Climate: Nocturnal Inversions Refute 2nd Law Arguments
R. C. Sutcliffe had been invited to write his book,Weather and Climate, by W. W. Norton & Company as part of their Advancement of Science Series. This series aimed to inform the intelligent reader about new developments in science and their relevance to everyday life. (From dustcover) It was published in 1966 and has become my reference for the history of this very young science.
The second sentence of his introduction was:
“It is then not unreasonable to suppose, indeed it could hardly be otherwise, that the problems presented by weather, by wind and rain and warmth, were amongst the earliest to force themselves on consciousness and that in a historic sense meteorology lay at the foundation of physical science. “
I am mystified about this last phrase. For in the second chapter he wrote:
“When it became firmly established from observations on mountains and in manned and free balloons that the air became steadily colder as the altitude increased, scientists were very ready to generalize and to assume that the cooling went on indefinitely to the limit of the atmosphere. This was the general belief until in 1899 the Frenchman Teisserene de Bort, announced to an astonished and even incredulous world that this sounding balloons had reached heights above which the temperature decreased no further. Sir Napier Shaw, the leading British meteorologist of the early decades of the century, called this the most surprising discovery in the whole history of meteorology.”
Another bit of history which illustrates that meteorology is a quite young science is one of the best kept secrets of WWII. Which was that the Japanese launched balloons carrying incendiary devices and more than a 1000 reached the USA as far east as the mid-west. So it was not until after WWII that weather balloon soundings of the atmosphere became common.
2nd Law arguments are all based upon the air became steadily colder as the altitude increased. And if those who make such arguments, had begun their meteorology studies using Meteorology Today by C. Donald Ahrens, there might be reason for some confusion. This textbook is now in its 10th Ed. but I quote from the 9th Ed.
“Nighttime Cooling: As the sun lowers, its energy is spread over a larger area, which reduces the heat available to warm the ground. … Both the ground and air above cool by radiating infrared energy, a process called radiational cooling. The ground, being a much better radiator than air, is able to cool more quickly. Consequently, shortly after sunset, the earth’s surface is slightly cooler than the air directly above it. … a couple paragraphs later he writes … A windless night is essential for a strong radiation inversion because a stiff breeze tends to mix the colder air at the surface with the warmer air above. This mixing, along with the cooling of the warmer air as it comes in contact with the cold ground, causes a vertical temperature profile that is almost isothermal (constant temperature) in a layer several meters thick. In the absence of wind, the cooler, more dense surface air does not readily mix with the warmer, less dense air above, and the inversion is more strongly developed, as illustrated in Fig. 3.15.”
Too bad I cannot copy and paste Fig. 3.15 because a picture is worth a thousand words. So I must describe the figure. It pictures the atmosphere’s temperature for the two cases—calm and windy—up to an altitude of 3 meters. The air temperature at surface during the calm night is about 4F less than that of the windy night. But the temperature of the windy night is about 2F less than that of calm night at an altitude of 1 meter.
However, I had also bought another meteorology textbook for a reference. This was Meteorology 3rd Ed. by Steven A. Ackerman and John A. Knox (A&K). They wrote:
“The range of diurnal and annual cycles in temperature depends on altitude, the distance from the ground. Figure 3-21 shows the temperature measured at various times on a cloud-free day in summer. We start at 3:00 PM (Fig. 3-21a). At this time, the temperature is highest close to the ground, where solar heating has raised the temperature to near its daily maximum. By 8:00 PM (Fig. 3-21b) the Sun is setting, and the temperature below an altitude of about 200 meters (0.2 kilometers) has cooled because energy loses have exceeded gains for several hours. The temperature increases up from the surface to 200 meters, and therefore, a temperature inversion is present.
By 5:00 AM (Fig. 3-21c) nighttime cooling of the surface and a lack of sunlight have led to many hours of energy deficits. As a result, the near-surface temperature has cooled significantly. However, the air higher up has cooled less. Therefore, the temperatures at 5:00 AM increases sharply in the lowest 600 meters of the atmosphere. The temperature inversion is near its peak in terms of depth and temperature difference between the bottom and the top of the inversion.
At sunrise, solar energy heats the ground, and conduction and convection transfer heat upward. This warms the air near the surface more effectively than higher up. By 10:00 AM (Fig. 3-21d) the temperature near the surface is warmer than above it and the inversion has dissipated.
A temperature inversion that develops near the ground during the night, as shown in Figure 3-21, is referred to as a nocturnal inversion (sometimes also called a radiation inversion because of the key role that terrestrial emissions play in its formation). Nocturnal inversions often occur on clear, calm nights and are more prevalent during winter than summer.”
A&K’s Figure 3-21 is based upon atmospheric sounding data. However, if one goes to http://weather.uwyo.edu/upperair/sounding.html one will find that the sounding data is never simply plotted temperature versus altitude as A&K had. Then there is another problem. Atmospheric soundings are commonly made at 12:00 PM and 12 AM (GMT) everywhere. So to find atmospheric soundings at 3:00 PM, 8:00 PM, 5:00 AM, and 10:00 AM local times one needs to find a site where the soundings are made at these times and then identify periods of times with the required atmospheric conditions.
Both Ahrens and A&K stressed the difference between calm and windy nighttime atmospheric conditions. While Ahrens’ Figure 3.15 provided a student with a limited understanding of the vertical extent of radiational cooling, the figure did use data to illustrate this difference. So, at first, I was very critical of what he wrote. It took me longer to see that atmospheric sounding data of A&K’s Figure 3-21 could never illustrate this difference which occurred below an altitude of 1 meter.
However, both figures support Ahrens’ statement—The ground, being a much better radiator than air, is able to cool more quickly. For the data shown in either figure forces this conclusion; for how else could the atmosphere near the surface cool below the temperature of the atmosphere only a fraction of a meter above the surface. How else could the cooler surface cool the atmosphere up to an altitude of 0.6 km during a summer night, if not by absorbing the downwelling infrared radiation being emitted by whatever (liquid and/or solid condensation nuclei and greenhouse gases that are warmer than the surface) in the atmosphere and then the cooler surface emitting infrared radiation according to its temperature upward toward space? And, given the magnitude of the nocturnal surface and atmospheric cooling that has been observed, is there any evidence that the transmission of the upwelling infrared radiation through the atmosphere to space is being much hindered?
Another factor, to which the student is not pointed, is that whatever (cloud, condensation nuclei, greenhouse gases) is emitting in the atmosphere, it is emitting upward as well as downward. What A&K did not describe, in words, is that at 5:00 AM in Fig. 3.21c there is a 4 km isothermal layer of maximum atmospheric temperature between 0.6 km and 1.0 km altitudes. And above 1.0 km the atmosphere’s temperature decreases with increasing altitude just as expected up to the tropopause. Hence, there is no evidence that the atmosphere above 1 km is being warmed by any of the upwelling infrared radiation being transmitted through it to space.
Finally, neither A&K nor Ahrens direct the students’ attentions to the fact that there is an important factor which could limit the nocturnal cooling of the earth’s surface even if the nighttime atmosphere was cloudless. This factor is the atmosphere’s dew point temperature.
There is much good data that is being generally ignored (not considered as it should be).
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