Lab 6 – Waves Generated by Large Storms
This exercise is a case study of a very quickly developing low pressure center (a bomb cyclone) and the response of the sea surface to the rapidly changing winds and pressures. While students may understand that hurricanes generate large waves, winter storms can also produce high seas very quickly, especially when the local seas combine with swell generated along the storm’s path. The waves generated by these intense storms travel to the shoreline and are responsible for large amounts of coastal erosion put infrastructure, ecosystems, and communities at risk . They also produce potentially dangerous conditions for ships at sea.
This lab is divided into three scaffolded activities that should be completed in order, although the instructor can stop the lab after any particular activity if the necessary learning outcomes have been met. The activities are intended for undergraduate students in Introductory Oceanography courses (for either marine science majors or non-science majors) with Activity 3 progressing towards more quantitative skills. This exercise, particularly the concepts in Activity 3 could also be extended to upper level marine science courses.
Approximate time involved: Activity 1 – 15 minutes, Activities 2 & 3 – 30 minutes each.
- LO1. Students will demonstrate basic data literacy in graph interpretation by identifying values of meteorological and oceanographic variables (with appropriate units) at specified times and describe their evolution over time.
- LO2. Students will identify specific values of barometric pressure in a time series and describe the changes occurring in barometric pressure during a specific period of time.
- LO3. Students will identify trends in wind speed in a time series and relate changes in barometric pressure to changes in wind speed to develop and establish the relationship between the two variables.
- LO4. Students will identify specific values of wind speed and maximum wave height in a time series and relate changes in wind speed to changes in wave height to develop and establish the relationship between the two variables.
- LO5. Students will identify specific values of wave period and wave height and use these to calculate wavelength and wave speed. Identified values of wave period will be used to explain the difference between sea and swell.
|Learning outcome||Activity 1||Activity 2||Activity 3|
|Outcome 1||guided practice||guided practice||independent practice|
Materials needed: calculator
What students should know before this activity
- Data literacy: Students should have completed Lab 2.1 and be familiar with how to read and interpret time series graphs. This includes identifying the minimum and maximum of a time series, identifying values at specific times, and understanding the units of different variables.
- Content knowledge: Ocean surface waves are often described by three characteristics – wave height, wave period, and wavelength. The speed at which a wave travels is the wavelength divided by the wave period (distance divided by time).
What instructors should know before this activity
- Wind speed, wind duration, and fetch are the primary variables responsible for the generation of surface waves in the ocean. Winds that blow faster and longer over a larger area (i.e., fetch) will generate larger waves. Waves at the location of the storm are choppy, irregular, and have a short wave period, usually less than 7 seconds. When waves move away from the storm, longer period waves travel faster away from the storm to other areas. For Activity #3, instructors should be familiar with how to calculate wave phase speed and wave frequency.
Optional pre-lab activities:
Introductory lecture on ocean wave generation and characteristics. A introduction in how ocean waves are measured may also be useful (e.g. https://cdip.ucsd.edu/m/documents/wave_measurement.html).
Pre/post-lab assessment questions – none
- Procedure: Explain that this exercise looks at changes in the ocean surface waves and local winds as a strong cyclonic storm passes over the instrument array. Emphasize that changes can occur quickly.
- Commonly encountered issues/questions/misconceptions:
- Be sure students are using the proper axis for their variable of interest.
- Emphasize that all answers should have the proper units.
- Sea usually has a period of 7 seconds or less and is generated by the local winds.
- Swell has a longer period than sea and has travelled into the area of the array from some distance away.
- Adaptations for different course levels and duration of activity (lab vs. lecture period): Activity is stand alone and may be used in as a lab activity, in-class exercise, or homework exercise.
- Reflection prompts:
- How did the wave height change as the wind speed increased?
- How did the dominant wave period change with the arrival of the swell?
Extensions – Videos, hands-on activities, upper level courses: Activity can be used in an upper-level course as a refresher in ocean wave characteristics.
- PowerPoint slides with background information: none
- Handouts/worksheets of the graphs and questions: students will turn in their answers for grading.
- Screen captures (especially for online courses) for accessing online resources–to supply to the students if external resources used (e.g. Google Earth): none
- Sneed, A. 2018. What Is This “Bomb Cyclone” Threatening the U.S.? Scientific American retrieved from https://www.scientificamerican.com/article/what-is-this-ldquo-bomb-cyclone-rdquo-threatening-the-u-s/
- NOAA GOES-East Captures East Coast ‘Bomb Cyclone’ (Video) from NOAA Environmental Visualization Laboratory, NOAA National Environmental Satellite, Data, and Information Service (NESDIS) : https://youtu.be/ApwsdTrtm3g or https://www.nesdis.noaa.gov/content/noaa-goes-east-captures-east-coast-bomb-cyclone-video
- The Historic “Bomb Cyclone” of January 2018 – This website is being updated Fall 2020, please refer to the following pdf of the page and above links for the information earth107-bomb-cyclone for Lab 6 . Source: Coastal Processes, Hazards, and Society by Barlow, T, Maygarden, D,Yarnal, B. licensed by Penn State’s College of Earth and Mineral Sciences (http:// e-education.psu.edu/oer/), Creative Commons license (cc By-NC-SA 4.0), https://creativecommons.org/licenses/by-nc-sa/4.0/, accessed (07/15/2020) Penn State University.