RAPID: Novel Experimental Quantification of Energetic Electron Properties During Ionospheric Modification

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This one-year RAPID project is aimed at providing unprecedented empirical constraints on the energy distribution of electrons generated during high-power ionospheric modification as a means of advancing understanding of electron acceleration processes. High-power, high-frequency (HF) radio wave transmitters are an important tool for the experimental investigation of fundamental plasma physics in the terrestrial ionosphere. Three HF heating facilities (HAARP, EISCAT, and Arecibo Observatory) have demonstrated the ability to induce overhead plasma densities approaching those created by solar photoionization, thereby enabling empirical studies of energetic electron production, acceleration and transport. Despite numerous experiments over the past several decades, however, the physical mechanisms responsible for electron acceleration during ionospheric modification remain unsettled. In order to tackle this problem, this project adopts a novel approach that involves the combination of plasma-line and ion-line detection by the Arecibo Observatory incoherent scatter radar (ISR). This is the most sensitive instrument of its kind, together with passive measurement of optical airglow emitted by Oxygen atoms at 844.6 nm and 630.0 nm. The research campaign will utilize nearly all of the facility and the PI-owned optical instrumentation on site at the Arecibo Observatory and at the nearby Culebra island in an unprecedentedly coordinated effort. Unlike past investigations of electron acceleration during ionospheric modification, the research analysis during this project will incorporate coincident empirical estimates of thermospheric Oxygen density, which the PI will derive from calibrated measurements of the Oxygen 844.6 nm emission line brightness. This research effort will be led by an early-career, female PI. The research agenda of this RAPID project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research The results from the intended research effort to obtain unprecedented empirical constraints on energetic electron acceleration during ionospheric modification will have far-reaching impact on fundamental theories governing the physics of weakly magnetized plasmas. Future investigations of electron energy loss from pitch angle scattering in the plasmasphere, for example, will benefit from the results of this work. Although advancing ionospheric plasma physics is the primary focus of the effort, the careful experimental design by the PI will also yield crucial constraints on the rate of Oxygen 844.6 nm emission line excitation via O+ radiative recombination. Moreover, the intended implementation of astronomical calibration at this near-infrared wavelength as well as at the Oxygen 630.0 nm emission line will provide a long-awaited means of cross-calibrating the facility calibration sources for future campaigns. Finally, the new Oxygen 844.6 nm emission line photometer can easily be configured to conduct routine passive measurements for community use. Even in the absence of HF ionospheric heating, the calibrated Oxygen 844.6 nm emission line data provide a means for Thermospheric Oxygen sensing. This capability, which currently is not possible at any other ISR facility, enables crucial investigations of ion-neutral coupling which are needed to advance physics-based models of the upper atmosphere. .