# Tag Info

## Hot answers tagged tides

14

I don't know about the size of land masses, but their distribution and the shape of ocean basins definitely play a big role. When considering the ideal case of an all-ocean globe, i.e. one with no land masses (equilibrium tidal theory), the combined effect of sun and moon give a theoretical tidal range of less than 1 m(1). As tidal ranges can be much larger ...

12

As SimonW points out strong tidal currents will modify the wave shape and significant height. The Wolf & Prandle (1999) study provides a neat summary description of the effects of currents (of any kind) on waves: (i) Wave generation by wind—the effective wind is that relative to the surface current, and the wave age (cp/U*) and effective surface ...

11

First of all, tides are not as simple as the "two-bulge" simplification. In reality, the diagram shown is misleading. The two bulges appear assuming an ocean of constant depth covers the entire surface of Earth. Clearly that is not the case and in the diagram you can see the continents. Considering the different sizes of the basins and the distinct ...

10

This question is quite interesting because it highlights some of the common misconceptions about tides. The animation from OSU shows their model results (not from a satellite as you mentioned, but from a model that assimilates satellite data) for the global tides for a day in 2010 a week removed from the full moon. The page can be easily access on the day ...

10

This is based on the overly-simplified model of tides being the result of tidal bulges. As I explained in my answer to a related question on the physics.SE sister site, those tidal bulges do not and cannot exist. Instead, the tides are dynamic responses to the tidal forcing functions from the Moon and the Sun, with the orbits of the three bodies about one ...

9

The dynamics of the tides are quite complex. The main idea is that gravity from the Moon and the Sun affect water (and everything else) on Earth. The issue is that there are several motions that alter the distance between the 3 systems and those motions cause interactions between the different frequencies involved. The Equilibrium Theory of Tides separates ...

9

There are many factors involved, so this is worth yet another answer. At the end of his/her answer aretxabaleta states: In general, the areas near the poles have a negative trend (sea level is dropping, not rising) because of the Glacial Isostatic Adjustment (GIA) as the crust is still rebounding from the previous glaciation. In mid-latitudes, on the ...

9

There are two main approaches to measuring sea level (and thus its change): local and satellite-based. To measure local sea level we can set up gauges on the coast that record the water level every so often - hourly is common. These use various methods, which have evolved over time, all aimed at having a very precise (sometimes down to millimetres) long-...

8

Sea level rise (SLR) is anything but spatially uniform. The satellite derived SLR rates that you present are a good example of the complexity of the spatial response. A good way to explore the spatial characteristics from observations is to use the data from the Permanent Service for Mean Sea Level (PSMSL). They have a good interactive map to investigate ...

7

How exactly to oceanographers measure sea level? By a number of mechanisms, some direct, others indirect. Various government agencies such as NOAA operate coastal tidal stations that measure local sea level height. There are about a thousand of these worldwide. In addition to these official tidal stations, there are even more private stations such as those ...

7

Tide prediction at some locale is more of an empirical art rather than an analytic science. It essentially is a reduction of decades or centuries of historical tide levels at the locale to Fourier-like coefficients. Tides at a locale are modeled as a sum of various frequency components, each with a magnitude and a phase offset from some reference. The ...

7

Tides arise from the differences in gravitational pull across an object. That's why their strength falls as $r^3$ instead of $r^2$ (where $r$ is the distance between the two objects). Visually it can be understood as follows Does that makes sense? The key is to consider the differences in gravitational pull felt by the Solid Earth and both the water ...

6

The boundaries to coastal models are frequently forced using information on water level (or, less commonly, velocities) predicted from databases of tidal constituents. These databases may be global or regional, and typically they offer a grid of points with constituents available at any of these points. The products listed below are all produced by global ...

6

Areas associated with velocity shear at a stratified interface are notably strong in the region of the Equatorial Undercurrent, straits (ex: strait of Gibraltar, the Bosphorus) and regions of the thermocline where internal waves are strong (South China Sea). These areas are typically associated with strong turbulence as a direct result of the strong velocity ...

6

The explanation of all the tidal constituents is pretty complex because of the interactions between the different frequencies involved. The harmonic analysis is an expansion of the Equilibrium Theory of Tides into a set of harmonic terms. The list of relevant periods includes: the lunar day (period of lunar rotation), 24.84 mean solar hours. the sidereal ...

6

A good estimate of the lunar tidal energy dissipated into the oceans is 2.5 Terawatts (Munk, 1997; Le Provost & Lyard, 1997). The value estimated comes mainly from two different sources: from harmonic calculations and from altimetry estimates using satellite observations (e.g., Topex/Poseidon). The input of energy into the coastal ocean is not uniform ...

6

(adding this as a separate answer as it's answering a different part of the question - one that wasn't there when I did my first answer...) To understand why a rise in sea level of as little as 10cm can be significant: Imagine a place that floods occasionally. Maybe just once a year, or less. Now think about how often it almost floods - where the water ...

6

The complications of calculating the moon's contributions to earth's heat budget are touched on in Emergence of a Habitable Planet (2007) by Zahnle, et.al. in Space Science Reviews, a paper trying to determine when in earth's history the planet's surface would become cool enough to support life. The portion of the paper that relates to tidal heating ...

5

The sea level will rise uniformly due to thermal expansion of the seas, but you are right that glaciers make things more complex. Basically when a massive glacier melts its gravitational pull is redistributed in the ocean. For example if all of the antarctic ice would melt sea levels would rise everywhere, but with a largest rise in the north pole and ...

5

As you have noted, this technology is new, and so far only small numbers of experimental tidal energy converters (TECs) have been deployed. For this reason, little has been possible in the way of measurement, and so as you note, all estimates are based on models or other means of prediction. To answer the second question first - how much the currents are ...

5

I don't find Ide et al's recent paper to be very convincing. They only studied three earthquakes - hardly a statistically representative sample. There are millions of earthquakes on record, and hundreds of really big ones, of more than about MM 7.0, so there is plenty of scope for a more rigorous study. They occur at all phases of the tides. Some have ...

5

A simple way to estimate the implications is to simplify the problem. If the orbits of Earth, Sun and Moon were circular and in the same plane, and the Earth had no tilt, the only remaining tidal constituents would be $M_2$ and $S_2$ (also the overtides and combination tides: $M_4$, $MS_4$...). The rest of the tidal constituents can be expressed as linear ...

5

Venice can't really be flooded by rivers, since there are none worth mentioning throughout the city. High tides are predictable, yes. Take a look at how Venice is situated. The historic city is sheltered behind low sandbanks/islands, which form the foremost coastline. Still the laguna is - obviously - connected to the open sea. Meaning: Huge waves, like in ...

5

If the winds subsided and the flooding was caused purely by tidal effects, which are astronomical events, shouldn't it have been predictable months, if not years in advance? The tides are only partially caused by astronomical events. There's always some difference between predicted and observed tide levels. The former typically only use astronomical ...

5

Both airborne planes and the Moon affect the tides, but the effect of airborne planes is so small as to be negligible. From your sources the mass of a Boeing 747 ($m_{747}$) is $447.696$ $(10)^3$ $kg$. Likewise, from your sources, the mass of the Moon ($m_{Moon}$ is $7.347$ $(10)^{22}$ $kg$. Typically a 747 would fly at an altitude ($r_{747}$) of around \$...

4

Starting from scratch and building a "toy model" is unlikely to be successful here, because while you could certainly model Newtonian tides, much of what happens on the continental shelves is tied very closely into the shapes of coastlines and bathymetry, the interaction between the inertia of the tidal wave and friction on the seabed, and so forth - a lot ...

4

As another answer has stated, tides can broadly be predicted far ahead by harmonic analysis (which is similar to taking a fourier transform of the tidal signal, but only allowing frequencies that correspond to various astronomical periods of the sun, the moon, and interactions between the two). There are some caveats to this. As David Hammen has noted, ...

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