decreasing over the south polar latitudes because of the human release of chloro-
fluorocarbons (CFCs) at other latitudes. These releases have been in the form of
CFC-based coolants, spray can propellants, and fire retardants. Inert near sea level,
CFCs react with ozone in the presence of ultraviolet energy to the effect that some
of the ozone has broken down. Indeed, a hole in the Antarctic ozone is now a regu-
lar feature of our atmosphere.
The atmosphere is quite varied with altitude. There are usually four
temperature-based layers denoted. The lowest layer is the troposphere. Averaging
the first 18 km of the atmosphere, the troposphere is a region that is heated by radi-
ation from Earth’s surface and so declines in temperature with altitude. The aver-
age planetary temperature is 15°C near the surface and this decreases with
altitude to− 65 °C at sharply defined top of the troposphere (the tropopause). The
tropopause acts like a lid so that daily weather—storms, clouds, and appreciable
amounts of humidity—are limited to the troposphere.The stratosphere is the sec-
ond temperature-defined layer and extends from 18 km to 50 km. This layer has
no surface-like weather and the air, although relatively well mixed, exists at tiny
fractions of its surface pressure.
The stratosphere contains most all of the world’s natural ozone, which nature cre-
ates and destroys at these elevations. The absorption of ultraviolet energy by ozone
makes some of it break apart while reradiating the energy in thermal infrared wave-
lengths. This release heats the stratosphere so that the temperature signature of the
stratosphere is one of increasing temperature with altitude. At the top of the strato-
sphere the temperature is slightly above 0°C. Above the stratosphere the atmos-
phere is not well mixed and there are altitudes that are rich in oxygen or in
helium, etc. The amounts of the gases are so minuscule that these altitudes are not
usually thought of as having air. The mesosphere extends up to 80 km where the
temperature declines to lower than− 80 °C where the atmosphere is at its coldest.
Interestingly, the next layer above the mesosphere is the hottest part of the atmos-
phere.Solar energyinteracting with the scant molecules and ions at these high alti-
tudes cause dramatic heating. Average temperatures are well over 1,000°C and can
approach 2,000°C when the sun is active. The huge temperature swings are not felt
near the planetary surface and not well understood as how they relate to weather and
climate. It is clear, however, that day-to-day weather changes are not a response to
the activity of the sun. The ionosphere is a non-temperature-based region of the
atmosphere extending from 60 to 400 km. It is noteworthy because of the occur-
rence of electrically charged molecules and atoms (ions). Ultraviolet and x-ray
energy emanating from the sun peel electrons off some of the matter; this is called
ionization. Although ionization affectsonly 1 percent of the gases, they become
strong electrical conductors. The ionization thus affects the propagation of radio
waves such that the transmissions can be greatly enhanced or blocked.20 Atmosphere