INGOMAR MIDDLE SCHOOL SCIENCE  TIDES           NAME: ______________________
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In the first part of this investigation we saw how the tide wave is a composite of partial tides and we used a model to demonstrate how the moon exerts its tidal influence on the ocean. This part of the investigation focuses on sources and interpretation of real-time tide observations and predictions.

Local tides result from a complex interplay of astronomical and non-astronomical factors. However, they can be predicted with a high degree of accuracy through a detailed analysis of the long-term tide record. Examine the Tide Table presented below for Humboldt Bay, CA for two days in June 2003. The tide height is measured in feet above or below Mean Lower Low Water (MLLW). MLLW is the standard datum level used in the U.S., based on low-tide water levels observed over a number of years. Times are local, Pacific Daylight Time (PDT), using a 24-hour clock. H is high tide and L is low tide.

Station No. 9418767 Humboldt Bay, North Spit, CA
(Water level data is referenced to MLLW)

During this two-day period for which data are given in the table, the predicted maximum high tide is _____ feet and the predicted minimum low tide is _____ feet.

Plot the tidal observations from the tide table on the Tidal Height Graph below. Draw smooth lines to connect the adjacent points you have plotted. You have drawn a tidal curve. It depicts expected local changes in water level over time. This tidal curve shows that during a one-day period, this location appears typically to experience [(0) (1) (2)] high tide(s) and [(0) (1) (2)] low tide(s).

As plotted on your diagram, the Humboldt tide is a [(diurnal) (semi-diurnal) (mixed)] tide.

The time between successive high tides is called the tidal period. The average tidal period for your tidal curve is about [(one quarter) (one half) (one)] day.

From the tidal curve you drew, determine the tidal range over the two-day period. It is the vertical distance between the highest high tide and the lowest low tide that occurred during the two days. The tidal range was _____ feet.

Notice that the high tides are not of the same height, nor are the low tides at the same height. Also, the times between successive high and low tides are not the same. This is due ultimately to the variations in the combined gravitational effects of the moon and sun, as their positions relative to Earth change continually. A total of 37 harmonic constants (partial tide components) are employed in the predictions you have plotted!

Real-time observed and predicted water levels (tides) are available online for many coastal locations in the U.S. J Go to DataStreme Ocean  and under "Physical & Chemical," click on "Tides." This will bring you to the NOAA National Ocean Service (NOS) Center for Operational Oceanographic Products and Services (CO-OPS). Click on "Tides Online," and then (on the left) "Select Stations By . . . State Maps." The interactive U.S. map allows you to access tide information from coastal locations in the U.S.

On the map click on Florida and then click on the red dot representing Panama City Beach. In the uppermost depiction, water level data are plotted in feet above MLLW (on the vertical axis) on a three-day graph with the time scale along the horizontal axis. The smooth blue curve represents the predicted tide based on the combination of partial tides. The red curve, composed of "X's", is the actual observed changes in water level. The vertical dashed line marks the time of the latest observation. (Also indicated on the tidal graph to the upper left are the most recent observed and predicted water heights.) According to the predicted water level curve, Panama City Beach experiences [(0) (1) (2)] high tide(s) and [(0) (1) (2)] low tide(s) each day. Such tides are described as [(diurnal) (semidiurnal) (mixed)]. The tidal range at Panama City Beach is about [(1.5) (4)] ft.

Use your browser's "back" button to return to the Florida map. Click on the dot for Mayport (Bar Pilots Dock). On the new map that appears, click on the dot representing Mayport. According to the actual and predicted water level curves, Mayport experiences [(0) (1) (2)] high tide(s) and [(0) (1) (2)] low tide(s) each day. The heights of predicted high tides are approximately equal and the heights of predicted low tides are approximately equal. Tides with these frequency and height characteristics are described as [(diurnal) (semidiurnal) (mixed)]. The tidal range at Mayport is about [(2) (4.5)] ft.

Although Panama City Beach (on the Gulf of Mexico coast) and Mayport (on the Atlantic coast) are located at about the same latitude, their tides differ significantly in both type and range. We can attribute this contrast in tides to differences in [(astronomical forces) (geographical setting of the two locations)].

Compare the predicted versus actual water levels at Mayport. Two factors that play major roles in producing differences between predicted and actual values are reported in the two graphs that immediately follow the water level graph. They are __________________ and ______________________.

Use your browser's "back" button to return to the U.S. map. Click on Washington State and then Neah Bay, WA. According to the actual and predicted water level curve, Neah Bay experiences [(0) (1) (2)] high tide(s) and [(0) (1) (2)] low tide(s) each day. The heights of high tides are [(approximately equal) (very different)] and the heights of low tides are [(approximately equal) (very different)]. Such tides are described as [(diurnal) (semidiurnal) (mixed)].