EDITOR’S NOTE: Part 4 of a series.
Our journey through Earth’s atmosphere continues upward. We started in the troposphere where we live and where nearly all our weather occurs. Then we climbed into the stratosphere, home to the ozone layer. Now, about 31 miles above Earth’s surface, we cross the stratopause and enter a place few people ever think about: the mesosphere.
The mesosphere stretches from roughly 31 miles to about 53 miles above Earth. While it may not get the attention of the layers above and below it, something happens here that almost everyone has witnessed.
Have you ever looked into the night sky and seen a streak of light race across it? We commonly call it a shooting star, but it isn’t a star at all. It is usually a tiny piece of rock or debris from space, called a meteoroid, entering Earth’s atmosphere at tremendous speed.
As it encounters the atmosphere, collisions with air molecules heat the surrounding gas and the object itself. The glowing streak we see is called a meteor. Most of these objects are destroyed before ever reaching the ground, and much of that activity occurs in the mesosphere. So, in a very real way, this distant layer of our atmosphere provides another form of protection.
Remember the temperature roller coaster we have been riding throughout this series. Temperature generally decreases as we climb through the troposphere. It then increases through the stratosphere because ozone absorbs ultraviolet radiation. Once we enter the mesosphere, temperatures begin falling again.
Near the top of the mesosphere, temperatures can approach -130°F, making it the coldest region of Earth’s atmosphere. The boundary at the top of this layer is called the mesopause, and it marks the transition into our next atmospheric layer.
Most clouds occur far below the mesosphere, but this layer can produce something extraordinary. Noctilucent clouds, sometimes called night-shining clouds, form extremely high in the atmosphere near the mesopause. Because they are so high, sunlight can still illuminate them after the Sun has set at Earth’s surface. Under the right conditions, they appear as delicate, glowing streaks against the darker evening sky.
The mesosphere is also difficult to study directly. It is too high for conventional aircraft and most weather balloons, yet too low for satellites to maintain normal orbits. Scientists instead rely on sounding rockets, radar, satellites, and observations from the ground to better understand this distant region.
And yet, even though it is dozens of miles above us, the mesosphere remains part of the same atmosphere surrounding you right now. When you see a meteor streak across the night sky, you get a brief glimpse of something happening within this otherwise invisible layer.
We have now traveled from the surface through the troposphere, stratosphere, and mesosphere. With every step upward, the air has become thinner and our surroundings increasingly unfamiliar. But our climb is not finished.
In Part 5 of Discovering the Atmosphere, we are heading into the thermosphere, where temperatures soar, the atmosphere becomes incredibly thin, and some of the most beautiful displays in our sky, the auroras, come to life.
Until then, keep looking out the window. Sometimes the atmosphere puts on its best show after the Sun goes down.
