Lab_09_Ocean_Waves

In this expedition you will investigate the movement of deep water waves, and how their patterns and characteristics are modified by the entrance in shallow water (water that is less than ½ their wavelength). A. DESCRIBING WAVES (WAVE CHARACTERISTICS) The main characteristics used by oceanographers to describe ocean waves are: • Wave length , L (distance between adjacent crests, or troughs) • Wave height, H (vertical distance between a crest and trough) • Wave steepness (H/L) • Wave amplitude (vertical distance between the highest crest or deepest through and the equilibrium line) • Wave period, T (time between two successive crests, or troughs) • Wave speed (L/T) • Wave frequency , the number of wave crests or troughs that pass a point in a given period of time. 1. Using the waves in Figure 1 below, • Calculate the wave length (round to the nearest 5 m) __________ • Calculate wave height (round to the nearest 0.5 m) __________ • Calculate wave steepness _____________ • Knowing that waves break when steepness is equal to or greater than 1/7, are the waves in Figure 1 breaking? (yes or no) Figure 1

ESSC 320, LAB 10 2 2. Using the waves in Figure 2 below, • Calculate the wave length (round to the nearest 5 m) __________ • Calculate wave height (round to the nearest 0.5 m) __________ • Calculate wave steepness (within two decimal digits) _____________ • Knowing that waves break when steepness is equal to or greater than 1/7, are the waves in Figure 2 breaking? (yes or no) Figure 2 B. DEEP WATER WAVES Recall from your textbook that deep water waves are waves that travel in water depth greater than half of their wavelength. The water molecules of a deep-water wave move in a circular orbit, and the diameter of the orbit decreases with the distance from the surface. The motion is felt down to a distance of approximately one half wavelength, where the wave's energy becomes negligible. The wave animation posted online shows the movement of water particles at and below the ocean surface as a series of swells is passing by, moving from left to right. 3. Using a ruler and the horizontal and vertical scales, estimate the following (you may need to stop the animation to measure and read time; use the orange arrow above the animation as reference point when counting wave crests): • wave length (round to the nearest 10 m) __________ • wave height (round to the nearest 5 m) __________ • wave period (round to the nearest second) _____________ • wave speed (within two decimal digits) _____________ • wave frequency (per minute) __________________ 4. At what depth should a diver descend to not feel water motion? _____________ meters.

ESSC 320, LAB 10 3 C. HOW THE WIND INFLUENCES THE DIRECTION AND HEIGHT OF DEEP WATER WAVES Most deep water waves originate as disturbances produced by the wind, and over the long-term average the direction of wave movement largely mirrors the prevailing winds . But on any given day, wind direction may be much different than the long-term average due to weather systems ( e.g . storm systems) traveling over the ocean. These wind shifts and related variations in wind speed alter wave characteristics, including the direction of wave movement and wave height. For this part of the lab, you will need to observe four maps posted on two different websites. Because you will be looking at conditions that are current at the time you look at the maps, I will need copies of the maps to grade your work. Before you continue, open a word processor, or PowerPoint, or Google Docs, and create a file where you will copy the maps (ESSC320_Lab_10_Maps). Go to the Oceanweather website (link posted online, or go to oceanweather.com/data) and obtain the most recent map of significant wave height (click on “global” on the menu on the left side of the screen). The map shows significant wave heights and wave direction for the current day and time 1 . Significant wave height is defined as the average height of the highest one-third of waves observed. On the map, they are displayed in feet and meters using a color-coded background (the legend is under the map). The black arrows represent the direction of wave movement, and are oriented perpendicular (90 degrees) to the advancing wave crests. 5. According the map, at which latitudes (both the Northern and Southern Hemispheres) the regions of highest significant wave heights covered a significant portion of the ocean surface? What were the maximum significant heights measured? Your answer must correctly identify latitude and longitude to the nearest 5 degrees. When you are done, right click on the map, and copy and paste it to the file you created (see highlighted instructions above). You will now compare significant wave heights (SWH) to the strength of the wind.  On the map, identify the region with the highest SWH, or with the largest amount of surface with high SWH (for example, the South Pacific).  Open a new window in your browser, and go to https://www.passageweather.com/ (link posted online).  Select from the menu on the left the same area you identified at the first step (step a) (e.g. South Pacific).  A new page will open, with three maps (scroll down to see them). Each map can be animated.  The first map from the top shows surface wind speed (colors) and directions (wind barbs, or wind arrows pointing in the direction towards which the wind is blowing).  The second map from the top shows isobars (lines joining points at the same air pressure) and atmospheric pressures (in colors).  The third map from the top shows significant wave heights. 6. Animate the surface winds map. Do you see any area where the winds are moving in a circular pattern? If yes, give latitude and longitude. If not, try another part of the world. HINT: if you are in doubt, check the EarthNullSchool website (link posted online) for a spectacular view of current wind strengths and directions. In the northern hemisphere atmospheric high pressure systems rotate clockwise and atmospheric low pressure systems (storms) rotate counterclockwise as seen from above. In the Southern Hemisphere, the rotations of atmospheric highs are counterclockwise and lows (storms) are clockwise. 1 The wind direction is derived from a model that is initialized using actual wind observations obtained by buoys plus remote sensing of the state of the sea by satellite.