Assignment 4_Waves_493af48ca4f97fb1c052766f8a106c4f
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Brooklyn College, CUNY *
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Course
3011
Subject
Geography
Date
Feb 20, 2024
Type
Pages
9
Uploaded by animaksimyan
The Argentine Basin Surface Mooring
buoy bobs with the waves after being
deployed in over 3 miles of water
(5.2km).
NOAA ship R/V Ron Brown in
high seas
Coastal erosion images from
USGS
ASSIG
N
ME
N
T 4 - OCEA
N
WAVES: LI
N
KI
N
G
THE MARI
N
E ATMOSPHERE A
N
D THE
OCEA
N
SURFACE
One of the most dramatic occurrences we see in the atmosphere are storm disturbances that
create strong winds, cloud cover, and precipitation. At mid-latitudes, these storm events occur
when a cold air mass and a warm air mass collide and are often referred to as extratropical
cyclones. In many cases, these storms are also referred to as low-pressure systems as the
atmospheric pressure decreases where these two air masses meet. Extratropical storms can vary
in duration and strength and at times can intensify quickly. Under the right conditions, an
extratropical storm may develop into what is called a ‘bomb’ cyclone. A bomb cyclone is a
unique event and is characterized by a very sudden drop in atmospheric pressure and changes in
winds around this area. The link to the animation below shows the cloud cover on January 4,
2018 at 8am as a storm passed over the New England continental shelf. At the time of this
animation, the storm is located just off the coast of New Jersey. The white streaks in the
animation show the direction and speed of the winds. Notice the speed of the winds associated
with the storm front.
https://www.ventusky.com/?p=37.1;-65.7;3&l=clouds-total&t=20180104/12
The waves created by these intense storms travel to the shoreline and are responsible for extreme
amounts of coastal erosion and flooding that puts infrastructure, ecosystems, and communities at
risk. In addition, they can produce extremely dangerous conditions for ships at sea. This means
that observing them and predicting where and when they will occur is important to society.
Background information
OOI Array:
Map of the
locations of
moorings and
mobile assets on
the Coastal
Pioneer Array.
https://oceanobservatories.org/array/coastal-pioneer-array/
Sensors (meteorological/water quality): https://oceanobservatories.org/site/cp01cnsm/
Sensors (surface waves): https://oceanobservatories.org/instrument-class/wavss/
The atmosphere and the ocean are interconnected, so the pressure changes and winds associated
with these storms cause changes on the ocean surface. In particular, winds blowing across the
ocean surface generate gravity waves. The size of these waves will depend on the speed and
duration of the winds and the distance the winds blow over the ocean, also known as fetch.
Surface ocean waves are generally classified by their wave height, wave period, and wavelength.
Using what you already know about waves, match
the definition of each wave
characteristic to the appropriate letter
in the figure below.
Wave height wavelength amplitude wave trough wave
crest
Scientists use meteorological stations and wave buoys that float on the ocean surface to monitor
the dynamic intersection between the atmosphere and ocean. These data help to develop and test
models for air-sea interactions and provide real-time warnings about dangerous conditions. This
exercise uses data from the central surface buoy in the OOI Pioneer Array to evaluate a quickly
developing low pressure center (a ‘bomb cyclone’) on the New England continental shelf and the
response of the sea surface to the rapidly changing winds and pressure.
Wave Crest
Wave Length
Amplitude
Wave Height
Wave Trough
4.1 – HOW DO ATMOSPHERIC CONDITIONS
AT THE OCEAN SURFACE CHANGE?
Your objective for this activity is to use OOI data to examine how the atmospheric conditions
above the ocean change. Specifically we will look at barometric pressure and wind speed at the
ocean surface for a one-week period (January 1 – January 7, 2018).
Questions:
1. What is the maximum and minimum barometric pressure during this week?
2. What is the day and time (each point is 1 hr) when the maximum and minimum occur?
3. What is the barometric pressure on January 3, 2018 at 1800?
4. Describe the changes, if any, to barometric pressure between January 1 and the end of
January.
5. What is the maximum and minimum wind speed during this time period?
6. When the storm passed over the instruments from January 4 to January 6, was the
relationship between barometric pressure and wind speed positive (e.g., both increasing or
The maximum is 1026 mbar.
The minimum is 965 mbar.
The maximum is on Jan. 3 at 2 pm
The minimum is on Jan. 4 at 6 pm.
The barometric pressure is 1024
Barometric pressure remains the same
The maximum wind speed is 19 m/s
The minimum wind speed is 0.8 m/s
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decreasing) or negative (one increasing and one decreasing)?
7. Recall that winds are generated by air moving from high pressure to low pressure. If the
barometric pressure had dropped more on January 4th (e.g., to 945 mbar), do you think the
winds would be weaker or stronger?
8. As wind speed increased on January 4th, what do you think happened to the height of the
waves at the location of the buoy?
4.2 - HOW DOES THE OCEAN REACT TO
CHANGES IN THE ATMOSPHERE?
Your objective for this activity is to use OOI data to investigate how the changes in the
atmosphere you examined in section 4.1 impact the ocean surface. Specifically you determine
how long high wind speeds were present at the instrument location and then look for any
relationships between these winds and the height of ocean surface waves that develop.
1. Calculate the total decrease in barometric pressure between January 4, 2018 0000 and
The relationship is negative because the barometric pressure is decreasing while the wind speed is increasing.
The winds would be weaker.
The height of the waves will likely increase
January 4, 2018, 1800 (points are 1 hr intervals).
2. How much did the winds increase during this same 18-hour time period?
3. Find the first time the wind speed exceeded 12 m/s and then the time when it dropped below
12m/s again. Calculate the total time the wind speed was above 12 m/s.
4. Identify the maximum wind speed and maximum wave height during the week.
5. Is there a positive or negative relationship between wind speed and wave height?
6. Do changes in wind speed and wave height happen at the same time or does one happen
before the other?
7. A storm like this is referred to as a ‘bomb cyclone’ if the barometric pressure drops by at
least 24 mbar in 24 hours. Does this storm fit the description of a bomb cyclone?
8. If the winds had reached higher speeds, what do you think would have happened to the
height of the waves near the buoy location?
9. An 8-meter wave height is about the same size as a two-story building. What are the possible
impacts of a wave this size?
The total decrease in the barometric pressure is 55 mbar
The winds increase by 13 m/s
The wind speed was above 12 m/s for a total of one hour
The maximum wind speed is 19 m/S
The maximum wave is 8 m
This shows a positive relationship
The changes in wind speed happen before the wave height
The height of the waves would increase.
Wave size is affected by wind speed, wind duration, and fetch. If there is a low wind speed small waves will form and if there is a high wind speed larger waves will form.
No it doesn’t
4.3 – WAVE DYNAMICS
Your objective for this activity is to use the OOI data to investigate the characteristics of the
waves that were measured at the buoy during the bomb cyclone event. In the previous activity
you looked at the height of the waves associated with the storm and here you will examine other
characteristics including the wave period and wavelength. Then you will determine the speed
that these waves travel across the ocean after they leave the storm area where they are generated.
1. What are the maximum and minimum values of significant wave period?
2. Do the largest and smallest values of wave period and wave height happen at the same time?
3. Compare the changes in wave height and wave period over time and determine if, in general,
they have a positive or negative relationship.
Wavelength and Wave Speed
The waves measured during this time storm at the buoy during this time are called deep-water
waves meaning the waves do not ‘feel’ the bottom because the water depth is greater than twice
the wavelength. Motion of the water as the wave passes by does not reach to the seafloor so there
is no movement of sand or disturbance to benthic organisms.
Recall that surface waves transmit energy on the ocean surface. Waves are typically
characterized by their wave height, wave period, and wavelength. They travel from where they
are generated (e.g., at the storm) to other areas. All waves travel at different speed based on their
wavelength.
The maximum value is 11
The minimum value is 4
Yes they do They have a positive relationship
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• The wavelength (L) is calculated using: L = gT
2
/2
π
, where g=9.8 m/s
2
and T is wave period in
seconds.
• The wave phase speed is calculated by the wavelength divided by wave period (just like the
speed of your car is distance divided by time): speed = L/T
Calculate wavelength and phase speed for a wave period of 6 seconds. Round your answers to
one decimal place.
If the wave period is 6 seconds, the wavelength is _____________meters.
The wave phase speed is _____________meters per second.
In the questions below, calculate the wavelength and wave phase speed for the waves
generated during this storm.
4. Using the equation above, find the wavelength (L) for the waves on January 5, 2018 at 0000
(remember, this was the time period of the largest wave height).
5. Based on your answer to #4, how fast were the waves traveling?
6. Explain how the speed of a wave changes with the wavelength.
7. This buoy is located 260 km from the coast of New Jersey. Based on the wave speed at the
time of maximum wave height it would take about 4.5 hours for these waves to travel from
the buoy to the coastline. Does that seem slow or fast to you? Explain your answer.
56.2
9.3
L= 9.8 (9.7 s)^212pi = 146.8m
146.8/9.7= 15.1 m/s
Wave speed and wavelength have a direct relationship. For example, the wave speed decreases and so will the wavelength.
It seems relatively slow because the wave speed is usually between 160-320 km/h and it took 4.5 hours to get to 260 km. Therefore it doesn’t seem in line with the timeline.
4.4 – INVESTIGATING OTHER WAVE EVENTS
In exercises 4.1 and 4.2 you saw that local atmospheric conditions can change quickly and this
can lead to rapid changes in wave height. Here your objective is to examine data over a 1-month
time period to investigate how/when wave height is related to local atmospheric conditions.
1. Do you see the same relationships between atmospheric pressure and wind speed that you
saw from the single storm event in the first exercise?
2. Based on changes in atmospheric pressure and wind speed from the graph, identify three time
periods when you would expect to see increases in wave height.
3. Based on the relationship you found between wind speed and wave height in the previous
exercise, when do you expect to see the largest wave height in the month of February?
4. Compare the measured wave height to the three time periods you predicted would be
greatest. How do they agree/disagree with your predictions?
5. Was your prediction of when the largest wave height would occur correct?
No
From February 11- February 14, Feb 18-19 and February 24-26 because the wind speed increases
February 26 because the wind speed is greatest.
They agree and disagree. I was correct with February 24-26th, but results are different for the other two time periods.
Yes
6. If there are time periods with large wave height that you did not predict, what do you think
caused those waves? Where do you think they were generated?
7. Waves are a potential source of renewable energy. How do you think the amount of wave
energy a system could harness would change during this week?
Wave heights could be caused by severe weather such as on the coast like in areas of long island. They could also be caused by high wind duration, not just wind speed.
Since it is windy the wave height will be greater and therefore wind energy would be greater.
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