Earth tide

Earth tide is the sub-meter motion of the Earth of about 12 hours or longer caused by Moon and Sun gravitation, also called "body tide" which is the largest contribution globally. The largest body tide contribution is from the semidiurnal constituents, but there are also significant diurnal constituents. There also semi-annual and fortnightly contributions due to the axial tilt.The use of the word "tide" is by analogy, and although the forcing is quite similar, the responses are quite different.

Tidal forcing

Earth tide effects

Volcanologists use the regular, predictable Earth tide movements to calibrate and test sensitive volcano deformation monitoring instruments. The tides may also trigger volcanic events. Seismologist have determined that microseismic events are correlated to tidal variations in Central Asia (north of the Himalayas). [ [http://hvo.wr.usgs.gov/volcanowatch/1998/98_05_28.html Volcano watch] , USGS.] The semidiurnal amplitude of terrestrial tides can reach about 55 cm at the equator which is important in GPS calibration and VLBI measurements. Also to make precise astronomical angular measurements requires knowledge of the earth's rate of rotation and nutation, both of which are influenced by earth tides.

Terrestrial tides also need to be taken in account in the case of some particle physics experiments. [ [http://news-service.stanford.edu/news/2000/march29/linac-329.html Accelerator on the move, but scientists compensate for tidal effects] , "Stanford online".] For instance, at the CERN or SLAC, 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 particle beam energy. [ [http://accelconf.web.cern.ch/accelconf/e00/PAPERS/MOP5A04.pdf CERN circumference deformation] ; [http://accelconf.web.cern.ch/accelconf/p93/PDF/PAC1993_0044.PDF CERN particle beam energy] affects. ]

Since tidal forces generate currents of conducting fluids within the interior of the Earth, they affect in turn the Earth's magnetic field itself.

Notes and references

*Paul Melchior, "Earth Tides", Pergamon Press, Oxford, 1983.