Waves

To be reviewed/updated - 28.03.2017

On Earth several factors must be considered concerning wave frequency and cause. The time of the year is important as is the axial tilt (obliquity). Earth revolves at a constant velocity as water is attracted by gravity towards Moon. There is a ‘bulge’ that maximises at Moon’s postion (High Tide) and diametrically opposite. Between the two (at 90°) there is a minimum (Low Tide). The position will affect the water and tides. Just ahead of Moon is the deepest point and this depth can be used to track Moon. Or the other way around. As Earth turns this (HT-LT-HT-LT) arrangement remains as Moon moves slowly ahead relative to Earth. The turning-away Earth makes it appear that Moon is slower, receding towards the west.

   The seas move with Earth (Moon’s gravity is insufficient to overwhelm Earth’s hold on the water.) This Earth-water combination results in a wave that causes the observed tides. The reason the ‘bulge’ moves ahead of Moon is probably a combination of the distance between Earth-Moon, the delay, and the revolution of Earth resulting in a dimishing gravitational attraction.

   Moon travels slightly faster than Earth (30.731km/s v. 29.786km/s = 0.945km/s), but Earth is also revolving eastwards (anti-clockwise or West to East) from Moon (1668km/h at the equator, 0.00km/h at a pole) as it orbits the Sun. The sea (water) moves around with Earth and the total depth will produce a roughly constant value. This can be demonstrated by adding FM (full Moon), LQ (last quarter), NM (new Moon) and FQ (first quarter) depths together for the same place. Considering high tide (HT) depths over all four phases throughout 2011 it is seen that HTs at Margate (FM) are around midnight. The second HTs are always about midday. HTs for LQ and FQ are approximately 6hr later and are dependent on the Earth-Moon interplanetary distance and the axial tilt.

   There is a gradual lessening of tidal depth between FM (or NM) and these intermediate quarters since Moon becomes the principal gravitational attractant. At the FM of Dec (10.12.2011), the Sun is nearest and in-line at perihelion (Winter Solstice = 22.12.2011). The shallowest tide will be at Sun aphelion (furthest) (Summer solstice = 21.06.2011). At FQ or LQ in June (2010/2011), again with Sun/Moon at 90°, Moon is the principal attractant. The gravitational influence of the Sun is constant throughout a lunation (FM → LQ → NM → FQ) except at a (FM) lunar eclipse when Earth blocks Sun → Moon. Moon gravity matched with Earth's rotation cause the tides and the total time (4 quarters FM, LQ, NM, FQ) always adds to around 24h.
   The tide (wave) movement can be seen in the behaviour of anchored ships/boats
(one anchor at the bow). The front of the vessel points into the deepening water, but the waves of an incoming/outgoing tide will always be toward the shore and maybe up to 90° of the flow of water. The erection of a tent by a central pole illustrates the motion - the upward direction is to the centre regardless of the perimeter (edge).
   There is an important distinction between the two types of wave. The one around the Earth (two waves: deepest → shallowest → deepest → shallowest = 24h) and those approaching/receding from the shore (frequency is generally 4-5 seconds). This frequency may be related to Earth → Moon distance (unknown).The origin of these waves is not (yet) known, though notably large lakes that are not tidal do not exhibit such a wave nature. A reasonable conclusion is that the two types of wave (12h x 2 = 24h and 4-5 second in/out nature during tides) are related.

   The mass of water that moves is billions and billions of tons and a smooth movement is highly improbable given that the underwater ground surface is not itself smooth. Immovable land masses create enormous buffeting around the planet and these land masses occur at very irregular locations. The water will crash into itself differently at myriad places and result in enormous turbulence on a global scale. There could never be any synchronisation over such a vast area of water.

   Water finds its own level and a following wind will have an effect. One must move, though not necessarily smoothly, into the other. The speed of the water (different depths vary = velocity gradient) is (perhaps) not enough (or shallow enough) to collapse the wave and form a ‘breaker’. The depth of the water is critical. Insufficient depth and the water will not remain stable. A surface wind can accelerate the surface water and create small local breakers. The velocity gradient is exceeded.

   Waves can be a relatively short width and this depends on the underwater terrain: a narrow channel or large and deep canyon. Any sort of trench whatever its size will funnel water as the tide comes in and the resulting wave can, therefore, be massive or small. The wave is a measure of the changing amplitude of water in that particular region and generally deeper water will exhibit a swell. In shallower areas, breaking waves manifest - the surface water moves faster than at depth (at or near the ground) and results in a collapsing wave.