WES WEEK NINE: 5-9 November 2001

• Hurricane Michelle heads north -- Hurricane Michelle, the eight hurricane of the season continued to move northward over the weekend.  Heavy rain spread across Cuba and other Caribbean islands, leading to flash flooding.  [CNN] -- To be updated late Sunday from http://www.cnn.com/WEATHER/ or [Disaster Relief] http://www.disasterrelief.org/
• Drought appears responsible for less than expected world cereal crop -- According to a report from the U.N. Food and Agriculture Organization, continued drought across large areas of Asia and North America appears to be causing the production of this year's cereal crops to be less than expected. [U.S. Water News Online]
• A new center opened to study effects of toxicants in fish -- The University of Illinois is opening a center that will study the effects of the exposure to toxicants from the large amounts of fish eaten by Laotian and Hmong refugees in northeastern Wisconsin.  The FRIENDS Children’s Environmental Health Center at the University of Illinois is concerned with the impact of PCBs and methyl mercury ingested especially by young people in the Laotian and Hmong communities in Green Bay and Appleton, since large quantities of fish are caught in the Fox River, which is runs through an area with many paper mills and other sources of pollution from heavy industry and agriculture.  FRIENDS stands for Fox River Environment and Diet Study. [EurekAlert!] 
• "Water banking" garners a prize -- The first  UNESCO International Water Prize for Innovation in Water Resources Management in Arid and Semi-Arid Areas was awarded to an Australian team of scientists for their work on the study of the collection, storage and retrieval of water from underground aquifers.  [CSIRO]
• A pioneering genomic study involving organisms near hydrothermal vents -- A team of scientists from the University of Delaware and Amersham Biosciences, Inc have been conducting some of the first DNA sequencing experiments at sea.  They have just conducted their 17 day investigation at some of the hydrothermal vents located nearly two miles deep in the Pacific Ocean, approximately 1200 miles off the coast of Costa Rica. [NSF]
• Earth diary - A summary of the week's major environmental events on Planet Earth. [CNN]

Concept of the Week: Seiche

You probably remember as a child agitating the bath water so that it sloshed back and forth in the tub. (If you never did this as a child, there’s still time.) You produced a seiche, a phenomenon first studied in Lake Geneva, Switzerland in the 1700s. A seiche (pronounced "say-sh") is a rhythmic oscillation of water in an enclosed basin (e.g., bathtub, lake, or reservoir) or a partially enclosed coastal inlet (e.g., bay, harbor, or estuary). With this oscillation, the water level rises at one end of a basin while simultaneously dropping at the other end. A seiche episode may last a few minutes to a few days.

A seiche is a standing wave. Whereas wind-driven waves (pages 181-182 in the WES textbook) are progressive in that they propagate through a body of water, standing waves are stationary. With progressive waves, crests and troughs travel along the wave surface but with standing waves, crests alternate vertically with troughs at fixed locations. For both progressive and standing waves, the restoring force is gravity.

With a typical seiche in an enclosed basin, the water level near the center does not change at all although that is where the water exhibits its greatest horizontal movement; this is the location of a node. At either end of an enclosed basin, vertical motion of the water surface is greatest (with minimal horizontal movement of water); these are locations of antinodes. The motion of the water surface during a seiche is somewhat like that of a seesaw: The balance point of the seesaw does not move up or down (analogous to a node) while people seated at either end of the seesaw move up and down (analogous to an antinode). Go to the University of Delaware’s Seiche Calculator at http://www.coastal.udel.edu/faculty/rad/seiche.html. Set the "Modal Number" to 1 and then press "Calculate" for a graphical simulation of a seiche in an enclosed basin.

Partially enclosed basins usually have a node located at the mouth (rather than near the center) and an antinode at the landward end. Go to the Seiche Calculator, set the "Modal Number" to 0.5 and then press "Calculate" for a simulation of a seiche in a basin open to the right. Furthermore, some basins are complex and have multiple nodes and antinodes; these can be simulated on the Seiche Calculator by selecting different values of "Modal Number" greater than one.

A seiche can be induced by wind, regional differences in air pressure, earthquakes, or tidal forces. For example, wind blowing persistently in the same direction down the long axis of a bay causes water to pile up at the downwind end of the bay. When the wind slackens, the water oscillates (as a seiche) back-and-forth from one end of the bay to the other until eventually the water calms to a horizontal surface. A line of thunderstorms moving eastward from Wisconsin in late May 1998 produced a seiche in Lake Michigan that killed several people by drowning at the southern end of the lake. Previous seiches have produced 8 to 10 ft waves on Lake Michigan. A tsunami generated a seiche in the harbor of Hilo, HI following a major earthquake in the Aleutian Islands on 1 April 1946.

The natural period of a seiche depends on the length and depth of the basin and generally ranges from minutes to hours: The period is directly proportional to basin length. For example, the natural period of a seiche in a small pond is considerably shorter than its period in a large coastal inlet. Also, for the same basin, the natural period is inversely proportional to water depth; that is, the period shortens as water deepens. Using the Seiche Calculator, you may wish to experiment with different values of basin length and depth. Conversely, one can determine the average depth of a lake by determining the period of the seiche and the length of the lake.

Usually a seiche in a lake or harbor is of little concern because the wave height is relatively low—often only a few centimeters. Under certain circumstances, however, a seiche may grow to great heights with serious consequences including flooding and damage to moored vessels. A seiche grows as a consequence of resonance, that is, when the period of the disturbance (e.g., wind, earthquake) matches the natural oscillation period of a specific basin. Recall again your youthful bathtub experience. By timing your rhythmic disturbance of the water to match the natural period of the tub (about 1 second), you were able to cause the seiche to build until the water splashed out of the tub and onto the floor. Through resonance, vibrations from the 1994 Northridge, CA earthquake caused swimming pools to overflow throughout Southern California. In bays open to the ocean, if the period of tidal forcing matches the natural period of the bay, resonance can greatly increase the tidal range.

Concept of the Week: Questions

1. Seiches are [(standing) (progressive)] waves.
2. The natural period of a seiche [(depends on) (is independent of)] the size of an enclosed basin.

• 4-5 November 1966...The River Arno surged above flood stage and caused irreparable damage to much of the architectural and art treasure of Florence Italy. Millions of historical library volumes were either damaged or destroyed. More than 15,000 vehicles were also destroyed. (Accord Weather Calendar)
• 5 November 1977...A slow moving storm produced five to nine inch rains across northern Georgia causing the Toccoa Dam to burst. As the earthen dam collapsed the waters rushed through the Toccoa Falls Bible College killing three persons in the dorms. Thirty-eight persons perished at a trailer park along the stream. Eighteen bridges were washed out in Madison County. (David Ludlum)
• 5 November 1987...Heavy rains in California's Death Valley National Park washed out many park roads. As much as 1.20 inches of rain fell at Scotty's Castle, compared with the annual rainfall average of 2.28 inches. As many as 8000 people attending a recreational encampment were stranded. (Accord Weather Calendar)
• 6 November 1994...Downtown San Francisco, CA was drenched with 6.19 inches of rain in 24 hours to set an all-time record for the city.
• 8 November 1914...On this date the longest "official" rain-free time span on record for the U.S. of 767 days ended in Bagdad, CA. Some meteorologists question the accuracy of this record kept by railroad employees at that time. (Accord Weather Calendar)
• 9 November 1913...The "Freshwater Fury", a rapidly deepening cyclone, caused unpredicted gales on the Great Lakes. Seventeen ships, including eight large ore carriers on Lake Erie sank drowning 270 sailors. Cleveland, OH reported 17.4 inches of snow in 24 hours, and a total of 22.2 inches, both all-time records for that location. During the storm, winds at Cleveland averaged 50 mph, with gusts to 79 mph. The storm produced sustained winds of 62 mph at Port Huron, MI, wind gusts to 80 mph at Buffalo, NY and buried Pickens, WV under three feet of snow. (9th-11th) (David Ludlum) (The Weather Channel)
• 9 November 1932...An unnamed hurricane struck Cuba, with winds reaching approximately 210 mph at Nuvitas. However, a storm surge was the main killer of 2500 people of 4000 residents at Santa Cruiz del Sur. Essentially no storm records exist, as the observer drowned, with records and instruments washed away. (Accord Weather Calendar)
• 10 November 1835...A severe storm crossed the Great Lakes with 19 ships lost and 254 sailors killed. (Intellicast)
• 10 November 1975...Another "freshwater fury" hit the Great Lakes. A large ore carrier on Lake Superior, the Edmund Fitzgerald, sank near Crisp Point with the loss of its crew of 29 men. Eastern Upper Michigan and coastal Lower Michigan were hardest hit by the storm, which produced wind gusts to 71 mph at Sault Ste Marie, MI and gusts to 78 mph at Grand Rapids, MI. Severe land and road erosion occurred along the Lake Michigan shoreline. A popular hit song by Gordon Lightfoot was inspired by the storm. (David Ludlum)

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Prepared by AMS WES Central Staff and Edward J. Hopkins, Ph.D., email mailto:hopkins@meteor.wisc.edu
© Copyright, 2001, The American Meteorological Society.