In the photograph above the troposphere is represented by the veneer of blue haze on the horizon that is about 2mm thick. The diameter of Earth is 12,756.32 km at the equator. With a little effort one could work out the radius of the sphere and check that figure.
The troposphere contains 75% of the mass of the atmosphere.
At sea level, a single square metre column of air is equivalent to a mass of 10.2 tons. At this density breathing is comfortable for humans. At an altitude of just 2 km density is so reduced that humans can suffer altitude sickness. Mexico City is at an altitude of 2240 meters. As a venue for the Olympic Games, it had its critics. At just 5.5 kilometres in elevation, the density of the air is halved and its temperature falls to minus 15°C.
The properties of Earth’s atmosphere owe much to the presence of abundant water at the surface of the planet and the character of solar radiation. The paucity of the atmosphere by comparison with the size of the Earth is surprising. The troposphere, wherein we see the weather action, is exceedingly thin at just 10km in mid latitudes, 16 km in the tropics and nonexistent at the poles in winter. With steep vertical and lateral gradients in temperature and density the troposphere effectively transmits heat from the Earths surface to space. This is due to the strength of evaporation and convection as heat movers. Within the troposphere water circulates very close to the surface of the Earth because of the steep temperature gradient with elevation. In the tropics the air at the surface holds about 16gr water/kg air. At 2km there is only 4gr water/kg air. Between the surface and 2km relative humidity falls from 80% to 45%. It follows that, in the upper troposphere the cloud comes and goes as the temperature of the air changes, because specific humidity changes very little at all. This upper atmosphere cloud is the Earths energy shield.
An appreciation of the thickness of the troposphere can be obtained if one considers that in a stiff morning walk of an hour and a half one can easily travel 10km.
By and large about half of the energy available in the form of solar radiation actually reaches the surface of the Earth. The proportion of solar radiation that reaches the surface varies with latitude, season and time. In the drivers seat sits the sun. As it heats the upper troposphere air temperature rises, relative humidity falls and the ice clouds (cirrus) of the upper troposphere that are the Earths radiation shield, disappear. Fortunately, most of the tropics is temperature saturated and extra solar energy increases evaporation rather than surface temperature and in this way the tropics avoid the extremes of temperature that are seen in arid areas on land. Thus the big swings in temperature occur in the atmosphere at condensation level (925hPa to 850hPa) where latent heat is released, rather than at the surface. Here, demonstrably, it is not the surface that heats the atmosphere but the release of latent heat that is responsible for air temperature.
However there is a zone of the tropics where cloud cover is light, the air is dry, the ozone content is a little higher (because the air is drier) and much solar radiation gets through to warm a sea that is relatively cool. That part of the tropics lies between the Equator and 30°south latitude. The least cloudy area within this zone can be found in the rain shadow of the Andes where the Humboldt current courses north.
The Exosphere is the outermost skin of the Earths atmosphere and it is well within the influence of Earths gravitational field. The base of the exosphere is defined as the height above which there is little chance of atomic collisions between particles. It is the height at which satellites travel and is considered to begin at about 500 kilometres from the Earths surface. The gases in this sphere are largely hydrogen and helium with any earthly gases entering it at great risk of loss to ‘space’ in ordinary rather than exceptional circumstances. Despite the rarity of the atmosphere at this elevation drag on satellites varies considerably over time. At 500 km elevation we are well past the point of maximum density in the ionosphere (300 km). However, drag can double during a major geomagnetic storm indicating a bulge in the thermosphere. These bulges are related to the change in the solar wind and the intensity of short wave radiation.
Two elements of solar activity are vital determinants of the extent of the Earth’s heat shield. The first is the intensity of short wave radiation that is capable of directly energising the atmosphere. This includes gamma, X ray and ultraviolet radiation. This varies with sunspot activity. If short wave radiation were the only factor influencing the amount of cirrus cloud we would have a regular temperature peak at sunspot maximum and a trough at sunspot minimum. But in fact, the maximum temperature is frequently achieved after solar maximum. This is when the solar wind peaks, as reflected in the aa index of geomagnetic activity. So the second factor influencing the Earths heat shield is the solar wind and one can imagine that the atmosphere on the dayside is gently pushed by the solar wind slipping towards the poles and into the slipstream of the nightside, allowing more very short wave radiation to reach the troposphere where temperature increases and the cloud disappears. This may be my imagination working overtime but it is consistent with surface and upper troposphere temperature data.
When the tropics warm the entire bathtub of the Earths oceans warm. At the poles which are devoid of solar radiation for half the year, winter temperatures are governed by the temperature of the ocean. It is here that the warming manifests. Since the Great Pacific Climate Shift of 1978 that occurred in the transition from the weak solar cycle 20 to the strong cycle 21, winter air temperatures in both hemispheres, pole-wards of 60°latitude, have risen by about 5°C. This statistic gives the lie to the AGW hypothesis and reveals the true nature of the phenomenon that we are dealing with. If this were not sufficient, consider the phenomenon of Antarctic warming in winter and cooling in summer. Summer cooling is driven by convection in the tropics. Antarctic has the coldest, densest air on the planet. What goes up must come down, but not necessarily in the same place.
The AGW guys must answer three questions.
1) Where are temperatures increasing?
2) When is the temperature increasing?
Then they must get out of the way.