Space weather underground program: low-cost magnetometer observations of the 2023 annular solar eclipse

The Space Weather UnderGround (SWUG) program is an educational outreach initiative in which high school and undergraduate students learn heliophysics fundamentals and build low-cost fluxgate magnetometers. The program has three primary goals: (1) training the future Science, Technology, Engineering, and Mathematics (STEM) workforce, (2) developing a cost-effective magnetometer network across the United States, and (3) providing high-spatial-resolution geomagnetic field data for heliophysics research. The Maryland SWUG program, launched in 2022, deployed a student-built magnetometer in Los Alamos, NM, in early October 2023 and operated it for ∼1 month to study geomagnetic field disturbances during the annular solar eclipse on 14 October 2023. Due to time and resource constraints, standard magnetometer calibration procedures could not be completed prior to the campaign; therefore, the SWUG magnetometer data were analyzed qualitatively rather than quantitatively. On geomagnetically quiet days, the instrument recorded a typical diurnal variation in the northward geomagnetic field component ( Δ X ): steady at night, turning southward after sunrise until late afternoon, and then returning to nighttime values. This pattern indicates that solar ionization of the upper atmosphere enhances westward ionospheric currents above Los Alamos. On the eclipse day, however, this southward progression was disrupted, suggesting weakened westward currents caused by the temporary reduction in solar illumination. Global ionospheric current maps derived from worldwide research-grade magnetometer networks independently confirmed the weakened westward current above Los Alamos during the solar eclipse. These results demonstrate that, with standard magnetometer calibration procedures, low-cost SWUG magnetometers can provide reliable and scientifically valuable data for heliophysics research.