Late one night in 1950, a graduate student was monitoring radio waves emitted by distant lightning when strange descending whistling tones came from a speaker. The student, Jack Mallinckrodt, mentioned the experience to his adviser, Robert Helliwell.

Robert Helliwell portrait

Robert Helliwell, an emeritus professor of electrical engineering, was remembered as ‘a man of great ideas and inventiveness.’ (Image credit: Stanford News Service)

“I suggested that if he took a short vacation perhaps the sounds would go away,” Helliwell wrote in an article for the October 1982 issue of Stanford Engineer. “But he didn’t and they didn’t. My curiosity was finally aroused and I spent a late night with Jack at the receiving station. Luckily, we both heard two distinct whistlers and I was instantly converted to belief in the reality of a strange new phenomenon.”

This chance observation started Helliwell on decades of research that led him from Stanford to Antarctica as he followed these mysterious radio noises and later sought to reproduce them with a transmitter. Through this work, he made fundamental discoveries about how radio waves can be used to investigate the ionized atmosphere high above Earth’s surface.

“He was a pioneer,” said Don Carpenter, professor emeritus of electrical engineering and one of Helliwell’s colleagues. “He did some of the earliest observations and interpretations of phenomena in our field.”

Helliwell died on May 3 in Palo Alto of complications from dementia. He was 90. A service will be held at Stanford Memorial Church on June 7 at 3 p.m.

Helliwell was born Sept. 2, 1920, in Red Wing, Minn. His father died when Helliwell was young. To escape the cold weather, his mother moved with him to Palo Alto, where she worked as a librarian for many years. Helliwell earned his bachelor’s, master’s and doctoral degrees from Stanford and joined the faculty in the Department of Electrical Engineering in 1946.

He changed the direction of his research after encountering “whistlers,” the name given to the very low frequency radio waves that he heard with Mallinckrodt that night in 1950. This natural event, which he described as “weird, strange and unbelievable as flying saucers” to a reporter for the Palo Alto Times in 1954, fascinated Helliwell for the rest of his career. His son David Helliwell said his father would often whistle a whistler.

Radio waves zoom around the Earth by bouncing off charged particles in the upper atmosphere. High-frequency signals from AM or FM radio stations travel between the Earth and the ionosphere, the partially ionized layer of the atmosphere that begins about 50 miles above the ground.

Very low frequency (VLF) radio waves shoot past the ionosphere and into the next region of space, the magnetosphere.

Here, the atmosphere is completely ionized. The Earth’s magnetic field controls the motions of charged particles, creating channels of ions aligned with the horseshoe-shaped magnetic field lines. These channels trap VLF radio waves, guiding them between opposite hemispheres along a path that reaches up to 15,000 miles from the surface.

Conducted international experiments

In 1957, Helliwell arranged one of the first experimental tests of this effect by using signals from a powerful communication transmitter. At a prearranged time, the VLF transmitter in Annapolis, Md., broadcast a series of pulses that traveled along a guided path in the magnetosphere. About one second later, a receiver placed in Chile by a graduate student detected the signals.

Soon Helliwell was using these manmade radio waves, as well as naturally occurring whistlers from lightning, to sense the properties of the charged particles that the waves encountered along their high-altitude paths.

Helliwell had some receivers at the Stanford campus to detect natural whistlers, but electrical noise from the city power lines interfered with his work. In 1957, he traveled to Antarctica to scout a new research site. The frozen continent provided the quiet conditions needed to detect interesting signals and transmit controlled waves.

With a team of students and staff, he built a radio transmitter with a 13-mile long antenna at Siple Station, located on a mile-thick ice sheet in West Antarctica. There, researchers sent radio waves into the magnetosphere, where they traveled along a charged channel to receivers in Canada. It was “like a lab experiment in space,” said Carpenter, who knew Helliwell for 55 years. The transmitted radio waves were amplified along their journey and often triggered waves at new frequencies.

“Helliwell’s crowning achievement was establishing the VLF transmitter in Antarctica,” Carpenter said.

The Stanford Radio Science Laboratory conducted ionospheric and magnetospheric experiments at Siple Station from 1971 until it closed in 1988. Today Stanford graduate students in the VLF Group are still analyzing data from that research.

Helliwell wrote what is considered a classic work on whistlers, Whistlers and Related Ionospheric Phenomena. He is the namesake for the Helliwell Hills, an Antarctic mountain range along the coast of Victoria Land on the Ross Sea.

“He was a man of great ideas and inventiveness,” said Evans Paschal, one of Helliwell’s students during the 1970s.

An immense sense of curiosity

Inquisitiveness seemed to be a hallmark of Helliwell’s work. In 1986, he told a Stanford reporter that he studied the magnetosphere to satisfy his curiosity. And a career of surprising results gave him plenty to ponder.

He took a scientific approach to everything,” said his son David, recalling family discussions at the dinner table. “If you voiced an opinion, you’d better be able to back it up.”

He encouraged his children to think carefully and creatively. “His mantra was ‘Make no assumptions,'” said his son Brad. “He always got us thinking about the engineering aspects of things.”

Brad Helliwell remembers his father teaching him about electrical filters using a rake and a pile of rocks. Small rocks slipped through the tines of the rake, but large rocks were trapped. “I’ll never forget that,” he said.

Robert Helliwell won the Antarctic Service Medal in 1966 and the Appleton Prize of the Royal Society of London in 1972, awarded for distinguished research in ionospheric physics. He was a fellow of the American Geophysical Union, a member of the National Academy of Sciences and chair of one of the Commissions of the International Union of Radio Science (URSI).

Helliwell came to Stanford as an undergraduate one year before his high school sweetheart, Jean (née Perham). He joined the fencing team and encouraged her to do the same. She went on to become the university’s first woman fencing coach. They had been married for 59 years at the time of her death in 2001.

He was also active in the community, participating in the Kiwanis Club and serving as the Scoutmaster of Boy Scout Troop 51, founded at Stanford in 1923, for several years. He often took the family on camping trips in the Sierra.

Helliwell is survived by his sons, Bradley of Sedona, Ariz., David of Arcata, Calif., and Richard of Colorado Springs, Colo.; his daughter, Donna, of Sunnyvale; four grandchildren and one great-grandchild.

Melissae Fellet is a science-writing intern at the Stanford News Service.