英語翻譯
Daily changes in the weather affect all of us,no matter what our job or profession.However,while there`s very little we can do to modify the weather,we can at least know what kind of weather to expect.For this we are indebted to our efficient weather-watchers.
Although it may sound funny to call scientists weather-watchers,there`s nothing funny about what they do.Specifically,weather-watchers are meteorologists who work for the United States Weather Bureau.They study the ocean of air that surrounds the earth and,with the information they get,predict our weather.
The atmosphere ranges in height from 300to 700miles above the earth and is divided into a series of layers or shell.The layer that is most interesting to the meteorolgist is the troposphere or the layer closest to the earth.It is in the troposphere that all our weather is formed.
What causes our weather is really a very simple process,Endless streams of hot air push up from the earth.As they rise,they are cooled by the freezing temperatures of the upper troposphere.Once it has become cold and heavy,the air sinks back toward the earth,but it can`t move down because of the rising hot air,In the meantime,planetary winds,which blow around the earth,or air currents keep both the cold air mass as well as the hot air mass in motion.