Читать книгу Weather For Dummies - John D. Cox - Страница 41

Don’t be too hard on the atmosphere. (After all, it’s the air you breathe. Without it, you’re sunk.) Imagine trying to live in a house where it’s always hot at one end and always cold at the other. That’s the situation the Earth’s atmosphere finds itself in. You don’t have to be an Eskimo or a Pacific Islander to figure out where the warm spots and the cold spots are, but it helps.

The low latitudes, around the Equator, get a lot of warm sunshine, and the high latitudes, around the poles, get very little. (Figure 3-1 shows the layout of the imaginary lines around the Earth called latitudes.) This temperature difference is no small matter. On the same day, it can reach 120 degrees below zero overnight in Antarctica and 120 degrees above zero in a subtropical desert. The atmosphere has to deal with these huge temperature differences all the time. They have a lot to do with what weather is all about.

FIGURE 3-1: Imaginary lines called latitudes divide the world into the Tropics, the polar regions, and between them, the mid-latitudes.

You might think things would be pretty comfortable in the middle of the house, the middle latitudes, where most people live in the world. Not too hot, like Goldilocks said, and not too cold. And certainly it’s true that, on average, the mid-latitudes are less extreme environments to live in. But there’s a catch, of course. In case you haven’t noticed, it is in the middle latitudes where you and I live that a lot of the masses of northbound tropical warm air and southbound cold polar air come together. And when they do, it’s not a pretty picture. In fact, it can get messy.

Those big storms with the long lines that twist together into a whirling low-pressure system on the weather map are called mid-latitude cyclones, or sometimes, extratropical cyclones. You might think of these storms as battles between opposing armies of hot air and cold air. The lines between them are very appropriately referred to as fronts — as in battlefronts. Weather scientists used to think of these storms exactly this way, although now the picture in their minds is more complicated. (The section later in this chapter, “News from the Fronts,” goes into more detail about these clashes.) Nobody who has lived through the devastation of a flood or a blizzard or an especially severe winter needs to be reminded that weather unleashes powerful forces that can do terrible things. You and I are bystanders to all of this, and the only thing to do when a battle is raging is to try to stay safe, warm, and dry.