U. students use glider to gather storm data
Glider 23, a yellow, torpedo-shaped glider, plunged through the Atlantic Ocean during Superstorm Sandy, capturing water current and temperature data from surface to sea floor.
During its 50-kilometer trek, the remote-controlled glider relayed information back to its operator at the Rutgers Coastal Ocean Observation Lab, providing researchers there with a more detailed map of the ocean’s structure that will ultimately allow them to create more accurate storm forecasts.
“To better forecast these storms it’s critical to get the ocean right,” said Greg Seroka, a University Ph.D. candidate at the Institute of Marine and Coastal Sciences who used the data to create weather models.
Scientists created ocean modeling as a system to track long-term climate changes, not to forecast storm systems, and only began adapting the models to improve weather forecasting in the last 10 years, Seroka said.
He said researchers at RU-COOL use gliders to get a better understanding of how the ocean mixes during a storm so they can improve ocean models and weather forecasting.
Glider data revealing the surface temperature and current changes not only make forecasts more detailed, but serve as verification that the model is accurate, he said.
How the Ocean Mixes
Water off the coast of New Jersey becomes layered during summer as the sun heats surface water, producing a dramatic temperature difference from the surface to sea floor, said Travis Miles, who drives the gliders during ocean runs.
Miles, a Ph.D. candidate from the Institute of Marine and Coastal Sciences, said the sun’s warming impact lessens with depth, leaving a layer of cold water oceanographers call the cold pool, stranded on the bottom along the continental shelf. Oceans stay stratified until strong winds begin to mix the water.
“Basically, [it’s] just like you’re mixing your coffee,” he said. “You know, you pour cream in, swirl it up and it actually mixes the cream throughout.”
Researchers are still trying to understand what causes ocean mixing and how it affects the water column, he said. But they do know sea surface temperature drives a hurricane’s strength, and strong winds can drag up the bottom cold water to act as a fire extinguisher for the hurricane.
During Hurricane Irene the churning surface water caused a six to eight degree Celsius temperature drop within 18 hours, Miles said.
“That’s a huge, huge amount of energy,” he said.
Hurricane Sandy, however, mixed the water column quickly but only chilled the waters two to three degrees over a 24-hour period, not enough to weaken the storm, Miles said.
Miles said researchers could use gliders to monitor surface temperatures during storms and create a better ocean model of storms to improve forecast methods.
While the ocean naturally mixes from August through December, glider data showed that a storm could churn the water in as few as eight hours, he said.
“These kinds of data sets are few and far between,” he said.
The Future of Forecasting
If researchers understood what happens to ocean temperatures during storms, they could add better information into forecasting models to give more accurate predictions and help save lives and property, Seroka said.
“The ocean drives the tropical storm, drives the atmosphere, drives the winds, drives the rain,” Seroka said.
Weather forecasts for Hurricane Irene in 2011 over-predicted the storm’s strength, Seroka said. A year later, many people did not evacuate low-lying areas because they thought Superstorm Sandy’s high storm surge forecasts were exaggerated.
But surface temperature was not the only factor in Sandy’s strength. A front over the Midwest injected more energy into the storm so that it continued to gain strength moving into New Jersey despite the water temperature drop-off, Seroka said.
The sea surface temperature is really the parameter that affects what happens in the atmosphere above, Seroka said.
“All this stuff occurs inside the ocean, but what actually is talking to the atmosphere is the surface of the ocean … and the bottom of the atmosphere talks to the surface of the ocean,” Seroka said.
Before gliders, oceanographers were unable to collect data during storms, said Oscar Schofield, a scientist at Rutgers Coastal Ocean Observation Lab.
When Schofield trained as a graduate student in the early 1990s, he went to sea for a month and returned with hundreds of measurements. By comparison, Glider 23 took a few measurements per second and returned a week after Sandy with thousands of data points, he said.
The new technique in storm forecasting is to include ocean models and the interaction between ocean and atmosphere to better represent the weather, Seroka said.
“Everything’s interacting, so the atmosphere’s continually interacting with the ocean,” Seroka said. “The ideal forecast would connect the two.”
Glider technology allows scientists to react faster as storm forecasts change and to conduct research in extreme weather, Schofield said.
“It allows you to see things in the ocean that were impossible,” he said. “We’re going to understand things about biology that we have no clue yet.”
If weather forecasts are only sometimes accurate, then people will not take warnings seriously and put themselves at risk, Miles said.
“If your forecast can be accurate consistently, people will pay attention to it,” Miles said.