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Tides - Coggle Diagram

- - - - This is the time it takes for the earth to rotate from an exact point under the moon to the same point
      - There is one total tidal cycle every lunar day, either diurnal, semidiurnal, or mixed semidiurnal
    - - The length of a lunar month can vary depending on how far the moon is away from the earth. A lunar month is longer than average when the moon is near apogee, and shorter than average when the moon is at perigee.
      - On average a lunar month is 2.22 days longer than a sidereal month
      - A lunar month is not the same as the time it takes the moon to make a full orbit around the earth. That is known as a sidereal month and takes 27 days 7 hours 43 minutes 12 seconds
      - Each lunar or tidal month will have two spring tides and two neap tides
  - - - Spring tides are when the tidal range is at its greatest. This happens during full or new moons
      - Neap tides are when the tidal range is at its least. This happens approximately 7 days after a spring tide when the sun and moon are at right angles rather than in line, also known as when the moon appears half full.
  - - - High water and low water are the points throughout the day at which the tide reaches its highest and lowest points. In the majority of areas there will be
      - When looking for predictions, you will first need to be looking at a specific location. Tidal times and ranges will be similar for nearby areas, but not exact.
      - Predictions given will include times for high and low water, as well as heights in terms of feet above station datum
    - - Mean high water springs and mean low water springs
      - These two datums are averages of either low or high tide during a spring tide
    - - Mean high water neaps and mean low water neaps
      - These two datums are the averages of either low or high tide during a neap tide.
      - This can be useful when planning longer expeditions to see how tides will change as a neap tide approaches
- - - - National Tidal Datum Epoch
        
        The specific 19-year period adopted by the National Ocean Service as the official time segment over which tide observations are taken and reduced to obtain mean values (e.g., mean lower low water, etc.) for tidal datums. It is necessary for standardization because of periodic and apparent secular trends in sea level. The present NTDE is 1983 through 2001 and is actively considered for revision every 20-25 years. Tidal datums in certain regions with anomalous sea level changes (Alaska, Gulf of Mexico) are calculated on a Modified 5-Year Epoch.
      - Station Datum
        
        A fixed base elevation at a tide station to which all water level measurements are referred. The datum is unique to each station and is established at a lower elevation than the water is ever expected to reach. It is referenced to the primary bench mark at the station and is held constant regardless of changes to the water level gauge or tide staff. The datum of tabulation is most often at the zero of the first tide staff installed.
      - HAT
        
        Highest Astronomical Tide
        
        The elevation of the highest predicted astronomical tide expected to occur at a specific tide station over the National Tidal Datum Epoch.
      - MHHW
        
        Mean Higher High Water
        
        The average of the higher high water height of each tidal day observed over the National Tidal Datum Epoch. For stations with shorter series, comparison of simultaneous observations with a control tide station is made in order to derive the equivalent datum of the National Tidal Datum Epoch.
      - MHW
        
        Mean High Water
        
        The average of all the high water heights observed over the National Tidal Datum Epoch. For stations with shorter series, comparison of simultaneous observations with a control tide station is made in order to derive the equivalent datum of the National Tidal Datum Epoch.
      - DTL
        
        Diurnal Tide Level
        
        The arithmetic mean of mean higher high water and mean lower low water.
      - MTL
        
        Mean Tide Level
        
        The arithmetic mean of mean high water and mean low water.
      - MSL
        
        Mean Sea Level
        
        The arithmetic mean of hourly heights observed over the National Tidal Datum Epoch. Shorter series are specified in the name; e.g. monthly mean sea level and yearly mean sea level.
      - MLW
        
        Mean Low Water
        
        The average of all the low water heights observed over the National Tidal Datum Epoch. For stations with shorter series, comparison of simultaneous observations with a control tide station is made in order to derive the equivalent datum of the National Tidal Datum Epoch.
      - MLLW
        
        Mean Lower Low Water
        
        The average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch. For stations with shorter series, comparison of simultaneous observations with a control tide station is made in order to derive the equivalent datum of the National Tidal Datum Epoch.
      - LAT
        
        Lowest Astronomical Tide
        
        The elevation of the lowest astronomical predicted tide expected to occur at a specific tide station over the National Tidal Datum Epoch.
      - GT
        
        Great Diurnal Range
        
        The difference in height between mean higher high water and mean lower low water.
      - MN
        
        Mean Range of Tide
        
        The difference in height between mean high water and mean low water.
      - DHQ
        
        Mean Diurnal High Water Inequality
        
        One-half the average difference between the two high waters of each tidal day observed over the National Tidal Datum Epoch. It is obtained by subtracting the mean of all the high waters from the mean of the higher high waters.
      - DLQ
        
        Mean Diurnal Low Water Inequality
        
        One-half the average difference between the two low waters of each tidal day observed over the National Tidal Datum Epoch. It is obtained by subtracting the mean of the lower low waters from the mean of all the low waters.
      - HWI
        
        Greenwich High Water Interval
        
        The average interval (in hours) between the moon's transit over the Greenwich meridian and the following high water at a location.
      - LWI
        
        Greenwich Low Water Interval
        
        The average interval (in hours) between the moon's transit over the Greenwich meridian and the following low water at a location.
      - Max Tide
        
        Highest Observed Tide
        
        The maximum height reached by a rising tide. The high water is due to the periodic tidal forces and the effects of meteorological, hydrologic, and/or oceanographic conditions.
      - Min Tide
        
        Lowest Observed Tide
        
        The minimum height reached by a falling tide. The low water is due to the periodic tidal forces and the effects of meteorological, hydrologic, and/or oceanographic conditions.
- - - - The point at which the sun crosses the Earth's celestial equator.
      - At this point, the Sun is directly over the Earth's equator and most in line with the elliptical of the Moon's orbit
      - Normal spring tides occur twice a month when the Sun, Moon, and Earth are most in line with each other. Because of the varying declinations of the Earth, it's orbit around the Sun, and the Moon's orbit around it these three bodies never quite line up. The equinoxes however, provide an opportunity for these declinations to align. If a spring tide were to happen near or during an equinox, the spring tide would have an even greater range than normal.
    - - Apogee is the point at which any orbiting object is furthest from the Earth, most notably the Moon
      - The further away an object is, the less gravitational effect it has and vice versa. This means that the moon has its greatest individual affect on the tides at perigee, and the least affect at apogee.
      - Inverse to that, Perigee is the point at which a satellite is closest to the earth