Lab 6 – Ocean Waves: Linking the Marine Atmosphere and the Ocean 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 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.
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.
- LO1. Demonstrate basic data literacy in graph interpretation by identifying values of meteorological and oceanographic variables (with appropriate units) at specified times and describe their change over time. [Lab 6.1, 6.2, and 6.3]
- LO2. Identify specific values of barometric pressure in a time series and describe the changes occurring in barometric pressure during a specific period of time. [Lab 6.1]
- LO3. Identify trends in wind speed in a time series and compare to changes in barometric pressure to establish the relationship between the two variables. [Lab 6.2]
- LO4. Identify specific values of wind speed and significant 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. [Lab 6.2]
- LO5. Identify specific values of wave period and wave height and establish a relationship between the two variables. [Lab 6.3]
- LO6. Use wave period to calculate wavelength and wave speed. Examine the relationship between wavelength and wave speed. [Lab 6.3]
- Key terms: barometric pressure, wind speed, wave height, wave amplitude, wave period, wavelength, wave phase speed, sea surface height
- OOI Array: Coastal Pioneer Array
- Sensors: Central Surface Buoy – bulk meteorological instrumentation suite and the surface wave spectra WAVSS Series A.
- Other need-to-know scientific background: students shall have completed a classroom lecture on the basic properties of surface waves.
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, drag the definition of each wave characteristic to the appropriate box in the figure below.
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.