Duderstadt, K. A., Dibb, J. E., Schwadron, N. A., Spence, H. E., Solomon, S. C., Yudin, V. A., … Randall, C. E. (2016). Nitrate ion spikes in ice cores not suitable as proxies for solar proton events. Journal Of Geophysical Research-Atmospheres, 121, 2994-3016. doi:10.1002/2015JD023805