DATASTREME WES WEEK NINE: 29 March - 2 April 2004

• A return to drought in the Southeast? With many areas across the Southeast experiencing little rain during the last several months, numerous wildfires have occurred in Alabama and Florida and thoughts of the recent drought have been rekindled. [USA Today]
• A rare event -- A tropical cyclone, or low pressure system, traveled across the South Atlantic and brushed the southern coast of Brazil, resulting in the loss of at least 2 people and destroying hundreds of homes. While American meteorologists claim that this rare system was a Category 1 hurricane (on the Saffir-Simpson Scale) based upon satellite measurements, their Brazilian counterparts initially maintained that this system was only a tropical storm. Regardless, a tropical cyclone of such intensity is very rare in the South Atlantic Basin, and would be the first hurricane on record for the region. [USA Today] [NASA Earth Observatory]
• Severe Tropical cyclone Fay hits northwest Australia -- A category 3 tropical cyclone on the Saffir Simpson scale named Fay hit the northwest coast of Australia at the end of last week. [NASA Earth Observatory] A gallery of images is available Gallery of images as Fay passed 60 miles to the west of Cable Beach in Broome Western Australia. [Broome Cam]
• Monitoring the discharge of river sediment from space-- The European Space Agency (ESA) recently released images obtained from the Envisat Medium Resolution Imaging Spectrometer (MERIS) onboard its Envisat satellite that shows a heavy sediment plume being discharged into the East China Sea from the Yangtze River. [ESA News]
• An orbiting "eye in the sky" resumes its mission-- The European Centre for Medium-Range Weather Forecasts recently reported that following a three year gap it will once again use the wind data over the oceans obtained from a radar scatterometer onboard ERS-2, a satellite operated by ESA, in its data assimilation step in the generation of numerical weather forecasts. [ESA News]

• An explanation to a Martian mystery -- A geosciences professor at the University of Arizona has offered an explanation for the spiral troughs that appear to emanate from the polar ice caps on Mars. Using a computer model, he has proposed that the deep canyons have been formed simply by alternate melting and refreezing cycles that occur during the short Martian summers. [University of Arizona]
• Civil War earthworks loosing battle to erosion-- A geology student from the University of Cincinnati recently reported on the erosion of the Confederate earthworks surrounding Charleston, SC as a result of exposure to rain and weather for nearly 150 years. [University of Cincinnati]

• Freshwater mussels help document pollution history--A Virginia Tech graduate student has developed a non-invasive method for determining the effects that pollution has had on the extinction of numerous species of freshwater mussels in a southwestern Virginia river. [EurekAlert!]
• Soil nutrient depletion confirmed by acid rain study--A research team from the University of Maine reported that the controlled addition of acid to a watershed resulted in a decrease in calcium and magnesium, nutrients crucial to forest soils. The nutrients migrating from the soil into rivers and lakes could also affect water quality. [EurekAlert!]

• Polluted groundwater to be pumped away from drinking water source -- A major power utility in Southern California plans to pump 20,000 gallons of groundwater contaminated with a chromium compound per day from a dumping site in the Mojave Desert in an effort to keep the water from reaching the Colorado River, a major source of Southern California's drinking water. [US Water News Online]
• Coastal water quality warning system flawed-- Scientists at the University of California at Irvine claim that the public in Southern California has not been correctly notified about coastal water a significant amount of the time. Their research has also provided new insights into the causes of coastal pollution. [University of California, Irvine]

• Guns for Water-- In a historic agreement, Israel will buy over 40,500 acre feet of fresh water annually from Turkey, with part of the 20-year arrangement being paid in military equipment. [US Water News Online]

• Global and US Hazards/Climate Extremes-- A review and analysis of the global impacts of various weather-related events, including drought, floods and storms during the current month. [NCDC]
• Global Water News Watch -- Other water news sources can be obtained through the SAHRA Project at the University of Arizona [SAHRA Project]
• Earthweek -- Diary of the Planet [earthweek.com] Requires Adobe Acrobat Reader.

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 from 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 estimate 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 changes in water level are 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.

• 29 March 1886...Atlanta, GA was drenched with a record 7.36 inches of rain in 24 hours. (The Weather Channel)
• 29 March 1920...Clear Spring, MD received 31 inches of snow in 24 hours to establish a state record. (Sandra and TI Richard Sanders - 1987)
• 29 March 1980...Heavy rains produced mudslides in Natchez, MS. The slides covered two buildings on Silver Street, killing 3 people and injuring 4. (Intellicast)
• 29 March 1989...Thunderstorms produced torrential rains in northeastern Texas and southwestern Arkansas. Longview, TX reported 14.16 inches of rain. More than 11 inches of rain at Henderson, TX caused a dam to give way, and people stranded in trees had to be rescued by boat. Total damage in northeastern Texas was estimated at $10 to 16 million. (The National Weather Summary) (Storm Data)
• 29–31 March 1848...Ice dam on Lake Erie near Buffalo, NY stopped flow of water over Niagara Falls for 30 hours. (The Weather Doctor)
• 31 March 2000...The water temperature of Lake Erie at Buffalo, NY was 39 degrees Fahrenheit on the last day of March, tying the maximum temperature for the date with that of 1998. Ice was present in 61 of 74 years on the 31^st, but this was third year in a row with open water. (Accord's Weather Guide Calendar)
• 1 April 1946...The Scotch Cap Lighthouse on Unimak Island in Alaska's Aleutian Islands was shaken by two earthquakes in a 27 minute span, then obliterated by a tsunami wave. The entire five-man crew was killed and the lighthouse antenna (105 ft above sea level) was washed away. Some debris was found 115 ft above sea level. The tsunami that propagated across the Pacific Ocean was responsible for more than 165 fatalities and over $26 million in damage. This tsunami was responsible for the development of the current Pacific Tsunami Warning System. (University of Washington) (Accord's Weather Guide Calendar) (US Coast Guard Historian's Office)
• 2 April 1958... One of the most destructive coastal storms in years battered New England (31 March-3 April). Some beaches between Portland, ME and Cape Cod, MA were eroded by approximately 50 ft. Miles of sea walls and bulkheads were either breached or demolished. Many beachfront cottages in Massachusetts, New Hampshire and Maine were sandblasted. (Accord's Weather Guide Calendar)
• 2 April 1997...An intense winter storm slammed the Maritime Provinces. Freezing rain knocked out power to more than 4,000 homes on Prince Edward Island. (The Weather Doctor)
• 3 April 1982...Wind-driven ice from Lake Winnebago in east central Wisconsin piled to 40-ft heights on the lake's eastern shoreline, damaging buildings in the Stockbridge area. Winds reached 80 mph across Wisconsin. (Accord's Weather Guide Calendar)
• 4 April 1933...Pigeon River Bridge, MN reported 28 in. of snow, which established the state 24-hr snowfall record. (4^th-5^th) (The Weather Channel)
• 4 April 1973...Sandia Crest, NM reported a snow depth of 95 in., a record for the state of New Mexico. (The Weather Channel)
• 4 April 1987...New England was in the middle of its second heavy rainstorm in 5 days. This was the same storm that produced record snows in the Appalachians. This storm dumped 4 to 7 in. of rain over the area and this, combined with snowmelt and rivers already at bankfull, produced record flooding, especially in Maine, where 2300 homes were flooded with 215 totally destroyed. Record water levels were reached at many dams. Damage in the state alone reached $100 million. (The National Weather Summary) (Storm Data) (Intellicast)

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URL: WES/news.html
Prepared by AMS WES Central Staff and Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2004, The American Meteorological Society.