Peter Niiler of the Scripps Institution of Oceanography did not set out to become an authority on ocean circulation. He says it was something he just happened to be good at. Peter credits much of his success to a rigorous education grounded in fundamentals and precision. One never got credit in college for an answer if the second decimal place was not correct.
Peter’s approach to studying the ocean circulation continues to be grounded in fundamentals and precision. One cannot develop a useful model of what drives global ocean circulation, he says, without understanding what is happening at the scale of a cubic centimeter. Yet his approach also encompasses a much broader vision of the ocean. For the past forty years, Peter has helped reshape how scientists study the ocean. Whereas oceanographers once focused on naming and defining currents, they now stress the processes driving these currents and measuring them accurately. And whereas oceanographers once limited their perspectives to small regions of the ocean, they now understand the importance of viewing the ocean on a global scale. It was his generation of scientists, Peter says, that helped bring about these changes.
Peter was born in Estonia in 1937. At age twelve, his parents brought him to western Pennsylvania. He studied engineering in college, and then applied mathematics and fluid mechanics in graduate school. Then at the urging of Henry Stommel, a pioneer in the study of ocean circulation, Peter joined Nova University in Fort Lauderdale, Fla., in 1966 where he studied the Florida Current and Gulf Stream in a small laboratory on a houseboat. He went on to teach oceanography at Oregon State University for eight years before joining Scripps as a professor in 1982.
Peter and a few of his colleagues have long understood the linkage between ocean circulation and the world’s climate. But he said that it wasn’t until the 1980s that these ideas gained more urgency among a broader group of earth scientists, prodded in large part by emerging evidence that the buildup of carbon dioxide in the atmosphere was altering the world’s climate. Yet unraveling the circulation remains daunting. Not only do the oceans contain a maze of often shifting current systems, they are filled with turbulence that can be viewed on a scale of just a cubic centimeter to the thousands of swirling eddies a few hundred kilometers wide.
Before the 1980s, most scientists were turning to data on sea surface temperature and salinity to gain insights about circulation. But Peter wanted to get back to basics: deploy instruments that directly measure the flow.
Oceanographers have been releasing drifters to track currents since the three-year British Challenger Expedition in the early 1870s. But Peter discovered that the available instruments were not up to the task. Not only were they expensive, costing up to $12,000 each, they did not follow the water that well. Wind and waves pushed them off course, and the equations engineers had devised to correct for these errors were far off.
So Peter and his colleagues set out to redesign the buoys. They increased the drogue size relative to the surface float to minimize the effects of wind and waves. They made the buoys tougher, increasing their longevity from 150 to 450 days. And they lowered the cost of each buoy to under $2,000.
The buoys relay their positions by transmitting radio signals at a precise frequency. A satellite receives the signals as it approaches and then passes the buoy. Computers then calculate the buoy’s position based on frequency changes due to the Doppler effect. Peter and his colleagues have since added sensors that measure water temperature, salinity, atmospheric pressure, and wind; data that has proven invaluable for calibrating satellites that collect the same information. Today Peter and his colleagues work closely with manufacturers to solve problems and update the designs while keeping costs down.
Yet simply measuring flow in isolated areas was not enough. To understand ocean circulation and its connection to climate, Peter realized he needed to steer scientists and government agencies towards a more global view of the ocean. He argued that it is not good enough for a circulation model to work in just one part of the ocean during one period of time. One cannot understand how water flows north through the Gulf Stream without understanding what is happening in the southern oceans.
To that end, Peter and his colleagues, in conjunction with the National Oceanic and Atmospheric Administration (NOAA), initiated the Global Drifter Program, a worldwide network of surface drifters. Over the past two decades, with the cooperation of a host of other countries, they distributed over 8,500 buoys to all parts of the ocean, shedding light on areas that had rarely been studied. Their goal was to maintain a network of 1,250 buoys, all reporting their data six to ten times each day. On September 18, 2005, Peter helped toss buoy number 1,250 into the North Atlantic off the coast of Halifax, Nova Scotia. The network was complete.
Combined with data from satellites, the Global Drifter Network now provides scientists with twice-weekly updates on currents and sea surface temperatures throughout the world. Some buoys also carry sensors that measure wind and atmospheric pressure. Atmospheric scientists use these data to improve marine and weather forecasts. But more importantly, according to Peter, scientists now have the tools to test global circulation models and monitor worldwide changes in sea surface temperatures and circulation brought about by global warming.
Since 2002, Peter has also worked with the Air Force Reserve’s Hurricane Hunters to deploy buoys in front of approaching hurricanes. In September 2005, a C-130 airplane dropped 20 buoys in front of Hurricane Rita, a storm that reached Category 5 on the Saffir-Simpson scale, as it swept through the Gulf of Mexico. Peter says that the dynamics of the ocean are as important as the atmosphere in determining the strength of a hurricane. Therefore models capable of predicting a hurricane's strength must incorporate information about the ocean.
Now that global observing systems of drifters are in place, Peter is optimistic about the progress scientists are making in understanding global circulation and its effect on climate. He’s confident that as numerical techniques improve and scientists gain a better understanding of fluid dynamics and the relationship between small-scale turbulence and large-scale motion, future models will become more robust.
Peter is also encouraged by the degree to which government agencies, universities, and scientists in disciplines ranging from physical oceanography to meteorology are now working together and sharing ideas and data. He is especially encouraged by the amount of international cooperation. The United States continues in the forefront of this global approach to ocean research, but many other countries are contributing, including Canada, Brazil, South Africa, Australia, New Zealand, Korea, and members of the European Union. The recognition that understanding ocean dynamics and climate requires global measurements with sensors in the water, Peter believes, is one of his generation’s most important legacies.