Nitrate deposition to surface snow at Summit, Greenland, following the 9 November 2000 solar proton event

Abstract

This study considers whether spikes in nitrate in snow sampled at Summit, Greenland, from August 2000 to August 2002 are related to solar proton events. After identifying tropospheric sources of nitrate on the basis of correlations with sulfate, ammonium, sodium, and calcium, we use the three-dimensional global Whole Atmosphere Community Climate Model (WACCM) to examine unaccounted for nitrate spikes. Model calculations confirm that solar proton events significantly impact HO x , NO x , and O 3 levels in the mesosphere and stratosphere during the weeks and months following the major 9 November 2000 solar proton event. However, solar proton event (SPE)-enhanced NO y calculated within the atmospheric column is too small to account for the observed nitrate peaks in surface snow. Instead, our WACCM results suggest that nitrate spikes not readily accounted for by measurement correlations are likely of anthropogenic origin. These results, consistent with other recent studies, imply that nitrate spikes in ice cores are not suitable proxies for individual SPEs and motivate the need to identify alternative proxies. IntroductionIdentifying the impact of solar particle storms on the atmosphere remains fundamental in understanding the Sun's influence on Earth's climate [Gray et al., 2010; National Research Council, 2012]. High-energy particles from these solar events increase odd nitrogen and odd hydrogen, catalytically destroying ozone and thereby potentially impacting climate through the chemistry, radiative budget, and dynamics of the upper atmosphere [e.g., Randall et al., 2005;Jackman et al., 2008]. In addition, these space weather events have the potential to disrupt power grids, communications technology, and spacecraft [National Research Council, 2008].Direct observations of solar energetic particle events have only been available since the midtwentieth century. A broader understanding of the potential frequency and intensity of these events requires a more extensive record of historical occurrences, motivating the search for indirect proxy evidence [Schrijver et al., 2012]. There are numerous analytical and predictive studies using nitrate ion (NO 3 À ) variability in polar ice cores as a proxy for solar energetic particle events [e.g., Zeller and Parker, 1981;Dreschhoff and Zeller, 1990;McCracken et al., 2001a;Shea et al., 2006;Kepko et al., 2009]. However, this relationship has been questioned, particularly with regard to the short timescales associated with individual events [e.g., Legrand and Delmas, 1986;Wolff et al., 2008Wolff et al., , 2012. Contemporary progress toward predicting space weather urgently awaits the resolution of whether or not NO 3 À spikes in ice cores can be used to infer past events [e.g., Barnard et al., 2011;Riley, 2012]. [1981] associated nitrate levels with solar activity through the correlation NO 3 À in Antarctic ice cores with cosmogenic carbon isotopes ( 14 C) in tree rings. Statistical correlation studies confirm the covariance between NO 3 À and cosmogenic radionuclides...

Large gradual solar energetic particle events

“…In contrast, studies using different polar ice core records did not show similar evidence of an SEP event associated with the Carrington event, and instead indicated that all the NO − 3 spikes were accompanied by chemical tracers that pointed to anthropogenic biomass burning, and therefore, the ice core NO − 3 spikes constitute an unreliable proxy for large SEP events that occurred in the past (Wolff et al 2012). More recently, Duderstadt et al (2014) investigated whether the nitrate spikes seen in . Specifically, they identified tropospheric sources of nitrates and used the three-dimensional global Whole Atmosphere Community Climate Model (WACCM) to conclude that while the November 9, 2000, SPE significantly enhanced the mesospheric and stratospheric nitrate levels, the associated atmospheric nitrate-column density is still too low for deposition in the surface snow.…”

Experimental evidence that microbial activity lowers the albedo of glaciers

“…However, in the short term, new cryoconite on glaciers undergoes an important decrease in albedo. The increase in anthropogenic NO 3 -deposition on glaciers (Lyons et al, 1990;Duderstadt et al, 2014) has been reported to reduce the microbial N limitation in cryoconite habitats (Telling et al, 2011). Enhanced anthropogenic NO 3 -input will likely lead to a significant decrease in N 2 fixation, allowing more bio-energy to be available for C fixation.…”

Extreme solar particle events: Can we assess the worst case scenario?

“…However, as shown by several recent studies (e.g., [28,29]), nitrate record is not suitable for that. In addition, no nitrate signal was found for the event of 775 AD even though date were of high quality [24].…”