Activity3part2
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Dec 6, 2023
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Geography 3 - Ocean and Atmosphere - Fall 2023 - Prof. Tim DeVries
Activity 3: Salinity, waves, and tides (Part 2: Analysis)
Purpose
In this activity you will analyze your observations from last week, to learn more about
the variations in salinity, waves, and tides along our coastline, and what factors affect
them.
Materials
•
Optical refractometer
•
1 seawater sample (obtained last week)
•
Computer with internet connection
Part A: Salinity and density
1. Obtain an optical refractometer, and instructions on its use, from your TA. Note that
the refractometer measures specific gravity, rather than density. To obtain density,
multiply the specific gravity by the density of pure water (1000 kg/m
3
). Measure the
salinity and density of your water sample(s). Record the values below for your
samples. (Salinity in ppt, density in kg/m
3
).
Campus Point
Salinity : 33ppt
Density : 1025kg/m^3
2. Why might the density value that you measured be different from the density value of
your sample when you took it (i.e. what factors might have caused a
change in the
density of your water sample). List 2 potential causes.
Temperature is a factor that may cause a change in density. If the temperature of the
water sample increases in temperature, then the density increases as well. Salinity of
the water is also a factor. The higher the salinity the higher the density
3. What was your sampling location (lagoon, campus point across from lagoon, or
campus point across from Anacapa housing)? Write down your group’s average
salinity and density at your sampling location on the board at the front of the class.
Campus point across from lagoon.
Average salinity: 33ppt
Average density: 1025kg/m^3
4. After everyone has written down their average salinity and density for their group’s
sampling location on the board, compare the salinity for all three locations. Which
location had the highest salinity? Which had the lowest? Is there any variability in
salinity from one location to another and if so what might be causing that?
Highest Salinity location: Lagoon
Lowest Salinity Location: Campus point (both locations)
The Lagoon has higher salinity than campus point ocean because the lagoon and the
ocean are separated by a barrier. The water in the lagoon evaporates, increasing
the salinity of the water.
5. Which location had the highest density? Which had the lowest? What might be
causing variability in density from one location to another?
Highest Density Location: Lagoon
Lowest Density Location: Campus point (both locations)
The lagoon had higher density because they have higher salinity. This variability is
caused by the variability of salinity level.This will include factors like temperature as
mentioned in the previous question.
Geography 3 - Ocean and Atmosphere - Fall 2023 - Prof. Tim DeVries
Part B: Tides
1. Go to the NOAA (National Oceanographic and Atmospheric Administration) tide
predictions website for Santa Barbara at
https://
tidesandcurrents.noaa.gov/noaatidepredictions.html?id=9411340
. Navigate to the
date of your observations. What was the tide height at the time of your observations
last week? Was the tide coming in or going out? Were your observations accurate?
Tide height: around 3.5ft
My observations were fairly accurate. The tides were coming in during the time of my
observation, which is similar to what the website states as it indicates the tide is
coming from low to high tides.
2. What was the time and water height of the highest tide on the day of your
observations? What was the time and water height of the lowest tide? What was
the range (high minus low)?
Highest tide: 6pm
Lowest tide: 12am
3. Go to the website
https://moon.nasa.gov/moon-in-motion/tides/
and view the
animations and explanations. Explain why there are two low tides and two high tides
per day (for most places on Earth, including Santa Barbara).
-
Most shorelines experience two high and two low tides per day. When the
ocean is facing towards or away from the moon, the bulge would be pulled
towards the moon or away from the moon (other side) causing high tides to
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occur. The sun also does the same. When the Sun, Earth, and Moon are
aligned (during full moons and new moons). Due to the earth's rotation and the
moons rotation, high tides occur two time each day.
4. What was the phase of the moon on the day of your observations? You can check
http://www.moonconnection.com/moon_phases_calendar.phtml
. Explain why the
swing between high and low tides is larger on full/new moons than during half
moons.
The moon was in the waning gibbous phase. This means that the tides were low. The
tide is larger on new/full moons because the moon and the sun are on the same
line, causing a combined force of gravitational force on the ocean water. Tides are
smaller during half moons because the forces are counteracting.
Geography 3 - Ocean and Atmosphere - Fall 2023 - Prof. Tim DeVries
Part C: Waves
1. You will compare your wave observations to data from the East Santa Barbara Buoy,
which is located in the Santa Barbara Channel and is the closest ocean buoy to
Goleta Point (you can check the location at
http://
www.ndbc.noaa.gov/station_page.php?station=46053
). Wave conditions at the East
Santa Barbara Buoy should be similar to wave conditions at Campus Point. You can
access the buoy wave data for the past 45 days at
http://
www.ndbc.noaa.gov/data/realtime2/46053.spec
. What was the average wave height
(WVHT) recorded by the buoy during the time at which you made your observations
last week? What was the average swell period (SwP)?
WVHT: 1.4
SwP:7.7
2. How do these match up with your observations? What factors could cause
differences between the waves height and period recorded at the East Santa
Barbara Buoy, and that which you observed? List 2 factors.
The friction of the seafloor causes the height and period of a wave to be shorter and
slower closer to shore. Shallow areas will be more affected by the friction of the
floor. Local wind conditions can also be a factor as wind patterns near the shore
can differ from those recorded at the buoy. Local winds can generate additional
waves that modify the characteristics of the original waves.
3. From what direction were the swells traveling (SwD)? Given that Campus Point
faces south (or southeast), what happens to these waves as they approach the
shore? Does this match up with what you observed at Campus Point?
SwD: W
Refraction, diffraction, and reflection can occur that causes the waves to change in
direction
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