Dear Dr. Universe: Why is it so cold up in the mountains if heat rises and it’s closer to the sun? –Andrea, 11
You’re right. If we took a trip into the mountains, we would find that it felt a lot colder. It all has to do with our atmosphere. We may not always think about it, but we are basically living in a giant ocean of air.
“It’s a big part of what makes Earth livable,” said my friend Shelley Pressley. She’s an environmental engineer at Washington State University’s Laboratory for Atmospheric Research. “Without gravity and our atmosphere, all the oxygen we breathe would fly out into space.”
Our atmosphere contains small building blocks, or gas molecules, that make up the air we breathe, she said. We can’t always see or feel how much gas there is, but we can measure it. We can calculate the mass of gas, or the number of molecules there are in a certain area.
Air is actually pushing down on us all the time, even if we can’t really feel it.
“Imagine you are standing on Earth’s surface,” Pressley said. “There’s a column of air above your head that stretches up to the top of the atmosphere. The column of air is pushing down on your head. This is pressure.”
“Now, climb the tallest mountain you can find and stand on it,” she adds. “The column of air pushing down on your head is shorter. It has less mass than the column in the first spot.”
The air pressure is greater when you are closer to the level of the ocean’s surface. Here, the building blocks or molecules are pretty squished together. When the gas’ pressure is greater, temperature increases.
Maybe you’ve heard people say the air is thinner up in the mountains, where there is less pressure and the molecules or building blocks are more spread out. When the pressure of a gas decreases, so does temperature.
Pressure is a big part of the answer to the first part of your question. The other part of your question involves the sun. Our sun is about 490 billion feet away from the surface of the Earth. While a mountain might seem tall, it’s pretty puny in comparison to the distance between Earth and our sun. It actually doesn’t make a huge difference in temperature.
Pressley said that pressure and our sun also have a lot to do with weather. When sunlight travels through the atmosphere, it heats the surface of the planet. When the surface gets warmer, it sends heat back up to air molecules near the surface and warms them up. The molecules of air rise. As they do, they expand and cool.
Somewhere else, air over a mountain that is even colder actually starts to sink. This sinking air gets compressed, squished together, and heats up. This mixing of air is called convection and is at the heart of our weather. This system also keeps the surface of our home planet warm enough to live—from the colder mountains to the warmer beaches around our world.