英文版 地理_厄尔尼诺和拉尼娜现象.pptVIP

Everybody wants to know what the weather is going to do each day-- and with good reason, considering the many destructive storms and tornadoes that have hit our earth  In 1997-1998, the weather effect known as El Ni?o has been a favorite topic of conversation, as it seems to have caused most of those weather woes. But just what is El Ni?o? Its a periodic disruption of the Pacifics climatic system. Whats in a name? The term “El Ni?o,” which refers to the Christ child（圣婴 ）, was given to this weather pattern by Peruvian（秘鲁的） fishermen who noticed that warm currents arrived one year at Christmastime. On average, El Ni?o occurs every two to seven years. Walker circulation cell(沃克环流圈) Usually, the wind blows strongly from east to west along the e’quator(赤道) in the Pacific. This actually piles up (堆积 )water (about half a meters worth) in the western part of the Pacific. In the eastern region, deeper water(which is colder than the sun-warmed surface water) gets pulled up from below to replace the water pushed west. So, the normal situation is warm water (about 30 C) in the west, cold (about 22 C) in the east. During an El Ni?o period, the winds pushing that water around weaken. As a result, some of the warm water piled up in the west slumps back down to the east, and not as much cold water gets pulled up from below. Both these tend to make the water in the eastern Pacific warmer. But it doesnt stop there. The warmer ocean water then affects the winds by lessening their strength! So if the winds get weaker, then the ocean continues to get warmer. This positive feedback is what makes El Ni?o grow. What?! El Ni?o has a sister! La Ni?a is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific, as compared to El Ni?o, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific. Typical La Ni?a Impacts: La Ni?a tends to bring nearly opposite effects of El Ni?o. Wetter than normal conditions across th