![]() The result is a reflected wave that propagates in the opposite direction to the incident wave. The waves reflect due to changes in water depth (for example when entering shelf seas) and at coastal boundaries. In real oceans, the tides cannot endlessly propagate as progressive waves. The respective distance between the nodes and antinodes are shown in the bottom right of the Figure and expressed in terms of wavelength. At other points (antinodes), the amplitude of the incident wave and the reflected wave amplify each other. At certain points (nodes), the amplitude of the incident wave and the reflected wave cancel each other out. ![]() Resonance between an incident and reflected wave and the resulting total wave. D/ λ <1/20) than the wavelength ( λ) which is in the order of thousands of kilometres. These tidal waves can be considered wide, relative to the Rossby radius of deformation (~3000 km in the open ocean ), and shallow, as the water depth ( D, on average ~4 kilometre deep ) in the ocean is much smaller (i.e. The ocean reacts to this external forcing by generating, in particular relevant for describing tidal behaviour, Kelvin waves and Poincaré waves (also known as Sverdrup waves). This gravitational attraction results in a tidal force that acts on the ocean. Tides are generated as a result of gravitational attraction by the sun and moon. Where the lines meet are amphidromes, and the tide rotates around them for example, along the Chilean coast, and from southern Mexico to Peru, the tide propagates southward, while from Baja California to Alaska the tide propagates northward. In Figure 1, the low tide lags or leads by 1 hr 2 min from its neighboring lines. Cotidal lines connect points which reach high tide at the same time and low tide at the same time. In most locations the "principal lunar semi-diurnal", known as M 2, is the largest tidal constituent. A separate amphidromic system is created by each periodic tidal component. There can still be tidal currents since the water levels on either side of the amphidromic point are not the same. At the amphidromic points of the dominant tidal constituent, there is almost no vertical change in sea level from tidal action that is, there is little or no difference between high tide and low tide at these locations. Īmphidromic points occur because interference within oceanic basins, seas and bays, combined with the Coriolis effect, creates a wave pattern - called an amphidromic system - which rotates around the amphidromic point. The term derives from the Greek words amphi ("around") and dromos ("running"), referring to the rotary tides which circulate around amphidromic points. ![]() As such, the concept of amphidromic points is crucial to understanding tidal behaviour. The tidal range (the peak-to-peak amplitude, or the height difference between high tide and low tide) for that harmonic constituent increases with distance from this point, though not uniformly. The amphidromic points are the dark blue areas where the lines come together.Īn amphidromic point, also called a tidal node, is a geographical location which has zero tidal amplitude for one harmonic constituent of the tide. The white lines are cotidal lines spaced at phase intervals of 30° (a bit over 1 hr). The M 2 tidal constituent, the amplitude indicated by color. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |