非洲沙塵揚起 減弱了大西洋的颶風 | 台灣環境資訊協會-環境資訊中心

非洲沙塵揚起 減弱了大西洋的颶風

2006年10月16日
ENS美國,威爾康辛州,麥迪遜報導;楊璧如、丁秋仁編譯;莫聞審校

2005年10月的威瑪颶風(圖片來源:NASA)根據美科學家最近研究指出,遠拂自撒哈拉沙漠的塵土有助於降低大西洋颶風強度。研究發現,當撒哈拉沙漠塵暴頻繁並吹向非洲西岸時,颶風活動的次數會減少;相對地,若塵暴屈指可數,颶風次數則較為頻繁。

研究學者表示,如果他們能確定證明沙塵暴協助減輕颶風,氣象預報員將可開始追蹤大氣中的塵土,並將之納入預測變因。這份研究於10日在《地球物理研究通訊》期刊中發表。

研究小組分析由1981至2006年這25年間的衛星資料,並研究其相關性。這項研究反應出對沙塵衝擊環境的關注提升。在某些年,上百萬噸的沙塵由撒哈拉沙漠升起,並飄過大西洋,有時這個過程僅需5天。

「人們並不了解沙塵潛在的衝擊,直到我們研究衛星資料後,才知道這些沙塵暴具有多大的威力,」報告的主筆作者艾文表示。他是威士康辛麥迪遜大學氣象衛星研究合作研究院(CIMSS)的研究員。「在波多黎各的夏季,有時因灰塵在天空中漂浮,使得夕陽顯得格外美麗。這些沙塵都是來自於非洲。」

當炎熱的沙漠空氣遇上撒哈拉南方薩赫勒區域的冷空氣,使得沙塵升起,並形成風。當粒子迴旋而上時,強勁的風勢將它們吹向西方,進入北大西洋。沙塵暴主要在夏季和冬季形成,但是有些時候並不會形成,其中之原因不明。

研究人員表示,這些研究結果是有道理的,因為颶風形成需要熱和濕氣加速,因此空氣中乾燥的沙塵分布層,很可能有助於降低颶風的形成。報告的共同作者,也是CIMSS科學家凡登解釋說,這也意味沙塵暴可能具有改變颶風方向的潛力,使其更往西移動,若果真如此,很不幸地,美國會有更多機會遭受颶風襲擊。 

African Dust May Mute Atlantic Hurricanes
MADISON, Wisconsin, October 11, 2006 (ENS)

Dust from the Sahara Desert may help reduce the intensity of Atlantic hurricanes, according to new research by U.S. scientists. The study found less hurricane activity in years when stronger dust storms rose from the Sahara Desert and blew off Africa's western coast and more intense hurricanes in years when dust was relatively scarce.

The researchers said that if they can conclusively prove that dust storms help to squelch hurricanes, weather forecasters could one day begin to track atmospheric dust, factoring it into their predictions for the first time. The study was published Tuesday in the journal "Geophysical Research Letters."

The research team analyzed 25 years of satellite data - dating from 1981 to 2006 - and noticed the correlation. The study reflects increasing attention to the environmental impact of dust. In some years, many million tons of sand rise up from the Sahara Desert and float right across the Atlantic Ocean, sometimes in as few as five days.

"People didn't understand the potential impact of dust until satellites allowed us to see how incredibly expansive these dust storms can be," said lead author Amato Evan, a researcher at UW-Madison's Cooperative Institute for Meteorological Satellite Studies (CIMSS). "Sometimes during the summer, sunsets in Puerto Rico are beautiful because of all the dust in the sky. Well, that dust comes all the way from Africa."

The dust rises when hot desert air collides with the cooler, dryer air of the Sahel region, just south of the Sahara, and forms wind. As particles swirl upwards, strong trade winds begin to blow them west into the northern Atlantic. Dust storms form primarily during summer and winter months, but in some years - for reasons that aren't understood - they barely form at all.

The findings of the study make sense, the researchers said, because dry, dust-ridden layers of air probably helps to "dampen" brewing hurricanes, which need heat and moisture to fuel them. That effect, explained coauthor and CIMSS research scientist Christopher Velden, could also mean that dust storms have the potential to shift a hurricane's direction further to the west, which unfortunately means it would have a higher chance of hitting the United States.