On Thu, 11 Feb 2016 17:55:47 +0000, Pete Barrett <
nor...@xxx.uk>
wrote:
Unfortunately he gives no simple concise explanation and calls on
physics which I haven't looked at for 60 years. I'm still trying to
work out whether or not he may be correct. The following is the most
concise description I can find. The original text includes a diagram
which I have inserted at the appropriate place via a link
"How Does the Ozone Layer Protect Earth from Sun's "Hottest"
Radiation?
The ozone layer, primarily 12 to 19 miles (20 to 30 km) above
Earth's surface, is not a static layer of gas, but is a region of
the atmosphere where sufficient solar ultraviolet radiation of
frequency greater than or equal to 1237 THz is available to
dissociate oxygen, leading to the formation of ozone, and
sufficient ultraviolet radiation at lower frequencies is available
to dissociate ozone. Ozone is dissociated most efficiently by solar
ultraviolet-B radiation with frequencies around 967 THz, although
some photodissociation is caused by frequencies as low as 887
THz.109 Thus, ozone is created and destroyed continually in a
sequence known as the Chapman cycle, which will be described in the
next chapter. The ozone layer is the last chance to absorb solar
ultraviolet radiation before it strikes Earth.
The green area in Figure 5.4
https://dl.dropboxusercontent.com/u/31088803/Fred001.jpg
shows the frequency distribution of excess ultraviolet-A and
ultraviolet-B radiation that reaches Earth when the ozone layer is
depleted by 1%, as calculated by Sasha Madronich.110 Actinic flux
on the y-axis is defined as the total intensity of sunlight
available to be absorbed by a molecule of air, including direct,
scattered, and reflected radiation coming from all directions, as
calculated by Madronich.111 Actinic flux is a more detailed and
complete representation of the "Amplitude or brightness" spectrum
plotted in Figure 5.2. Note the substantial increase in UV-B and
the lesser amount of increased UV-A radiation reaching Earth when
ozone is depleted by only 1 %.
Recognizing that radiant energy is simply a function of
frequency times the Planck constant (E=hv), and that the higher the
frequency the higher the color temperature of the radiation, then
it is easy to understand why the mean surface temperature of Earth
is determined primarily by the highest frequencies of ultraviolet
radiation reaching Earth as well as by the length of time Earth is
exposed to this very "hot" radiation.
What Is the Primary Radiative Surface of the Earth System?
The major warming observed in Earth's atmosphere is in the
stratosphere (Figure 5.1), where temperatures at the stratopause,
31 to 34 mi (50 to 55 km) above Earth's surface, are maintained at
tens of degrees warmer than temperatures at the tropopause, at 5.6
to 10.6 mi (9 to 17 km) altitude. This warming is done primarily by
solar ultraviolet energy dissociating molecular oxygen (O2) and
many other chemical species. The stratosphere acts as an "electric"
blanket, in the sense that the energy to warm the blanket does not
come from the body under the blanket, i.e. from Earth, but from
another source, in this case, Sun.
Temperatures at the stratopause vary greatly with season but
commonly range from 8.6 to 37蚌 (-13 to +3蚓) in the tropics, -5.8
to 45蚌 (-21 to +7討 in mid latitudes, and -4 to 68蚌 (-20 to
+20蚓) near the poles112 and average close to 5蚌 (-15蚓).113
Thus, solar energy causing photodissociation of oxygen and
other chemical species in the stratosphere plays the major role in
keeping Earth warmer than it would be in the absence of an
atmosphere. The stratopause is the key radiant surface into space
of the Earth/ atmosphere system, and it can continue to radiate
only because heat from both a Sun-warmed stratosphere and a
Sun-warmed Earth rises continuously through the stratosphere below,
replacing the heat radiated from the stratopause. Temperature drops
with increasing altitude above the stratopause and below the
mesopause just as in the troposphere, so that turbulence is likely
active there.
The temperature profile shown in Figure 5.1 is the balance
within the atmosphere of heat flowing into and out of the
Earth/atmosphere system."
Just for the hell of it, here is Figure 5.1
https://dl.dropboxusercontent.com/u/31088803/Fred002.jpg
Ward makes the point that it seems to be common to base calculations
of energy flux on the simple radiant spectrum while in fact the energy
carried is also a function of frequency. This means that the UV-B
energy absorbed by the ozone layer is 48 times that absorbed most
strongly by CO2.
He atrributes the current(?) temperature hiatus to the Montreal
protocol on Substances that Deplete the Ozone Layer (a protocol to the
Vienna Convention for the Protection of the Ozone Layer) is an
international treaty designed to protect the ozone layer by phasing
out the production of numerous substances that are responsible for
ozone depletion.
--
Regards,
Eric Stevens