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Long-period Tide
Long-period tides are gravitational tides with periods longer than one day, typically with amplitudes of a few centimeters or less. Long-period tidal constituents with relatively strong forcing include the ''lunar fortnightly'' (Mf) and ''lunar monthly'' (Ms) as well as the ''solar semiannual'' (Ssa) and '' solar annual'' (Sa) constituents. An analysis of the changing distance of the Earth relative to Sun, Moon, and Jupiter by Pierre-Simon de Laplace in the 18th century showed that the periods at which gravity varies cluster into three species: the semi-diurnal and the diurnal tide constituents, which have periods of a day or less, and the long-period tidal constituents. In addition to having periods longer than a day, long-period tidal forcing is distinguished from that of the first and second species by being zonally symmetric. The long period tides are also distinguished by the way in which the oceans respond: forcings occur sufficiently slowly that they do not excite su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fortnight
A fortnight is a unit of time equal to 14 days (two weeks). The word derives from the Old English term , meaning "" (or "fourteen days," since the Anglo-Saxons counted by nights). Astronomy and tides In astronomy, a ''lunar fortnight'' is half a lunar synodic month, which is equivalent to the mean period between a full moon and a new moon (and vice versa). This is equal to 14.77 days. It gives rise to a lunar fortnightly tidal constituent (see: Long-period tides). Analogs in other languages In many languages, there is no single word for a two-week period, and the equivalent terms "two weeks", "14 days", or "15 days" ( counting inclusively) have to be used. * Celtic languages: in Welsh, the term ''pythefnos'', meaning "15 nights", is used. This is in keeping with the Welsh term for a week, which is ''wythnos'' ("eight nights"). In Irish, the term is ''coicís''. * Similarly, in Greek, the term δεκαπενθήμερο (''dekapenthímero''), meaning "15 days", is used. * T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tides
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can be used for any given locale to find the predicted times and amplitude (or "tidal range"). The predictions are influenced by many factors including the alignment of the Sun and Moon, the phase and amplitude of the tide (pattern of tides in the deep ocean), the amphidromic systems of the oceans, and the shape of the coastline and near-shore bathymetry (see '' Timing''). They are however only predictions, the actual time and height of the tide is affected by wind and atmospheric pressure. Many shorelines experience semi-diurnal tides—two nearly equal high and low tides each day. Other locations have a diurnal tide—one high and low tide each day. A "mixed tide"—two uneven magnitude tides a day—is a third regular category. Tides va ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sea Surface Height
Ocean surface topography or sea surface topography, also called ocean dynamic topography, are highs and lows on the ocean surface, similar to the hills and valleys of Earth's land surface depicted on a topographic map. These variations are expressed in terms of average sea surface height (SSH) relative to Earth's geoid. The main purpose of measuring ocean surface topography is to understand the large-scale ocean circulation. Time variations Unaveraged or instantaneous sea surface height (SSH) is most obviously affected by the tidal forces of the Moon and the Sun acting on Earth. Over longer timescales, SSH is influenced by ocean circulation. Typically, SSH anomalies resulting from these forces differ from the mean by less than ± at the global scale. Other influences include temperature, salinity, tides, waves, and the loading of atmospheric pressure. The slowest and largest variations are due to changes in Earth's gravitational field (geoid) due to the rearrangement of contin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Satellite Altimetry
Satellite geodesy is geodesy by means of artificial satellites—the measurement of the form and dimensions of Earth, the location of objects on its surface and the figure of the Earth's gravity field by means of artificial satellite techniques. It belongs to the broader field of space geodesy. Traditional astronomical geodesy is ''not'' commonly considered a part of satellite geodesy, although there is considerable overlap between the techniques. The main goals of satellite geodesy are: # Determination of the figure of the Earth, positioning, and navigation (geometric satellite geodesy) # Determination of geoid, Earth's gravity field and its temporal variations (dynamical satellite geodesy or satellite physical geodesy) # Measurement of geodynamical phenomena, such as crustal dynamics and polar motion Satellite geodetic data and methods can be applied to diverse fields such as navigation, hydrography, oceanography and geophysics. Satellite geodesy relies heavily on orbi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seth Chandler
Seth Carlo Chandler, Jr. (September 16, 1846 – December 31, 1913) was an American astronomer, geodesist, and actuary. He was born in Boston, Massachusetts to Seth Carlo and Mary (née Cheever) Chandler. During his last year in high school he performed mathematical computations for Benjamin Peirce, of the Harvard College Observatory. After graduating, he became the assistant of Benjamin A. Gould. Gould was director of the Longitude Department of the U.S. Coast Survey program, a geodetic survey program. When Gould left to become director of the national observatory in Argentina, Chandler also left and became an actuary. However, he continued to work in astronomy as an amateur affiliated with Harvard College Observatory. Chandler is best remembered for his research on what is today known as the Chandler wobble. His research on polar motion spanned nearly three decades. Chandler also made contributions to other areas of astronomy, including variable stars. He independent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
