Tidal force

Tidal forces have periods of 8.8 and 18.6 years [67]. The variations in the tidal forces arise because the orbital planes of the Moon and the Earth are slightly inclined with respect to each other and because the Sun, Moon, and Earth form a mutually rotating gravitational system so that the magnitude of the tidal force depends on their relative positions. 

For comparison, the periods of enhanced blue crab yield, of maxima of air temperatures at Philadelphia (which is close to the Chesapeake Bay), of minima of rainfall at Philadelphia, and of enhanced tidal forces (leading to high tides) are listed in Table 5. The explanation we offer for the agreement among the periods so listed is that high tides wash nutrient into the surface waters of the Bay, and higher temperatures warm the surface waters, and minimum rainfall allows the surface waters to become more saline, all of which factors are salubrious for crab growth. 

Why temperatures and rainfall near Chesapeake Bay should be affected by variations of the tidal forces is not so clear. However the atmosphere and stratosphere are pulled away from the earth by tidal forces just as are the waters of the earth. These forces vary by as much as 10 percent during the tidal periods [67] resulting in density variations in the stratosphere with the same periods the consequent density variations may affect the relative rates of stratospheric chemical reactions, causing disturbances of temperature and rainfall on the ground with the tidal periodicities. 

Comets are generally considered to be weakly consolidated, and active comets are commonly observed to split into fragments. This is sometimes due to the tidal forces of a close planetary encounter, such as affected comet Shoemaker-Levy when it passed close to Jupiter in 1992 and broke into 21 pieces. More commonly, a comet spontaneously fragments multiple times over its orbit period, without any obvious cause. Disintegrating comets leave trails of small particles in their wakes. These trails are known as meteor streams, and when the Earth passes through such a meteor stream, as it does several times a year, a meteor shower occurs. Meter-sized rocks are known to occur within cometary meteor streams. 

Salt marshes stands of rooted vegetation which are flooded and drained by tidal forces. 

Swenson, E.M., and Sasser, C.E. (1992) Water level fluctuations in the Atchafalaya Delta, Louisiana tidal forcing versus river forcing. In Dynamics and Exchanges in Estuaries and the Coastal Zone, Coastal and Estuarine Studies 40 (Prandle, D., ed.), pp. 191-208, American Geophysical Union, Washington, DC. 

Valle-Levinson, A., and Wilson, R.E. (1994b) Effects of sill processes and tidal forcing on exchange in eastern Long Island Sound. J. Geophys. Res. 99, 12667-12681. 

Tidal sea level oscillations. In the Black Sea, tides are formed under the action of the tidal forces in the basin proper, which is limited in size therefore, the tides are small. Over the entire sea area, tides feature a semidiurnal or irregular semidiurnal character. The prevalence of this type of tides is related to the closeness of the semidiurnal period to that of the first mode of free oscillations in the Black Sea (uninodal seishe). 

A convenient presentation of the tidal forces is in a series of periodic functions. The most important tidal components are given in Table 2.1. 

Constituent day The time of the rotation of die eardi widi respect to a fictitious celestial body representing one of the periodic elements in the tidal forces. It approximates in lengdi die lunar or solar day and corresponds to the period of a diurnal constituent or twice the period of a semidiurnal constituent. The term is not applicable to the long-period constituents. 

The Roche Urn it was first described by Edouard Roche in 1848. It is the closest distance a body held together by self-gravity can come to a planet without being pulled apart by the planet s tidal (gravity) force. As a result, large moons cannot survive inside the Roche Limit. On July 7,1992, Comet Shoemaker-Levy 9 broke apart into 21 pieces due to tidal forces when it passed within Jupiter s Roche Limit on the subsequent pass, each of the comet s pieces collided with Jupiter. 

Tidal forces are inversely proportional to the cube of the distance, so the recession rate is inversely proportional to the sixth power of the distance. 

---