North Wall events refer to high wind and wave events that occur along the north edge of warm, fast, western boundary currents. These events occur along the Gulf Stream off the mid-Atlantic states of the U.S. and along the Kuroshio Current near Japan and Taiwan. This module explores the relationships between atmospheric stability, winds, waves, and ocean currents during North Wall events. Using three different case studies, we examine the relevant aspects of several topics, including the synoptic setting, ocean currents, evolution of the marine boundary layer, growth of ocean waves, and potential wave-current interactions.
After completing the module, you should be able to do the following:
With regard to Synoptic conditions:
* Identify the synoptic weather pattern that may result in a North Wall event.
* Identify the oceanographic setting that favors a North Wall event.
With regard to the marine boundary layer (MBL):
* Describe the evolution of the MBL during a cold season North Wall event.
* Describe the evolution of the MBL during warm and cold air advection.
* Describe the synoptic and oceanographic conditions that lead to an unstable MBL.
With regard to winds in the MBL:
* Describe how the SST-air temperature difference affects MBL stability.
* Describe how MBL stability affects wind speeds at the surface.
* Describe why NWP models may have difficulty forecasting accurate surface wind speeds during a North Wall event.
With regard to ocean waves during a North Wall event:
* List the 3 basic factors that contribute to wave growth.
* Assess the reliability of a model wave forecast using a wave nomogram.
* Assess the reliability of a model wave forecast using ship and buoy observations.
With regard to wave-current interactions:
* Describe the wave-current interactions that increase wave heights.
* Estimate the changes to swell that occur when it runs into an opposing current.
* Describe how waves refract in the presence of current loops and meanders.
* Describe conditions leading to rogue waves.
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