Graduate students in the Meteorology and Physical Oceanography department at RSMAS deploy a sub-surface mooring in the Straits of Florida to measure the surface wave field.
So you want to go fishing this weekend to catch a nice big tuna to grill on the BBQ. What’s the weather like? You don’t want to get seasick! That means you don’t want the wave heights to be too large, nor the wave period too long (Did you know?…seasickness intensifies with an increasing period of oscillation1 ).
If you want to know what is happening in the waters offshore of Miami, you can take a look at the National Weather Service (NWS) website. Every day the NWS provides forecasts of the wind and wave conditions over the Straits of Florida, which are used by commercial fisherman, shipping companies and recreational boaters. The wave forecasts are based on model predictions. However, this region is highly dynamic due to the presence of the fast flowing Florida Current (named the Gulf Stream further north); this current interacts with the wave field and represents a challenge to the wave forecasting models.
Dr. Nick Shay leads the Upper Ocean Dynamics Laboratory at UM Rosenstiel School of Marine and Atmospheric Science, which has operated shore based high frequency (HF) radar systems for over a decade. These radars remotely measure near-real time surface currents across the Straits of Florida with high accuracy2. HF radar also has the ability to measure the wave field over the surface of the Straits of Florida. This has attracted increasing interest in recent years, as to provide operational real-time observations of the wave field can help improve the model forecasts.
But first, the accuracy of the HF radar wave measurements must be evaluated using in-situ observations of the wave field. This is why the WHARF experiment was conceived.
Mr. Matthew Archer, a PhD student working in Dr. Shay’s lab, is the recipient of a prestigious award to deploy an acoustic wave and current profiler (AWAC) (http://www.nortekusa.com/usa/support/student-equipment-grants/2013-grants/awards). The AWAC is built by Nortek for long-term deployment in the ocean, to measure the surface wave field and ocean currents. This instrument will gather data over a 4-month period, during the transition from spring to summer, to measure the in-situ wave heights and currents during different weather conditions.
On April 22nd, the mooring was successfully deployed offshore of Miami Beach, which gave the students experience of working at sea. The AWAC was attached to a buoy that was moored to the ocean bottom with an anchor – in our case, a train wheel! The instrument, which is moored in 300-m water depth, floats 40-m below the surface, facing upward to measure the surface waves and currents far offshore of the coast, within the Florida Current.
Using this in-situ dataset, the radar system can be calibrated to make sure that the wave data are accurate. The radar provides data every 20-min, which will be provided in near-real time on the lab website. The results of the WHARF project will provide valuable information that can be used in the further development of the NWS marine forecasts, benefiting shipping and navigation as well as the construction and management of sustainable coastal developments. It will also give UM Rosentiel scientists data to investigate the relationship between strong currents and the surface wave field, a topic which is not fully understood.
The project was made possible by funding from SECOORA (Southeast Coastal Ocean Observing Regional Association).
1 Cheung, B. and A. Nakashima, 2006. A review on the effects of frequency of oscillation on motion sickness. In: Technical Report; No. DRDC-TR-2006-229. Defense research and development Toronto (Canada).
2 Parks, A. B., L. K. Shay, W. E. Johns, J. Martinez-Pedraja, and K.-W. Gurgel, 2009. HF radar observations of small-scale surface current variability in the Straits of Florida. In: J. Geophys. Res., 114, C08002, doi:10.1029/2008JC005025.