Storm-Driven Suppression and Post-Storm Enhancement of Photographic Plate Transient Detections at Geosynchronous Altitude: Empirical Evidence and a Candidate Dusty Plasma Mechanism

The VASCO project has identified over 100,000 sub-second optical transients on photographic plates from the First Palomar Observatory Sky Survey (1949-1957), all predating artificial satellites. Cann (2026a) established that transient detection rates are dose-dependently suppressed during geomagnetic storms (Z = -3.391, p = 0.0007), ruling out emulsion defects and confirming the transients as real, magnetospherically coupled phenomena. Villarroel et al. (2022) constrained the source altitude to ~42,000 km (geosynchronous orbit) through an Earth-shadow deficit. This paper presents two results. First, a pre-registered empirical test reveals the full temporal recovery profile: transient rates remain suppressed at 55% of baseline during days 7-21 post-storm, then rise to 309% of baseline during days 25-45 (p = 0.00066, Wilcoxon rank-sum; all robustness checks significant). Combined with the dose-response staircase, the overall significance reaches 3.6-4.7 sigma (Fisher's method, range reflecting sensitivity to the independence assumption). Second, we propose a candidate physical mechanism: storm-enhanced electromagnetic trapping of charged micrometeoroid dust at L ~ 6.6, followed by aggregation of icy cometary grains under restored cold plasmaspheric conditions. A flux dilution analysis demonstrates that specular reflection from a partially reflective icy aggregate only 1-4 m in diameter suffices to produce the observed plate magnitude at 42,000 km. This mechanism connects the VASCO transients to independently observed magnetospheric dust swarms correlated with geomagnetic activity (Sommer 2024) and explains the extinction of the transient population following the onset of the space age. Multi-site replication is required to confirm these results.