It was recognized at the very outset of the space age that a complete description and understanding of plasmas in space would only be achieved if electric fields (from DC to high frequencies) could be measured together with the particle fluxes and the magnetic fields. Professor Forrest Mozer, an eminent and groundbreaking space physics member of AGU, is the recipient of the 2018 John Adam Fleming Medal. Professor Mozer invented and pioneered the flight of the spherical double-probe techniques that revolutionized experimental space plasma research, techniques that are continuing to make major advances in the field to the present.
Without the electric fields, essential physical quantities such as the Poynting flux could not be determined in the plasmas. Unlike most particle fluxes and magnetic fields, electric fields are generally much more difficult to measure because spacecraft carrying instruments can easily disturb the fields. Early space-age discussions involved the possible feasibility of using electron beams and long antennae of various types. However, double probes proved from the outset to be far superior. In addition to his double-probe innovations, Professor Mozer also was the first to develop and fly (on the International Sun-Earth Explorer 1 (ISEE-1) Earth-orbiting spacecraft) a burst memory device for the capture of waveform bursts (electric and magnetic), which included the first microprocessor flown in space in a science experiment. Such waveform capture, generally triggered by a large-amplitude wave, has become essential in experimental magnetosphere research to return electric (and magnetic) field data that would otherwise be lost and thus not available for complete physical interpretation and application to theory.
Professor Mozer, his students and his colleagues, and, eventually, investigators around the world have employed his electric field and waveform capture inventions and subsequent improvements to make fundamental contributions in many areas of space plasma physics. For example, it was long recognized that electrons and ions produce aurora emissions. Professor Mozer and his students and colleagues, using data from his instruments, discovered that electrostatic shocks (at altitudes of ~1 Earth radius) accelerated the electrons downward into the atmosphere to make discrete auroras. He also discovered double layers and solitary waves in the plasmas in auroral regions and their relevance for acceleration processes.
Without Mozer’s double-probe and waveform burst techniques flown on many spacecraft (including the recent Cluster, Time History of Events and Macroscale Interactions during Substorms (THEMIS), Van Allen Probes, and Magnetospheric Multiscale (MMS) missions), instances of space plasma reconnection and their physical nature would not have been identified or understood. The very first measurements of the Hall electric field at Earth’s magnetopause were possible because of the double-probe technique. More recently, on the MMS spacecraft, he and his colleagues measured the parallel acceleration of electrons by Fermi reflection from time domain structures in reconnection regions.
In addition to his pioneering contributions over more than 5 decades in space plasma physics, Professor Mozer invented and patented in 1974 the first integrated circuit speech synthesizer in a commercial product. This was motivated in part by his mentoring of a sight-challenged physics graduate student. As an entrepreneur he has cofounded two companies to develop and market speech systems. Professor Mozer, a true Renaissance physicist, amply deserves the John Adam Fleming Medal recognition by AGU.
—Louis J. Lanzerotti, New Jersey Institute of Technology, Newark; also at Alcatel-Lucent Bell Laboratories (retired), Murray Hill, N.J.
I thank the American Geophysical Union and the Fleming Committee for the honor and satisfaction associated with my receiving the Fleming Medal. I accept it on behalf of the students, postdocs, researchers, engineers, and software developers who did the heavy lifting for which I am being honored. I thank every one of them for making our research both fun and exciting.
This all started in the 1960s when it was known that electrons were accelerated to relativistic energies in the Van Allen radiation belts and auroras but the electric fields responsible for this acceleration were neither measured nor understood. It occurred to me that one might use Langmuir probe theory to put a bias current on a pair of separated spheres and to then measure their potential difference to determine the electric field. The sensors were required to be spherical in order to symmetrize their responses in the directed sunlight, magnetic field, and plasma flow. We tried this detection scheme for the first time on a French sounding rocket flown from Andenes, Norway, in October 1966, and we made the first electric field measurements in the ionosphere. My colleagues in this endeavor were Arne Pedersen, Ulf Fahleson, Carl-Gunne Fälthammar, Mike Kelley, and Paul Bruston.
We continued this research at Berkeley by flying many sounding rockets and more than 100 electric field measuring balloons. Then, in 1976, we had the opportunity of flying a three-axis double-probe electric field experiment on an Air Force piggyback satellite called S3-3. On this flight, we made the first DC and low-frequency electric field measurements above the ionosphere. We observed extremely large parallel electric fields that we called electrostatic shocks and that accelerated electrons to make the discrete auroras that are featured in most auroral pictures. Our team of graduate students and postdocs at that time included Mary Hudson, Bill Lotko, Bob Lysak, John Wygant, Cindy Cattell, Roy Torbert, Bob Ergun, and Gar Bering, all of whom went on to distinguished careers as faculty members at other universities.
Our electric field research continues actively to this day with collaborations involving Ivan Vasko, Oleksiy Agapitov, Vladimir Krasnoselskikh, Solène Lejosne, Ilan Roth, and many others.
And last, I want to thank the group that made all of this seem worthwhile: my children, Mike, Todd, Dana, Laura, Sam, and H.K. Thanks, kids, I love you.
—Forrest S. Mozer, Space Sciences Laboratory and Physics Department, University of California, Berkeley