Carol Tichio
Wright State University

Tides Exercise

    For teachers:    Collecting tide data from areas around the United States and the world is a fun addition to other school topics like social studies, history, etc. Ask the social studies teacher which states are being studied at present or that the students like best. Ask the reading teacher in which state the plot of a book occurs.  I picked Eastport, Maine, because I was there a few summers ago.

   For non-teachers:  Pick widely separated places that interest you.  North American data are easier to find but you can use other country's tide data if you can figure out how to access them.

Assignment:

     Compare tidal information from at least three (3) sites. In your comparison, include a comparison of the sites over at least a month. Also include a comparison over a smaller time scale of less than 7 days. This shorter duration will allow you (or your students) to see the data in more detail.
    Your comparison may include graphs using the exact same vertical scale (tidal range) so that you can see the difference between stations. It may include graphing all three sites on the same graph or on three separate graphs that are aligned by time. In your comparison, you may include a map of the area, but a description is adequate.  Discuss the type of tide (semidiurnal, etc.) at each location and explain why you think the tidal ranges differ between your stations.  [Remember the water level depends on the reference level you select, it is the tidal range from low to high that is significant.]. 
    Find the phases of the moon during your month-long graphed data and relate it to the tides you observed.

1) Go to a site where tidal information is available. The National Oceanic Survey of NOAA keeps this information..

http://tidesandcurrents.noaa.gov.
    One way to access data is to click on “New Zoomable Data Map”.  Use the Zoom In tool to zoom in to the station you want.  When you have zoomed in enough the name of the station will appear on the map.  Now click on the Data icon, then click on the station again. A new window with station information should open. On the left edge select Tide/Water Level Data and under that Verified Data.
 

    Select the start and ending times of your desired data. {If  Verified Data isn’t available for that time interval, pick another time interval.} For Interval select Hourly, every 6 minutes is way too much data.
 

    Select whether you want the data relative to mean sea level (MSL), mean low low water (MLLW), etc. (I usually choose relative to mean sea level.)
 

    Select what units you want. For this exercise (and I hope all others) select meters.
 

    Select GMT (Greenwich Mean Time) because it will show the time dependence of tidal differences between stations even in different time zones.
 

    Select “view data” and the data will appear.  Under the File menu use Save Page As a text file. 

    Open a new worksheet in Excel then open the file you just saved.  This will start the import wizard. 

Choose "Fixed Width" and Start import at the first row of the data table. (You can scroll the little box in the wizard until you see where the first row of the long data listing starts; 33 for my test).  Click Next. 
Click before and after the day number and before and after the hour number to isolate these two entries. 
Click before and after the verified water level number(which is the last column) to isolate the water level values, then click Next.
Highlight the first column which has the station number, year and month then select the "Do not import column (skip)", also "Do not import" the space between date and hour.  Don Not Import the section with the colon and minutes and predicted water level  Do Not Import  the far right section which may be blank.  Click Finish.  Your spreadsheet should have 3 columns: day, hour, and verified water level.

 
In your spreadsheet, you’ll have to change time units to something that can be graphed.  To do this you need to add 24 hours for each day after the first. 

To do this use the following procedure.
 

Insert a blank column between B and C. 

Type the following formula in cell C1

=(a1-$a$1)*24+b1
 

Then use the Copy/Paste commands to copy a version of this formula into the rows 2 through the bottom of your table.  This will give time in continuously increasing hours.  The first day is set to day zero [a1-$a$1] then the number of hours is added.
 

Delete any junk in your spreadsheet below the end of the data.
 

 Now you are ready to plot water level as a function of time.  Highlight columns C and D by clicking the label at the top of C and wiping the cursor to the top of D.  Click on the Chart icon (looks like a bar graph or shelf of books).  This opens the Chart wizard.  Choose XY (Scatter) {never use Line Graph for things in this course} and the sub-type with lines but no data point marks, then Next.

If it looks reasonable, click Next again.  Now proceed to fix up the graph with labels, improved scales, etc.

You can go to Chart Options on the Chart pull down menu at the top to access other options.
 

When you are done, click Finish.
 

To plot a shorter section of data, highlight the limited section of columns C and D that you want, click on the Chart icon, and continue as before.
 

Follow a parallel procedure for all 3 of your tide station sites.
 

     Make a Word document and paste the relevant graphs into it.  Add your discussion and conclusions, noting particularly the items mentioned at the beginning of this document.
 

    Submit your report as an email attachment.  Don’t send the large spreadsheets with the long data files