文章大意：这是一篇说明文。文章主要介绍了北美大陆东海岸的极端天气情况，分析了其带来的影响，并通过具体的数据、实例来唤起人们对环境保护的重视和对人类现状的忧患意识。
4 . Why the East Coast has had such a weak winter
Overall, winter across the East Coast this year has been pretty weak. “I was in shorts and a T-shirt,” said Jeff Weber, a research meteorologist (气象学家) at the University Corporation for Atmospheric Research. Meteorologists descended upon Boston in mid-January for the annual meeting of the American Meteorological Society. January is Boston's coldest month, but during the weather conference, meteorologists experienced 75 degrees Fahrenheit temperatures.
A major reason is that the polar vortex (极地涡旋) — which is a circulating stream of air that forms over the Arctic during winter — has stayed rigid and in place, keeping its cold air mostly locked up north. Consequently, little of this exceptionally chilly air has got into the U.S. this winter.
Arctic blasts (北极寒流), like those in January 2019, happen when the polar vortex becomes unstable, allowing frigid air to spill south. “But this winter, instead of a weak polar vortex, we’ve had strong polar vortex conditions,” said Andrea Lang, an atmospheric scientist at the University of Albany who researches changes in seasonal winter weather.
The polar vortex has stayed strong because other weather systems, sometimes originating from the Pacific. Ocean, haven’t come along and knocked the spinning vortex out of place.
A frequent culprit (问题的起因) in disturbing the polar vortex is a powerful stream of air traveling some 30,000 to 35,000 miles up in the atmosphere (where jets fly) which we commonly call the jet stream. The jet stream shoots from west to east around Earth at speeds of 120 to 250 miles per hour, but can become dramatically wavier when it’s disturbed by strong storm activity or encounters masses of hot or cold air.
But this winter season, the meandering (蜿蜒前进的) jet stream has not knocked the polar vortex off its pole, explained Lang. Instead, the jet stream has bent dramatically south, right through the heart of the central U. S.
Atmospheric scientists are deeply interested in why a perturbed polar vortex has become more frequent. There’s evidence that the incessantly warming Arctic — the fastest-warming place on Earth — has led to a weaker and less stable polar vortex, which means more outbreaks of freezing Arctic air. Just not this winter — so far, anyway.
1. What does Jeff Weber mean by saying what he wore?
| A．To introduce his dressing style. | B．To express his feeling then. |
| C．To prove the abnormal weather. | D．To show his love of winter. |
2. What do we know about the weather in Boston in January 2019?
| A．It was as warm as that of this year. |
| B．It was very cold owing to the arctic blast. |
| C．The polar vortex stayed rigid and in place. |
| D．The polar vortex was weak and unstable. |
3. Which of the following best explains the underlined word “perturbed” in the last paragraph?
| A．Fixed. | B．Frozen. | C．Heated. | D．Disturbed. |
4. How does the jet stream usually affect the polar vortex?
| A．By bending north and knocking it off. |
| B．By moving from east to west around Earth. |
| C．By waving and meandering powerfully. |
| D．By turning to the south dramatically. |
