Commentary on “Atmospheric ionization by high-fluence, hard-spectrum solar proton events and their probable appearance in the ice core archive” by A.L. Melott et al. and “Nitrate ion spikes in ice cores not suitable as proxies for solar proton events” by K.A. Duderstadt et al.

摘要

The papers, “Atmospheric ionization by high-fluence, hard-spectrum solar proton events and their probable appearance in the ice core archive” by Melott et al. [2016] and “Nitrate ion spikes in ice cores not suitable as proxies for solar proton events” by Duderstadt et al. [2016] both investigate the probability that solar proton events can produce nitric ions enhancements detectable in the ice core record as suggested by a number of previous publications investigating ice core data [e.g., Zeller and Dreschhoff, 1995; McCracken et al., 2001; Smart et al., 2014]. Both groups of authors make similar assumptions about the probable atmospheric ionization by large, hard spectra, solar proton events, and about the subsequent production of nitric oxides in the lower and middle atmosphere. Nevertheless, both come to opposing conclusions: Duderstadt et al. [2016] conclude that only very high fluence solar proton events produce enough total anorganic nitrogen compounds (NOy) to affect the ice core record, and that those have an occurrence frequency of less than one in every ~10.000 years, i.e., are unlikely to have occurred during the Holocene. Melott et al. [2016] conclude that the ice core record can be a good reservoir of hard spectra solar proton events occurring much more frequently. The reason for this apparent disagreement is in my opinion the different assumptions made by both authors about the nature of an observable increase in the ice core record; I will come back to that later.