The Stratosphere Is Home to Earth's Ozone Layer

When you get right down to it, we're all creatures of the troposphere. This atmospheric layer is where almost all of the weather-related phenomena on Earth unfold. Although the troposphere begins at the Earth's surface, its upper boundary is less consistent. Depending on your latitude and the current season, the top of the troposphere might be located anywhere from 4 to 12 miles (7 to 20 kilometers) overhead.

Above the troposphere, we have — in order — the stratosphere, mesosphere, thermosphere and exosphere. Let's go back and talk about those first two levels.

The troposphere-stratosphere boundary, or tropopause, separates two areas with inverted temperature trends. Inside the troposphere, the global average temperature decreases with altitude. Yet it's a different story in the stratosphere, where things get warmer as you go higher. Eventually, you'll hit the stratosphere's ceiling 31 miles (50 kilometers) up. Beyond that point, the trend starts to reverse itself; things get pretty chilly in the mesosphere.

Ozone gas safeguards this planet from excessive ultraviolet (UV) radiation sent over by the sun. Made up of oxygen atoms, ozone — like many sunscreens — absorbs UV light. Entire ecosystems would fail if not for that critical service. Our atmosphere's supply of the gas is mostly limited to the famous ozone layer. And about 90 percent of this layer is contained within the stratosphere.

On a related note, the ozone explains why stratospheric temperatures climb at higher altitudes. Not only does it absorb the sun's UV rays, but it also soaks up infrared radiation from the troposphere. The result? A stratosphere that grows toastier by the mile.

Most clouds are in the troposphere. Be they cirrus, stratus or cumulonimbus, you need water droplets and/or ice crystals to make clouds. So the relatively wet troposphere is a great environment for them. But the stratosphere? Not so much. By and large, it's just too dry to facilitate cloud formation.

Still, the cloud shortage isn't necessarily a bad thing. The stratosphere combines (largely) cloud-free skies with limited turbulence, making it attractive to airline pilots. Indeed, most commercial planes hit their cruising altitudes in the lower atmosphere of the stratosphere. When stratospheric clouds do form, they're sometimes created by the mixing of ice with volcanic dust. Also, the polar regions see stratosphere-level clouds during the wintertime.

The same reason the stratosphere is attractive to commercial jets makes it ideal for other flying objects like weather balloons and high-altitude reconnaissance balloons. Near Space Labs, for instance, creates technology capable of flying into near space to collect data for insurance, conservation, disaster response, urban sprawl and more. Its Swifty is an autonomous, high-altitude balloon that flies into the stratosphere between 60,000 and 85,000 feet (18,288 and 25,908 meters). Swifty has a robot aboard that can take between 154 and 400 square miles (386 and 1,000 square kilometers) of imagery per flight.

Aerospace and defense contractor Aerostar has several different unmanned airships capable of flying in the stratosphere. Some of these high-altitude balloons simply move with the current, but others, like Aerostar's Thunderhead Balloon Systems, have navigation capabilities.

The term "polar vortex" gets a lot of mileage these days. What you may not realize, however, is that the Arctic region witnesses two different kinds of polar vortices. All year long, the swirling tropospheric polar vortex encircles the Arctic; its edge is usually found between the latitudes of 40 and 50 degrees north. Traveling from west to east that jet stream helps separate cold air and warm southern currents.

Higher up, there's the stratospheric polar vortex. Like its counterpart below, this one moves in a counterclockwise direction. But the stratosphere's vortex is seasonal, collapsing every spring and then reforming in the winter.

The winds are at their strongest when there's a big temperature contrast between the Arctic and the regions at lower latitudes. However, the Arctic is warming up at a rapid pace. Some scientists argue that climate change is weakening the stratospheric polar vortex, allowing the ultra-cold winds it normally traps to head south. (Maybe the same temperature increase is screwing up the tropospheric jet, too.)

We'd be remiss if we didn't acknowledge the Southern Hemisphere's polar vortex. Located above Antarctica, this is more powerful than its counterpart to the north.

Collecting them isn't easy, but scientists have been known to find microorganisms adrift in the stratosphere. Researchers in a study published in August 2018 in the journal Frontiers in Microbiology designed and built an air-capturing probe they installed on a NASA plane. The gadget detected bacteria whizzing around above the local tropopause at altitudes of 7 miles (12 kilometers).

UV radiation and extreme temperatures make the stratosphere a rough place for living things. To survive up there, some bacteria depend on sun-blocking pigments and protective outer shells. Fast DNA reparation is another life-saving trick.

Hitching rides on storms and volcanic eruptions, microbes use the stratosphere as an atmospheric superhighway. Here, winds carry them across the continents at great speeds, allowing the microbes to disperse. The fact that life can tolerate our stratosphere — even for limited periods — could profoundly impact the hunt for Martian organisms.