Robert Helliwell, a
electrical engineer whose study of radio waves emitted by lightning opened a new window to understanding the upper layers of the Earth's atmosphere, died May 3 in Palo Alto of complications of dementia. He was 90.
Helliwell specialized in bouncing radio waves off the ionized particles in the upper atmosphere, transmitting them over long distances to deduce the structure of those upper layers. Among other things, he showed that the Earth's ionosphere, an envelope of electrons and charged atoms and molecules beginning about 36 miles above the Earth's surface, actually extends as high as 20,000 miles, not the 200 miles researchers had previously believed.
"He was a pioneer," said his colleague Don Carpenter, a professor emeritus of electrical engineering at Stanford University. "He did some of the earliest observations and interpretations of phenomena in our field."
Helliwell's career path began late one night in 1950 when one of his graduate students, Jack Mallinckrodt, heard some strange descending whistling tones while monitoring radio waves produced by distant lightning.
"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."
The whistlers proved to be very-low-frequency radio waves, which Helliwell began to monitor regularly and to reproduce with radio transmitters. If the entire atmosphere were electrically neutral like that at the Earth's surface, the radio waves would propagate directly into space, continuing in a straight line forever. But charged particles in the ionosphere and the magnetosphere above it can trap the waves and carry them long distances around the Earth or bounce them back to the surface the way a mirror bounces light.
In one of his first tests, in 1957, Helliwell sent radio signals from a transmitter in
, Md., that were designed to be funneled through channels of ions in the magnetosphere. A graduate student with a radio receiver picked them up in Chile.
Helliwell continued his tests with receivers on the Stanford campus, but local interference marred his reception. In 1957, he traveled to
to establish a new research site where the quiet conditions would allow better reception.
He and his students built a radio antenna 13 miles long atop a mile-thick glacier at Siple Station in West Antarctica and continued to use it until the station closed in 1988. Students at Stanford are still analyzing data collected there. His work was formally recognized when a mountain range along the coast of Victoria Land on the Ross Sea was named the Helliwell Hills.
Robert Arthur Helliwell was born Sept. 2, 1920, in Red Wing, Minn. His father died when he was young and his mother moved to Palo Alto to escape the cold weather. He earned his undergraduate and graduate degrees at Stanford and joined the faculty in 1946, spending his entire career there.
He married his high school sweetheart, Jean Perham, and they had been married for 59 years when she died in 2001. He was active in his community, serving as a member of the Kiwanis Club and as scoutmaster of Boy Scout Troop 51 at Stanford.
Helliwell is survived by three sons, Bradley of Sedona, Ariz., David of Arcata, Calif., and Richard of
, Colo.; a daughter, Donna, of
; four grandchildren; and one great-grandchild.