Earth’s atmosphere has evolved over the last 4 .6 billion years
– Now, its composition and structure is relatively stable
Characteristics of the Atmosphere
Our atmosphere
is a dynamic mixture of various gases that envelops earth and protects it from
excessive and harmful solar radiation, and other onslaught, from outer space
 It is a thin film of air,
extending for about 300 miles above Earth
 Held together by Earth’s gravity, it has mass, and
it exerts pressure on Earth’s surface
 It serves as an insulator, maintaining viable temperatures on Earth
 It also serves as a shield, blocking out much of sun’s ultraviolet radiation,
and protecting us from meteor showers and space debris
Its importance becomes apparent when compared with conditions on our moon
Composition of the Atmosphere
Permanent or “Constant”
Gases
• Nitrogen (78%)
• Oxygen (21%)
• Argon (0.93%)
These gases are called
"permanent gases" because
their concentration remained
virtually the same for much of
recent earth history.
These are important for maintaining life and
driving a number of processes near Earth’s surface
Variable or “Greenhouse” Gases
Even though they represent a tiny portion of the
atmosphere as a whole (‹ 0.07%), they exert a
great control over our environment
• Carbon Dioxide
• Methane
• Ozone
• Water Vapor
+ Particulates
•
The Greenhouse Effect
Greenhouses keep the temperature inside warmer than outside. Sunlight
(shortwave radiation) passes through the panes of glass. Materials within
the greenhouse (plants, floors, walls, benches, etc.) absorb this energy.
• Absorbed radiation is reradiated as heat (long-wave radiation). The glass
panes block the long wave radiation, thus trapping the heat, keeping the
air warm inside the greenhouse.
• Carbon Dioxide (CO2) makes up only .036% of the atmosphere by
volume. Carbon dioxide is essential to the photosynthesis
processes of plants, in which oxygen is a byproduct
• Methane (CH4) makes up far less of the atmosphere (.0002%) than
carbon dioxide, but it is 20+ times more potent than CO2 as a
greenhouse gas. Methane has been on the rise over the last several
decades
• Ozone (O3) is both beneficial and harmful to life on Earth. Much of the
ozone in the atmosphere is found in the stratosphere [stratosphere]
There, ozone absorbs UV light from the Sun, preventing it from
reaching the surface
Ozone is also found in the lowest layer of the
atmosphere, the troposphere. Here ozone can act
as an eye and respiratory irritant. Ozone also causes
cellular damage inside the leaves of plants, disrupting
the photosynthesis apparatus.
The Ozone Hole Problem
Without the ozone blanket, humans would be exposed to serious
sunburn and potential risk of skin cancer.
However, human-produced compounds such as chlorofluorocarbons
(CFCs) and halides containing chlorine and bromine destroy ozone, and
have disrupted the fragile stratospheric ozone layer over the Antarctic and
the Arctic – the “Ozone Hole”
Ozone Hole
over Antarctica
Sep 2009 – 9.2 Million Square Miles
•
Water Vapor
water in gaseous state – is an extremely important gas found in the
atmosphere – mostly in the lower atmosphere (troposphere).
It can vary from 4% in the steamy tropics to nearly nonexistent in
the cold dry regions of the Antarctic.
Water vapor is a good absorber of earth's outgoing radiation and
thus is considered a greenhouse gas.
•
Particulates
play several important roles in atmospheric processes.
Include dust, dirt, soot, smoke, and tiny particles of pollutants,
and they are concentrated in the troposphere. Major
natural sources of particulates are volcanoes, fires,
wind-blown soil and sand, sea salt, and pollen.
 Human sources such as factories, power plants,
trash incinerators, motor vehicles, and construction
activity also contribute particulates to the atmosphere.
Colors of the Atmosphere
Due to atmospheric scattering of
the wavelengths of the visible light
spectrum
See p. 94 in Text:
The most spectacular sunrises and
sunsets are a result of light being
refracted from particulates in the
atmosphere.
Structure of the Atmosphere:
Vertical Layers
by Temperature
Characteristics
Troposphere
(the Lower Atmosphere)
Stratosphere
(the Upper Atmosphere
Starts here)
 The properties of the first two layers –
Troposphere and Stratosphere – affect
most of what we study in physical
geography, especially weather & climate
 Together, these 2 layers extend to about
30 miles above Earth’s surface
 Layers above the stratopause have relatively little
impact on our environment
 99.9 percent of the gases (by volume) that comprise earth’s atmosphere
is to be found in these two layers, and 98% of its mass lies within
16 miles above sea level

Most of the water vapor and particulates in the atmosphere
are concentrated in one layer – the troposphere, which is
also characterized by “turbulent” air – an “ocean of air”

Most of the ozone concentration – the ozone layer – is
confined within the stratosphere, generally characterized
by “stagnant” air
Mesosphere and Beyond
• In the Mesosphere, which extends to 50 miles above sea level,
air temperatures begin to decrease with increasing altitude
• The air of the mesosphere is thus extremely thin and air pressure very small
• The Mesopause separates the mesosphere from the thermosphere above
• In the Thermosphere temperature increases with increasing altitude –
temperatures are generally high, but the heat content is very
low due the low density of air at this level
• The thermosphere extends to about 120 miles, where it
starts to gradually merge into Exosphere, which in
turn merges into interplanetary space – so there is
no “top” of the atmosphere!
Layers by Chemical
Composition
Layers by Function
Layers by Chemical Composition
Emphasis on the chemical makeup of the atmosphere led to another
dichotomous layering system: Homosphere and Heterosphere.
Homosphere, extending to about 50 miles above the surface, is
virtually homogenous in terms of the proportions (percent by volume)
of the various gases, except for a few areas of concentration of a few
gases, like ozone and water vapor.
Heterosphere starts from an altitude of about 50 miles and extends
into the vacuum of outer space, and within it atmospheric gases are
no longer evenly mixed but separated into distinct sublayers of
concentration, caused by earth’s gravity in which the heavier
gases are pulled down and the lighter gases drift farther
outward. The nitrogen sublayer is lowermost, followed by
atomic oxygen, then by helium, and then atomic hydrogen.
This sphere corresponds to thermosphere and ionosphere
in terms of its altitudinal limits.
Layers by Functional Characteristics
Another system, using protective function as the determining
criterion, identified two atmospheric layers: the Ozonosphere
and the Ionosphere
The ozonosphere is the concentrated layer of ozone found in the
stratosphere, 10 – 30 miles above the surface. Ozone (O3) absorbs
ultraviolet light, and even though relatively constant through millions of
years, seasonal fluctuations of ozone, especially over the Arctic and
Antarctic, are common.
The ionosphere, 40 – 250 miles above the surface, is not really
a layer of the atmosphere, but an electrified field of ions and
free electrons – it absorbs cosmic rays, gamma rays, X-rays,
and shorter wavelengths of ultraviolet radiation.
The spectacular display of aurora lights are generally
found in this region.
Effects of the Atmosphere on Insolation,
and Earth’s Radiation Budget
As sun’s energy passes through Earth’s Atmosphere, the actual amount of
Insolation, or Incoming Solar Radiation, received at a particular location
depends on many factors:
• Latitude
• Time of Day
• Time of Year
All the above are also related to the angle of sun’s rays
• Atmospheric Thickness
• The Transparency of the Atmosphere (which includes
the amount of cloud cover, moisture/water vapor,
carbon dioxide, and particles in the air)
Together, all these factors determine what is called:
Earth’s Radiation Budget
(See diagram 3.15, p. 60)
Earth’s Radiation Budget
To summarize the Radiation Budget:



34% of the insolation is returned to space;
19% is retained in the atmosphere, and
47% eventually reaches the surface.
 The 47% received at the surface is
ultimately returned to the atmosphere
by various Heat Energy Transfer
processes, and the Earth’s Radiation
Budget is said to be in Equilibrium.
 However, the radiation budget is a dynamic one
– alterations in one element affect the other elements –
and there is growing concern that one of the
elements, human activity, is causing the
atmosphere to absorb more Earth-emitted
energy, thus raising global temperatures.
[Greenhouse Effect and Global Warming]
Earth as a Greenhouse
The Greenhouse Effect in the Earth context is defined as a
system in which sun’s shortwave radiation enters freely and
is absorbed, then reradiated as long-wave infrared radiation.
The long-wave radiation is largely retained within the system,
as much of it is absorbed by the greenhouse gases and reemitted in all directions, adding additional heat energy to the
atmospheric and earth systems, thereby continuing the
generally beneficial Greenhouse Effect.
Without Greenhouse Effect, the heat would escape
to outer space ← acts as Insulator
 Average temperature of the Earth would drop
from an average of +15 degrees to
-18 degrees Celsius (59˚F to – 65˚F)
 Life as we know it could not survive!
Potential Negative Consequences
How can the Greenhouse Effect be harmful to us?
 Rising levels of greenhouse gases evidently cause a rise
in global temperatures:
Global mean surface temperatures have increased by
.5 - 1˚ F since the later part of the 19th century
 Rising temperatures have caused a decrease in snow
cover and sea ice in the Northern Hemisphere
 Global sea level has risen by 4-8 inches over the past
hundred years – Additional sea level rise and
inundation of coastal regions is feared as
Antarctic ice sheets and shelves, and
smaller alpine glaciers melt
 The frequency of extreme precipitation
events has increased throughout the U.S.
and the world (e.g., 2010 Pakistan Floods)
Watch "Global Warming 101" Courtesy of National Geographic
Obvious Next Questions:
How do Insolation and Heat Energy Transfer
processes relate to Weather and Climate
phenomena on Earth?
Weather and Climate
Weather: refers to the condition of atmospheric
elements at a given time, and for a specific area.
Climate: average of weather conditions for 30+
years (including atmospheric anomalies).
Weather and Climate are of prime interest to the
Physical Geographer because they affect and
are interrelated with all of Earth’s environments.
5+ Basic Elements of the Atmosphere
– the main ingredients of weather and climate
-- Also called Elements of Weather and Climate
• Solar Energy
-- Insolation and Heat Energy Transfer
•
•
•
•
+
Temperature
Pressure
Wind
Precipitation
Air Masses (and Fronts)
to be discussed later in conjunction with
Weather Systems
As we will see in the next set of topics, Earth’s
Weather and Climate are the results of the intricate
interrelationships between Earth and the Sun, and
between the component spheres of our Atmosphere
and our Geosphere: