El-nino


There's trouble in the air. Specifically, in the west coast of the Americas, where the sea surface has been heated to abnormal extremes by an ominous, intermittent flood of hot water called El-Nino. The term. "El-Nino," which means "the child," was originally in reference to a warm current arriving annually during the Christmas season off the coast of Peru and Ecuador. The term was later restricted to the particularly strong periodic warmings that disrupt the local fish and bird populations, and extend westward across the equatorial Pacific Ocean to near the date line. What is an El-Nino? El-Nino is the warming of the Pacific waters that is brought about from time to time by naturally occurring oscillations in atmospheric pressure and ocean movements in th equatorial Pacific. The warmer ocean pumps more energy and moisture into the atmosphere and this in turn alters wind and rainfall patterns around the world. The atmospheric cirulation also changes when the sea-surface temperatures in the eastern tropical Pacific rise above normal. In normal, non-El Nino conditions, the trade winds blow towards the west across the tropical Pacific. These winds pile up warm water in the west Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Ecuador. The sea surface temperature is about 8 degrees C higher in the west, with cool termperatures off South America, dut to an upwelling of cold water from deeper levels. This cold water is nutrient-rich, supporting high levels of primary productivity, diverse marine ecosystems, and major fisheries. Rainfall is found in rising air over the warmest water, and the east Pacific is relatively dry. Warming of the Pacific waters is not the only thing El-Nino is to be blames for. The current El-Nino warming has been so strong, is has added noticeable zip to atmospheric winds and slowed Earth's spin, suggest scientists who track the planet's rotation. El-Nino exert these profound effects by speeding up the eastward movement of the atmosphere, relative to the solid body of te planet. The change shows up in the analyses of the atmosphere's angular momentum-a property comparable to the momentum of a spinning tire. "From mid-March through late November 1997, the angular momentum remaind significantly above average" (Monastersky 45-46). During non-El Nino years, winds in the tropics blow from east to west, whereas winds over the rest of the globe travel from west to east. Combined, they give the atmosphere a net eastward momentum. The atmosphere routinely trades some of this momentum back and forth with the solid Earth as winds drag across the surface of the planet and push against the mountain ranges. In the Northern Hemisphere's winter, the atmosphere speeds up and Earth slows. In summer, the reverse happens. El-Nino also boosts the atmosphere's angular momentum by slowing down the tropical easterlies and speeding the westerlies outside the tropics. As the atmosphere speeds up during El Nino, earth itself slows down to conserve the combined angular momentum. John M. Gipson of NASA's Goddard Space Flight Center in Greenbelt, Md., has tracked the planet's spin by monitoring changes in the length of the day. Over a typical year, the day shortens and lengthens by roughly 1 millisecond, mostly because of shifts in atmospheric angular momentum. During the current El Nino, the day has grown longer by four-tenths of a millisecond. Last year, Earth squeaked past the previous record high for globally averaged temperatures, continuing a balmy trend that has made this decade the hottest in more than a century of temperature data. "All of us are pretty happy with the agreement of the different methods," says Thomas R. Karl of the National Climate Data Center (NCDC) in Asheville, NC. "There are differences [among the teams' findings], but they are small" (Karl 38). Earth's land and ocean surface last year was 0.42 degrees C warmer than the long-term average of 16.5 degrees C for the reference period 1961 through 1990, says Karl. The NCDC team analysed data from more than 5,000 land stations and from water temperature reading collected by satellite sensors, buoys, and ships. 1997 came in almost a tenth of a degree warmer than the previous record years, 1990 and 1995, which were virtually identical in the NCDC data. Researchers play down the differences among these three years becuase the uncertainties in the figures exceed the gaps between them. The important message is that 9 of the top 10 warmest years on record have occurred since 1987. Such evidence adds weight to arguments that humans are altering climate in noticable ways. It is likely that greenhouse emissions are playing a role in the sustained upward trend in temperatures. El Nino helped push Earths temperature into a new territory last year by producing a vast pool of warm water in the equatorial Pacific Ocean. Even without El Nino, however, global temperatures would have remained high. During the first few months of 1997-before El Nino blossomed-the land surface was already quite warm. In contrast to the global pattern, eastern North America stayed ...