What is the Troposphere? Weather Breeder
We live at the bottom of a “Sea” of air called the atmosphere.
This thin envelope of life-sustaining gases surrounding the earth
is divided into several spherical layers characterized by abrupt changes
in temperature, the result of differences in the absorption of incoming
solar energy.
About 75% of the mass of the earth’s air is found in he atmosphere’s
innermost layer, the troposphere, this thin and turbulent
layer of rising and falling air currents and wind is the planet’s
weather breeder.
Throughout the earth’s long history the composition of the
troposphere has varied considerably. Today, about 99% of the volume
of clean, dry air in the troposphere consists of two gases: nitrogen
(78%) and oxygen (21%). The remainder has slightly less than 1% argon,
0.036% carbon dioxide, and trace amounts of several other gases. Air
in the troposphere also holds water vapor in amounts varying from
0.1% by volume at the frigid poles to 5% in the humid tropics.
The average pressure exerted by the gases in the atmosphere decreases
with altitude because the average density decreases with altitude.
Temperature also declines with altitude in the troposphere but abruptly
begins to rise at the top of this zone, called the tropopause.
This temperature change limits mixing between the troposphere and
upper layers of the atmosphere.
What is the Stratosphere? Earth’s Global Sunscreen
The tropopause marks the end of the troposphere and the beginning
of the stratosphere, the atmosphere’s second layer. Although
the stratosphere contains less matter than the troposphere, its composition
is similar, with two notable exceptions: Its volume of water vapor
is about 1,000 times less, and its volume of ozone (O3) is about 1,000
times greater.
Stratospheric ozone is produced when some of the oxygen molecules
there interact with lightning and ultraviolet (UV) radiation emitted
by the sun. Ozone is continuously being formed and destroyed, but
as long as the rates of these two reversible processes are equal,
the average concentration of ozone in the stratosphere remains constant.
The “global sunscreen” of ozone in the stratosphere keeps
about 99% of the sun’s harmful ultraviolet radiation from reaching
the earth’s surface. This UV filter allows humans and other
forms of life to exist on land; helps protect humans from sunburn,
skin cancer, cataracts, and damage to the immune system; and prevents
much of the oxygen in the troposphere from being converted to ozone,
a harmful air pollutant. The trace amounts of ozone that do form in
the troposphere are a component of urban smog that damage plants and
the respiratory systems of humans and other animals.
Thus, our good health, and that of many other species, depends on
having enough ozone in the stratosphere and as little ozone as possible
in the troposphere.
Temperature rises with altitude in the stratosphere until there is
another temperature reversal at the stratopause. This change
marks the end of the stratosphere and the beginning of the atmosphere’s
next layer: the mesosphere.
