Insights into Mesospheric Chemistry by Ionospheric Heating at HAARP

During three ionospheric heating campaigns in 2025, including the 2025 Polar Aeronomy and Radio Science (PARS) summer school held by the University of Alaska Fairbanks, the University of Florida’s Ionospheric Radio Lab (IRL) performed a variety of active ionospheric heating experiments using the High-frequency Active Auroral Research Program’s (HAARP) Ionospheric Research Instrument (IRI).  High frequency (HF) partial reflection and HF cross-modulation experiments were used to investigate the dynamic response of the mesosphere to short time-scale heating.  ELF/VLF wave generation experiments were designed to identify the location of the ELF/VLF source region and to quantify the spatial distribution of the auroral electrojet currents.  Additionally, VLF scattering experiments were designed to characterize mesospheric HF heating by moving the HAARP-generated scattering body in a proscribed manner.

UF made a concerted effort to detect the effects described above at seven widely spaced radio receiver locations, each of which was selected to be extremely radio quiet.  Noise at each site was mitigated at the receiver by operating using a sinusoidal power generator. The logistical effort required all UF graduate students’ effort, and we are especially grateful for the efforts of our colleagues at Auburn University and at the University of Alaska Fairbanks for their help operating these remote sites.

In this paper, we present observations and analysis for the experimental efforts studying HF propagation, ELF/VLF wave generation, and VLF scattering with a particular emphasis on insights provided into mesospheric dynamics.  We comment on the possible future impact of the (now-operational) HAARP Lidar on these analyses: a potentially important diagnostic for the mesospheric electron density and electron temperature, as well for as the spatial distribution of electrojet currents above HAARP.