Glantz, M.H. 1994. The Impacts of Climate on Fisheries. UNEP Environment Library No. 13. Nairobi, Kenya: UN Environment Programme, 36 pp. Glantz, M.H. (Ed.). 1992. Climate Variability, Climate Change and Fisheries. Cambridge, UK: Cambridge University Press, 450 pp. Glantz, M.H., R.W. Katz, and N. Nicholls (Eds.). 1991. Teleconnections Linking Worldwide Climate Anomalies. Cambridge, UK: Cambridge University Press, 535 pp. P.W. Glynn, 1990. Global ecological consequences of the 1982-83 El Nino-Southern Oscillation. Henry F. Diaz and Vera Markgraf (Eds.), 1992. El Niņo: Historical and Paleoclimatic Aspects of the Southern Oscillation S. George Philander, 1990. El Niņo, La Niņa, and the Southern Oscillation Warren S. Wooster and David L. Fluharty, (Eds.), 1985. El Niņo North: Niņo Effects in the Eastern Subarctic Pacific Ocean ______________________________________ El Nino and La Nina Written by Tom Murphree for the Forthcoming Book, "Watching Weather" By Tom Murphree and Mary Miller with the Exploratorioum Written for a Popular Audience Published by Henry Holt, New York, NY, Due out in August 1998 ______________________________________ In the western U.S., Arizona and New Mexico are famous for their dry weather and deserts, while Oregon and Washington are known for their persistent rain and dense forests. But in each of these regions, the average weather and the actual weather can be quite different from each other. During the winter of 1992-1993, the Southwest had exceptionally high rain and snow falls, and major flooding. At the same time, the Pacific Northwest was suffering through a drought. Three years later, during the winter of 1995- 1996, the stories were reversed. Oregon and Washington had extremely heavy rain and snow, and devastating floods, while the Southwest went through one of its worst droughts in years. Despite their differences, these two regions and these two extreme winters had a very important feature in common: Their extreme weather could be traced back to unusual ocean temperatures in the tropical Pacific, over five thousand miles away. During the 1992-1993 winter, the sea surface was cooler than normal in the western part of the tropical Pacific and warmer in the central and eastern part. Since tropical storms tend to form over the warmest water, these changes in the sea surface temperature (SST) led to fewer tropical storms than usual in the western Pacific and more than usual in the central and eastern Pacific. These unusual patterns of SSTs and storms is part of what's called an El Nino event, a closely linked set of unusual conditions in the tropical Pacific ocean and atmosphere that can lead to dramatic weather changes all over the world. The name El Nino means "the boy" and is a shortened version of the Spanish name given by fishermen along the tropical Pacific coast of South America to an ocean warming that they often noticed occurring around Christmas and which they called El Nino de Navidad, or the Christ Child. Scientists have since recognized that this coastal warming is just one small part of a grand rearrangement of the entire tropical Pacific ocean and atmosphere that occurs about every two to seven years. In this rearrangement, the normal patterns of SST and storms change, and remain changed for about a year. During this period of El Ni¤o conditions, major disruptions of the weather and climate far from the tropical Pacific are likely. In the U.S., for instance, El Nino events generally lead to winters that are drier in the Pacific Northwest and wetter in the Southwest. These remote impacts of El Nino events occur when changes in the tropical storms alter the winds blowing into and out of the tropics. The wind changes lead to disruptions in the normal path of the subtropical and midlatitude jets and storm tracks. So during the 1992-1993 winter, an unusually persistent jet and storm track developed that extended from near Hawaii into southern California, Arizona, and New Mexico and brought an exceptional number of warm wet storms out of the subtropics. February 1993 was especially wet in Arizona, leading to flooded homes, the loss of many winter vegetable crops, and a big increase in produce prices. Meanwhile, the jet and storm track that would normally have spent much of the winter bringing rain and snow to Oregon and Washington shifted north into northern British Columbia, leaving the Northwest dry. Three years later, in 1995-1996, the tropical Pacific SST and storm anomaly patterns were reversed, so that the western part was warmer and stormier than normal, while the central and eastern was cooler and less stormy. Again, the atmosphere far away responded to these changes, only this time the responses tended to be reversed. Over the western U.S., the shifts in the jets and storm tracks brought many warm moist winter storms and record amounts of rain and snow to Oregon and Washington, and unusually few and weak storms to the Southwest. The reversed conditions in the tropical Pacific are part of what's called a La Nina event. La Nina is Spanish for the girl and is used by scientists to describe how this event is the opposite of an El Nino event. Like El Ninos, La Ninas also occur about every two to seven years and last about a year. The changes a La Nina brings to the tropical Pacific, and its remote impacts, can be just as large as those during an El Nino. One of the main reasons they are so large is that the tropical Pacific takes up a very big chunk of Earth's surface, extending from Indonesia in the west to South America in the east, and from about 15 south to 15 north --- an area of about 20 million square miles, or more than five times the area of the 48 states. This huge tropical region is a giant fluid solar collecting panel, absorbing much of the solar energy that drives the world's weather. The trade winds that blow westward and toward the equator over the tropical Pacific cause water warmed at the surface to also flow westward. This creates an accumulation of especially warm water near New Guinea and Indonesia, sometimes called the western tropical Pacific warm pool, that at the surface is about 80-85 F year-round. The warm pool is actually a layer that floats on the cooler water below. Near New Guinea, the layer is about 700 feet thick. This warm thick layer makes the tropical western Pacific a tremendous reservoir of energy for the atmosphere. The atmosphere's response to this ready source of energy is some exceptionally dramatic weather, including about 45% of the world's hurricanes, known as severe tropical cyclones or typhoons or in this area. (By comparison, the Atlantic produces only about 12% percent of the hurricanes.) The intense storm activity, including some of the highest rainfall and latent heating in the world, also help create the East Asian jet stream, the strongest jet in the world. The strength of this jet is due mainly to the large temperature gradient between the tropical western Pacific to the south of the jet and cold Siberia to the north (see chapter 3). Many of the storms that travel east with this jet hit the west coast of the U.S. and then head further east across the country, some getting all the way to the east coast or beyond (see chapters 3 and 4). As the trade winds create currents that pile up water in the warm pool, they also remove water from the eastern Pacific, creating a sea surface that's about 1-1/2 feet higher in the west. The trades also produce a sea surface temperature difference, with the eastern waters being about 65-70 F, or 15 F cooler than in the west. The cooler water inhibits storm formation, so the eastern tropical Pacific is a relatively quiet region for tropical storms, compared to further west. This makes the jets that flow north and south of the tropical eastern Pacific relatively weak too. So long as the trades blow normally, these sea level, SST, storm, and jet patterns hold steady. But if the trades change, then lots of rearrangements can happen. The trades are driven by the difference between the high pressure in the eastern Pacific and the low pressure near Indonesia (see chapter 3). At the beginning of an El Nino event, the high pressure in the east, near Tahiti or Easter Island, say, gets lower while the low pressure in the west, near Indonesia, gets higher. So the pressure difference gets smaller and the trades weaken. This causes the tropical western Pacific to cool down while the central and eastern Pacific warms up --- for example, by an eastward flow of water out of the warm pool. As the sea surface temperatures change, so do the tropical storms that feed on warm water. The tropical western Pacific gets less stormy while the eastern gets more stormy. This in turn disrupts the normal midlatitude jet streams and the storm tracks that run along side the jets (see chapter 4). This chain of events for an El Nino event is roughly reversed for a La Nina event, with a La Nina event starting with an increase in the east-west pressure difference and the trades. The links in the chain of events that come before the pressure and trade wind changes aren't yet known. One possibility is a change in Indian Ocean temperatures. Another is a change in the snow fall over Tibet. A large Tibetan snow fall might cause Tibet to stay cool well into the spring and summer, slowing down the development of the Asian summer monsoon and causing weaker trade winds to blow across the Pacific and into Asia. The events by which El Ninos and La Ninas come to an end are also not understood, although some scientists think there may be feedbacks between the tropical Pacific ocean and atmosphere that cause an El Nino to bring itself to an end as it sets the stage for a La Nina to follow, which then brings itself to an end and prepares the stage for the next El Nino. These jet and storm changes that El Ninos and La Ninas trigger outside the tropics are greatest during the winter, when the temperature differences between the warm tropics and the cold higher latitudes are greatest. That's part of why El Ninos and La Ninas have their biggest impacts on the U.S. during November- March. The changes in Earth's weather that occur during El Nino and La Nina events can be very big and very expensive. The cost to the U.S. of the 1982- 1983 El Nino event, one of the biggest on record, has been estimated in the billions of dollars, due mainly to property damage and lost work time caused by heavy rains, snows, and floods. This has prompted a lot of research into the causes of El Nino and La Nina events, and how to predict them and their impacts. One study has estimated that the benefits to the U.S. of accurate El Ni¤o and La Nina forecasts would be worth about 1-2 Billion dollars a year. Good forecasts depend on thorough observations of the key regions of the ocean, atmosphere, and land that create El Ninos and La Ninas and their impacts. In the tropical Pacific, an array of shore stations, balloons, planes, buoys, ships, and satellites keep watch on changes in pressure, wind, sea level, currents, air and sea temperatures, humidity, rain, and many other weather factors. But there are still large areas, such as in and over the ocean between Hawaii and Mexico, where little data is being collected. Even with much better observations, El Nino and La Nina forecasts would still have a lot of weaknesses. What's most wanted are forecasts that give people one to several months to prepare for the impacts of El Ninos and La Ninas. But forecasts with that sort of lead time have a very high predictability barrier to contend with (see chapter 5). Many forecasts of El Ninos and La Ninas and their impacts rely on observations of what's gone on during past events. For instance, during past El Ninos, the extreme southern U.S. has generally received unusually heavy winter rain and snow fall, so forecasts of El Nino impacts usually predict heavy precipitation there. But each El Nino event is different in the tropical Pacific and, even more so, in its impacts outside the tropics. So predictions based on past events can be very iffy. This is especially true for places like central California and much of the southern Great Plains, where the impacts from one El Nino event to the next can be quite different. In central California, where I live, past El Ninos and La Ninas have helped create very wet, very dry, and very normal winters --- which makes it tough when people ask me what to expect from future El Ninos and La Ninas. ________________________________________________________________________________ Sidebar for "Watching Weather" Blame it on El Nino (Or Maybe on Global Warming?) Have you had some really strange weather lately? How about unusual forest fires, floods, droughts, or cranky in-laws? Maybe you could blame it all on El Nino. And why not? Seems like every weird phenomenon gets pinned on El Nino. How about the Oakland Hills fire that wiped out hundreds of homes in October 1991, or the Houston floods in December 1991, the marlin happily swimming off the coast of Oregon and Washington in August 1997, and hurricane Nora raining on southern Arizona in Septemeber 1997? For some people, those all look like the handiwork of El Nino. And maybe some really are. But the quick and easy way in which some people heap the blame on El Nino --- and the media leaps to report their claims --- makes scientists who study El Nino and its impacts cringe, or at least sigh in frustration. The ways in which El Nino events affect the world are complex. They are also the ways in which many other natural disruptions affect the world. For example, El Ninos, volcanic eruptions in the Philippines, weak monsoon rains in India, and heavy snow cover in Siberia can all disrupt the jets and storm tracks that cross the North Pacific and head into the U.S. Jets and storm tracks are very energetic and unstable parts of the atmosphere. Lots of disturbances, even fairly little ones, can tweak them and set them on strange courses, in roughly the same way that lots of disturbances can make a pencil standing on end tip over, or a house of cards collapse. So figuring out what caused a tweaked storm track that led to flooding in one area and drought in another is not an easy matter. There are many leads that a meteorologic detective needs to check out before blaming EN or anything else. Fortunately for El Nino, it's been able to share some of the blame lately. It seems that if the latest natural disruption is not the work of El Nino or his "wicked sister" (as one popular science article has labelled La Nina), then it's surely a sign of global warming! ________________________________________________________________________________