Geomagnetic storm suppression of photographic plate transient detections in the POSS-I archive: an independent physical variable strengthening the nuclear test correlation

TL;DR

This study finds geomagnetic storm activity significantly influences photographic transient detection rates in the POSS-I archive, strengthening the correlation with nuclear tests and suggesting a physical link to radiation belt phenomena.

Contribution

It identifies geomagnetic activity as an independent variable affecting transient detections, enhancing the nuclear test correlation and ruling out alternative transient sources.

Findings

Transient detection rates decrease with increasing geomagnetic storm intensity.

Including geomagnetic activity in models strengthens nuclear test detection correlation.

Transient sources are likely physically linked to radiation belt environment.

Abstract

Bruehl & Villarroel (2025) reported a correlation (p = 0.008, 2.6 sigma) between atmospheric nuclear weapon tests and photographic plate transient detection rates in the Palomar Observatory Sky Survey (POSS-I) archive, independently replicated by Doherty (2026) using negative binomial regression with weather controls. I identify geomagnetic storm activity, measured by the planetary Kp index, as an additional independent variable modulating transient rates in the same dataset. Transient detection rates follow a monotonic dose-response across five Kp intensity bins, from 17.4% during geomagnetically quiet periods to 2.4% at Kp 8-9 (Cochran-Armitage trend: Z = -3.391, p = 0.0007). Nuclear test days are not geomagnetically quieter than the baseline; they are slightly more storm-influenced. A multivariate logistic regression including Kp and lunar-phase controls strengthens the nuclear-transient correlation from 2.6 sigma (p = 0.009, OR = 1.53) to 3.1 sigma (p = 0.002, OR = 1.70). The dose-response rules out emulsion defects and spectrally inert orbital debris as the primary transient source, indicating a population physically coupled to the radiation belt environment at geosynchronous altitude. A self-contained reproduction script is provided as supplementary material.