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Meteorology

气象学

Pollution from ships is changing maritime weather

船舶污染正在改变海洋天气

Lighting strikes are double the average in shipping lanes

航道发生闪电的次数比平均值多出一倍



MODERN, broad-beamed merchant vessels are well able to withstand the rough and tumble of the waves, but sailors still prefer to avoid storms at sea if they can. Containers may come loose in heavy weather and there is always a chance of lightning knocking out communications. It is therefore ironic that some storms may be caused by ships themselves. That, at least, is the conclusion reached by Joel Thornton of the University of Washington, in Seattle, and his colleagues in a paper just published in Geophysical Research Letters. They demonstrate that lightning strikes the Indian Ocean and the South China Sea almost twice as often along shipping lanes as it does other areas of these waters.

体积庞大的现代商船能很好的抵御惊涛骇浪,但水手仍尽量避开海洋风暴。集装箱船在恶劣天气下可能散架,而且经常因闪电导致通讯中断。讽刺的是,有些风暴可能是船舶自身造成的。至少,美国西雅图市华盛顿大学的乔尔•桑顿及其同事在《地球物理研究通讯》上发表的论文中得出这一结论。他们证明在印度洋和南中国海,航道发生闪电的次数比周围海域多出一倍。



Dr Thornton and his team considered 1.5bn strikes recorded in this part of the world by the World Wide Lightning Location Network (an international collaboration led by Dr Thornton’s colleague, Robert Holzworth) between 2005 and 2016. As the map shows, those strikes that happened over the ocean were concentrated in places most plied by ships. In particular, the shipping lane that passes from the south of Sri Lanka to the northern entrance of the Straits of Malacca, and thence down the straits to Singapore, positively glows with lightning. (Its westward extension to the Suez canal was outside the study area.) So do the lanes from Singapore and the western part of Malaysia that head north-east across the South China Sea.

桑顿博士及其团队研究了2005-2016年期间,“全球闪电定位网络”(桑顿博士的同事罗伯特•霍兹沃斯带领的一支国际联盟)所记录的发生在这片海域的15亿次闪电。正如地图所示,这些闪电集中发生在船舶最密集的海域,尤其是从斯里兰卡南部到马六甲海峡北部入口,向下通往新加坡的航道,闪电十分明显(向西通往苏伊士运河不在研究范围内)。从新加坡、马拉西亚西部,沿东北方向穿过南中国海的航道也是如此。

Neither changes in vertical wind shear nor differences in horizontal air movements seem likely to be causing this concentration of thunderstorms, for other measurements suggest that these weather-modifying phenomena are the same inside shipping lanes as they are in neighbouring parts of the atmosphere immediately outside those lanes. Nor does it seem plausible that the ships themselves (admittedly made of metal, and also the tallest structures on what is otherwise a flat surface) are responsible for attracting all the extra strikes involved. Though the area of the lanes is small compared with the whole ocean, it is vast compared with the area actually occupied by vessels. Most of the extra bolts are hitting the sea rather than craft sailing across it.

雷暴的聚集似乎既不是垂直风切变,也不是大气水平运动差异造成的,因为其他测量结果表明在航道内和周围海域的大气中,引起天气变化的现象是相同的。船舶自身吸引更多闪电似乎也说不通(不可否认船身是金属的,也是水平面最高的物体)。航道相比整个海洋来说很小,但相比船只实际占用的海域还是广阔的。大多数增加的闪电击中海洋,而不是从中航行的船只。

粒子加速器

Particle accelerator

The most likely explanation is particulate pollution emitted by the ships using the shipping lanes. Marine diesel burned offshore is generally high in sulphur, and its combustion produces soluble oxides of that element which act as nuclei for the condensation of cloud-forming droplets. Typical marine clouds in unpolluted areas are composed of large droplets and do not rise to high altitude, but Dr Thornton and his team reckon that smaller droplets, of the sort that condense around oxides of sulphur, might more easily be carried upward by convection—forming, as they rose, into towering storm clouds that would act as nurseries of lightning bolts.

最可能的解释是航道中的船只排放颗粒物污染。船舶燃烧的柴油一般硫含量较高,在水滴凝结形成云团过程中,燃烧产生的可溶性硫氧化物发挥着关键作用。无污染海域的云团一般由大水滴构成,并且不会升到高空,但桑顿博士及其团队认为硫氧化物周围凝结成的小水滴更容易被对流带到高空,形成高耸的暴风云,成为闪电的温床。

As to what can be done about this extra lightning, change may already be in hand. At the moment, standard “bunker” fuel has an average sulphur content of 2.7%. From 2020 that should fall to 0.5% if refiners and shipowners obey rules being introduced by the International Maritime Organisation, the body responsible for trying to impose order on the world’s shipping.

至于如何应对增加的闪电,变化可能已经显现了。目前,船用燃料油的平均硫含量为2.7%,如果炼油厂和船东遵守 “国际海事组织”(负责维护世界航运秩序)实施的规则,2020年硫含量将减少到0.5%。

Ships are also being sailed more efficiently, often by slowing them down, which reduces the amount of fuel consumed per nautical mile. That is how Maersk Line—one of the world’s biggest container-ship operators—has cut its fleet’s fuel consumption by 42% since 2007.

船舶一般通过减速也提高了航行效率,减少每海里的耗油量。马士基航运公司是全球最大的集装箱船运营商之一,2007年以来通过这种方式将船队的耗油量减少了42%。

On top of this, ship propulsion is becoming more efficient, as heat-recycling systems and new types of engine are introduced. In a few decades, therefore, the storminess of shipping lanes may have returned to normal. In the meantime, for any who may doubt humanity’s ability to affect the weather, Dr Thornton’s work provides strong evidence that it can.

另外,船舶动力也在提高效率,热再生系统和新型发动机得到采用。因此未来几十年,航道的风暴天气有可能恢复正常。与此同时,对于人类影响天气能力的质疑者来说,桑顿博士的研究充分证明人类能够做到。