Wednesday, 4 November 2009

News Article: If You Must Know: How Did the Chinese Create Snow?

Quoting entirely from the original website:

If You Must Know: How Did the Chinese Create Snow?

"Everybody complains about the weather," the old saying goes, "But nobody does anything about it." That is, until now. A Nov. 1 snowfall in Beijing - the city's earliest since 1987 - is due, Chinese scientists say to a campaign of "cloud-seeding" to encourage precipitation. If true, it's the wettest success yet in a long-standing effort to bring moisture artificially to the parched northern regions of China. So how'd they do it? (See pictures of the science of snowflakes.)

Beijing's first snow of season 'artificially induced'AFP – Pedestrians make their way across the snow in Tian'anmen Square in Beijing on November 1. Chinese …

For those who haven't had a meteorology class since middle school, a quick review of Weather 101: Colder air encourages precipitation, so when the temperature drops at high altitude, water naturally condenses out of the air. Clouds are formed when this moisture, suspended in tiny droplets or crystals, meets a condensation nuclei - small particles of dust or ice that are blown about the upper atmosphere. Without these small particles, clouds can't form.

The method of cloud-seeding used by the Chinese involves dosing the atmosphere with silver iodide, a chemical solution either dropped from planes or shot up from the ground. (Other methods use salt or dry ice.) The silver iodide particles supercharge cloud formation, as they act as excellent condensation nuclei. Once clouds form, they also start a positive feedback effect. As droplets freeze and are added to the cloud, they release their heat, creating an updraft which draws additional moisture from the ground into the atmosphere.

That's the theory, anyway. The effectiveness of cloud-seeding is still disputed, because it's difficult to say with any certainty that cloud-seeding is responsible for a storm rather than Mother Nature. But if you choose to believe in cloud-seeding, the Chinese scientists may have even overdone it. The snowstorm lasted for 11 hours, disrupting flights in and out of Beijing and hampering shipping off the Chinese coast. Still, expect few complaints from the generally dry region; it's the most accumulation the city's seen in a decade, and further proof the Chinese may be becoming the world's best at managing weather. In a 2008 experiment, scientists seeded clouds in advance of the Beijing Olympics, successfully ensuring clear skies for the opening ceremony.

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Vocabulary:

cloud-seeding (n) -- producing clouds by using chemicals

precipitation (n) -- rain or snow

long-standing (adj) -- long-time

parched (adj) -- (of land or crops) very dry

disputed (adj) -- disagreed

accumulation (n) -- collection of water from rain or snow

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If you have been paying attention to the weather these days, you would have realised that this year, the rainfall in Hong Kong has been very little. In fact, we are soon facing a very bad drought due to 14% less rainfall in the first 10 months of the year in the entire Guangdong[1]. As you should know, most of our drinking water comes from Dongjiang and that is provided by the Guangdong provincial government under contract signed, but when there is not enough for the people in Guangdong, there won't be enough for people in Hong Kong. Sooner or later, Hong Kong may also need to ration (to limit the use of) water.

I was actually hoping for the previous two typhoons to hit Hong Kong, because that could have brought us a lot of water (and hitting concrete city like Hong Kong is better than hitting other less storm-protected countries), but unfortunately, they never came. If silver iodide(AgI) works for Beijing[2], we might still have a chance to improve the situation, but it all looks bleak (almost hopeless) when dry wind is blowing from the north during our winter time. I guess we will need to see what happens when spring comes, when the air gets a little wetter.

So you see how much global warming can change the planet? We must do our parts and heal the world!