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Atlantic Hurricane/El Niño Project: Teachers Guide

Introduction and Rationale
This activity provides the student with the opportunity to study data that will enable them to develop a deeper understanding of the El Niño phenomena as well as investigate a possible relationship between El Niño events and frequency/severity of Atlantic Hurricanes. Rationale for conducting this investigation is based upon the fact that El Niño events change convective patterns locally over the Pacific Ocean and globally the general atmospheric circulation. When the equatorial trade winds weaken, warm waters build up in the Eastern Pacific. Subsequently, large amounts of water evaporate at the surface. This sequence of events creates a low pressure system, or trough in the Eastern Pacific. Researchers are uncertain as to what triggers the weakening in the trade winds. What is agreed upon is that these changes impact the the general atmospheric circulation pattern and can alter climate conditions across the globe.

Results of Research to Date
According to Gray (Colorado State Unv., 1984) and O'Brien, Richards and Davis (Florida State Unv., 1995), El Niño is commonly associated with diminished hurricane activity in the Atlantic. The Florida State researchers analyzed Hurricanes (only) between 1949-1992 and found that there was a 21% probability of 2 or more hurricanes striking the U.S. during an El Niño year. In a "normal" year, there is a 46% chance of the same event. Notice that this study limited itself to hurricanes (not tropical storms) that struck the U.S. mainland only. They also defined an El Niño event according to the scheme developed by the Japanese Meteorological Agency (reference JMA Atlas, 1991). According to the JMA, an El Niño is said to have begun when within the region bounded by +/-4 degrees of the equator from 150-90 deg. West experiences 6 consecutive months of sea surface temperatures of at least 0.5 deg. C above normal. They further limited the criteria by stating that the series of six consecutive months must begin before September, and must include October, November, and December. They found that an El Niño typically starts in late summer and lasts for about a year. According to these definitions, the winter of 1994-95 was not an El Niño winter, and thus the extreme hurricane season in 1995 was not a summer following an El Niño winter. Your students as they work through this investigation will need to establish their own criteria for when an El Niño begins and ends. You may wish, depending upon the group, to share with them the JMA's criteria.

Other researchers, such as William Gray of Colorado State, using different criteria, do consider the events of 1995 to be related to the El Niño. This presents another problem: when El Niño occurs, it clearly changes the upper atmospheres positions of me an ridges and troughs, however, it rarely does so the same way twice! Dr. Gray of Colorado State believes that this past years Hurricane season, while it followed a El Niño year, was severe in the Atlantic as a result of other dynamics such as unusually large convective activity over Western Africa producing an unusual number of tropical waves in the Eastern Atlantic.

This lab ideally will allow the student to develop their own criteria for when an El Niño is occurring. The student will also be able to look at Atlantic Hurricanes and Tropical Storms from a variety of perspectives. These include intensity, frequency, and storm track. I have included storm tracks (acquired from a Purdue Univ. web site) for the years in question (1981-1996), however, their maps do not provide hurricane tracks, only tropical storm tracks. At the University of Hawaii, I accessed more complete maps of storm tracks for all storms from 1994 and 1995, however I have not yet found maps that track hurricanes from earlier years. These images are included in your package, and are titled "improved storm track 1994, 1995." The Purdue web site does have JPEG files for individual hurricanes available for download, some samples from the past couple of years have been included for study here. The web address for accessing these images appears later in this paper.

Images have been provided of Pacific Ocean "Sea Surface Temperature Anomalies" (ssta). These images are in 3 month intervals from late 1981 to early1996. I have taken the images and used them with a shareware program called "Graphic Converter." This program allows the student to view the images in a "slide show" format. They can control the speed of the slide show and stop at various images for detailed study. I suggest beginning the activity by having the students study the "ssta" images, and identify when El Niño Events have occurred over the past couple of decades. A key labeled "sstakey.jpg" depicts which colors indicate above normal sea surface temperatures. The key appears both at the beginning of the slide show sequence and at the end.

A final but important note: when you or your students are viewing the sea surface temperature anomalies, the date appears in coded form in the upper left corner of the screen. The code is easily analyzed, the year appears first, followed by the month in numerical format. For example: "847" means "1984, July." The one exception to this format used was for October which is labeled as "99." For example, October 1984 is "8499." This was done to insure that "Graphic Converter" would create a slide show in order from oldest to most recent image.

Additional graphics provided included an image depicting El Niño vs. Normal sea surface temperature patterns in this folder. It is labeled "Normal vs. El Niño Vertical Profile." I suggest that the students view the series of ssta images to get a feel for the dynamic changes that take place in the Pacific Ocean. Then study the image "Normal vs. El Niño Vertical Profile" to learn how to recognize an El Niño event, as well as to discover what changes take place in the atmosphere over the Pacific when an El Niño occurs. The students can then view the slide show again of sea surface temperature anomalies, and begin to identify when El Niño events have occurred.

Additional images/diagrams that you may wish to provide the students with include:

"El Niño 1986-pres. SST tmp/anom": This image presents essentially a summary of the entire sequence of images prepared for student analysis. Both sea surface temperatures and anomalies are presented from 1986-1996.

"El Niño @ eqtr. temp/wind": This image depicts "normal" sea surface temperatures at the equator with depth, and compares this profile to an "El Niño" scenario. Additionally, surface winds are depicted along the equator across the Pacific under both "normal" and "El Niño" conditions.

According to the literature, El Niño events have occurred in 1982-83, 1986-87, 1991-92, 1993, and 1994. By studying the series of "ssta" images, students should be able to identify within a couple of months when each event began to develop and later subside. Researchers are quick to point out that it is unusual for El Niño's to occur in such rapid succession as has been seen in the first half of this decade.

You may wish to share the following with your students, or for your information: "El Niño was originally recognized by fishermen off the coast of South America in the late 1800's as the appearance of abnormally warm water in the Pacific ocean which usually arrived shortly after the beginning of the year. This localized phenomenon is now known to be part of a very large and complex system of atmospheric and oceanic interactions called the El Niño Southern Oscillation or ENSO for short. The mechanisms of the ENSO are the dynamic and thermodynamic interactions between the atmosphere, oceans and land surfaces. In most years it doesn't even occur, and in others, such as 1982, the effects are felt around the world with devastating impact. An ENSO event can reverse ocean currents and trade wind patterns, cause drought and wildfires in one part of the world, and bring torrential rains to other, usually dry, regions of the earth. In fact, the 1982 El Niño event, may be one of the most powerful climate oscillations in modern history!

The strength of this phenomenon varies greatly from year to year. But why does it appear in certain years and not in others? Can we predict and prepare for the next episode? These and many other questions are perplexing scientists today. Currently, there are many scientists involved in the monitoring, detecting and modeling of the ENSO. Many are using sophisticated measurement devices and various satellite instruments to analyze past El Niño events to enable them to model and predict future events." (This was taken from the "What is El Niño?" web page.

Atlantic Hurricane/El Niño Project: Student Activity

El Niño is a phenomena that affects many aspects of our planets major systems. In short, El Niño is a warming of the waters off of Peru in the Pacific Ocean. This phenomena, first noticed by fishermen in the late 19th century, has been determined to occur periodically, usually every three years or so, however lately the frequency seems to have increased. Why does El Niño occur? What controls when it occurs? What impacts does El Niño have upon the atmosphere? biosphere? hydrosphere (other oceans)? In this investigation, you will be provided with several sets of data and asked to answer one question: Does El Niño have any impact upon Atlantic Hurricanes?

Lets ask why is this even a possibility worth considering. It is known that El Niño can change patterns in the upper atmosphere, particularly in the Northern Hemisphere. Torrential rains in California and the Midwest in recent years have been blamed on El Niño. Unusual warmth in the Northeast in the winter of 1995-96 was also blamed on El Niño. Based upon these observations, it seems reasonable to ask whether El Niño is impacting Atlantic Hurricanes.

To answer whether El Niño is impacting Atlantic Hurricanes, you need to study the various data sets presented in this activity. The questions raised in the introductory paragraph, while valuable, can not be addressed from the data presented here.

To begin your study, go to the file called "Pacific Ocean ssta." You will see a color coded temperature key first. Note: the data set is showing you "sea surface temperature anomalies." This means that the colored images are showing you warmer and cooler than normal temperatures, not a specific temperature. You may pause to familiarize yourself with what is above normal and what is below normal. Once familiar, you can continue to view the data. Note: it covers the years 1981 to 1996. The date is presented in the upper left corner and is coded as follows: year, month. For example: 837 is July, 1983. One exception to this pattern is any data from October which is presented as month "99." This means that October 1986 looks like this: 8699. This was done to insure that the program would read the images in proper sequence.

Now that you have viewed the "ssta" data once, you should study the image called "Normal vs El NiñoVertical Profile." This image will reveal to you precisely where the warming that you are looking for takes place. After studying this image, report your observations in writing to your instructor. Note the difference between the two sea surface temperature patterns. Next, discuss what changes occur in the atmosphere when El Niño develops. Submit this to your instructor, and upon approval return to the ssta data and determine when El Niño events have occurred over the past two decades. (For Example...From my analysis of the data provided, clearly identified El Niño events can be seen between July 1982-Jan 1984; Aug. 1986-Jan 1988; Aug 1991-Aug 1992; April 1993-Jan 1994; Oct 1994-May 1995)

Now that you have identified when El Niño's have occurred, you need to study the Hurricane data supplied. There are two primary sets of data for you to study. One set lists all of the storms that occurred each season, reports the minimum pressure achieved for each storm, maximum winds, and classifies them according to the Saffir-Simpson scale. Study this data in the file called "Hurricane Info."

Your Scientific Investigation and Report
Study the data provided, keep an open mind as to what relationship (if any) may exist. Realize that it might not be a simple relationship such as El Niño events increase or decrease the number of hurricanes each season. As you study the data, prepare tables or charts that will help you to ascertain whether any relationships exist. Be sure to present these products in the scientific report that you should prepare to report the results of this investigation.

(Depending upon the group, you may wish to guide the students through the various approaches that can be taken in studying the data. For example, you may choose to direct the students to prepare a table comparing El Niño years to non-El Niño years vs number of hurricanes. Additional comparisons can be made between El Niño years and non-El Niño years by categorizing the storm tracks. You could for example, break down the tracks storms into those that cross the 75 deg. West longitude vs. those that do not. Comparing date of occurrence vs type of season could also yield statistically significant results.

Anticipated Results (Teacher Information Only)
Years 1981,1982,1984,1985,1988,1989,1990 were clearly not El Niño years, while 1983,1987,1992,1993 were El Niño years. Arguments could be made in either direction for 1986,1991,1994 and 1995. During the El Niño years, the average number of storms was 6.5, and hurricanes was 3.5. During non-El Niño years, the average number of storms was 11.1, and hurricanes was 5.8. Opportunities to discuss statistical significance are presented here, since the data is based upon only 7 seasons for non-El Niño years and 4 seasons for El Niño years. Similar studies can be conducted for any variations in tracks that occur or strength or part of the season when the storms occur.

I prefer to keep investigations such as this as open-ended, and allow the students to study the data to see what they can make of it. They are expected to conclude their study with a written report and an oral defense of their conclusions.

Image of Alan Sills and a caption that reads: Alan Sills West Essex Regional High School North Caldwell, NJ.

email Alan Sills

Additional narrative on this topic, as well as interactive maps can be accessed from the following world wide web sites:

El Niño Theme Page: Interactive page to request data on lat/long maps, depth section plots, animations etc...from 1991-1996

El Niño Theme Page: Links to El Niño Data

"What is El Niño?", Sea Surface Temp. Data from 1985

Earth Space Research Group...El Niño Scenario

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