EDITOR’S NOTE: Part 1 of a series
Every time I look out my window, I look through something we rarely stop to think about. We cannot see it, hold it, or usually even feel it unless the wind begins to blow, yet it surrounds us every second of every day. It gives us the air we breathe, carries clouds across the sky, produces our weather, protects us from harmful radiation, and helps regulate the temperature of our planet. It is Earth’s atmosphere, and over the next several columns, we are going to take a journey through it.
Most of us learned somewhere along the way that the atmosphere has different layers. Maybe you remember memorizing names such as the troposphere, stratosphere, mesosphere, thermosphere, and exosphere in science class. Those names probably appeared on a diagram with colorful bands stacked neatly above Earth. But the real atmosphere is far more interesting than a diagram in a textbook. Each layer has its own characteristics, and together they form an enormous protective envelope extending hundreds of miles above us.
The atmosphere itself is a mixture of gases held around Earth by gravity. Near the surface, dry air is made up primarily of nitrogen, at about 78 percent, and oxygen, at roughly 21 percent. The remaining portion includes argon, carbon dioxide, and other trace gases. There is also water vapor, and for meteorologists, that small and highly variable ingredient is incredibly important. Water vapor provides the raw material for clouds, fog, rain, snow, thunderstorms, and many other things that make weather so fascinating.
What might surprise you is how quickly the atmosphere changes as we travel upward. Air pressure and density decrease dramatically with altitude because there are fewer air molecules above you pressing downward. Temperature changes too, but not in one simple direction. In some layers, temperature decreases as altitude increases. In others, it actually increases. Those temperature trends are one of the primary ways scientists define the different layers of our atmosphere.
Our journey begins right here at the ground in the troposphere, the layer where we live and where nearly all of our familiar weather occurs. Clouds develop here. Thunderstorms tower through it. Cold fronts and warm fronts move through it. Snowstorms, hurricanes, tornadoes, fog, rain, and those beautiful summer afternoon cumulus clouds all belong primarily to this lowest layer. For a meteorologist, the troposphere is home territory.
Above it is the stratosphere, perhaps best known as the home of the ozone layer. Unlike the troposphere, temperatures generally increase with height through much of the stratosphere because ozone absorbs ultraviolet radiation from the Sun. Higher still is the mesosphere, where temperatures once again decrease with altitude. This is also the region where most meteors burn up as they encounter Earth’s atmosphere, creating the streaks of light we commonly call shooting stars.
Continue upward and we reach the thermosphere, where temperatures can become extremely high because sparse atmospheric particles absorb energetic solar radiation. Parts of the ionosphere overlap this region, making it important for radio communication and producing some of the conditions associated with the aurora. Eventually we transition into the exosphere, the atmosphere’s extremely thin outermost region, where Earth’s atmosphere gradually fades into space.
One of the fascinating things about these layers is that there are no visible lines separating them. If you could travel straight upward, you would not suddenly cross a stripe in the sky announcing, “Welcome to the Stratosphere.” Scientists identify the boundaries by observing how temperature and other atmospheric properties change with altitude. The transition between the troposphere and stratosphere, for example, is called the tropopause. Other boundaries include the stratopause and mesopause.
And while we often picture the atmosphere as enormous, compared with Earth itself it is remarkably thin. Think about the photographs of Earth taken from space. That delicate blue glow hugging the planet represents the atmosphere protecting everything living beneath it. Almost all of the atmosphere’s mass is concentrated relatively close to Earth’s surface. We live at the bottom of an ocean of air, with the weight of that air above us creating atmospheric pressure.
That ocean of air is also constantly moving. Uneven heating from the Sun, Earth’s rotation, differences between land and water, changes in pressure, and countless other factors keep the atmosphere in motion. On a local scale, that movement might be the afternoon breeze outside your window. On a larger scale, it becomes the jet stream steering weather systems across the country. Add enough heat, moisture, instability, and wind to the equation, and that same atmosphere can produce everything from a gentle spring shower to a violent thunderstorm.
That is why understanding the atmosphere matters. Weather does not simply “happen in the sky.” It is the result of an enormous, interconnected system governed by physics. A thunderstorm developing over southeast Missouri is part of the same atmosphere that contains the jet stream miles overhead and, much farther above that, the regions where auroras glow and satellites travel.
Over the next several editions of Weather from My Window, we are going to climb through this atmosphere one layer at a time. We will begin close to home with the troposphere and discover why temperature normally decreases as we climb, why most weather remains confined to this layer, and just how high our weather-making portion of the atmosphere extends. From there, we will continue upward through the stratosphere, mesosphere, thermosphere, and finally into the exosphere.
There is an entire world above our heads that most of us rarely consider. We spend our lives at the very bottom of it, watching only a tiny portion from our windows. Sometimes understanding weather means looking at the clouds. Other times, it means looking far beyond them.
For this series, that is exactly where we are headed.
