【英语时差8,16】风力农场的科学原理（在线收听）

 As interest increases in alternative energy, wind power has emerged as one of the best alternatives to fossil fuels. Which is why wind farms are popping up throughout the United States and around the world. But you can’t just set up a wind farm anywhere and expect it to produce enough power. Why? Because some places are windier than others. Wind happens because when sunlight hits the earth, it warms some spots more than others, creating warmer and cooler areas that fluctuate throughout the year. Because warm air weighs less than cold air, it rises, leaving in its wake an area of low air pressure. Then cooler, higher pressure air whooshes in to replace the warm air. And that’s what we call wind.