A direct comparison of impulsive nitrate enhancements observed in multiple polar ice cores from both hemispheres is presented for the years 1940-1950.
During that time period, four ground-level solar cosmic ray events (GLEs) were recorded by ionization chambers. We show that large and sudden enhancements in the nitrate records from both hemispheres were observed within weeks of the dates of the GLEs. The observation of impulsive nitrate enhancements simultaneously in both hemispheres shortly after a solar proton event is strong evidence in support of a causal connection and argues strongly for rapid gravitational precipitation of atmospheric nitrates.

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 1 (SH), pages 729-732