Neap Tides

Neap Tides
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Fig 5.7 – When the moon, earth and sun are lat right angles, during a half moon the gravitational pull is lessened and we experience neap range tidal cycles.

At the first quarter an last quarter of the lunar month (roughly 7 & 21 days) the sun and the moon are at right angles to the earth (Fig 5.7). This diminishes their combined gravitational pull and lessens the tidal bulge of water surrounding the earth.

At these times we have neap tides with lower than normal high tides and higher than normal low tide. The average of these lower than usual high tides are called mean high water neaps MHWN and average of higher than usual low tides is called mean low water neaps MLWN.

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Fig 5.8 – The neap tide range is less than spring tide range. The tide levels oscillate between these ranges over the 29.5 day lunar cycle.

The difference between MHWN and MLWN is known as the Neap Range (Fig 5.8). As you can see in the neap range is much less than the spring range. We can normally expect high tide level to be somewhere between MHWS and MHWN and low water to be between MHWN and MLWS. The tidal range is therefore continually changing over the course of a lunar month and the tidal range oscillates between the spring and neap ranges as the moon orbits the earth.