Water on the Move The Ebbs and Flows of the Sea

 

Going Further Of Tides and Time Purpose To use the Internet as a source for real and current data. To demonstrate the rhythmic patterns of tides throughout a month. To chart the relationship between tides and phases of the moon. Historical tidal gauge at Anchorage, Alaska where the tidal range is typically 35 feet. Photo courtesy of NOAA's Oceanographic Products and Services Division. Materials a computer with Internet access and spreadsheet software Background Information In most parts of the world, the difference between high and low tide amounts to only a few feet. Nevertheless, this change in water level still is enough to be very important in some areas. In many places at low tide, the water is too shallow to allow boats to move effectively into an out of harbors, whereas at high tide it is deep enough for them to do so. Because of their effect on navigation, tides have been studied for many years, and today physical oceanographers know quite a bit about their causes and characteristics. Procedure Go to NOAA's tide predictions web site and choose a reference station in or near your home state. Tide predictions are given for the next six months. Decide which month you are going to chart then, using your mouse, select the data for that month onscreen. Copy the selected data (from the Edit menu, choose Copy) and paste it into your spreadsheet program. You may need to parse the data into individual cells; consult your spreadsheet user's manual for guidance. In your spreadsheet program, make a chart of high and low tides plotting the days of the month against the tide predictions. What kind of patterns do the data reveal? You can also use our data and plot it with colored pencils on some graph paper: High and Low Tides for Boston, Massachusetts January, 1999 Date Low High Date Low High 1 -0.5 11.9 17 0.7 10.4 2 -0.6 11.9 18 0.5 10.6 3 -0.5 11.8 19 0.3 10.8 4 -0.3 11.5 20 0.1 10.8 5 0 11 21 0 10.7 6 0.3 10.4 22 0 10.5 7 0.7 9.8 23 0 10.1 8 1.1 9.3 24 0 9.8 9 1.4 8.8 25 0 9.5 10 1.5 8.5 26 -0.1 9.3 11 1.4 8.3 27 0.2 10.6 12 1.5 9.2 28 0.2 10.8 13 1.5 9.4 29 0.1 11.1 14 1.4 9.6 30 -0.1 11.3 15 1.2 9.9 31 -0.2 11.3 16 1 10.2 Going Further Gather tide data for additional locations; try sites in Alaska and Hawaii. Compare the high tides for each of the locations. Look at maps for each of the areas and form a hypothesis for why these tides reach different heights. Tides are cyclical and closely follow the phases of the moon. During the new and full moons, the distance between the high and low tides increases, which means that high tides get higher and low tides get lower. Use your chart to predict when the new moon or full moon will occur. Check your predictions by looking up moon phase data for the month you plotted at the US Naval Observatory's moon illumination page.

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