64 Fog-Low

Fog FOCUS Question Why does fog form?

雾焦点问题为什么会形成雾?

Clouds Near the Ground High in the mountains of Costa Rica is a beautiful cloud forest. The mountains are covered with trees, mosses, and other plants. They are also often covered with something else—cloud! In this forest, clouds stay near the ground. Clouds that are close to the ground are called fog. Let's find out why some clouds stay near the ground instead of rising into the sky.

哥斯达黎加的高山上有一片美丽的云雾森林。 山上覆盖着树木、苔藓和其他植物。 它们还经常被其他东西覆盖——云!在这片森林里，云停留在地面附近。 靠近地面的云叫做雾。 让我们来看看为什么有些云停留在地面附近而不是上升到天空。

Making Clouds Clouds are made of droplets of water floating in the air. The water begins as liquid on the ground. Sunlight warms the water until it turns into a gas called water vapor. The water vapor rises into the air. This process is called evaporation (ee-vap-uh-RAY-shun). The air higher in the sky is cold. As water vapor rises, it cools down. The water vapor turns back into droplets of water. This process is called condensation (con-den-SAY-shun). The water droplets join together to form clouds.

云是由漂浮在空中的水滴构成的。 水一开始是地面上的液体。 阳光使水变暖，直到它变成一种叫做水蒸气的气体。 水蒸气上升到空气中。 这个过程叫做蒸发(ee- vapor -uh- ray -shun)。 高空的空气是冷的。 当水蒸气上升时，它会冷却下来。 水蒸气又变成了水滴。 这个过程被称为冷凝(冷凝- say -shun)。 水滴聚在一起形成云。

Making Fog Sometimes the air is cold closer to the ground. This cold air cools the water vapor before it rises very high. The water vapor condenses near the ground. The low cloud that forms is fog. Whether fog forms depends on two things: moisture and air temperature. Water evaporates into the air. Another word for moisture in the air is humidity. The more water vapor the air has, the higher the humidity. The air near the ground must be very humid for fog to form. Science in Your World Fog makes it hard to see. Drivers must drive slowly. Sailors look for lighthouses to know if they are close to shore.

有时离地面越近空气越冷。 冷空气在水蒸气上升到很高之前就把它冷却了。 水蒸气在地面附近凝结。 形成的低云就是雾。 雾的形成取决于两个因素:湿度和气温。 水蒸发到空气中。 空气中水分的另一种说法是湿度。 空气中的水蒸气越多，湿度就越高。 接近地面的空气必须非常潮湿才能形成雾。 雾使人难以看清。 司机必须慢慢开。 水手们寻找灯塔，以知道他们是否接近海岸。

Air temperature is also important. When warm, humid air gets cooler, water vapor condenses. The temperature at which water vapor in the air condenses is called the dew point. The dew point affects whether or not fog will form. In places with dry air, the dew point is low. The air would have to get much colder for water vapor to condense into fog. In places with moist air, the dew point is high. The air doesn't have to cool down as much for water vapor to condense. Fog can form when the air temperature near the ground is close to the dew point. Water vapor in the moist air can easily condense and turn into a low cloud—fog!

气温也很重要。 当温暖潮湿的空气变冷时，水蒸气凝结。 空气中水蒸气凝结时的温度称为露点。 露点影响是否会形成雾。 在空气干燥的地方，露点很低。 空气必须变得更冷，水蒸气才能凝结成雾。 在空气湿润的地方，露点很高。 空气不需要那么低的温度来凝结水蒸气。 当地面附近的空气温度接近露点时，就会形成雾。 潮湿空气中的水蒸气很容易凝结成低空云雾!

Different Types of Fog Not all fog is the same. Fog can be thick or wispy. It can rise up a slope or sink into a valley. The type of fog depends on how and where it forms. Look at the diagrams on these two pages to learn how different types of fog form. Radiation Fog (or Ground Fog) After the Sun goes down the ground and the surrounding air get cooler. When the air temperature reaches the dew point, the water vapor condenses into fog. Advection Fog Warm moist wind blows over chilly water or ground. The moist wind gets colder and condenses into fog. Word Wise Have you heard the phrase "in a fog"? This can mean a person is confused dazed, or not thinking clearly. Can you explain why?

不同类型的雾并非所有的雾都是一样的。 雾可以很浓，也可以很细。 它可以上升到斜坡上，也可以沉入山谷。 雾的类型取决于形成的方式和地点。 请看这两页上的图表，了解不同类型的雾是如何形成的。 辐射雾(或地面雾)太阳下山后，周围的空气变冷。 当空气温度达到露点时，水蒸气凝结成雾。 平流雾温暖潮湿的风吹过冰冷的水面或地面。 潮湿的风变冷并凝结成雾。 你听说过“在雾中”这个短语吗? 这意味着一个人很困惑，晕头晕脑，或者思考不清楚。 你能解释一下原因吗?