在1997年——厄尔尼诺（El Niño）现象最强的年份之一，喜剧演员克里斯·法利（Chris Farley）曾在《周六夜现场》（Saturday Night Live）上表演：“我是厄尔尼诺，所有其他热带风暴必须在厄尔尼诺面前低头”，如今，厄尔尼诺现象再次发生，并再次引起了公众的关注。然而，厄尔尼诺现象并不像克里斯·法利所说的那样是一种热带风暴，而是一种自然气候模式，其完整周期被称为厄尔尼诺-南方涛动（El Niño-Southern Oscillation，ENSO），在大约每两到七年之间循环发生，由太平洋上空风和水之间的推拉作用引起。当厄尔尼诺现象发生时，巨大的温暖水体会从东向西延伸穿过太平洋。这种现象与正常情况下的“中性状态”非常不同，在中性状态下，热带西太平洋比东太平洋更温暖。厄尔尼诺现象的关键特征是太平洋赤道地区高于正常温度0.5摄氏度以上的温暖洋流，且偏高现象持续至少3个月。然而，厄尔尼诺现象的影响不仅仅限于海洋，它对气候系统的其他方面和其他地方的天气也产生影响，类似多米诺骨牌效应。例如，东南亚地区通常会因上升的潮湿空气带来多雨天气，而厄尔尼诺现象会带来下沉的空气从而导致截然相反的干燥天气和干旱。在2016年，厄尔尼诺现象导致了印度尼西亚的干旱、食物短缺和大规模野火。与此同时，在其他地区，如东非和南美部分地区则可能出现大规模降雨和严重洪水。大气环流模式的变化也会改变美国的急流（jet stream），给美国南部和北部分别带去较冷和较热的天气。此外，厄尔尼诺现象还会影响全球的飓风活动，由于大气层变得更加稳定，大西洋地区的飓风活动通常会有所减少。然而，今年的温暖海水可能成为飓风的燃料，因此目前尚不确定哪种影响将占上风。目前，本次发展成为强厄尔尼诺现象的可能性略高于平均水平。在未来几个月内，厄尔尼诺现象将逐渐增强，预计将在北半球的冬季达到顶峰。尽管目前……[查看全文]
El Niño is Back. What Does That Mean For You?
Andrea Thompson: And today we’re talking El Niño.Jeff DelViscio: Because it’s back.[CLIP: Chris Farley on Saturday Night Live: “I am El Niño. All other tropical storms must bow before El Niño.”]Thompson: Okay, so just in case you didn’t catch the reference, that was comic Chris Farley...DelViscio: …in 1997 on Saturday Night Live. Farley did the bit because that year was one of the strongest El Niño on record.Thompson: So it was definitely on the public’s mind in a big way. Though he got the science wrong.DelViscio: It was hilarious, but yep. El Niño isn’t a tropical storm, like he said.Thompson: What it actually is … a natural climate pattern.DelViscio: It’s a cycle, really … a push and pull between wind and water over the Pacific Ocean.Thompson: Right. The whole cycle is actually called ENSO–the El Niño-Southern Oscillation. The oscillation part is because it seesaws between warm and cold states about every two to seven years.DelViscio: Okay, so, Andrea, let’s help everyone sorta mentally picture this.Thompson: Right, sure, well, imagine we’re out in the tropical Pacific, kinda hovering above the Earth, looking down.DelViscio: And we’d need to be able to see the temperature of the ocean below us, right?Thompson: That’s right. And that’s important because when El Niño really gets going what we’d see is this tremendously large lobe of warm water that starts to stretch across the equatorial pacific from east moving west.DelViscio: And that’s not how it normally looks in that part of the Pacific, right?Thompson: Right. Normally, during the “neutral” setting the western tropical Pacific is much warmer than the eastern.DelViscio: So that’s just one way to tell if an El Niño is in effect. But how warm is that lobe of water? And how long does it last?Thompson: Ithas to be 0.5 C above normal. And it has to stay that way for at least three months. And, by the way, it has a counterpart, La Niña, with cold waters, 0.5 C below average. But that’s a podcast for another day.DelViscio: Got it. So we’ve got this big anomalous water feature. But the effects of the El Niño don’t stop at the ocean, do they?Thompson: Nope. The whole climate system is interconnected. And the ocean affects the atmosphere. And the Niño on what happens with weather elsewhere. It’s like a weather domino effect when it gets going.DelViscio: Okay, let’s do a rundown of some of those dominos. What are they and where do they happen?Thompson: Okay, here are some major examples of effects:Instead of usual rising air and rainy conditions in southeast Asia, that area sees subsiding air, which means dry weather and can cause drought.In 2016 there was a major drought in Indonesia that caused food shortages and helped fuel huge wildfires.Meanwhile other places, such as part of eastern Africa and parts of South America, often see higher rainfall, which can cause major flooding.Changes in looping air patterns also alter things like the jet stream across the U.S. and tends to bring cooler weather to the south and warmer to the north.Also, because it’s not all bad news, we do tend to see less hurricane activity in the Atlantic. That’s because the atmosphere is more stable—hurricanes need unstable air to get going.(But this year there are also super warm ocean waters—that’s like hurricane fuel—and it’s hard to know which influence will win out. So TBD on that one.)DelViscio: Wow. That’s a global weather monkey wrench. But, you know, the reason we’re talking about this today on the podcast is because the Niño is here. So, “news we can use” time. Do you know what we might expect from this one?Thompson: Well, very tricky to forecast, but right now, there are slightly better-than-even odds that this event will develop into a strong one. It should build in strength in the coming months. And El Niños typically peak in the Northern Hemisphere winter...[full transcript]
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