观察这次澳大利亚山火产生的大量烟雾乌云
Watch Australia's Wildfires Spawn Massive Smoky Thunderclouds
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2020-01-13 12:13
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火星译客

The wildfires currently tearing through Australia aren't just unprecedented—they're catastrophic, as one fire researcher put it. Climate change and fierce heat waves have dried the landscape into swaths of tinder, and all it takes is a single spark to unleash wildfires so powerful.

正如一位火灾研究人员所说,目前席卷澳大利亚的野火不仅是史无前例的,而且是灾难性的。变化的气候和猛烈的热浪把这片土地变成了一片火海,而引发如此猛烈的野火只需要一点微小的火星。

Researchers have been catching Australia's fires in the act of producing pyrocumulonimbus clouds, or pyroCbs. These ominous phenomena take two ingredients: a mass of hot air that produces an updraft, in this case columns of smoke-filled air. And two, they need an unstable atmospheric environment that allows the updraft to continue rising higher than it otherwise would, says Scott Bachmeier, a research meteorologist at the University of Wisconsin, Madison. As the mass climbs higher, the smoky air cools and forms into a pyrocumulonimbus cloud, a soup of water and smoke particles towering miles into the sky. (Though to be clear, the cloud itself isn't on fire.)

研究人员一直在追踪澳大利亚的火灾,以及火灾产生高温积雨云(pyroculonimbus clouds,简称pyroCbs)。威斯康星大学麦迪逊分校的气象学专家,斯科特巴赫梅尔称,这些可怕的现象有两种成因:第一,一团产生上升气流的热空气,这种热空气类似一个充满烟雾的空气柱。第二,它们需要一个不稳定的大气环境,使上升气流继续上升,高于它本来应有的高度。随着质量的上升,烟雾弥漫的空气冷却并形成一团焦积雨云,一团水和烟雾颗粒的混合物高耸在数英里外的天空中。(要说清楚的是,云本身并没有着火。)

Video: Scott Bachmeier/University of Wisconsin-Madison 

视频:Scott Bachmeier/威斯康星大学麦迪逊分校

If you take a look at the GIF above, you can see two pyroCbs sprouting, captured by satellite in the infrared spectrum. In the top panel we see the fires, and the bottom panel shows cloud-top temperatures. Red pixels indicate the heat of the wildfire, whereas violet indicates a cloud-top temperature of -70 degrees C. The colder it is, the higher the altitude. The low temperatures reveal that a pyroCb is soaring into the sky.

如果你看一看上面的GIF,你可以看到两个高温积雨云正在形成,这是由卫星在红外光谱中捕捉到的。在上面的面板上,我们看到了火灾,下面的面板显示了云顶的温度。红色像素表示野火的热度,而紫色则表示云顶温度为-70摄氏度。温度越低,则说明海拔越高。这个低温表明一朵高温积雨云正飞向天空。

And another one forming here.

另一朵高温积雨云正在这里形成。

Video: Scott Bachmeier/University of Wisconsin-Madison 

视频:Scott Bachmeier/威斯康星大学麦迪逊分校

For hundreds of millions of years, thunderclouds and their lightning have been natural partners to fire. Any wildfire is likely to spread when strong surface winds carry embers perhaps miles ahead. “But what's carried aloft by the pyroCb updraft are copious amounts of smoke particles, which then get carried up to or even ejected above the pyroCb cloud top,” says Bachmeier. If wildfires are sprouting pyroCbs that strike the landscape with lightning without also dumping water, the conflagration will spread all the more readily.

千百万年来,雷云和它们的闪电一直是火的天然伙伴。任何野火都有可能在地面强风作用下蔓延数英里。巴赫梅尔说:“但是高温积雨云携带到高空的是大量的烟雾颗粒,而后这些烟雾颗粒上升到高温积雨云云顶,甚至喷射到高温积雨云云顶之上。”。如果野火初露势头,而闪电袭击此处,同时又没有降雨,大火就会更容易蔓延。

So a pyroCb isn't directly floating embers downwind to start new fires, but it could well be depositing lightning strikes into dry vegetation. The cloud could also contribute extremely strong downdrafts that push embers along at the surface. In addition, pyroCbs deposit smoke pollutants miles high in the upper atmosphere. Luckily, that keeps at least some of the wildfire's smoke away from human lungs.

因此,高温积雨云并不是直接用随风漂浮的余烬引发新的火灾,但这些灰烬很可能会因为雷击而沉积到干燥的植被中。云层也会产生强烈的下沉气流,推动地表的灰烬。此外,高温积雨云会在高层大气中沉积数英里高的烟雾污染物。幸运的是,这至少让一些野火的烟雾远离了人类的肺部。

Scientists are also monitoring the movement of the wildfires' smoke from space. In this image, the massive plume of brown-gray smoke is at lower left.

科学家们也在利用卫星监测野火烟雾的运动。在这张图片中,巨大的棕灰色烟雾在左下方。

Video: Scott Bachmeier/University of Wisconsin-Madison 

视频:Scott Bachmeier/威斯康星大学麦迪逊分校

And in this haunting clip, the GOES satellite shows that the high-altitude smoke has actually crossed the Pacific and reached South America. (Red flashes being smoke detection.)

而在这段令人难忘的视频中,GOES卫星显示,高空浓烟实际上已经穿越太平洋,到达南美。(红色闪光表示探测到的烟雾。)

Video: Scott Bachmeier/University of Wisconsin-Madison 

视频:Scott Bachmeier/威斯康星大学麦迪逊分校

These fires have been devastating for the people and wildlife of Australia. But they also give scientists the opportunity to watch in real-time as smoke spews off the continent. The goal of studying pyroCbs, Bachmeier says, is to better understand the behavior of smoke: to see what impact it “is having on short-term weather near and downstream of the fires, and perhaps the smoke's long-term effects on climate change." How much carbon, for instance, might pyroCbs contribute to the atmosphere? “It's a relatively young science, but interest in the phenomenon is rapidly growing.”

这些火灾对澳大利亚的人民和野生动物造成了毁灭性的破坏。但它们也给科学家们提供了一个机会,让他们能够实时观察到大陆上喷出的烟雾。Bachmeier说,研究高温积雨云的目的是为了更好地了解烟雾的作用机理:看看它“对火灾附近和下游的短期天气有什么影响,也许还能预测烟雾对气候变化的长期影响”。例如,高温积雨云可能会对大气贡献多少碳?“这是一门相对年轻的科学,但科学家们研究这一现象的兴趣正在迅速增长。”

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