Earth tide
Earth tide (also known as solid-Earth tide, crustal tide, body tide, bodily tide or land tide) is the displacement of the solid earth's surface caused by the gravity of the Moon and Sun. Its main component has meter-level amplitude at periods of about 12 hours and longer. The largest body tide constituents are semi-diurnal, but there are also significant diurnal, semi-annual, and fortnightly contributions. Though the gravitational force causing earth tides and ocean
Tide raising force
The larger of the periodic gravitational forces is from the Moon but that of the Sun is also important. The images here show lunar tidal force when the Moon appears directly over 30° N (or 30° S). This pattern remains fixed with the red area directed toward (or directly away from) the Moon. Red indicates upward pull, blue downward. If, for example the Moon is directly over 90° W (or 90° E), the red areas are centred on the western northern hemisphere, on upper right. Red up, blue down. If for example the Moon is directly over 90° W (90° E), the centre of the red area is 30° N, 90° W and 30° S, 90° E, and the centre of the bluish band follows the great circle equidistant from those points. At 30° latitude a strong peak occurs once per lunar day, giving a significant diurnal force at that latitude. Along the equator two equally sized peaks (and depressions) impart semi-diurnal force.
Body tide components
The Earth tide encompasses the entire body of the Earth and is unhindered by the thin
The tide components with a period near twelve hours have a lunar amplitude (Earth bulge/depression distances) that are a little more than twice the height of the solar amplitudes, as tabulated below. At new and full moon, the Sun and the Moon are aligned, and the lunar and the solar tidal maxima and minima (bulges and depressions) add together for the greatest tidal range at particular latitudes. At first- and third-quarter phases of the moon, lunar and solar tides are perpendicular, and the tidal range is at a minimum. The semi-diurnal tides go through one full cycle (a high and low tide) about once every 12 hours and one full cycle of maximum height (a spring and neap tide) about once every 14 days.
The semi-diurnal tide (one maximum every 12 or so hours) is primarily lunar (only S2 is purely solar) and gives rise to
Since these displacements affect the
Tidal constituents
Principal
Semi-diurnal | |||
Tidal constituent |
Period | Amplitude (mm) | |
vertical | horiz. | ||
M2 | 12.421 h | 384.83 | 53.84 |
S2 (solar semi-diurnal) | 12 h | 179.05 | 25.05 |
N2 | 12.658 h | 73.69 | 10.31 |
K2 | 11.967 h | 48.72 | 6.82 |
Diurnal | |||
Tidal constituent |
Period | Amplitude (mm) | |
vertical | horiz. | ||
K1 | 23.934 h | 191.78 | 32.01 |
O1 | 25.819 h | 158.11 | 22.05 |
P1 | 24.066 h | 70.88 | 10.36 |
φ1 | 23.804 h | 3.44 | 0.43 |
ψ1 | 23.869 h | 2.72 | 0.21 |
S1 (solar diurnal) | 24 h | 1.65 | 0.25 |
Long Term | |||
Tidal constituent |
Period | Amplitude (mm) | |
vertical | horiz. | ||
Mf | 13.661 d | 40.36 | 5.59 |
Mm (moon monthly) | 27.555 d | 21.33 | 2.96 |
Ssa (solar semi-annual) | 0.5 yr | 18.79 | 2.60 |
Lunar node | 18.613 yr | 16.92 | 2.34 |
Sa (solar annual) | 1 yr | 2.97 | 0.41 |
Ocean tidal loading
In coastal areas, because the ocean tide is quite out of step with the Earth tide, at high ocean tide there is an excess of water above what would be the gravitational equilibrium level, and therefore the adjacent ground falls in response to the resulting differences in weight. At low tide there is a deficit of water and the ground rises. Displacements caused by ocean tidal loading can exceed the displacements due to the Earth body tide. Sensitive instruments far inland often have to make similar corrections. Atmospheric loading and storm events may also be measurable, though the masses in movement are less weighty.
Effects
Seismologists have determined that microseismic events are correlated to tidal variations in Central Asia (north of the Himalayas);[citation needed] see: tidal triggering of earthquakes. Volcanologists use the regular, predictable Earth tide movements to calibrate and test sensitive volcano deformation monitoring instruments; tides may also trigger volcanic events.[4][5]
The semidiurnal amplitude of terrestrial tides can reach about 55 cm (22 in) at the equator which is important in
Terrestrial tides also need to be taken in account in the case of some particle physics experiments. [8] For instance, at the CERN or the SLAC National Accelerator Laboratory, the very large particle accelerators were designed while taking terrestrial tides into account for proper operation. Among the effects that need to be taken into account are circumference deformation for circular accelerators and also particle-beam energy. [9][unreliable source?] [10][unreliable source?]
In other astronomical objects
Body tides also exist in other
See also
References
- ^ Paul Melchior, "Earth Tides", Surveys in Geophysics, 1, pp. 275–303, March, 1974.
- ^ John Wahr, "Earth Tides", Global Earth Physics, A Handbook of Physical Constants, AGU Reference Shelf, 1, pp. 40–46, 1995.
- ^ Michael R. House, "Orbital forcing timescales: an introduction", Geological Society, London, Special Publications; 1995; v. 85; p. 1-18. http://sp.lyellcollection.org/cgi/content/abstract/85/1/1
- , 2007.
- USGS.
- ISBN 9783898889896, Sec. 7.1.1, "Effects of the solid Earth tides" [1]
- ^ User manual for the Bernese GNSS Software, Version 5.2 (November 2015), Astronomical Institute of the University of Bern. Section 10.1.2. "Solid Earth Tides, Solid and Ocean Pole Tides, and Permanent Tides" [2]
- ^ Accelerator on the move, but scientists compensate for tidal effects Archived 2010-03-25 at the Wayback Machine, Stanford online.
- ^ "circumference deformation" (PDF). Archived from the original (PDF) on 2011-03-24. Retrieved 2007-03-25.
- ^ particle beam energy Archived 2011-07-20 at the Wayback Machine affects
- S2CID 120669399.
- S2CID 53690707.
- S2CID 926755. 83.
Bibliography
- McCully, James Greig, Beyond the Moon, A Conversational, Common Sense Guide to Understanding the Tides, World Scientific Publishing Co, Singapore, 2006.
- Paul Melchior, Earth Tides, Pergamon Press, Oxford, 1983.
- Wylie, Francis E, Tides and the Pull of the Moon, The Stephen Greene Press, Brattleboro, Vermont, 1979.