Four Facts About The Stratosphere

You often hear the adjective "stratospheric" in conversation. It refers to something very high, such as the jumping ability of a basketball player, or the national debt as described by a government critic. Paradoxically, however, the real stratosphere isn't very high when compared to other parts of the atmosphere. It's only the second atmospheric layer – the troposphere is below it and the mesosphere, thermosphere and exosphere extend for hundreds of miles above it.

The stratosphere altitude is still high, though. It extends from about 6 miles (10 kilometers) to about 30 miles (50 kilometers). There's a lot of stratospheric space to explore in that 24-mile-wide band of rarified air that sometimes just touches the top of Mt. Everest.

All terrestrial activity, including all weather, takes place in the troposphere, which extends from the ground to the boundary of the stratosphere, which is called the tropopause. As anyone who has ever climbed a mountain knows, temperature decreases with height in the troposphere. Not so in the stratosphere. The temperature at the bottom of the stratosphere can be a chilly –75 degrees Fahrenheit (-60 degrees Celsius), but at the top, ice could melt, because the average temperature is 32F (0C). The positive temperature gradient is called a temperature inversion, and it's what distinguishes the stratosphere from the layers above and below it and defines it as a distinct atmospheric layer.

Pilots wanting to create a smooth ride for their passengers fly above the tropopause in the stratosphere, where there are no thunderstorms or rain. There is hardly any wind there, partly because the air is thinner, but more importantly, the fact that the temperature increases with height means that there is no cold air accumulating at higher elevations and forming convection currents as it falls. This eliminates one of the primary causes of the eddy currents and breezes that occur in the troposphere. Air currents still exist in the stratosphere, but they are steady and free of turbulence.

The reason for the positive temperature gradient in the stratosphere in the presence of ozone in the upper part of the atmospheric layer. Ozone is formed when three oxygen molecules join together, and this happens in the stratosphere because of the intensity of the sun's ultraviolet radiation. The formation of ozone absorbs this radiation – fortunately for the organisms on the ground, which would die of radiation poisoning if the ozone layer wasn't there.

One of the more interesting stratosphere facts is that the ozone layer is responsible for its existence. Ozone heats up as it absorbs ultraviolet sunlight, and that's why there is positive temperature gradient in this atmospheric layer.

Swans symbolize grace and beauty in cultures all around the world, and the ability of the whooper swan (Cygnus cygnus) to coast into the lower layers of the stratosphere at an altitude of 32,000 feet (10,000 m) only reinforces that reputation. What could be more picturesque than a swan flying over Mt. Everest? Since whooper swans migrate between China and other countries in southeast Asia, some photographer may actually capture an image of that someday, if one hasn't already.

The common crane (Grus grus) has roughly the same habitat and almost the same connotation of gracefulness as the whooper swan. It can also fly to an altitude of 32,000 feet (10,000 m), straight over Mt. Everest and into the stratosphere. The highest-flying bird in the world, however, is Rüppel's griffon vulture (Gyps rueppellii). It won't ever be seen around Mt. Everest because it lives in Africa. This bird can reach an altitude of 37,000 feet (11,277 m), which puts it well above the tropopause, from where it can more easily spot prey. All three of these birds deserve to be characterized as stratospheric.