EK小课堂是10位培元生态编辑部的小编辑们定期给大家呈现生态小知识的栏目。我们肉眼可见的极端天气越来越多，由此更多的人意识到了气候变化带来的严重问题，但如何解决呢？首先要了解这个问题是什么，其次才会有解决方案。EK小课堂就是小编辑们让大家更多了解问题是什么，让大家一起来探寻解决办法。希望大家喜欢并点赞，更希望大家可以传播给更多的人。

本期由王雅信、冯绍原2位小编辑，为读者们带来关于海洋酸化和热带气旋的知识分享。

（王雅信）

“王雅信，14岁，北京市第三十五中学项目部学生（北京市西城区赵登禹路8号），行政班初三项目二班（初三18班）。参加过学校编程项目，'机甲大师Robomaster'比赛等，对信息技术与编程方面感兴趣，曾主导科学性项目编辑以及实践类课题。喜爱钢琴、篮球与音乐制作。”

海洋酸化简介 Brief introduction to Ocean Acidification 

2003年，“海洋酸化”这个术语第一次出现在英国著名科学杂志《自然》上。海洋酸化即海水由于吸收了空气中过量的二氧化碳（CO2），导致酸碱度降低的现象，随着海水中积蓄的二氧化碳不断积蓄，使本该呈弱碱性的海水逐渐向酸性转变。酸碱度一般用pH值来表示，范围为0-14，pH值为0说明酸性最强，pH值为14说明碱性最强。蒸馏水的pH值为7，代表中性。海水应为弱碱性，海洋表层水的pH值约为8.2。当空气中过量的二氧化碳进入海洋中时，海洋就会酸化。

In 2003, the term "ocean acidification" first appeared in the leading British scientific journal Nature. Ocean acidification refers to the phenomenon that seawater absorbs excessive carbon dioxide (CO2) from the air, resulting in the decrease of pH. With the continuous accumulation of carbon dioxide stored in the seawater, the seawater that should be weakly alkaline gradually changes to acid. PH is generally expressed by pH value, with a range of 0-14, pH value of 0 indicates the strongest acidic, and pH value of 14 indicates the strongest alkaline. The pH of distilled water is 7 and represents neutral. Sea water should be weakly alkaline, and the pH value of Marine surface water is about 8.2. When excess carbon dioxide in the air enters the ocean, the ocean acidifies.

科学家研究表明，自1750年工业革命开始至今的200多年的时间里，由于人类活动影响，到2012年，过量的二氧化碳排放已将海水表层pH值降低了0.1，这表示海水的酸度已经提高了30%。预计到2100年海水表层酸度将下降到7.8，到那时海水酸度将比1800年高150%。

Scientists show that in the more than 200 years since the beginning of the Industrial Revolution in 1750, excessive carbon dioxide emissions had reduced the surface pH value of seawater by 0.1 by 2012, indicating that the acidity of seawater has increased by 30 percent. The surface acidity of seawater is expected to drop to 7.8 by 2100, which will be 150% higher than in 1800.

海洋酸化的原因—人类活动 The cause of ocean acidification- -human activity

海洋与大气在不断进行着气体交换，排放到大气中的任何一种成分最终都会溶于海洋。在工业时代到来之前，大气中碳的变化主要是自然因素导致的，这种自然变化造成了全球气候的自然波动。

The oceans and the atmosphere are constantly exchanging gas, and any component emitted into the atmosphere eventually dissolves in the oceans. Before the industrial age, the changes in carbon in the atmosphere were mainly caused by natural factors, which caused the natural fluctuations in the global climate.

但是从1750年工业革命开始，人类开采使用煤、石油和天然气等化石燃料，并砍伐了大量森林，至21世纪初，已经排出超过5000亿吨二氧化碳。人类活动释放到地球大气层中的二氧化碳，大约有三分之一到二分之一被海洋吸收，这使得大气中的碳含量水平逐年上升。受海风的影响大气成分最先溶入几百英尺深的海洋表层，在随后的数个世纪中，这些成分会逐渐扩散到海底的各个角落。研究表明，在19世纪和20世纪，海洋吸收了人类排放的二氧化碳中的30%，并且仍在以约每小时一百万吨的速度吸收着。到目前为止海水的平均pH值从8.19下降到了8.05，相当于海水的酸度增加了30%。

But since the Industrial Revolution in 1750, humans have used fossil fuels such as coal, oil and natural gas, and cut down lots of forests. By the early 2000s, more than 500 billion tons of carbon dioxide had been emitted. About a third to a half of the carbon dioxide released into the earth's atmosphere by human activities is absorbed by the ocean, which makes the carbon level in the atmosphere rise year by year. Influenced by the sea breeze, the atmosphere first enters the ocean surface hundreds of feet deep, and over the following centuries, it will gradually spread to the corners of the sea floor. Research shows that in the 19th and 20th centuries, the oceans absorbed 30 percent of the human carbon dioxide, and were still absorbing it at a rate of about a million tons per hour. The average pH of seawater so far has dropped from 8.19 to 8.05, equivalent to a 30% increase in the acidity of seawater.

2005年，研究灾难和突发事件的专家詹姆斯·内休斯研究发现，距今5500万年前，海洋里曾经出现过一次生物灭绝事件，罪魁祸首就是溶解到海水中的二氧化碳，估计总量达到45000亿吨。此后海洋至少花了10万年时间才恢复正常得以渡过难关。

In 2005, the disaster and emergency experts James hughes found that 55 million years ago, the ocean once encountered a biological extinction event, the culprit was carbon dioxide dissolved into the water, estimated to 4.5 trillion tons. It took at least 100000 years for the ocean to recover from its difficulties thereafter. 

2012年3月，一支由美国、英国、西班牙、德国和荷兰21名研究人员组成的国际科学家团队在最新一期《科学》杂志上发表报告称，受人类排放温室气体的影响，地球正经历过去3亿年来速度最快的海洋酸化进程，众多海洋生物会因此面临生存威胁。

In March 2012, an international team of scientists composed of 21 researchers from the United States, the United Kingdom, Spain, Germany, and the Netherlands reported in the latest issue of Science that the Earth is experiencing the fastest ocean acidification process in the past 300 million years due to human emissions of greenhouse gases, posing a threat to the survival of many marine organisms. 

海洋酸化的危害 Hazards of ocean acidification

海洋吸收了人类每年排放到大气中的约23%的二氧化碳。这些二氧化碳与海水发生反应，导致海洋酸化，威胁着海洋生物和海洋生态系统，进而威胁到粮食安全、旅游业和沿海人类生活。

The ocean absorbs about 23% of the carbon dioxide that humans emit into the atmosphere every year. These carbon dioxide react with seawater, leading to ocean acidification, posing a threat to marine life and ecosystems, thereby threatening food security, tourism, and coastal human life.

生态危害 potential ecological risk

工业革命以来，人类活动释放的CO2有超过1/3被海洋吸收，使表层海水的氢离子浓度近200年间增加了三成，pH值下降了0.1。作为海洋中进行光合作用的主力，浮游植物的门类众多、生理结构多样，对海水中不同形式碳的利用能力也不同，海洋酸化会改变物种间竞争的条件。

Since the Industrial Revolution, over one-third of the CO2 released by human activities has been absorbed by the ocean, resulting in a 30% increase in hydrogen ion concentration in surface seawater over the past 200 years and a 0.1% decrease in pH value. As the main force of photosynthesis in the ocean, phytoplankton have numerous categories and diverse physiological structures, and their ability to utilize different forms of carbon in seawater also varies. Ocean acidification can change the conditions for species competition.

浮游植物：由于全球变暖，从大气中吸收CO2的海洋上表层也由于温度上升而密度变小，从而减弱了表层与中深层海水的物质交换，并使海洋上部混合层变薄，不利于浮游植物的生长。由于浮游植物构成了海洋食物网的基础和初级生产力，它们的“重新洗牌”很可能导致从小鱼小虾到鲨鱼、巨鲸的众多海洋动物都面临冲击。

Phytoplankton: Due to global warming, the density of the surface layer of the ocean that absorbs CO2 from the atmosphere also decreases due to temperature rise, which weakens the material exchange between the surface and deep seawater, and thins the mixed layer in the upper part of the ocean, which is not conducive to the growth of phytoplankton. Due to the fact that phytoplankton form the foundation and primary productivity of the marine food web, their "reshuffling" is likely to cause impacts on many marine animals, from small fish and shrimp to sharks and giant whales.

软体动物：一些研究认为，到2030年，南半球的海洋将对蜗牛壳产生腐蚀作用，这些软体动物是太平洋中三文鱼的重要食物来源，如果它们的数量减少或是在一些海域消失，那么这些海域的三文鱼的数量就会大量减少甚至消失。

Molluscs: Some studies suggest that by 2030, the oceans in the southern hemisphere will have corrosive effects on snail shells. These molluscs are important food sources for salmon in the Pacific Ocean. If their numbers decrease or disappear in some waters, the number of salmon in these areas will significantly decrease or even disappear.

鱼类：海洋酸化会导致小丑鱼和小热带鱼智商下降。《美国国家科学院院刊》的最新报道：模拟了未来50～100年海水酸度后发现，在酸度最高的海水里，鱼仔起初会本能地避开捕食者，但它们很快就会被捕食者的气味所吸引──这是它们的嗅觉系统遭到了破坏的结果。

Fish: Ocean acidification can cause a lower IQ in clownfish and small tropical fish.The latest report in the Proceedings of the National Academy of Sciences: After simulating the acidity of seawater for the next 50 to 100 years, it was found that in the highest acidity seawater, fish larvae instinctively avoid predators at first, but they are quickly attracted to their scent - a result of the destruction of their olfactory system.

珊瑚礁：海洋酸化会阻碍珊瑚礁的生长繁殖，珊瑚或将消失。2013年3月，日本一个研究小组在新一期英国《自然·气候变化》杂志上发表了关于海洋酸化影响珊瑚礁生长的报告。研究小组发现，当海水pH值平均为8.1的时候，珊瑚生长状态最好。当pH值为7.8时，就变为以海鸡冠为主。如果pH值降至7.6以下，两者都无法生存。目前天然海水的pH值稳定在7.9至8.4之间，而未受污染的海水pH值在8.0至8.3之间。海水的弱碱性有利于海洋生物利用碳酸钙形成外壳。研究小组指出，海水pH值预计本世纪末将达7.8左右，酸度比正常状态下大幅升高，所以届时珊瑚有可能消失。

Coral reefs: Ocean acidification can hinder the growth and reproduction of coral reefs, and corals may disappear. In March 2013, a Japanese research group published a report on the impact of ocean acidification on coral reef growth in the new issue of the British journal Nature Climate Change. The research team found that coral grows best when the average pH value of seawater is 8.1. When the pH value is 7.8, it becomes dominated by sea cockscomb. If the pH drops below 7.6, neither can survive. At present, the pH value of natural seawater is stable between 7.9 and 8.4, while the pH value of uncontaminated seawater is between 8.0 and 8.3. The weak alkalinity of seawater is beneficial for marine organisms to utilize calcium carbonate to form shells. The research team pointed out that the pH value of seawater is expected to reach around 7.8 by the end of this century, and the acidity is significantly higher than normal, so corals may disappear by then.

气候影响 climatic impact

气候变暖：通过减少生物源含硫化合物的产生的方式，海洋酸化具有潜在可能导致气候变暖加剧。《自然—气候变化》上的一项研究称，海水pH值的降低导致了二甲基硫化物浓度的下降。海洋生物排放是大气硫元素的最大天然来源——大气中的硫元素能够增强大气对辐射的反射率，从而降低地球表面温度。在评估了未来在不同气候条件下海洋生物排放硫元素的变化情况后，研究表明到2100年，海洋生物对硫元素的排放将下降18%左右，从而会引起地球温度上升0.23℃~0.48℃（32.414℉~32.864℉）。

Climate warming: By reducing the production of sulfur compounds from biological sources, ocean acidification has the potential to exacerbate climate warming. A study in Nature Climate Change suggests that a decrease in seawater pH leads to a decrease in the concentration of dimethyl sulfide. Marine biological emissions are the largest natural source of atmospheric sulfur - sulfur in the atmosphere can enhance the reflectivity of the atmosphere towards radiation, thereby lowering the Earth's surface temperature. After evaluating the changes in sulfur emissions from marine organisms under different climate conditions in the future, research shows that by 2100, the emissions of sulfur from marine organisms will decrease by about 18%, which will cause an increase in Earth temperature by 0.23 ℃ to 0.48 ℃ (32.414 ℉ to 32.864 ℉).

影响人类生计 Affect human livelihood

据估计，在有些水域，海洋的酸度将达到贝壳都会开始溶解的程度。当贝类生物消失时，以这类生物为食的其他生物将不得不寻找别的食物，事实上人类将会遭殃。联合国粮农组织估计，全球有5亿多人依靠捕鱼和水产养殖作为蛋白质摄入和经济收入的来源，对其中最贫穷的4亿人来说，鱼类提供了他们每日所需的大约一半动物蛋白和微量元素。海水的酸化对海洋生物的影响必然危及这些人口的生计。

It is estimated that in some waters, the acidity of the ocean will reach the point where shells will begin to dissolve. When shellfish disappear, other organisms that feed on them will have to search for other foods, and in fact, humans will suffer. The Food and Agriculture Organization of the United Nations estimates that over 500 million people worldwide rely on fishing and aquaculture as sources of protein intake and economic income. For the poorest 400 million people, fish provides about half of their daily animal protein and trace elements needs. The acidification of seawater will inevitably endanger the livelihoods of these populations due to its impact on marine life.

防范措施 Measures to prevent ocean acidification

在2008年10月的国际海洋酸化研讨会上，与会科学家指出，海洋酸化的自然恢复至少需要数千年，遏制它的唯一有效途径就是尽快减少CO2的全球排放量。因此，减少燃煤、石油和天然气等化石燃料的使用以及提倡使用可再生能源、如风能、太阳能和水能等新型能源也是目前人类减少碳排放必须要采取的举措。

At the International Symposium on Ocean Acidification in October 2008, participating scientists noted that the natural recovery of ocean acidification requires at least thousands of years, and the only effective way to curb it is to reduce global CO2 emissions as soon as possible. Therefore, reducing the use of fossil fuels such as coal, oil, and natural gas, as well as promoting the use of renewable energy sources such as wind, solar, and water, are also necessary measures for reducing carbon emissions.

其次，保护海洋生态系统也是缓解海洋酸化的重要举措。海洋生态系统具有一定的自净能力，能够吸收和储存二氧化碳。因此，保护珊瑚礁、海草床和其他海洋生态系统，能够减轻海洋酸化的影响。此外，减少海洋捕捞以及人为的污染行为对保护海洋同样是重要的。

Secondly, protecting marine ecosystems is also an important measure to alleviate ocean acidification. Marine ecosystems have a certain degree of self-cleaning ability, which can absorb and store carbon dioxide. Therefore, protecting coral reefs, seagrass beds, and other marine ecosystems can mitigate the impact of ocean acidification. In addition, reducing marine fishing and human pollution behavior is equally important for protecting the ocean.

第三，加强国际合作是应对海洋酸化的重要手段。海洋酸化是全球面临的挑战，需要各国共同努力。国际社会应加强合作，分享经验和技术，全球应该共同行动应对海洋酸化的问题。欧美等国正开始研究遏制海洋酸化的对策，2009年8月13日，来自26国，逾150位科学家签署《摩纳哥宣言》，呼吁各国决策者将二氧化碳排放量稳定在安全范围内，以避免危险的气候变迁及海洋酸化等问题。

Thirdly, strengthening international cooperation is an important means to address ocean acidification. Ocean acidification is a global challenge that requires joint efforts from all countries. The international community should strengthen cooperation, share experience and technology, and work together globally to address the issue of ocean acidification. Countries such as Europe and the United States are starting to study strategies to curb ocean acidification. On August 13, 2009, more than 150 scientists from 26 countries signed the Monaco Declaration, calling on decision-makers to stabilize carbon dioxide emissions within a safe range to avoid dangerous climate change and ocean acidification issues.

中国也已将海洋酸化列入重点支持方向。中国在不同的外交场合就对此重申一个重要承诺-“中国的二氧化碳排放量力争于2030年前达到峰值；中国努力争取2060年前实现碳中和（即二氧化碳排放量与消耗量达到平衡）。”

China has also included ocean acidification as a key support direction. China has reiterated an important commitment to this in various diplomatic occasions - "China's carbon dioxide emissions will peak before 2030; China will strive to achieve carbon neutrality (i.e. achieve a balance between carbon dioxide emissions and elimination) by 2060”

第四，加强公众教育和意识的提升也是应对海洋酸化的重要方面。同时应该向公众提供环保和可持续发展的生活方式，减少对海洋的污染和破坏，应该成为公众的共识。

Fourthly, strengthening public education and raising awareness is also an important aspect of addressing ocean acidification. At the same time, it should be a consensus among the public to provide environmentally friendly and sustainable lifestyles to reduce pollution and damage to the ocean. 

（冯绍原）

“我叫冯绍原，目前就读北京三十五中学初三项目2班，爱好编程（Pathon, C++学习中），篮球，画画，电子游戏；性格平和自恰，乐观向上。希望通过培元认识更多志同道合的老师和朋友。”

初识热带气旋 Introduction of tropical cyclone

热带气旋，也称台风或者飓风，起源于温暖的热带海洋，其特点是低气压、大风和暴雨。热带气旋从海面汲取能量，只要停留在温暖的海面就能保持强度，其产生的风速超过每小时119千米（74英里），在极端情况下甚至可以超过每小时240千米（150英里），阵风可能超过每小时320千米（200英里）。伴随这些强风的还有暴雨和一种被称为风暴潮的破坏性现象，即海面可能比正常水平高出6米（20英尺）。 

Tropical cyclone, also called typhoon or hurricane, an intense circular storm that originates over warm tropical oceans and is characterized by low atmospheric pressure, high winds, and heavy rain. Drawing energy from the sea surface and maintaining its strength as long as it remains over warm water, a tropical cyclone generates winds that exceed 119 km (74 miles) per hour. In extreme cases winds may exceed 240 km (150 miles) per hour, and gusts may surpass 320 km (200 miles) per hour. Accompanying these strong winds are torrential rains and a devastating phenomenon known as the storm surge, an elevation of the sea surface that can reach 6 metres (20 feet) above normal levels.

气旋剖析 Anatomy of a cyclone

热带气旋是一种紧凑的圆形风暴，直径一般约为320千米（200英里），其风围绕着一个低气压中心区域旋转。风的动力来自这个低压核心和地球自转。地球自传通过一种被称为科里奥利力的现象使风的路径发生偏转。因此，热带气旋在北半球为逆时针旋转方向，在南半球为顺时针旋转方向。 

热带气旋的风场可分为三个区域。首先是环形外围区域，通常外半径约为160千米（110英里），内半径约为30~50千米（20~30英里）。在这一区域，风速向中心均匀增加。第二个区域称为眼墙，通常距离风暴中心15~30千米（10到20英里），风速在这个区域达到最大值。眼墙围绕的内部区域称为风眼，风眼处的风速迅速降低，气流比较平静。下文将详细介绍气旋的这三个主要结构区域。 

Tropical cyclones are compact, circular storms, generally some 320 km (200 miles) in diameter, whose winds swirl around a central region of low atmospheric pressure. The winds are driven by this low-pressure core and by the rotation of Earth, which deflects the path of the wind through a phenomenon known as the Coriolis force. As a result, tropical cyclones rotate in a counterclockwise direction in the Northern Hemisphere and in a clockwise direction in the Southern Hemisphere.

The wind field of a tropical cyclone may be divided into three regions. First is a ring-shaped outer region, typically having an outer radius of about 160 km (100 miles) and an inner radius of about 30 to 50 km (20 to 30 miles). In this region the winds increase uniformly in speed toward the centre. Wind speeds attain their maximum value at the second region, the eyewall, which is typically 15 to 30 km (10 to 20 miles) from the centre of the storm. The eyewall in turn surrounds the interior region, called the eye, where wind speeds decrease rapidly and the air is often calm. These main structural regions are described in greater detail below.

风眼（The eye）

热带气旋的一个特征是具有“风眼”，风眼位于热带气旋的中心区域，这里晴朗，温暖，气压低。通常海洋表面的气压约为1,000毫巴，但在热带气旋中心，气压通常在960毫巴左右，在西太平洋非常强烈的“超强台风”中，气压可能低至880毫巴。除了中心气压低之外，整个风暴的气压变化也很快，大部分变化发生在中心附近。这种快速变化会产生巨大的气压梯度力，这也是热带气旋另一个结构-“眼墙”出现强风的原因（如后文所述）。 

风眼内的水平风是轻微的，当空气被拉入眼墙表面时，会有微弱的向下运动，即下沉。当空气下沉时会被轻微压缩并变暖，于是热带气旋中心的温度会比风暴的其他区域高出5.5℃（10°F）。由于温度较高的空气在凝结前可容纳更多的水分，因此风眼一般没有云层。关于风眼内空气“压抑”或者“闷热”的报道，很可能是对从眼强的狂风暴雨转变为风眼的平静状态的一种心理反应。

A characteristic feature of tropical cyclones is the eye, a central region of clear skies, warm temperatures, and low atmospheric pressure. Typically, atmospheric pressure at the surface of Earth is about 1,000 millibars. At the centre of a tropical cyclone, however, it is typically around 960 millibars, and in a very intense “super typhoon” of the western Pacific it may be as low as 880 millibars. In addition to low pressure at the centre, there is also a rapid variation of pressure across the storm, with most of the variation occurring near the centre. This rapid variation results in a large pressure gradient force, which is responsible for the strong winds present in the eyewall (described below).

Horizontal winds within the eye, on the other hand, are light. In addition, there is a weak sinking motion, or subsidence, as air is pulled into the eyewall at the surface. As the air subsides, it compresses slightly and warms, so that temperatures at the centre of a tropical cyclone are some 5.5 °C (10 °F) higher than in other regions of the storm. Because warmer air can hold more moisture before condensation occurs, the eye of the cyclone is generally free of clouds. Reports of the air inside the eye being “oppressive” or “sultry” are most likely a psychological response to the rapid change from high winds and rain in the eyewall to calm conditions in the eye.

眼墙（The eyewall）

热带气旋最危险、破坏力最大的部分是眼墙，这里的风力最强，降雨量最大，深层对流云从接近海洋表面的地方上升到15,000米（49,000英尺）的高度。如前文所述，强风产生的原因是风眼附近大气压的快速变化导致了巨大的压力梯度力。实际上，风在距离地面大约300米（1000英尺）的高度达到最大速度。在距离地面较近的地方，风速会因为摩擦力而减慢，而在300米以上的地方，风速会因为水平气压梯度力的减弱而减慢。这种减慢与风暴的温度结构有关。热带气旋中心的空气温度较高，这种较高的温度导致中心大气压力随高度降低的速度比周围大气压力降低的速度慢。热带气旋中心的气压差较小，导致水平气压梯度随高度增加而减弱，进而导致风速减慢。

表面的摩擦力除了会降低风速外，还会导致风向最低气压区转移。流入低压风眼的空气通过膨胀而冷却，反过来又从海面吸收热量和水蒸气。受热最大的区域具有最强劲的上升气流，眼墙处的垂直风速也最大，可达每秒5~10米（16.5~33英尺），或每小时18~36千米（11~22英里）。虽然这个速度远低于水平风速，但上升气流对嵌入眼墙的高耸对流云的存在至关重要，因为热带气旋的大部分强降雨都来自这些云层。 

气旋眼内空气的上升运动也导致气旋风眼在高空比在海洋表面更宽。当空气螺旋上升时会保持其角动量，而角动量取决于与气旋中心的距离以及中心周围的风速。由于风速随着高度的增加而减慢，因此空气在上升过程中必然远离风暴中心。 

当上升气流达到稳定的对流层顶部（对流层的上边界，距离海洋表面约16千米[10英里]）时，空气就会向外流动。科里奥利力使外流偏转，在高空形成广泛的反气旋环流。因此，热带气旋高层的水平环流与海洋表面附近的水平环流相反。

The most dangerous and destructive part of a tropical cyclone is the eyewall. Here winds are strongest, rainfall is heaviest, and deep convective clouds rise from close to Earth’s surface to a height of 15,000 metres (49,000 feet). As noted above, the high winds are driven by rapid changes in atmospheric pressure near the eye, which creates a large pressure gradient force. Winds actually reach their greatest speed at an altitude of about 300 metres (1,000 feet) above the surface. Closer to the surface they are slowed by friction, and higher than 300 metres they are weakened by a slackening of the horizontal pressure gradient force. This slackening is related to the temperature structure of the storm. Air is warmer in the core of a tropical cyclone, and this higher temperature causes atmospheric pressure in the centre to decrease at a slower rate with height than occurs in the surrounding atmosphere. The lessened contrast in atmospheric pressure with altitude causes the horizontal pressure gradient to weaken with height, which in turn results in a decrease in wind speed.

Friction at the surface, in addition to lowering wind speeds, causes the wind to turn inward toward the area of lowest pressure. Air flowing into the low-pressure eye cools by expansion and in turn extracts heat and water vapour from the sea surface. Areas of maximum heating have the strongest updrafts, and the eyewall exhibits the greatest vertical wind speeds in the storm—up to 5 to 10 metres (16.5 to 33 feet) per second, or 18 to 36 km (11 to 22 miles) per hour. While such velocities are much less than those of the horizontal winds, updrafts are vital to the existence of the towering convective clouds embedded in the eyewall. Much of the heavy rainfall associated with tropical cyclones comes from these clouds.

The upward movement of air in the eyewall also causes the eye to be wider aloft than at the surface. As the air spirals upward it conserves its angular momentum, which depends on the distance from the centre of the cyclone and on the wind speed around the centre. Since the wind speed decreases with height, the air must move farther from the centre of the storm as it rises。

When updrafts reach the stable tropopause (the upper boundary of the troposphere, some 16 km [10 miles] above the surface), the air flows outward. The Coriolis force deflects this outward flow, creating a broad anticyclonic circulation aloft. Therefore, horizontal circulation in the upper levels of a tropical cyclone is opposite to that near the surface.

雨带（Rainbands）

除了风眼周围的深对流层（空气垂直运动的紧凑区域）外，中心周围通常还有成带排列的次级层。这些条带通常被称为雨带，呈螺旋状伸向风暴中心。在某些情况下，雨带相对于移动的风暴中心是静止的，而在其他情况下，雨带似乎围绕中心旋转。旋转云带通常与风暴轨道的显著摆动有关。如果热带气旋接近海岸线时出现这种情况，预报的登陆位置与实际的登陆位置可能会有很大差异。

当热带气旋登陆时，地表摩擦力会增加，这反过来又会增加气流向眼墙的汇聚，并增加空气在眼墙内的垂直运动。增加的潮湿空气的汇集与上升是热带气旋带来暴雨的原因， 24小时内的降雨量可能超过250毫米(10英寸)。有时风暴可能会停滞不前，使暴雨在一个地区持续数天。据报道，在极端情况下，5天内的降雨总量可达到760毫米（30英寸）。

In addition to deep convective cells (compact regions of vertical air movement) surrounding the eye, there are often secondary cells arranged in bands around the centre. These bands, commonly called rainbands, spiral into the centre of the storm. In some cases the rainbands are stationary relative to the centre of the moving storm, and in other cases they seem to rotate around the centre. The rotating cloud bands often are associated with an apparent wobbling of the storm track. If this happens as the tropical cyclone approaches a coastline, there may be large differences between the forecast landfall positions and actual landfall.

As a tropical cyclone makes landfall, surface friction increases, which in turn increases the convergence of airflow into the eyewall and the vertical motion of air occurring there. The increased convergence and rising of moisture-laden air is responsible for the torrential rains associated with tropical cyclones, which may be in excess of 250 mm (10 inches) in a 24-hour period. At times a storm may stall, allowing heavy rains to persist over an area for several days. In extreme cases, rainfall totals of 760 mm (30 inches) in a five-day period have been reported.

热带气旋的存期 Life of a cyclone

环流系统在增强为成熟的热带气旋时要经历一系列阶段。风暴以热带扰动的形式开始，通常发生在东风波中的松散积雨云开始出现微弱环流的迹象时。一旦风速增加到每小时36千米（23英里），风暴就会被归类为热带低压。如果环流继续加强，最大风速超过每小时63千米（39英里），则称为热带风暴。一旦最大风速超过每小时119公里（74英里），风暴就会被归类为热带气旋。

A circulation system goes through a sequence of stages as it intensifies into a mature tropical cyclone. The storm begins as a tropical disturbance, which typically occurs when loosely organized cumulonimbus clouds in an easterly wave begin to show signs of a weak circulation. Once the wind speed increases to 36 km (23 miles) per hour, the storm is classified as a tropical depression. If the circulation continues to intensify and the wind speeds exceed 63 km (39 miles) per hour, then the system is called a tropical storm. Once the maximum wind speed exceeds 119 km (74 miles) per hour, the storm is classified as a tropical cyclone.

形成（Formation）

热带气旋的能量主要来源于温暖海洋通过海面蒸发产生的水蒸气和海洋热量的转移。当温暖潮湿的空气上升时会膨胀并冷却，很快达到饱和，并通过水蒸气的凝结释放出潜热。在这个过程中，位于正在形成的热带扰动中心的核心气柱被加热和润湿。上升的暖空气与较冷环境之间的温差使上升的空气产生浮力，从而进一步加强其上升运动。 

如果海面太冷就没有足够的热量可用，蒸发率就会过低，以致无法为热带气旋提供足够的能量。如果温暖的表层海水不够深，能量供应也会被切断，因为正在形成的热带系统会改变下层的海洋。从深层对流云中降下的雨水会使海面降温，风暴中心的强风会产生湍流。如果由此产生的混合作用将表层以下的冷水带到海面，热带系统的能量供应就会被切断。

暖空气的垂直运动本身不足以引发热带系统的形成，但是如果暖湿气流进入了一个已经存在的大气扰动，就会进一步发展。上升的空气通过两种方式使扰动中心变暖，一种为释放潜热，另一种为从海面直接传递热量，于是扰动中心的大气压降低，气压降低导致海面风力增强，这反过来又增加了水蒸气和热量的传递，进一步加剧了海面气流上升。因此，扰动中心的变暖和海洋表面风的增加在正反馈机制中相互促进。

The fuel for a tropical cyclone is provided by a transfer of water vapour and heat from the warm ocean to the overlying air, primarily by evaporation from the sea surface. As the warm, moist air rises, it expands and cools, quickly becoming saturated and releasing latent heat through the condensation of water vapour. The column of air in the core of the developing disturbance is warmed and moistened by this process. The temperature difference between the warm, rising air and the cooler environment causes the rising air to become buoyant, further enhancing its upward movement.

If the sea surface is too cool, there will not be enough heat available, and the evaporation rates will be too low to provide the tropical cyclone enough fuel. Energy supplies will also be cut off if the warm surface water layer is not deep enough, because the developing tropical system will modify the underlying ocean. Rain falling from the deep convective clouds will cool the sea surface, and the strong winds in the centre of the storm will create turbulence. If the resulting mixing brings cool water from below the surface layer to the surface, the fuel supply for the tropical system will be removed.

The vertical motion of warm air is by itself inadequate to initiate the formation of a tropical system. However, if the warm, moist air flows into a preexisting atmospheric disturbance, further development will occur. As the rising air warms the core of the disturbance by both release of latent heat and direct heat transfer from the sea surface, the atmospheric pressure in the centre of the disturbance becomes lower. The decreasing pressure causes the surface winds to increase, which in turn increases the vapour and heat transfer and contributes to further rising of air. The warming of the core and the increased surface winds thus reinforce each other in a positive feedback mechanism.

加强（Intensification）

热带气旋的动力依赖于风暴的外部温度低于其中心温度，因此大气温度必须随着高度增加而迅速下降。只要周围的空气较冷和较重，在环流中心的温暖饱和的空气就会不断上升，这种垂直运动使深层对流云层得以形成。中心区上升的空气也会在海拔5000米（16000英尺）左右的大气层中从周围吸入一些空气。如果外部空气相对潮湿，环流将继续加强；但如果外部空气足够干燥，则可能会蒸发上升气柱中的部分水滴，导致空气温度低于周围空气，这种冷却会导致形成强大的下沉气流，扰乱上升运动并抑制其发展。 

要形成热带气旋特有的快速旋转，低压中心必须距离赤道至少500千米（300英里）。如果初始的干扰太靠近赤道，那么科里奥利力的作用就会太小，无法提供必要的旋转。科里奥利力使被吸入低压中心的空气发生偏转，形成气旋的旋转。围绕低压中心形成的环流方向在北半球是逆时针的，在南半球则是顺时针的。 

热带气旋加强的最后一个条件是，风速随距离海面高度的变化的变化必须很小。如果风速随高度增加过多，气旋中心将不再垂直对准提供能量的温暖海面，受暖区域将和低压中心分离，前文所述的正反馈机制将受到抑制。热带地区有利于热带气旋发展的条件包括：气温从北到南的变化通常较小。这种相对缺乏温度梯度的情况使风速在高度上保持相对恒定。

The dynamics of a tropical cyclone rely on the exterior of a storm being cooler than its core, so it is necessary that the temperature of the atmosphere drop sufficiently rapidly with height. The warm, saturated air rising in the centre of the circulation tends to keep rising as long as the surrounding air is cooler and heavier. This vertical movement allows deep convective clouds to develop. The rising air in the core also draws in some air from the surrounding atmosphere at altitudes of around 5,000 metres (16,000 feet). If this external air is relatively humid, the circulation will continue to intensify. If it is sufficiently dry, then it may evaporate some of the water drops in the rising column, causing the air to become cooler than the surrounding air. This cooling will result in the formation of strong downdrafts that will disrupt the rising motion and inhibit development.

For the development of the rapid rotation characteristic of tropical cyclones, the low-pressure centre must be located at least 500 km (300 miles) away from the Equator. If the initial disturbance is too close to the Equator, then the effect of the Coriolis force will be too small to provide the necessary spin. The Coriolis force deflects the air that is being drawn into the surface low-pressure centre, setting up a cyclonic rotation. In the Northern Hemisphere the direction of the resulting circulation around the low is counterclockwise, and in the Southern Hemisphere it is clockwise.

A final requirement for the intensification of tropical cyclones is that there must be little change in the wind speed with height above the surface. If the winds increase too much with altitude, the core of the system will no longer be vertically aligned over the warm surface that provides its energy. The area being warmed and the surface low-pressure centre will move apart, and the positive feedback mechanism described above will be suppressed. Conditions in the tropics that encourage the development of tropical cyclones include a typically minor north-to-south variation in temperature. This relative lack of a temperature gradient causes wind speed to remain relatively constant with height.

消散（Dissipation）

当热带气旋无法再从温暖的海水中汲取足够的能量时就会消散。如前文所述，热带气旋会搅动更深更冷的海水，从而导致自身消散。此外，移动到陆地上空的风暴会突然失去能量来源，强度也会迅速减弱。

热带气旋停留在海洋上空并向高纬度地区移动，当遇到较冷的海水时，会改变其结构，变成外热带气旋，从热带气旋向外热带气旋转变的标志是风暴的直径增大，雨带重组后形状从圆形变为逗号形或者v形。外热带气旋的中心气压通常较高，因此风速较低，受南北温度变化的影响，外热带气旋会在几天内减弱并消散。

Tropical cyclones dissipate when they can no longer extract sufficient energy from warm ocean water. As mentioned above, a tropical cyclone can contribute to its own demise by stirring up deeper, cooler ocean waters. In addition, a storm that moves over land will abruptly lose its fuel source and quickly lose intensity.

A tropical cyclone that remains over the ocean and moves into higher latitudes will change its structure and become extratropical as it encounters cooler water. The transformation from a tropical to an extratropical cyclone is marked by an increase in the storm’s diameter and by a change in shape from circular to comma- or v-shaped as its rainbands reorganize. An extratropical cyclone typically has a higher central pressure and consequently has lower wind speeds. Extratropical cyclones, which are fueled by a north-to-south variation of temperature, weaken and dissipate in a few days.

热带气旋造成的破坏 Tropical cyclone damage

水平风（Horizontal wind）

大风会造成与热带气旋相关的一些最严重的破坏性影响。在最强烈的热带气旋中，持续风速可高达每小时240千米（150英里），阵风可超过每小时320千米（200英里）。特定地点受极端风力影响的时间长短取决于风暴的大小和移动速度。在热带气旋的直接袭击下，一个地区可能会经受几个小时的强风，在此期间，即使是最坚固的建筑物也可能受损。风力随着风速的增加而迅速增强，每小时100千米（62英里）的持续风速可产生718帕斯卡（每平方英尺15磅）的压力，而风速大约增加一倍达到每小时200千米（124英里），压力几乎增加了五倍，达到3,734帕斯卡。迎风面积大的建筑物可能会受到巨大的冲击力，在热带气旋期间经常会观察到建筑物被破坏的程度不同，正是由于建筑物相对风的方向不同造成的。

High winds cause some of the most dramatic and damaging effects associated with tropical cyclones. In the most intense tropical cyclones, sustained winds may be as high as 240 km (150 miles) per hour, and gusts can exceed 320 km (200 miles) per hour. The length of time that a given location is exposed to extreme winds depends on the size of the storm and the speed at which it is moving. During a direct hit from a tropical cyclone, an area may endure high winds for several hours. In that time even the most solidly constructed buildings may begin to suffer damage. The force of the wind increases rapidly with its speed. Sustained winds of 100 km (62 miles) per hour exert a pressure of 718 pascals (15 pounds per square foot), while an approximate doubling of wind speed to 200 km (124 miles) per hour increases the pressure almost fivefold to 3,734 pascals. A building with a large surface area facing the wind may be subjected to immense forces. Some of the local variability in damage that is often observed during tropical cyclones is due to the direction that buildings face relative to the prevailing wind.

龙卷风（Tornadoes）

热带气旋中心附近的持续强风会造成严重破坏，与这些风暴相关的另一种风灾是龙卷风。大多数达到风暴强度的热带扰动在登陆时都会伴有龙卷风。龙卷风的数量各不相同，但大约75%的热带气旋产生的龙卷风少于10个。

龙卷风是如何产生的尚不清楚，但地表摩擦可能起了作用，它使热带气旋登陆时风速减慢，地表附近的风速降低而高处的风速受的影响较小，从而形成低空的水平旋转，这就是龙卷风。在上升气流的作用下，龙卷风会向垂直方向倾斜，从而产生龙卷风所需的集中的旋转。

The intense sustained winds present near the centre of tropical cyclones are responsible for inflicting heavy damage, but there is another wind hazard associated with these stormstornadoes. Most tropical disturbances that reach storm intensity have tornadoes associated with them when they make landfall. The number of tornadoes varies, but about 75 percent of tropical cyclones generate fewer than 10.

How the tornadoes are generated is not clear, but surface friction probably plays a role by causing the wind to slow as the tropical cyclone makes landfall. Wind speeds near the surface decrease while those at higher levels are less affected, setting up a low-level horizontal rotation that becomes tilted into the vertical by updrafts, thus providing the concentrated spin required for a tornado.

阵风、下沉气流和漩涡（Gusts, downbursts, and swirls）

除龙卷风外，热带气旋还会产生其他局部的风灾。当热带气旋登陆时，表面摩擦会降低风速，但会增加湍流，这使得高空快速移动的空气被输送到表面，从而增加了阵风的强度。还有证据表明，热带气旋下沉气流是由空气蒸发冷却驱动的。这些下沉气流与强雷暴时可能出现的微爆类似，其风向通常与气旋的风向不同，因此可以识别。与热带气旋相关的其他小规模风的特征是漩涡，这些漩涡非常小，强度大，持续时间短，出现在嵌入眼墙的对流塔下，因为峰值风仅持续几秒钟，所以不被归类于龙卷风。漩涡可按逆时针或顺时针方向旋转，峰值风估计接近每小时320千米（200英里）。

In addition to tornadoes, tropical cyclones generate other localized damaging winds. When a tropical cyclone makes landfall, surface friction decreases wind speed but increases turbulence; this allows fast-moving air aloft to be transported down to the surface, thereby increasing the strength of wind gusts. There is also evidence of tropical cyclone downbursts, driven by evaporative cooling of air. These downbursts are similar to microbursts that may occur during severe thunderstorms. The winds associated with them typically flow in a different direction than those of the cyclone, allowing them to be identified. Other small-scale wind features associated with tropical cyclones are swirls. These are very small, intense, and short-lived vortices that occur under convective towers embedded in the eyewall. They are no classified as tornadoes because their peak winds last only a few seconds. Swirls may rotate in either a counterclockwise or a clockwise direction, and their peak winds are estimated to approach 320 km (200 miles) per hour.

风暴潮（The storm surge）

在沿海地区，风暴潮，即海平面的上升，往往是与热带气旋相关的最致命的现象。伴随强热带气旋而来的风暴潮可高达6米（20英尺）。大部分风暴潮是由眼墙中的强风与海面之间的摩擦造成的，这种摩擦会使海水顺着风吹的方向堆积起来。

风暴潮的一小部分是由于热带气旋的气压变化造成的，风暴边缘的大气压力较高，导致气压最低的风眼下的海面隆起。然而，由于水的密度比空气的密度大，这种气压引起的浪涌幅度很小，风暴直径范围内气压下降100毫巴会导致风眼下的海面上升约1米（3英尺）。

风暴潮造成的洪水是热带气旋登陆造成死亡的主要原因。风暴潮造成死亡的极端例子包括1900年德克萨斯州加尔维斯敦的6000人死亡，以及1970年东巴基斯坦（现孟加拉国）估计高达9米（30英尺）的风暴潮造成的30多万人死亡。

In coastal regions an elevation of sea level—the storm surgeis often the deadliest phenomenon associated with tropical cyclones. A storm surge accompanying an intense tropical cyclone can be as high as 6 metres (20 feet). Most of the surge is caused by friction between the strong winds in the storm’s eyewall and the ocean surface, which piles water up in the direction that the wind is blowing.

A small part of the total storm surge is due to the change in atmospheric pressure across the tropical cyclone. The higher atmospheric pressure at the edges of the storm causes the ocean surface to bulge under the eye, where the pressure is lowest. However, the magnitude of this pressure-induced surge is minimal because the density of water is large compared with that of air. A pressure drop of 100 millibars across the diameter of the storm causes the sea surface under the eye to rise about 1 metre (3 feet).

Flooding caused by the storm surge is responsible for most of the deaths associated with tropical cyclone landfalls. Extreme examples of storm surge fatalities include 6,000 deaths in Galveston, Texas, in 1900 and the loss of more than 300,000 lives in East Pakistan (now Bangladesh) in 1970 from a storm surge that was estimated to be 9 metres (30 feet) high.

降雨量（Rainfall）

热带气旋通常会给其影响的地区带来大量降雨，大部分与眼墙的深对流云和风暴边缘的雨带有关。降雨量通常为每小时几厘米，短时降雨量更高。据报道，一些地区的总降雨量达到500~1000毫米（20~40英寸）的情况并不少见。这样的降雨量可能会超过排水系统的承受能力，导致局部地区洪水泛滥。

Tropical cyclones typically bring large amounts of water into the areas they affect. Much of the water is due to rainfall associated with the deep convective clouds of the eyewall and with the rainbands of the outer edges of the storm. Rainfall rates are typically on the order of several centimetres per hour with shorter bursts of much higher rates. It is not uncommon for totals of 500 to 1,000 mm (20 to 40 inches) of rain to be reported over some regions. Rainfall rates such as these may overwhelm the capacity of storm drains, resulting in local flooding.

气旋的命名 Naming a cyclone

太平洋和印度洋盆地的风暴是根据世界气象组织下属的区域委员会建立的系统命名的。每个区域拥有自己的名称清单，对清单的修改（如删除一个名称）需要在正式会议上批准。

Pacific and Indian basin storms are named according to systems established by regional committees under the auspices of the World Meteorological Organization. Each region maintains its own list of names, and changes to the list (such as retiring a name) are ratified at formal meetings.

跟踪和预测Tracking and forecasting

20世纪上半叶，热带气旋的识别主要基于天气条件的变化、海面状况以及已受风暴影响地区的报告，这种方法几乎没有时间来发出预警，导致死亡人数居高不下。随着时间的推移，观测网络和技术也在不断改进，20世纪60年代，气象卫星的出现大大提高了对热带气旋的早期探测和跟踪能力。

一组地球静止卫星（停留在地球固定位置上空的卫星）由多个国家运营，每颗卫星都以可见光和红外波长连续显示地球表面的情况，后者对跟踪热带气旋的发展阶段最为重要。卫星图像不仅可以显示风暴的位置，还可以用来估计风暴的强度，因为特定的云层模式是特定风速的特征。

虽然卫星图像提供了热带气旋位置和强度的一般信息，但有关风暴强度和结构的详细信息必须通过飞机直接获取，这些信息对于提供尽可能准确的警报至关重要。在许多情况下，热带风暴的命名或其从热带风暴升级为热带气旋的依据是飞机观测数据提供的。

预报员利用卫星和飞机提供的各种观测信息来确定飓风的当前位置和强度，一旦确定热带气旋可能登陆，就会对可能受影响的地区发出警告，在特别易受影响的地区，可根据观察结果开始撤离。

In the first half of the 20th century the identification of tropical cyclones was based on changes in weather conditions, the state of the sea surface, and reports from areas that had already been affected by the storm. This method left little time for advance warning and contributed to high death tolls. Observation networks and techniques improved with time; with the advent of weather satellites in the 1960s, the early detection and tracking of tropical cyclones was greatly improved.

An array of geostationary satellites (those that remain over a fixed position on Earth) is operated by a number of countries. Each of these satellites provides continuous displays of Earth’s surface in visible light and in infrared wavelengths. It is the latter that are most important in tracking the stages of tropical cyclone development. Satellite images not only show a storm’s location but also can be used to estimate its intensity because certain cloud patterns are characteristic of particular wind speeds.

Although satellite images provide general information on the location and intensity of tropical cyclones, detailed information on a storm’s strength and structure must be obtained directly, using aircraft. This information is essential in providing the most accurate warnings possible. In many cases, the naming of a tropical storm, or its upgrade from tropical storm to tropical cyclone, is based on aircraft observations.

Forecasters use a variety of observational information from satellites and aircraft to determine the current location and intensity of the storm. Once forecasters have determined that a tropical cyclone is likely to make landfall, warnings are issued for the areas that may be affected. In especially vulnerable areas, evacuation may be initiated based on the watch.