什么是极地涡旋天气系统？
📖 逐句对照翻译
Weather experts say extreme cold in many parts of the United States this winter has been driven by a polar vortex.
气象专家表示，美国许多地区今年冬季的极端寒冷天气是由极地涡旋引起的。
But what is this weather system and how does it work?
但这个天气系统是什么，它又是如何运作的呢？
The National Oceanic and Atmospheric Administration (NOAA) describes a polar vortex as strong westerly winds that form each winter in the atmosphere above the North Pole.
美国国家海洋和大气管理局（NOAA）将极地涡旋描述为每年冬季在北极上空大气中形成的强劲西风。
These cold winds move about 16 to 48 kilometers above the surface in the Arctic area in the part of the atmosphere called the stratosphere.
这些冷风在北极地区地表以上约16至48公里处移动，位于大气层中被称为平流层的部分。
At times, the polar vortex can weaken, causing masses of cold air to break off and move south.
有时，极地涡旋会减弱，导致大量冷空气脱离并南下。
A polar vortex can also push warmer air in northerly directions.
极地涡旋也可能将较暖的空气推向北方。
The Associated Press (AP) reports that several vortex events have affected parts of the U.S. this winter.
美联社报道称，今年冬天，美国部分地区遭遇了多起极地涡旋事件。
Experts say weather forces in the Arctic have combined to push colder air to the U.S. and Europe.
专家表示，北极的天气力量共同作用，将更冷的空气推向美国和欧洲。
Temperature readings that take into account the effects of wind, called windchill readings, fell to minus 51 degrees Celsius in parts of the U.S. Midwest.
美国中西部部分地区考虑到风寒效应的温度读数——即风寒指数——降至零下51摄氏度。
Meteorologists say windchill readings are colder than air temperature readings.
气象学家表示，风寒指数读数比气温读数更低。
The U.S. National Weather Service (NWS) warned people in affected areas that such low temperatures can cause frostbite and hypothermia if skin is not protected from the cold.
美国国家气象局（NWS）警告受灾地区民众，这样的低温如果皮肤不加以保护，可能会导致冻伤和体温过低。
Weather officials also warned that long-term cold temperatures can cause water pipes in or around homes to freeze and burst.
气象官员还警告说，长期低温可能导致住宅内或周围的水管冻结并爆裂。
The NWS noted that almost every U.S. state – except for Hawaii, California and Florida – is expected to report low windchill temperatures.
美国国家气象局指出，预计美国几乎所有的州——除了夏威夷、加利福尼亚和佛罗里达——都将报告较低的风寒温度。
The coldest temperatures were expected in the midwestern states of Kansas, Nebraska and Missouri.
预计最冷的地区将出现在中西部的堪萨斯州、内布拉斯加州和密苏里州。
In an explanation on its website, NOAA states that the polar vortex always surrounds both of Earth’s poles.
在其网站的一份解释中，NOAA指出极地涡旋始终环绕着地球的两极。
The systems strengthen in the winter and weaken in the summer.
这些系统在冬季增强，在夏季减弱。
Every year or so, the polar vortex becomes weaker.
每隔一年左右，极地涡旋就会变得更弱。
This can cause the system to be “pushed off the pole or split into two.”
这可能导致系统“偏离极点或分裂为二”。
This can lead to cold air at the surface being pushed southward and warm air being pushed to the north.
这可能导致地表冷空气向南推进，而暖空气则被推向北方。
NOAA says its weather models are predicting low temperatures for states including Oklahoma, Colorado, Nebraska, Missouri, Illinois and Iowa.
美国国家海洋和大气管理局表示，其天气模型预测俄克拉荷马州、科罗拉多州、内布拉斯加州、密苏里州、伊利诺伊州和爱荷华州等州将出现低温天气。
Other states likely to have very low temperatures are Wyoming, Montana, North Dakota, South Dakota, Minnesota, Wisconsin and Michigan.
其他可能遭遇极低气温的州包括怀俄明州、蒙大拿州、北达科他州、南达科他州、明尼苏达州、威斯康星州和密歇根州。
The agency said some storms could bring heavy snow or flooding during that time.
该机构表示，在此期间，一些风暴可能会带来大雪或洪水。
I’m Bryan Lynn.
我是布莱恩·林恩。
Bryan Lynn wrote this story for VOA Learning English, based on reports from The Associated Press, Reuters, Agence France-Presse, NOAA and NASA.
布莱恩·林恩根据美联社、路透社、法新社、美国国家海洋和大气管理局以及美国国家航空航天局的报道，为VOA慢速英语撰写了这篇报道。
