Phil Erickson, MIT Haystack Observatory

Progress in Understanding Our Ionosphere, Atmosphere, and Near-Earth Space through URSI Commission G: Selected 50 Year Highlights

50th Anniversary Plenary Speaker, January 11, 2024

Abstract: URSI Commission G - ionospheric radio and propagation - focuses on ionospheric communications and remote sensing of ionized media. The Commission deals with the study of Earth’s ionosphere in both a basic and applied sense, in order to provide a broad understanding necessary for radio communications along with the physics, chemistry, and electrodynamics of ionized media in near-Earth space. Particular focus areas include (a) Global morphology and modeling of the ionosphere; (b) Ionospheric space-time variations; (c) Development of tools and networks needed to measure ionospheric properties and trends; (d) Theory and practice of radio propagation via the ionosphere; and (e) Application of ionospheric information to radio communications. To achieve these objectives, Commission G works closely with other URSI Commissions, corresponding bodies of the ICSU family (e.g. IUGG, IAU, COSPAR, SCOSTEP) and other relevant organizations (e.g. ITU, IEEE). The history of US Commission G parallels the origins and history of URSI itself, as the earliest 20th century remote sensing tools for the charged upper atmosphere were radio wave based, occurring well before the advent of spacecraft direct sampling of these regions. We briefly review the 50 year history of Commission G in this light, with its participants and studies driving many significant firsts in global radio science. These include (1) continued innovations in HF ionosondes, considered the oldest active ionospheric remote sensing technique; (2) the extremely powerful collective Thomson/incoherent scatter radar technique for providing full altitude profiles of the thermal ionospheric plasma state; (3) the incisive development of global ionospheric total electron content observations and science using global navigation satellite signal (GNSS) scientific receivers and processing; (4) in conjunction with Commission H, active plasma experiments investigating fundamental physics using HF transmissions from ionospheric heaters; (5) ionospheric modeling advances and coupling to whole-atmosphere frontier models, including the important development of the IRI empirical ionospheric model; and (6) multi-wavelength radio scintillation investigations of ionospheric plasma irregularities and deep electron density depletions. Throughout, we will highlight common themes in these advances based on technology advances in radio wave capture, combined with increasingsophistication in first-principles understanding of ionospheric physics and space weather dynamics.

Biography: Dr. Philip J. Erickson is a Principal Research Scientist and the director of Haystack Observatory, a multidisciplinary radio and radar remote sensing observatory operated by Massachusetts Institute of Technology for studies of near-Earth space, Earth dynamics, and the radio universe. He has been a Haystack scientist for 29 years and has led the observatory’s Atmospheric and Geospace Sciences group since 2015 in its active and passive radio remote sensing programs, using a variety of techniques and RF signals at femtowatt to megawatt levels. Erickson is the principal investigator for the NSF funded Millstone Hill Geospace Facility, which encompasses the large aperture mid-latitude Millstone Hill UHF incoherent scatter radar system, global GNSS total electron content observations, and the Madrigal distributed database. He is also the principal investigator for a forthcoming NASA Heliophysics dual small satellite mission to study Earth’s radio aurora in low Earth orbit using MF and HF frequency electromagnetic vector sensors. Erickson’s research focuses on linear and nonlinear dynamics of Earth’s ionosphere, thermosphere, plasmasphere, and radiation belts, along with collective Thomson and fundamental plasma irregularity scattering mechanisms. His association with URSI Commission G began in graduate school at Cornell University, where he received a PhD in space plasma physics in 1998 under the direction of radio remote sensing pioneers and Commission G members Donald Farley, Michael Kelley, and Wesley Swartz. Erickson is an associate editor for Frontiers in Astronomy and Space Science, advises on the board of the HamSCI citizen science initiative, and serves on a number of committees including the National Academy of Science, Engineering, and Mathematics (NASEM) Committee on Radio Frequencies. He is co-chair of the NASEM Panel on the Physics of Ionospheres, Thermospheres, and Mesospheres within the 2024-2033 Decadal Survey for Solar and Space Physics (Heliophysics).