Tropopause facts for kids

The tropopause is between the troposphere and the stratosphere. The layers are not to scale.

The tropopause is like an invisible border in Earth's atmosphere. It's the place where the troposphere (the layer closest to us, where weather happens) meets the stratosphere (the layer above it). Think of it as a ceiling for most of our weather!

At the tropopause, something interesting happens to the air. The air stops getting colder as you go higher, and it becomes very, very dry. This special boundary is important for many reasons, especially for airplanes.

What is the Tropopause?

The tropopause is a transition zone, not a sharp line. It's where the air changes how it behaves. Below it, in the troposphere, the air gets colder the higher you go. But once you reach the tropopause, this cooling stops. Above it, in the stratosphere, the air actually starts to get warmer again!

This boundary also marks a big change in how air moves. In the troposphere, air mixes a lot, creating clouds and storms. But the tropopause acts like a lid, keeping most of this mixing below it. This is why it's often called the "cold trap."

Where is the Tropopause Found?

The height of the tropopause isn't always the same. It changes depending on where you are on Earth and the time of year.

• Near the Equator: Close to the equator, where it's usually warmer, the tropopause is much higher. It can be about 17 to 18 kilometers (around 11 miles) above the ground.
• Near the Poles: At the North and South Poles, where it's much colder, the tropopause is lower. It can be only about 8 to 9 kilometers (around 5 miles) high.

This difference in height is because warm air expands and rises higher, pushing the tropopause up. Cold air is denser and sinks, keeping the tropopause lower.

Why is the Tropopause Important for Airplanes?

Many large commercial airplanes fly in or just below the tropopause. There are several good reasons for this:

• Smoother Flights: Above the troposphere, there's much less turbulence. This means a smoother ride for passengers.
• Less Weather: Most weather, like clouds, rain, and storms, happens in the troposphere. By flying near or above the tropopause, planes can avoid bad weather.
• Fuel Efficiency: The air at this altitude is thinner. This means less air resistance, allowing planes to fly more efficiently and save fuel.

Pilots often aim to fly in this stable region to ensure a safe and comfortable journey.

Air Temperature and Dryness

One of the most defining features of the tropopause is the temperature. In the troposphere, as you climb higher, the temperature drops. This is why mountain tops are colder than valleys. But at the tropopause, the temperature stops falling. It reaches its coldest point, often around -56.5 °C (-70 °F).

Above the tropopause, in the stratosphere, the temperature actually starts to rise again. This warming happens because of the ozone layer. The ozone layer absorbs harmful ultraviolet (UV) radiation from the sun, which heats up the air around it.

The air at the tropopause is also incredibly dry. Most of the water vapor in the atmosphere stays in the troposphere, where it forms clouds and precipitation. The tropopause acts like a barrier, trapping this moisture below it. This is why the stratosphere above is almost completely dry.

See also

In Spanish: Tropopausa para niños