NASA从太空看厄尔尼诺现象的影响

发布时间：2008-04-04 00:00:00 点击：430

[导读] NASA的数据帮助科学家们更多地了解厄尔尼诺现象的机制，地球气候和天气系统的相互影响以及这些周期性气候事件是如何影响我们的日常生活的。

中国科技网12月21日报道（张微 编译）今年冬天的气候模式与以往有很大的不同，这是因为赤道东太平洋异常温暖的海水造成的，这一事件就是我们常说的厄尔尼诺现象。受厄尔尼诺现象影响，预计加利福尼亚降雨量将增加，而澳大利亚的降雨量减少。这次的厄尔尼诺现象自去年夏天开始，太平洋已经经历了热带风暴的增加和浮游植物的减少。

厄尔尼诺现象是由于异常的风和海洋环流所引发的，是一种不定期发生的天气现象。虽然起源于赤道太平洋，但是厄尔尼诺现象却有着深远的影响。在全球范围内，它影响降雨、海洋生产力、大气层气体和风暴。在局部范围，它影响水供给，渔业和食品来源。

由于其科学的专业知识和拥有十多个地球观测卫星，使得NASA成为观察厄尔尼诺现象对局地和全球影响的领导者。NASA的数据帮助科学家们更多地了解厄尔尼诺现象的机制，地球气候和天气系统的相互影响以及这些周期性气候事件是如何影响我们的日常生活的。

发现厄尔尼诺现象的关键影响，以及NASA如何从太空研究这些影响：

降雨

厄尔尼诺现象经常会加快降雨模式的变化，在世界各地导致特大洪水、山体滑坡和干旱。

在正常年份，非厄尔尼诺条件下，赤道附近的太平洋信风从东吹向西——从南美洲吹向东南亚——带动温暖的表层海水一起移动。温暖的海水蒸发，增加空气的湿度，产生了南亚地区每年的季风。受厄尔尼诺现象影响，信风会停下来重新回到东部，东南亚和澳大利亚的附近海水就会比正常年份的温度低，这往往会导致干旱的发生。而南美洲的海水仍然比较温暖，这就会激发风暴和洪水。在厄尔尼诺现象肆虐期间，加利福尼亚和美国南部也往往会遭受更多的降雨。

全球降水测量任务(GPM)，NASA和日本宇航局合作，利用多个卫星的数据，跟踪全球降水量，并建立了全球降水分布图，每半小时更新数据。科学家们利用卫星数据研究降雨和降雪模式变化，更好地了解地球气候和天气系统。

飓风

厄尔尼诺也会影响热带风暴的形成。厄尔尼诺与大西洋飓风的关联性较小，更多地是引发太平洋的飓风和台风。

热带气旋经过水温较暖地带会增强，遇到水温较凉水域会平息。在厄尔尼诺影响期间，正常的上升流(指海水由较深层上升到较浅层的过程)，在赤道东太平洋受到抑制。因此太洋的平均温度比正常年份高，这有助于热带风暴的形成。

2015年北太平洋飓风季特别频繁，部分原因就是今年的厄尔尼诺现象。NASA在太空中的一套仪器，可以研究风暴的各个方面，例如降雨活动，云层高度，地表风速和海洋热量。

海洋生态

厄尔尼诺不仅影响陆地，它还影响海洋食物网，体现在海洋颜色的变化——海水颜色受到微小植物，沉积物和有色溶解有机物的影响。在厄尔尼诺影响期间，渔业崩溃以及食物链高层动物缺乏食物，特别是在赤道东太平洋。

在正常年份，赤道东太平洋的深海海水上涌，将营养丰富的低温海水带到大洋表面。当上涌的海水到达表面时，丰富的养分和阳光会帮助浮游植物(海洋食物网最底层的微小藻类)生长。在厄尔尼诺影响期间，海水上涌受到抑制，大洋深处富含营养的海水不再上涌到表层，从而降低的浮游植物的数量。由于食物减少，鱼类种群数量下降，严重影响渔业产业。

NASA卫星对海洋颜色的测量是通过海水表层叶绿素(帮助浮游植物进行光合作用的一种绿色色素)，观察厄尔尼诺影响期间赤道东太平洋总的叶绿素含量。科学家们将在当前厄尔尼诺影响期间，继续使用SeaWIFS监测海洋颜色的变化。

臭氧

厄尔尼诺也会影响臭氧，这是一种对地球系统和人类健康都起着重要作用的化合物。在地表，臭氧影响空气质量。在对流层，臭氧是一种温室气体，阻止热量逃逸到太空，从而保持地表温度。

当强烈的厄尔尼诺现象发生时，热带环流会发生重大变化，导致大气层气体如臭氧的重新分布。这些变化发生在整个对流层垂直方向上发生，在厄尔尼诺影响期间，导致印度尼西亚臭氧水平升高，而太平洋中部和东部地区的大部分热带地区臭氧水平下降。

科学家们利用美国宇航局的Aura卫星测量对流层中的臭氧浓度。凭借十多年的Aura卫星数据，研究人员能够将厄尔尼诺现象和人类活动影响如火灾，引起的臭氧浓度变化区分开来。

大部分臭氧存在于地球的平流层(高于飞机飞行的高度)，在这里臭氧扮演者盾牌的角色，吸收和屏蔽来自太阳的、对人类有害的紫外线。NASA从20世纪70年代末就一直通过卫星在监测平流层的臭氧浓度和臭氧层，而且会继续利用Aura卫星，以及NASA与美国国家海洋和大气管理局的联合任务，Suomi国家极地轨道伴随卫星，对臭氧进行监测。虽然厄尔尼诺现象对对流层臭氧的影响更大，但是科学家们正在研究它如何改变了平流层的臭氧浓度，有时热带地区臭氧浓度的改变会达到15%左右。

火灾

厄尔尼诺现象的影响，会改变整个热带地区的降水和火灾模式。在厄尔尼诺肆虐的年份里，火灾的数量和强度都会增加，尤其是那些湿润地区突遇干旱的情况下。在过去的厄尔尼诺事件中，印度尼西亚、中美洲以及亚马逊南部和中部地区都比往年的火灾次数频繁。

火灾破坏热带雨林，农田和牧场，他们还排放温室气体二氧化碳和甲烷，这些气体在大气中的吸收热量，导致全球变暖。例如，在2002年和2006年的厄尔尼诺事件中，亚洲赤道地区的火灾排放气体比正常年份增加10倍。

美国宇航局Aqua 和Terra卫星上的中分辨率成像光谱仪(MODIS)提供了全球火灾活动图像。MODIS是专门用来观察火灾的，能够帮助科学家们辨别明火和闷烧灰烬。MODIS的时间序列数据(2000年至今)覆盖了一次强烈的厄尔尼诺事件，能够将火灾活动变化与火灾排放到大气中的粒子与气体数量联系起来。

How NASA sees El Nino effects from space

This winter, weather patterns may be fairly different than what's typical—all because of unusually warm ocean water in the east equatorial Pacific, an event known as El Niño. Because of El Niño, California is expected to get more rain, while Australia is expected to get less. Since this El Niño began last summer, the Pacific Ocean has already experienced an increase in tropical storms and a decrease in phytoplankton.

El Niño is an irregularly occurring weather phenomenon created through an abnormality in wind and ocean circulation. While it originates in the equatorial Pacific Ocean, El Niño has wide-reaching effects. In a global context, it affects rainfall, ocean productivity, atmospheric gases and winds across continents. At a local level, it influences water supplies, fishing industries and food sources.

With its scientific expertise and more than a dozen Earth-observing satellites, NASA is a leader in observing the local and global effects of El Niño. NASA data help scientists learn more about the mechanics of El Niño events, the interconnectedness of Earth's climate and weather systems and how our daily lives are affected by these periodic climate events.

Discover some of El Niño's key impacts and how NASA studies them from space:

Rainfall

El Niño often spurs a change in rainfall patterns that can lead to major flooding, landslides and droughts across the globe.

In normal, non-El Niño conditions, Pacific trade winds near the equator blow from east to west—from South America to Southeast Asia—moving warm surface water with them. The warm ocean water evaporates, adds moisture to the air, and produces annual monsoons in the South Asian region. When the trade winds stop and move back east during an El Niño, water near Southeast Asia and Australia is cooler than normal, often leading to drought. Water also remains warm near South America and often spurs storms and flooding. During an El Niño, California and the Southern United States also tend to receive more rain.

The Global Precipitation Measurement mission (GPM), a joint effort of NASA and Japan Aerospace eXploration Agency, tracks precipitation worldwide and creates global precipitation maps updated every half-hour using data from a host of satellites. Scientists use the satellite data to study changes in rain and snow patterns and gain a better understanding of Earth's climate and weather systems.

Hurricanes

El Niño also influences the formation of tropical storms. El Niño events are associated with fewer hurricanes in the Atlantic, but more hurricanes and typhoons in the Pacific.

Tropical cyclones typically grow stronger as they travel over warm water and dissipate over cold water. During El Niño, normal upwelling—the processes that brings colder, deeper water to the ocean surface—is suppressed in the east equatorial Pacific. As a result, the average temperature in the Pacific is warmer than normal and aids the formation of tropical storms.

The 2015 hurricane season in the North Pacific was particularly busy, partially due to this year's El Niño. NASA has a suite of instruments in space that can study various aspects of storms, such as rainfall activity, cloud heights, surface wind speed and ocean heat.

Ocean Ecology

While El Niño affects land, it also impacts the marine food web, as evidenced in the color of the ocean—the hue of the water influenced by the presence of tiny plants, sediments and colored dissolved organic material. During El Niño, fisheries collapse and animals up the food chain starve, specifically in the east equatorial Pacific Ocean.

Under normal, non-El Niño conditions, deep ocean waters upwell in the eastern equatorial Pacific, bringing nutrient-rich, cold water to the surface. When the water reaches the surface, this combination of abundant nutrients and sunlight helps phytoplankton—microscopic algae that form the base of the marine food web—to grow. During El Niño conditions, upwelling is suppressed, and the deep, nutrient-rich waters no longer reach the surface, causing less phytoplankton productivity. With less food, the fish population declines, severely affecting fishing industries.

NASA satellites measure the color of the ocean to derive surface chlorophyll, a pigment in phytoplankton vital for photosynthesis, and observe lower total chlorophyll amounts during El Niño events in the equatorial Pacific Ocean. Scientists will continue to use SeaWIFS to monitor the ocean color during this current El Niño season.

Ozone

El Niño also influences ozone, a compound that plays an important role in the Earth system and human health. At ground level, ozone affects air quality. Higher in Earth's atmosphere in a layer known as the troposphere, ozone is a greenhouse gas, which stops some of the heat from escaping to space and keeps the surface warm.

When a strong El Niño occurs, there is a substantial change in the major east-west tropical circulation, causing a significant redistribution of atmospheric gases like ozone. These changes occur vertically throughout the troposphere, and cause higher ozone levels over Indonesia and lower levels over much of the tropical central and eastern Pacific Ocean during an El Niño.

Scientists use NASA's Aura satellite to measure ozone concentrations in the troposphere. With more than a decade of Aura data, researchers are able to separate the response of ozone concentrations to an El Niño from their response to changes in human activity, such as human-produced fires.

Most ozone is found in Earth's stratosphere—higher than where most planes fly—where it acts as a shield that absorbs and screens humans from most harmful ultraviolet light from the sun. NASA has been monitoring stratospheric ozone and the ozone layer via satellite starting in the late 1970s and continues to make measurements with the Aura satellite as well as Suomi National Polar-orbiting Partnership, a joint satellite mission with the National Oceanic and Atmospheric Administration. Although El Niño has a greater effect on ozone in the troposphere, scientists are learning how it also modifies ozone concentrations in the stratosphere, sometimes changing concentrations in the tropics by about 15 percent.

Fires

El Niño conditions shift patterns of rainfall and fire across the tropics. During El Niño years, the number and intensity of fires increases, especially under drought conditions in regions accustomed to wet weather. During past El Niño events, Indonesia, Central America and the southern and central Amazon experienced more fire activity than normal.

While fires damage rainforests, croplands and grazing lands, they also emit greenhouse gases—carbon dioxide and methane—that trap heat in the atmosphere and contribute to global warming. For instance, during the 2002 and 2006 El Niño events, fire emissions in equatorial Asia increased by a factor of 10 compared to normal years.

NASA's MODIS instruments on the agency's Aqua and Terra satellites provide a global picture of fire activity. MODIS was specifically designed to observe fires, allowing scientists to discern flaming from smoldering burns. The long time series of MODIS data (2000-present) now cover a strong El Niño event, linking estimates of changing fire activity to the amount of particles and gases that fires release into the atmosphere.

来源：中国科技网 作者： 2015年12月21日　13:04

地址：http://www.wokeji.com/guojipindao/dujiabianyi/201512/t20151221_2067578.shtml

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