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I.  The objectives of this exercise are:
        1.  To become familiar with Ocean Tide Models, what they do, why they are generated, and how the models relate to tidal cycles predicted for the deep ocean.
        2. To become familiar with coastal tide prediction models and how they relate to coastal water movement.
        3. To recognize the relationship between deep ocean tide models and coastal tide predictions.
        4. To become familiar with Topex-Poseidon sea surface altimetry data and how these data are used to understand ocean water movement induced by tides
        5. You will use information from two CDs:
                a.  A Collection of Global Ocean Tide Models, published by JPL
                b. WXTIDE32 version 2.6  Tide Prediction Program
                        Copyright 1998-2000 Michael Hopper

You may want to review the unifying theories explaining tides (Equilibrium Tide Theory, Dynamic Tide Theory) and the definition of amphidromic systems from your old MARS 120 text.

I. A Collection of Global Ocean Tide Models
 A. Open the CD:
      1.  Select My Computer, select the CD drive and click on the index icon
      2. scroll down and click on the Contents icon
        a. read the Introduction
        b. read the Essential Definitions and be sure you understand the following terms:
                1. pure ocean tide
                2.  barotropic tide
                3. short period and long period tides
                4. M2, S2, K1 and O1 tides components  (see handout)

B. Go back to the CD main page
    1. scroll down and click on the Documents icon
    2. open Plots,
        a. Barotropic Tides in the Global Oceans from a Nonlinear Tidal Model  Assimilating Altimetric Tides
        b. scroll down to Introductory Figures of General Interest
        c. Examine Figures 1-4
        d. Make note of the following information:
            1. Where in the North Pacific are the M2, S2, K1 and O1 tidal components largest? smallest?
            2. In the eastern North Pacific, what is the approximate latitude and longitude of the M2 amphidromic node?  The S2 node?  The K1 and O1 nodes?
            3. In which direction does the M2 amphidrome rotate?  The numerical value of the co-phase lines on these images are difficult to read.  So it is difficult to determine rotation direction from these images.  So, you can use information from a the second CD, wxTide26 to confirm rotation direction.
            4. Which one (M2, S2, K2 or O1) produces the largest tidal range (amplitude)?
            5. Determine the composite tidal range off the coast of California, if all four tidal components positively reinforce each other.
        e. Examine figures 5 and 6, current ellipses associated with the M2 and S2 tidal components.
            1. What is the period of rotation of the M2 ellipse?  In other words, how long does it take for a parcel of water to travel around that ellipse?
            2. What is the period of rotation of the S2 ellipse?
            3. What are the effects of tidal currents on water mass movements in the California Bight predicted by Topex models?.
 

II.  WXTIDE32 version 2.6
        Tide Prediction Program
        Copyright 1998-2000 Michael Hopper (mikehopper@usa.net)
        www.GeoCities.com/SiliconValley/Horizon/1195/

    1. Insert CD; select My computer; select CD drive; double click to open wxtide26 folder; double click on WXTIDE32 (blue icon) to open.  You may need to expand the view to fit the entire screen by clicking on the upper right corner of the view window.
    2. Things to note:
        a. Grey indicates hours of darkness
        b. Yellow indicates hours of daylight
        c. Blue indicates rising tide hours
        d. Green indicates falling tide hours
    3. Under OPTIONS, select Graph, then choose Preferences:
        a. Choose display units as meters
        b. Choose the year, month and day of interest (to begin, look at tides for Sept 24, 2005, the first day of the Sproul cruise).
        c. click on OK
    4. Under OPTIONS, choose Location:
        a. on the upper right, select a general region (for example, N. America, Pacific)
        b. on left, scroll down to the location you want to view
        c. Note that you can sort stations alphabetically or by lat/lon
    5. Note the station information given in the upper left of the Location menu
    6. Place the cursor at any point on the graph, hold down the left mouse key.  A text box will appear that gives time, date, tide height for that place on the graph
    7. Note that you can scroll right (earlier time) or left (later time) using the scroll bar at the bottom of the page.  Numbers along the scroll line are hours.  Date and time is displayed when the scroll bar box is activated and is also given at the top of the page.

Your task:  Please take careful notes.  You will use this information when you write the lab report.
    1. Determine the tidal cycle for the dates of the Fall 2005 Sproul Cruise.  Make note of the high and low tide times, tide height and the phase of the moon at THREE tide stations near the cruise track.  Compare the information given for the three sites.
    2. Using the Locations Option set for alphabetical arrangement, select San Diego Bay Entrance, California Current.
        a. Use the scroll option to view the tidally induced current on the date of the Sproul cruise
        b. Compare the tidally induced current velocity to the time in the tidal cycle.  At what times in the tidal cycle is the current velocity highest?  In which direction is the tide moving the water (into the bay; out of the bay)? At what times is the current slack?
        c. Determine how (direction, extent) the tidally induce current affected the ships speed at the times it was entering and exiting the harbor during the three legs of the cruise.
    3. Determine the rotation direction of the amphidromic system that affects the California Bight by determining the HH and LL tide time for at least FOUR open ocean tide stations along the coast of California.  Compare the progression of tide times to determine whether the tide wave is progressing northward or southward.
        a.  Note that you can use the map feature to zoom to tide station locations of interest.  When you have the Location menu open, a second blue icon will appear in boxes open bar along the bottom of the monitor.  Click on the second icon and the map view will open.  View the map and Location boxes simultaneously.  Click on a location on the map and the Location menu will automatically go to the nearest tide station.

III.  Considering the information you found using the WXTide26 and Topex/Poseidon Global Ocean Tide Models CD, summarize the following in both table and text format:
        a. The rotation direction and periodicity of the amphidromic system that affects the west coast of North America
        b. How the two different approaches to tide modeling fit together ( Do the two models support each other? Contradict each other?)
        c. The portion of the water column influenced by tide wave motion
        d.  The range of velocities of tidal currents near the entrance to San Diego Bay.  Is the range of velocities of tidal currents experienced over the entire California Bight likely to be similar, larger or smaller that observed near the entrance to San Diego Bay?  Why?
        e. What is different about tide measurements made by tide gauges and altimetry data filtered to examine the effects of tides on ocean surface elevation?