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发表于 2010-11-9 23:38:33
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复习笔记-lecture的points
第三篇气象学 Firstof all, let’s look at why temperaturestend to be higher in city than in the rural area. This happensbecause almost 50 percent of the urban areas are comprised of hard surfaces like pavedstreet, parking lot, buildings and roof tops. As the result, any amount of rainfall is quickly repelledby this service and carried away by storm drains and gutters. Especially waterjust doesn’t have the chance to stand around until evaporate and during theprocess of the evaporation that heat is removed from the air. So in citieswhere there is lessevaporation temperatures will be higher and of course there are also beissue of added heatcoming from building heating system, from industry, cars and even human body.Even we being in the city itself, temperatures can vary significantly. For example, in winter,streets that get a lot of use will be a lot of use will be 2 or 3 degree warmer than lesstravel streets. In place where car sits for a while like a stoplight can be inanother 3 degrees warmer. On the other hand, low spots in the city where coldair collect will be much colder than higher places. Rain and snowfall are also affected byurbanization. Cities tend to get quiet less snowfall than the surroundingcountryside because of warmer temperature in the city. But rainfall in the citycan be 5 to 10 percent higher. That happens because of two factors. First, the warmer city temperature,second the larger numberof dust particles in the urban air. It seems dust particles areimportant requirement for condensation. The water vapor in the atmosphere isable to change to liquid by planning to dust particles suspended in the air. Sowhere there’s the higher number of dust particles, condensation take place moreeasily. That’s why fogsand clouds are usually more frequent around the city. Once condensationtakes place the rainfall is not far behind. In the London area, for example,thunderstorms can produce 30 percent more rainfall than the surroundingcountryside. Some urbanclimatologists go so far as they argue that they can see a patternincreasing the rainfall during the workweek. They believe rainfall amounts aresmall aroundthe weekend because the dust particle generated by cars and factories arereduced. |
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