4/14/2023 0 Comments Neap tide graphLunar Semi-diurnal Tide (M 2), occurring every 12.4 hours Three of the important tidal constituents from the model are illustrated by a static co-tidal image, summarising the tide amplitude (or half-range) and the phase (or timing of high water), and a movie of the tide wave height as it regularly cycles around New Zealand. Key: P= Moon’s perigee, and N,F = New and Full Moon. The model has been calibrated with measurements from the sea-level network and is the basis of the tide forecasting service.Ĭontrasting tides at Kaikoura (east) versus Foxton (west). NIWA has built a computer tidal model to simulate 16 of the most important tides across the entire Exclusive Economic Zone (EEZ) around New Zealand. The rising and falling tide we observe at the beach or in an estuary comprises many different tides (or constituents) of various strengths and cycle times, each resulting from a particular feature of the gravitational attraction by the Moon and Sun on Earth’s waters. These are called perigean tides, so-called because they occur when the Moon is closest to the Earth (i.e., its perigee) in its elliptical or non-circular orbit every 27.5 days. Contrast that with the mid-eastern coasts and the Chatham Islands, where the biggest tides occur only once a month. On our west coasts and in Tasman/Golden Bay, we have large tidal ranges (up to 4 m) during spring tides (following New of Full Moon), and much smaller neap tides, when the Moon is in the 1 st and last quarter phases. The most noticeable difference is between the east and west coasts (see plot). The nature of the tides varies considerably from place to place around NZ. Overall, tides account for about 95% of the variation in sea level we see on the NZ coast. Some of the recorders have also been tsunami enabled to store sea-level measurements quickly at 1-minute intervals to better describe the various waves that make up a tsunami event. The data is also used for processing hydrographic surveys of the sea bed topography. “ Sea level on the move?” is an article on the network and why the need for high-quality data. The primary motivation is to collect high-quality and accurate measurements of sea level and tides for scientific studies of storm surge, tides and global warming at open coast sites that are unaffected by port activities or rivers. The NIWA sea-level recorder network is supported by some regional and district councils, the University of Canterbury and by the National Tidal Facility (Adelaide). NIWA coordinates a network of open coast sea-level recorders around the New Zealand coast. These predictions are only intended for information and are not to be used for navigation or engineering design as heights are not surveyed in the local Chart Datum.įor tide predictions at New Zealand ports, visit Toitū Te Whenua Land Information New Zealand website. Predictions of high and low tides anywhere in New Zealand’s marine area are based on computer model simulations of the tide behaviour in the SW Pacific.
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