DATASTREME OCEAN WEEK SEVEN: 15-19 March 2004

• Boaters saved by a satellite -- Ten people on board a capsized catamaran were rescued off the Hawaiian island of Lanai last week because their distress signal was relayed through the international Search and Rescue Satellite-Aided Tracking System (COSPAS-SARSAT) to the US Coast Guard. [NOAA News]

• Help is available to help ship pilots avoid bridges -- NOAA officials recently announced additional improvement to the Physical Oceanographic Real-Time System (PORTS^®) [NOAA News]

• Commercial fishing for swordfish banned -- The National Marine Fisheries Service has announced a ban on long-line commercial fishing for swordfish in the Pacific in an effort to protect endangered sea turtles. [ENN]

• Climate system in the North Pacific contains more than one signal -- Scientists with the Pacific Marine Environmental Research Laboratory and the University of Washington reported that their analysis of sea surface temperature and pressure data indicate a change in the climate of the North Pacific during the last 5 years that appears to mean that the system is more complicated than had been previously described by the Pacific Decadal Oscillation (PDO). They based findings upon satellite derived sea surface temperatures off the U.S. West Coast and in the Gulf of Alaska. [EurekAlert!]

• Deep ocean circulation appears to be a significant factor in climatic change -- Scientists at the University of California report that the deep ocean circulation within the North Atlantic basin along with salinity changes in the Caribbean Sea appear to control warm and cold climatic episodes in the Northern Hemisphere. [EurekAlert!]

• Extended North American droughts may be linked to North Atlantic temperatures -- After studying the century-long US drought patterns along with multi-decade variations in North Pacific and North Atlantic sea surface temperatures, scientists with the Midwestern Regional Climate Center and the US Geological Survey report that the long-lasting and widespread droughts appear to be associated with above average sea surface temperatures in the North Atlantic. [EurekAlert!]

• 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]
• Earthweek -- Diary of the Planet [earthweek.com] Requires Adobe Acrobat Reader.

Concept of the Week: Seiche Model

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. (Refer to pages 141-142 in your DataStreme Ocean textbook for more on seiches.)

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.

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 less 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.

Concept of the Week: Questions

1. In an enclosed basin the node of a seiche is located [(at either end) (near the center)] of the basin.
2. The natural period of a seiche [(depends on) (is independent of)] the size of an enclosed basin.

• 15 March 1493...Christopher Columbus returned to Spain after his first voyage to the New World.
• 15 March 1778...Nootka Sound, Vancouver Island was discovered by Captain Cook.
• 15 March 1946...For the first time, U.S. Coast Guard aircraft supplemented the work of the Coast Guard patrol vessels of the International Ice Patrol, scouting for ice and determining the limits of the ice fields from the air. (USCG Historian's Office)
• 15 March 1960...Key Largo Coral Reef Preserve in the Florida Keys was established as the nation's first underwater park. This preserve currently includes John Pennekamp Coral Reef State Park and the adjacent Florida Keys National Marine Sanctuary.

• 16 March 1521...Portuguese navigator Ferdinand Magellan reached the Philippines. He was killed the next month by natives.

• 16 March 1834...The HMS Beagle anchored at Berkeley Sound, Falkland Islands.

• 16 March 1889...A war between the U.S. and Germany was likely averted as a hurricane sank all three U.S. and three German warships in the harbor at Apia, Samoa. Joint U.S., German and Samoan rescue cooperation led to the Treaty of Berlin (1889) that later settled the dispute. (Accord's Weather Calendar)

• 17 March 1891...The British steamer Utopia sank off the coast of Gibraltar.

• 17 March 1898...The USS Holland, the first practical submarine, made its first dive in the waters off Staten Island, New York for one hour and 40 minutes. (Naval Historical Center)

• 17 March 1941...USCGC Cayuga left Boston with South Greenland Survey Expedition on board to locate airfields, seaplane bases, radio and meteorological stations, and aids to navigation in Greenland. (USCG Historian's Office)
• 17 March 1959...The submarine USS Skate (SSN-578) surfaced at the North Pole. (Naval Historical Center)

• 19 March 1866...The immigrant ship Monarch of the Seas sank in Liverpool killing 738 people.

• 20 March 2000...A large iceberg measuring approximately 170 mi by 25 mi calved off Antarctica's Ross Ice Shelf near Roosevelt Island. The iceberg was approximately 2.5 times the size of New York's Long Island. (Accord's Weather Guide Calendar)

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