Hear05 -

A. N. Volkov, L. M. Chen, R. J. Patterson Affiliation: Institute for Atmospheric and Space Physics, University of Colorado Boulder

The High-frequency Earth Atmospheric Research (HEAR) campaign aims to bridge observational gaps in atmospheric wave dynamics between 20–120 km altitude. This paper presents HEAR05, a focused investigation of infrasound (0.01–20 Hz) and ultra-low frequency (ULF, 0.001–1 Hz) wave coupling from the lower atmosphere to the ionosphere. Using a distributed network of ground-based microbarometers and fluxgate magnetometers at four mid-latitude sites (40°–55°N), we analyzed wave events during solar-minimum conditions (2025–2026). Results show coherent ULF wave signatures in both magnetic and pressure fields, with horizontal phase velocities of 150–300 m/s, consistent with acoustic-gravity modes. Infrasound from mountain-associated sources correlated with sporadic E-layer modulation (Δf o E ~ 0.3 MHz). HEAR05 provides a validated methodology for continuous upper-atmosphere wave monitoring, with implications for satellite drag prediction and radio communication. hear05

Infrasound, ULF waves, atmospheric coupling, ionospheric variability, HEAR05, magnetometer array 1. Introduction Understanding energy transfer from the lower atmosphere to the ionosphere remains a challenge in space weather physics (National Academies, 2022). While large-scale tides and planetary waves are well characterized, the role of infrasound (frequencies below human hearing) and ULF waves in modulating ionospheric electron density is underexplored (Williams et al., 2020). The HEAR program was established to systematically observe high-frequency (in the spatiotemporal sense) atmospheric oscillations. HEAR05 specifically targets the 0.001–20 Hz band using a dedicated ground array. A. N. Volkov