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[气象讯息]“混血风暴”桑迪

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更多 发布于:2012-11-05 15:51
THE HYBRIDIZATION OF SANDY - HOW A SUPERSTORM CAME TO BE
 
“桑迪”的混血结构——超级风暴的形成  

 
Every so often, a quiet corner of researchsuddenly grabs the spotlight. Such was the case this week when a Category 1Atlantic hurricane morphed into Superstorm Sandy, wreaking tens of billions ofdollars in damage and taking scores of lives in the eastern United States.
 
有些时候一些不受关注的研究会突然特别吸引眼球。本周一级飓风“桑迪”在大西洋上变性为一个“超级风暴”,袭击美国东海岸并给当地带去了数百万美元的损失和大量的伤亡,关于这种“超级风暴”是如何演变而来的很快称为一个热门话题。
 
Sandy’s destiny as a hybrid storm was flagged to the public several daysbefore landfall, when the irresistible name “Frankenstorm”—coined by a NOAAmeteorologist—went viral. (Of course, in the original Mary Shelley novel, itwas the scientist rather than the monster who was dubbed Frankenstein, as BayArea meteorologist Jan Null pointed out to me.
 
在登陆前的几天,“桑迪”的这种“混血”的特征已经相当显著,NOAA的气象学家创造了一个新词“怪物风暴”(Frankenstorm)用来描述类似于“桑迪”这种“混血”的超级风暴。不过气象学家Jan Null告诉我,而玛丽·雪莱(Mary Shelley)的小说Frankenstein(《弗兰肯斯坦》)描写的则是科学家而不是怪物。
 
While there have been hybrid storms before,Superstorm Sandy was a creation distinct in meteorological annals, as it pulledtogether a variety of familiar ingredients in a unique way. Sandy could be the storm that launches athousand dissertations—or at least a few—and some of its noteworthy aspectshave implications for hurricane warning in general. Warning: there’sa bit of unavoidable weather geekery in the material below, although I’ll tryto keep it as accessible as possible.
 
“桑迪”之所以被描述为一个“混血”风暴是因为他通过一种独一无二的途径混合了各种各样的常见因子。它的出现必然将引起大量的论坛进行讨论,其中的一些将深深影响未来的飓风预警。
 
WHEN A HURRICANE SHAPESHIFTS
 
飓风变性

 
Extratropical transition is the formalname for what happened in the 12 to 24 hours before Sandycrashed ashore near Atlantic Cityon Monday evening, 29 October. “Extratropical” means “outside the tropics,” sotechnically speaking, it would apply to any cyclone (low-pressurecenter) that’s located in the midlatitudes or polar regions. But there’s a morebasic distinction used by meteorologists: whether a low is warm-core orcold-core.
 
“桑迪”核心在10月29日清晨登陆大西洋城海岸前的12~24小时出现了热带外变性。所谓“热带外变性”是指“由于不在不在热带地区而导致的热带气旋变性过程”,通常意义上它可以出现在任何温带和寒带气旋中,但一般来说气象学家口中的“热带外变性”是指一个暖心的气旋变为冷心的过程。
 
A hallmark of tropical cyclones (knownas hurricanes, typhoons, or cyclones in various parts of the world)is that their circulations revolve around a core of warm air. Hurricanesdraw energy from oceanic heat and moisture, and they thrive when thesurrounding air is uniformly warm and humid and upper-level winds steering thestorm are relatively weak.  In contrast, an extratropical low istypically positioned at or near the intersection of a cold front and warmfront. Such a low is helped rather than hindered by temperature and moisturecontrasts and the accompanying strong winds of the polar jet stream.
 
热带气旋(包括飓风、台风、以及其他部分热带洋区的气旋)的特点是它们的螺旋形环流环绕着一个相对暖的空气团(暖心)。飓风从海洋中获得热量和水汽,当它所处位置的大气异常暖湿并且高空的风力较弱时飓风能快速发展。然而在另一方面,一个热带外气旋总是位于一条暖锋和一条冷锋的交接位置,其强度的发展通常是由强烈的温湿梯度,并且伴随着强烈的高空急流。
 
Here are three of the routes that warm- andcold-core systems can take as they evolve:
 
在以下三种情况下,气旋的暖心和冷心可以互相演变。
 
1、It’s not unusual at all for a tropical cyclone to shift fromwarm-core to cold-core. In an average year, one or more hurricanes will evolveinto extratropical storms in a fairly straightforward manner as they move intothe North Atlantic. As colder, drier airintrudes into the warm core, the storm typically loses symmetry and beginstilting toward the coldest upper-level air.
 
1、热带气旋演变为一个冷性气旋并不罕见。每年平均有一个或更多的热带气旋因为移动到更冷的北大西洋而转变为热带外冷心气旋。当寒冷而干燥的温带、极地大气进入热带气旋的暖心时,整个暖心结构将失去其对称性,并且涡管向高空寒冷的大气倾斜。
 
2、It’s also possible for an extratropical cyclone to develop what’sknown as a warm seclusion. In this case, a pocket of warm, moist air isdrawn into the cold-core circulation, then pinched off through a complicatedset of dynamics involving air pulled down from the stratosphere. This is dubbedthe Shapiro-Keyserprocess, after veteran researchers Mel Shapiro (now atNCAR) and Daniel Keyser (Universityof Albany, StateUniversity of New York). Some of the Atlantic’smost intense storms of any type have emerged from warm seclusions (seeanimation at right). These are most common in winter over the far North Atlantic, but rarely do they move onto themid-Atlantic coast, especially in mid-autumn.
 
2、一个热带外气旋当发生被俗称为“暖隔离”的过程时也可能会增强。当暖而潮湿的气旋进入一个气旋性冷心环流时,它们被一些难以理解的动力学过程(包括来自平流层的寒冷气流供应)隔断。这个过程被称为Shapiro-Keyser过程,由目前在NACR的Mel Shapiro和Daniel Keyser(阿尔巴尼大学,纽约州立大学)共同发现。大西洋上的一些强烈风暴就是由“暖隔离”过程导致的,通常这发生在北大西洋的冬季,不过偶尔仲秋时节也会在大西洋中部出现。
 
3、Once in a while, an extratropical cyclone will get a boost of energyby absorbing the remnants of a hurricane. Well east of NewEngland, the iconic “perfect storm” of October 1991 was fueled byheat and moisture from the late Hurricane Grace. While it never moved ashore,this great storm still pushed destructive surf into much of the U.S. EastCoast.
 
3、有时,一个热带外气旋也可以通过吸收一个消散了的热带气旋的残骸来增强自身。在东英格兰地区,1991年10月标志性的“完美风暴”就充满了由上一个飓风“葛瑞丝”(Grace)带来的庞大暖湿气团,尽管“葛瑞丝”从未登陆,但它所带来巨大的风暴潮仍然对东海岸造成了巨大的破坏。
 
AND THEN THERE’S SANDY . . .
 
“桑迪”的形成

 
Meteorologists are still parsing the maps,but it appears that Sandymay have incorporated elements from all three of the above processes. WhileSandy was still a hurricane, the storm’s outer edges began to reveal someaspects of an extratropical cyclone, with an enormous zone of strong surfacewind and “a great chimney of upper-level outflow,” as Shapiro puts it (seesatellite image.) The storm’s warm core briefly intensified about a day beforelandfall (see diagram).
 
气象学家仍然在分析各种天气图,然而它们都显示“桑迪”可能同时具有上一节中提到的三种过程。尽管在登陆前“桑迪”仍然是一个飓风,其边缘环流已经显示出热带外气旋的特征,但近地面大面积的强风和中心热带性质的“高层流出大烟囱”显示其核心部分依然保持有热带性质。在登陆前的24小时,“桑迪”的暖心甚至还有所增强。
 
Then, a few hours before landfall, Sandy began a sharp curvetoward the west, moving toward the heart of the approaching midlatitude troughof low pressure. In Shapiro’s view, this marked an apparent warm seclusiontrying to take place on top of the storm’s fast-decaying warm core. I asked Shapiro how often he’s seen a stormlike Sandy. Hereplied, “Never.”
 
然后,在登陆前几小时,“桑迪”开始向西急剧倾斜,向中纬度靠近中的低压槽移动。“桑迪”认为,这标志着“桑迪”中心附近的“暖隔断”取代了快速减弱中的“桑迪”暖心。在Shapiro的记忆中,似乎并不存在与“桑迪”类似的气旋。
 
The one that may come closest in Shapiro’sview is the “Long Island Express” hurricane of 1938, which killed hundreds ofNew Englanders as it slammed ashore virtually without warning. “There was adramatic upper trough coming in from Canada,just like there was with Sandy,”says Shapiro. The 1938 storm raced northwards at speeds of close to 70 mph,making it the fastest-moving hurricane on record, and hooked northwest afterlandfall. While not as much of a speed demon, Sandydid accelerate to a forward motion of nearly 30 mph as it curved west andapproached New Jersey.Upper-air observations from the 1930s are sparse, however, so it might not bepossible to pin down the commonalities between the two events.
 
Shapiro认为最接近“桑迪”结构的气旋可能是1938年的长岛飓风,当时它在几乎没有预警的情况下登陆新英格兰地区并造成数百人死亡。“和SANDY一样,当时正有一个高压槽从加拿大而来”Shapiro说。1938年的风暴以接近70英里/小时的速度向东北快速移动,这是有记录以来移动速度最快的飓风,并且在登陆后急转西北向。尽管没有如此高速,“桑迪”在向西移动时还是有一个显著的加速,登陆新泽西海岸时它的移动速度在30英里/小时左右。尽管20世纪30年代的高空观测资料是非常稀少的,但这两个风暴之间的共性依然相当显著。
 
TWO STORMS IN ONE?
 
二合一的风暴?

 
Chris Davis, head of NCAR’s Advanced StudyProgram, has carried out extensive research on how warm- and cold-coreprocesses interrelate. Like Shapiro, Davis findsSandy anintriguing case. “It seems to have had a remnant inner core that was somewhattropical, embedded in a much larger nontropical structure,” says Davis. He notes othercases where a remnant warm core can persist well into a storm’s extratropicallife. “You end up with two definable structures at once,” he says. “There was apoint where you had a huge arc of cloud over land, but you also had a completeeyewall surrounding the inner core.”
 
Chris Davis,NCAR-ASR的领导者,开展了大量关于冷暖心结构互相影响和转变的研究。和Shapiro一样,Davis发现“桑迪”是一个相当有趣的例子。“看上去“桑迪”中心一个残留有部分热带性质的核心镶嵌在一个庞大的热带外结构中”Davis说。他留意到很多飓风在其转变为热带外气旋后的生命历程的部分时间内仍然能残存一个热带性质的核心,“你完全可能在一个系统中找到两种截然不同的结构”他说,“在某些时间点,你可以同时看到一个巨大的热带外气旋特有的弧状云带的中心镶嵌着一个具有完整眼墙结构的核心”。
 
Sandy’s vast wind field provides more evidence for the warm-within-coldtheory. Along with a small central core of winds near hurricane force, focusedon Sandy’ssouth side, there was a second maximum of high wind well to the north. Itpounded portions of New England with wind gusts as high as 86 mph in Rhode Island. This outerwind band later moved into Long Island and New York City.
 
“桑迪”巨大的大风圈从侧面佐证了暖心镶嵌在冷结构的理论。在“桑迪”南侧有飓风核心导致的强风区,同时在其环流的北部出现了风速第二高值区。新英格兰罗德岛测得的最大阵风达到了86英里/小时。这个外围的强风带后来影响了纽约和长岛。
 
This dual wind structure isn’t a commonoccurrence with hurricanes. Fortunately, computer models predicted the unusualouter band of high wind more than a day ahead of time. And upper-airobservations caught its development several thousand feet above ground a fewhours before the winds mixed down to the surface. As a result, the NationalWeather Service provided a specific “nowcast,” putting people in the New York area—especiallythose in skyscrapers—on alert that dangerous hurricane-force gusts could occurin a window of several hours on Monday evening. Gustsreached 90 mph at Islip, in central Long Island, and 79 mph at John F. Kennedy InternationalAirport, in Queens.
 
这种双大风核心的结构并不会出现在一般的飓风中。幸运的是,计算机模型在其出现前一天就预测出了这条不寻常的外围强风带,同时高空观测在强风带触及地面前几个小时就在高空中观测到了它的存在。所以NWS发布了特别预报(nowcast)来提醒纽约地区的居民(特别是在摩天楼中的)可能在周一晚间出现的强阵风。在长岛中心地带的艾斯利普阵风达到了90英里/小时,而位于皇后区的约翰·肯尼迪机场的数据是79英里/小时。
 
There’s still much to digest about thephysics of this remarkable weather event, not to mention the host of societalissues it’s raised. What’s heartening to researchers is that computer models,by and large, predicted many of Sandy’smost unusual features days ahead of time. That gave forecasters confidence inpredicting unprecedented impacts to the most densely populated part of thenation, regardless of whether Sandy was dubbed a hurricane, an extratropicalstorm, a hybrid, or—in the label that now seems to be winning out—a“superstorm.”
 
对于不同寻常的飓风“桑迪”,仍然有许多难以理解的部分需要去研究,更不必说它引起的社会问题了。计算机在登陆几天前就预测出“桑迪”不同寻常的结构特点给了预报员很大的信心去发布那些人口稠密地区从未有过先例的预报,而不用去考虑“桑迪”届时是否仍然会是一个飓风、“混血”风暴还是“超级风暴”。
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1楼#
发布于:2012-11-06 01:55
一开始还以为“暖隔离”就是锢囚(occlude)……有没有关联
 
Then, a few hours before landfall, Sandy began a sharp curvetoward the west, moving toward the heart of the approaching midlatitude trough of low pressure. In Shapiro’s view, this marked an apparent warm seclusion trying to take place on top of the storm’s fast-decaying warm core.
 
这个怎么理解……移动怎么成为系统变性的标志,是说和中纬度槽吸引加速变性吗。后面一句也没大明白 又是“暖隔断” 是米雷那样吗
 
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发布于:2012-11-06 13:42
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金杯:一开始还以为“暖隔离”就是锢囚(occlude)……有没有关联
 
Then, a few hours before landfall, Sandy began a sharp curvetoward the west, moving toward the heart of the approaching midlatitude trough of low pressure. In Shapiro’s view, this marked an apparent war .. (2012-11-06 01:55)

并不是移动,而是中心垂直上升轴的倾斜代表了变性。

一般来说,典型中纬度温带气旋的中心随着高度的升高向高空槽的中心倾斜,而热带气旋的中心轴则一般保持垂直(也即为啥不能有强风切)。
南印度洋温带气旋110902SI01:EC:<940,GFS:923.9!
http://forum.typhoon.gov.cn/read.php?tid=44978
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发布于:2014-09-26 14:11
金杯锛氁豢蓟挂晕芭衾搿本褪秋狼(occlude)……有没有关联
 
Then, a few hours before landfall, Sandy began a sharp curvetoward the west, moving t...
鍥炲埌鍘熷笘
暖隔离又叫做暖先囚。形成过程和锢囚很像
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lfs20052005
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发布于:2014-09-27 00:24
西太有沒有可能出現類似情況?
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发布于:2014-09-27 14:20
lfs20052005锛毼魈袥]有可能出現類似情況?鍥炲埌鍘熷笘
你是指桑迪还是暖隔离?若是温带气旋的暖隔离在西北太平洋也不少。
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发布于:2014-10-04 19:36
lfs20052005锛毼魈袥]有可能出現類似情況?鍥炲埌鍘熷笘
暖心有锋面的气旋西北太平洋不少
但是sandy暖心和对流强到足已归类热带气旋的例子估计没有
这种风暴能影响经济中心怕是更难
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