King tides are simply the very highest tides. Conversely, the low tides that occur at this time are the very lowest tides. They are naturally occurring, predictable events. Tides are actually the movement of water across the Earth’s surface caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the earth which manifest in the local rise and fall of sea levels. Tides are driven by the relative positions of the earth, moon, and sun, the elliptical orbits of the celestial bodies, land formations, and relative location on the earth. In the lunar month, the highest tides occur roughly every 14 days, at the new and full moons, when the gravitational pull of the moon and the sun are in alignment. These highest tides in the lunar cycle are called spring tides. The proximity of the moon in relation to the earth and the earth in relation to the sun also has an effect on tidal ranges. The moon moves around the earth in an elliptical orbit that takes about 29 days to complete. The gravitational force is greatest when the moon is closest to the earth (perigee) and least when it is farthest from the earth (apogee – about two weeks after perigee). The moon has a larger effect on the tides than the sun but the sun’s position also has an influence on the tides. The earth moves around the sun in an elliptical orbit that takes a little over 365 days to complete. Its gravitational force is greatest when the earth is closest to the sun (perihelion – early January) and least when the sun is farthest from earth (aphelion – early July). The king tides occur when the earth, moon and sun are aligned at perigee and perihelion, resulting in the largest tidal range seen over the course of a year. Alignments that are ‘near enough’ occur during approximately three months each winter and again for three months in the summer. During these months, the high tides are higher than the average highest tides for three or four days. The predicted heights of a king tide can be further augmented by local weather patterns and ocean conditions. Winter king tides may be amplified by winter weather making these events more dramatic. In the northern hemisphere, the term king tide is used to describe each of these winter high tide events. On Australias East Coast, the highest of each of these periods (i.e., one in winter and one in summer, totaling two per year) are known as the king tides. In this region of the world, the winter king tide usually occurs at night and therefore goes unnoticed. Consequently the summer king tide usually catches the most attention. Links to more information and resources about the tides, and king tides: NOAA National Ocean Service Tides Tides and water levels
Posted on: Thu, 30 Jan 2014 03:37:06 +0000
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