You are welcome to do any or all of the Extra Credit options below

Oceanography 101

Linda Khandro

Extra Credit (10 points) Name______________

You will need to print the second page, with the tidal graph.

Tide Prediction:

People going into or out of a harbor, or anchoring near a shore, need to know in advance about the behavior of the tide. The tide is caused by the gravitational pull of the moon and the sun on the oceans, and the rotation of the earth, but its exact pattern at any particular spot on the coast depends very strongly on the shape of the coastline and on the profile of the sea floor nearby. So even though the forces that move the tide are well understood, the tides at any one spot are essentially impossible to calculate theoretically. What we can do is to record the height of the tide at that spot over a long period of time, and use these measurements to predict the tides in the future.

A Typical Tidal Record:

The graph below shows the tidal record for two weeks (January 1-14, 1884) at Bombay, India. The tide was recorded on a cylindrical sheet that turned once every 24 hours. Each daily curve is labeled with its date. Some obvious features: Note that on the graph, time increases to the LEFT.

· there are usually two high tides and two low tides each day;

· the tides come about 50 minutes later each day;

· during the two-week period there is considerable variation in the daily pattern of highs and lows;

· there is usually a difference in height between two consecutive high tides (the diurnal inequality).

Procedure:

1. Learn how to follow each date, starting with January 14, by outlining the date curve with a colored pencil. Now use this website to find the phases of the moon for these dates, Jan 1 – 14, 1884. http://www.timeanddate.com/calendar/?year=1884&country=35 .

2. Match the appropriate moon phases from the website with spring and neap tide dates and times from the graph, for the entire month of January. You have 2 weeks of data on the graph, and must extrapolate backwards in time to find the remaining possible tide heights. Type your answers into the chart below:

Moon Phase Tide Height Date Time

Spring tide:

Neap tide:

Spring tide:

Neap tide:

From George H. Darwin's article "Tides" in the 9th edition of the Encyclopaedia Britannica. Note that in this graph, time increases to the left.