Leslie Charles “Les” Hale was a distinguished researcher in ionospheric physics and atmospheric electricity and a professor of electrical engineering at the Pennsylvania State University in University Park for 30 years. He died in Las Cruces, New Mexico, on 26 December 2003 of heart failure following complications from hip replacement surgery.
Born in Alamogordo, New Mexico, on 26 June 1932, Hale was raised primarily by his mother and was completely on his own at age 19. Two events in his early years planted important seeds for his subsequent professional career in electromagnetics and rocketry: when, at age 12, he read a copy of QST, a publication about amateur radio, and shortly thereafter, when he witnessed the launch of a captured German V-2 rocket from White Sands Proving Ground. Hale enjoyed being an amateur radio operator for the rest of his life, and he was principal investigator on more than 100 sounding rockets for the upper atmosphere and ionosphere, a US record.
Hale earned his BS (1952), MS (1954), and PhD (1958) all in electrical engineering, at the Carnegie Institute of Technology (now Carnegie Mellon University) in Pittsburgh. His doctoral thesis, supervised by James B. Woodward Jr, was entitled “Initial Excitation and Amplitude Rise in Electronic Oscillators.”
After joining Los Alamos Scientific (now National) Laboratory as a member of a group of “space cadets” in the post-Sputnik era, Hale began his rocket-based space investigations there when he helped initiate one of the first missions to Venus. In 1962, he was a senior research fellow in space research at University College London. There, he met Arthur Waynick, founder of Penn State’s Ionosphere Research Laboratory, and subsequently joined Penn State’s electrical engineering faculty. During his first year at the university, he met Roberta MacMillan, his future wife, who would later assist him with the editing and typing of all his scientific papers. He remained at Penn State as the A. Robert Noll Distinguished Professor of Electrical Engineering for the duration of his career.
Hale’s pioneering efforts with rockets included the use of retarding potential analyzers for “deep space” ionization measurements, the development of continuum-flow probe techniques for middle atmosphere ionization measurements, early measurements of nitrogen oxide in the middle atmosphere, and interpretation of “blunt probe” electrical conductivity data to indicate the importance of aerosol particles in middle-atmosphere ionization processes. His investigations in the late 1950s to early 1990s involved the challenging tasks of measuring middle-atmosphere electric fields during thunderstorms and during geomagnetically disturbed and quiet periods.
Hale reveled in bucking the conventional wisdom. One good example is when he put forth his own theory about the physical origin of the extremely low-frequency “slow tail,” an electromagnetic feature radiated from lightning discharges. Robert Wattson-Watt and, later, James Wait held the view that dispersion of white noise produced by the return stroke and propagating in the Earth–ionosphere waveguide explained the slow tail. Ted Pierce followed by Marx Brook proposed that continuing current in the lightning return stroke was necessary for slow tails. Hale, though, emphasized Lee Tepley’s observations that slow tails were too common to be explained by continuing currents and rejected their primary role. As an alternative to the ideas of Wait, Hale advanced the idea that the slow tail waveforms were controlled by the round-trip propagation delay between Earth and ionosphere. The jury is still out on this issue.
The most important contribution Hale made to atmospheric electricity and the global circuit was his persistent insistence on the AC aspects and the role of capacitive coupling (in his customary electrical engineering perspective) between lightning and the lower ionosphere. Hale’s paper in Nature with student Mike Baginski in 1987, a decade prior to the heyday of research activity on red sprites, emphasized the transient energy dissipation by lightning in the mesosphere, where sprites were later identified by other researchers. His prescient ideas about coupling from lightning also extended to the magnetosphere, and his expectation of coupling into the opposite hemisphere along magnetic field lines led him, with interested collaborators, to search for conjugate field sites.
Hale’s earlier use of rocket probes to explore the electrical properties of the nighttime magnetosphere also laid an important foundation for understanding sprite incidence in that region. The suppressed conductivity, which he interpreted as aerosol-scavenging of electrons, and the extended relaxation time enabled the short-duration stressing and ionization by lightning to produce the red sprite at high altitude.
In 1993, Hale formally retired and returned to New Mexico, but he remained active in research and communicated with colleagues until his death. In his later years, he focused on the newly discovered red sprites in the mesosphere over large thunderstorms.
Hale and his family enjoyed both playing and watching a competitive game of tennis. His athletic sons could not defeat him because of his powerful serve. At scientific conferences, he was renowned for his gracious chauffeuring of friends and colleagues to his favorite restaurants. His ideas and collegiality are sorely missed by the scientific community.
