Possible effect of extreme solar energetic particle events of September–October 1989 on polar stratospheric aerosols: a case study

Abstract

Abstract. The main ionization source of the middle and low Earth's atmosphere is related to energetic particles coming from outer space. Usually it is ionization from cosmic rays that is always present in the atmosphere. But in a case of a very strong solar eruption, some solar energetic particles (SEPs) can reach middle/low atmosphere increasing the ionization rate up to some orders of magnitude at polar latitudes. We continue investigating such a special class of solar events and their possible applications for natural variations of the aerosol content. After the case study of the extreme SEP event of January 2005 and its possible effect upon polar stratospheric aerosols, here we analyze atmospheric applications of the sequence of several events that took place over autumn 1989. Using aerosol data obtained over polar regions from two satellites with space-borne optical instruments SAGE II and SAM II that were operating during September–October 1989, we found that an extreme major SEP event might have led to formation of new particles and/or growth of preexisting ultrafine particles in the polar stratospheric region. However, the effect of the additional ambient air ionization on the aerosol formation is minor, in comparison with temperature effect, and can take place only in the cold polar atmospheric conditions. The extra aerosol mass formed under the temperature effect allows attributing most of the changes to the "ion–aerosol clear sky mechanism".

Nitrate ion spikes in ice cores not suitable as proxies for solar proton events

“…These figures confirm the conclusion by Usoskin et al . [] and Mironova and Usoskin [] that ion pair production rates in the lower stratosphere are 1–2 orders of magnitude less than in the midstratosphere, even during hard spectrum events.…”

“…These enhancements are similar in relative magnitude to the twofold to fivefold nitrate spikes measured in Greenland ice cores and attributed to SPEs. 1972, October 1989, January 2012, and March 2012and GCR rates (annual mean) from 1972[Usoskin et al, 2010Mertens et al, 2013;Jackman et al, 2014]. Journal of Geophysical Research: Atmospheres 10.1002/2015JD023805 By placing these hypothetical SPEs in the context of probability distributions and upper limit estimates, we can assess the frequency that such events might occur and consequently the potential usefulness of nitrate as a proxy for individual SPEs.…”

“…Figures 1 and 2 show the differential energy spectra and ion pair production rates for several SPEs in this study. The vertical axis of Figure 1 represents the midpoint energy levels of the GOES proton channels (unequally spaced), and the black dashed lines denote 30 MeV and 200 MeV cutoffs corresponding to Mironova and Usoskin [2013] that ion pair production rates in the lower stratosphere are 1-2 orders of magnitude less than in the midstratosphere, even during hard spectrum events.…”

What is the solar influence on climate? Overview of activities during CAWSES-II

“…This interaction makes it difficult to utilise regression or superposed epoch analysis in statistical studies of cosmic ray events. Reflecting this, atmospheric impacts of individual GLE events were analysed for 1989 (Mironova and Usoskin 2013(Mironova et al 2012), and 2000, 2001and 2003(Mironova and Usoskin 2014. The results suggested that an enhancement of ionisation rate by a factor of about 2 in the polar region with the night/cold/winter conditions can lead to formation or growing of aerosol particles in the polar middle stratosphere.…”

“…A number of publications have studied the effects of transient solar events (SEP or ground level enhancement (GLE) of CR) on the lower stratosphere and upper troposphere in the polar regions (Calisto et al 2013;Mironova et al 2012;Mironova and Usoskin 2013;Mironova and Usoskin 2014;Usoskin et al 2011), including calculation of atmospheric ionisation from nearly all GLE events since 1956. The results indicated that there is no straightforward relation between the strength of the GLE events (as measured by neutron monitors) and the ionisation effect in polar atmosphere.…”