Of Wings, Waves, and Winds
WHOI oceanographer explores the mysteries of albatross flight
"Great albatross! The meanest birds
Spring up and flit away,
While thou must toil to gain a flight,
And spread those pinions grey;
But when they once are fairly poised,
Far o'er each chirping thing
Thou sailest wide to other lands,
E'en sleeping on the wing."
For Phil Richardson, it began with a simple question. How do albatrosses soar so effortlessly, flying around the world without flapping their wings?
On an expedition in 1997 to the South Atlantic Ocean off Cape Town, South Africa, he added himself to the list of sailors, scientists, and poets who for centuries have been captivated by this wide-winged symbol of power and elegance overhead. Long before Samuel Taylor Coleridge immortalized the bird in The Rime of the Ancient Mariner, sailors looked on them with awe. "Certain great fowles as big as swannes, soared about us," wrote the great English sailor Richard Hawkins in 1593.
More than 400 years later, Richardson, an oceanographer at Woods Hole Oceanographic Institution (WHOI), found himself similarly fascinated by the bird's dramatic, swooping flight pattern, its grace and efficiency.
"It was surprising and delightful to see them almost magically soar upwind in wind speeds of 10 to 20 knots," Richardson said.
A lover of sailing, plane piloting, and the natural patterns of the ocean, Richardson was intrigued by the aerodynamics of the bird and its soaring capacity. His scientific instincts kicked in.
He wondered how albatrosses could soar in any direction they chose. What particularly amazed him was how the albatross seemed to fly into the wind, without losing speed or steadiness in their flight, and with no wing flapping and scant apparent effort.
Other work got in the way, but a decade after he first observed the albatrosses, Richardson found time to pursue his wonder. He pored over historical studies of albatross aerodynamics, adding his own experiences and insights, and he slowly constructed a new picture to explain the mechanics of albatross flight.
Nearly 14 years after his 1997 cruise, Richardson published his findings in the winter 2011 issue of the journal Progress in Oceanography. To achieve his new understanding, Richardson capitalized on interests and experiences over a life's journey.
A boy's life
Richardson grew up loving the wind and the water. Raised on a cattle ranch north of San Francisco, he was particularly fond of science class, even though he missed school from time to time for cattle roundups.
His father, Arthur Richardson, who died when Richardson was four, was an architect. So was his grandfather and great-grandfather, Henry Hobson Richardson, who designed Trinity Church in Boston. The younger Richardson tried architecture, too, he said, "but it didn't take."
Richardson's stepfather, George Wheelwright III, was a physicist-turned-rancher who co-founded Polaroid Corporation with Edwin Land, the pioneering camera inventor. Wheelwright moved out West after working as a flight navigator during World War II.
As a boy, Richardson picked up a love of flying. He enjoyed model planes, and when he grew older, he earned a pilot's license. He enjoyed gliders, too, even hang-gliding. A lifelong love for sailing began on the old sailboat that his family used when they summered in Maine.
After graduating from high school, Richardson left behind his days on the cattle ranch and headed off to study civil engineering at the University of California, Berkeley. After college, in the Vietnam War era, Richardson opted for alternative service, becoming an officer with the U.S. Coast and Geodetic Survey, a federal agency that surveyed and charted waterways and coastal regions.
Soon after, Richardson had a conversation with his cousin, Columbus Iselin, a former director of WHOI, who encouraged him to earn a Ph.D. in physical oceanography at the University of Rhode Island. Upon graduation, Richardson came to work at WHOI in 1974.
Not much was known about the ocean's currents at that time. Research methods had yet to advance significantly from 19th-century approaches. A few nascent current meters existed, but oceanographers more often than not measured ship drifts or sent off messages in bottles to see where they ended up.
"They would record where the bottles were picked up and how long they took to get there," Richardson said. "They'd put out hundreds of those things. But you only knew where a bottle started and stopped. We wanted to know how it got there. What was its real path?"
Pioneering studies in physical oceanography
To find out more about the movement of the ocean's currents, Richardson and others began taking advantage of new technologies. Their "bottles" evolved into sophisticated floats equipped with scientific instruments, which drifted along with currents. At first, oceanographers used military listening systems to record acoustic signals from subsurface floats; or they used surface drifters that they tracked via radio signals or satellites to reveal something about the fluid pathways through the ocean.
"It was a time of interesting theories," Richardson said. "It was not easy to make measurements, so almost any measurement you made told you something new about the ocean. It was very exciting. As my father was an architect, I guess I studied the architecture of the ocean."
Over his long oceanographic career, Richardson used floats, satellites, and hydrography—measurements of water's physical characteristics, such as temperature and salinity—to examine many of the major currents in the Altantic Ocean. Each is something like a major highway in a global oceanic "interstate" system. He investigated the North Brazil Current transporting water northwestard over the equator; the Caribbean Current; the Gulf Stream; and the Agulhas Current carrying water from the Indian Ocean to the southern tip of Africa.
The Agulhas Current doesn't import water directly into the Atlantic, but as the Agulhas veers back eastward off South Africa, huge, swirling rings of water called eddies pinch off and spiral westward into the South Atlantic. Eddies spinning off from major currents became another major focus of Richardson's research, and he explored their formation, pathways, and impacts.
"Phil contributed to a better understanding of ocean currents and eddies," said Amy Bower, a senior scientist in Woods Hole's Department of Physical Oceanography and a colleague and friend of Richardson. "His figures are often used in textbooks, because of their clarity and his ability to portray complex ocean current circulation patterns in a relatively simple way."
Richardson's knowledge of ocean currents and his natural curiosity occasionally prompted forays into peripheral scientific territory. In the months leading up to the quincentennial of Columbus's 1492 voyage, for example, Richardson was intrigued by questions about which still-unverified island Columbus first landed on in the New World. He collaborated with WHOI researcher Roger Goldsmith, applying scientific information on the effects of currents, winds, and variations in Earth's magnetic field to records in Columbus's logbook on his distances traveled and compass readings.
"We didn't have a lot of information about the early explorers," Richardson said, "just as we don't have a lot of information about the albatross."
After a long career, Richardson formally retired in 1999, though he remains at Woods Hole as a scientist emeritus.
"When you're a full-time scientist, you can't follow up on many of your interests," he said. But after he retired, he had time to pursue curiosities like albatross flight. In doing so, Richardson applied more than his understanding of the ocean's currents. He also drew on his love of sailing and flying.
Albatrosses spend the majority of their long lives above the ocean. By the age of 50, an albatross has typically flown at least 1.5 million miles. Adults routinely fly hundreds of miles to gather food before returning home to feed a youngster. Placing its beak next to its offspring's, the adult albatross injects liquid food, converted from its prey of fish, squid, or krill, directly into the baby's beak. In recent times, many albatrosses are being lured to their deaths by bait on long fishing lines, Richardson said.
The young birds face a perilous path to adulthood. About 40 percent don't make it, because they themselves become prey or because they don't learn to fly well enough.
"Gravity and drag relentlessly force a gliding albatross down through the air," Richardson wrote in his paper. "To continously soar, an albatross must extract sufficient energy from the atmosphere." But how?
Richardson knew waves had to play a vital role. Strong prevailing winds blow steady parades of waves across great stretches of the ocean, especially in the vast Southern Ocean. That makes the ocean surface and winds above it "lumpy and bumpy and gusty," he said. "An albatross can take advantage of that."
Early on, like many other students of albatross flight, Richardson assumed that the birds use updrafts of air that flow up the backs of waves—similar to updrafts that form over ridges on land. Certainly albatrosses exploit wave updrafts. And certainly they also gain energy from tailwinds blowing horizontally. But these couldn't account for the "accelerated twisting, turning, swooping flight of albatrosses" that Richardson had observed. Nor could it answer a question that kept nagging him: "How can they be flying into the wind and, at the same time, keep up alongside our ship?"
Richardson was inspired by a theory described by the Nobel laureate physicist Lord Rayleigh in a paper written in 1883. Rayleigh knew that horizontal winds don't blow uniformly; often they can blow faster the higher you ascend. He proposed a two-layer scheme with an imaginary boundary, above which winds blew faster. This boundary is often referred to as a "wind shear." A bird flying up across a wind shear would abruptly gain airspeed and could use this pulse of kinetic energy to climb upward. Then the bird could turn and swoop downward. Descending through the boundary, it would gain airspeed by flying against weaker winds.
Richardson saw something similar going on in the ocean. Building on a hypothesis by British scientist Colin Pennycuick, he outlined the following scenario. In the trough of waves, there is little wind, because the waves block it. But above the waves and their troughs, winds blow brisky across the ocean in thin layers, stacked somewhat like cards in a deck: Lower layers are slowed by air-sea friction near the ocean surface, but wind speeds increase as you go farther from the surface and higher up.
An albatross ascending from a wave trough at an angle would encounter progressively faster winds. This would increase the bird's speed through the air—a burst of kinetic energy that it uses to climb to heights of 10 to 15 meters. Then the albatross makes a tight turn downwind and swoops down into another wave trough, adding airspeed as it descends through the wind shear into progressively slower winds. Each addition of airspeed balances the loss of energy caused by drag on the bird. With another turn in the trough, the albatross ascends to begin the cycle again. Each swoop cycle takes about 10 seconds. (See accompanying diagrams.)
This phenomenon is called dynamic soaring. The pilot in Richardson knew that in the late 1990s, radio-controlled glider pilots began using the same tactic—looping in strong winds blowing over ridges, rather than waves—to achieve surprisingly fast speeds. A new world's record of 468 miles per hour was set this year with an albatross-sized glider.
Into the wind
As he did with his diagrams portraying complex ocean currents, Richardson devised a relatively simple model that captures the essential physics of dynamic soaring of albatrosses, incorporating both winds and waves. Evaluating the two theories of albatross flight, he concluded that using wind shear, rather than updrafts from waves, accounted for 80 to 90 percent of the energy needed for albatrosses to fly.
Using his model, he calculated that albatrosses need a minimum wind speed of 7 knots to soar. He also calculated that an albatross could soar upwind at a speed of 12 knots, "which is just what I observed from our ship," he said.
But how did they fly upwind? Then Richardson thought about his experience sailing. That was his Eureka moment.
"To travel upwind, a sailor tacks into the wind, alternating sailing in a direction around 45 degress to the right and then to the left of the wind direction," he said. "That's what albatrosses are doing—they're tacking!"
Again using his model, Richardson calculated that the fastest course upwind for an albatross is to tack about 30 degrees to the right and left of the wind. "One trick I observed is that the birds climb upwind but often dive perpendicular to the wind to maximize their average velocity in an upwind direction," he said.
To paint a more precise picture of albatross flight, Richardson said he would love to see sophisticated microsensors developed that could be attached to albatrosses. Such sensors could measure the nuances of the albatrosses' flights and their navigation through wind and wave patterns.
Richardson isn't alone in his interest in the mechanics of soaring and gliding. "Flight dynamics at small scales has suddenly become a hot topic," he said. "Bird, bat, and insect flight has become very interesting to the military." The new autonomous "drone" flying vehicles being developed for military usage, especially the smaller ones, may benefit from the study of bird flight dynamics.
For his own part, Richardson is moving on to new hobbies. His latest interest is photography. He loves capturing the beauty and grace of birds in flight. Whether or not you can chart the path of an albatross or analyze the mechanics of its flight, Richardson said, you can recognize nature's beauty in a snapshot of a bird in flight. And beyond photography, there is plenty of oceanographic data still to be analyzed, he said. The oceanographer in him will never give up that passion. There are endless patterns of wind and water to ponder.
Originally published: March 17, 2011