Possible effect of extreme solar energetic particle event of 20 January 2005 on polar stratospheric aerosols: direct observational evidence

Abstract

Abstract. Energetic cosmic rays are the main source of ionization of the low-middle atmosphere, leading to associated changes in atmospheric properties. Via the hypothetical influence of ionization on aerosol growth and facilitated formation of clouds, this may be an important indirect link relating solar variability to climate. This effect is highly debated, however, since the proposed theoretical mechanisms still remain illusive and qualitative, and observational evidence is inconclusive and controversial. Therefore, important questions regarding the existence and magnitude of the effect, and particularly the fraction of aerosol particles that can form and grow, are still open. Here we present empirical evidence of the possible effect caused by cosmic rays upon polar stratospheric aerosols, based on a case study of an extreme solar energetic particle (SEP) event of 20 January 2005. Using aerosol data obtained over polar regions from different satellites with optical instruments that were operating during January 2005, such as the Stratospheric Aerosol and Gas Experiment III (SAGE III), and Optical Spectrograph and Infrared Imaging System (OSIRIS), we found a significant simultaneous change in aerosol properties in both the Southern and Northern Polar regions in temporal association with the SEP event. We speculate that ionization of the atmosphere, which was abnormally high in the lower stratosphere during the extreme SEP event, might have led to formation of new particles and/or growth of preexisting ultrafine particles in the polar stratospheric region. However, a detailed interpretation of the effect is left for subsequent studies. This is the first time high vertical resolution measurements have been used to discuss possible production of stratospheric aerosols under the influence of cosmic ray induced ionization. The observed effect is marginally detectable for the analyzed severe SEP event and can be undetectable for the majority of weak-moderate events. The present interpretation serves as a conservative upper limit of solar energetic particle effect upon polar stratospheric aerosols.

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

“…We conclude that the present results show variations of the aerosol optical and microphysical parameters (in the cold polar stratosphere) that are similar to the aerosol variations detected after the GLE in January 2005 (Mironova et al, 2012). The recognized effect, during these two GLEs (20 January 2005 and29 September 1989), is found at the same altitude range of 10-20 km.…”

“…Previous phenomenological studies (Mironova et al, 2008(Mironova et al, , 2012 yielded that there is a small, marginally detectable effect of an extreme SEP (e.g., such as the one of 20 January 2005) on the aerosol particles in the lower-middle polar stratosphere during stable winter/summer conditions. However, an appropriate model able to explain the observed features is still missing.…”

“…Cosmic rays produce a direct effect on the Earth's atmosphere via ionization of the ambient air and form the main source of the atmospheric ionization for the lower and middle atmosphere (Bazilevskaya et al, 2008). There are some indications that it may affect properties of the atmospheric aerosols (Kazil et al, 2008;Mironova et al, 2008Mironova et al, , 2012 and possibly even cloud formation (Carslaw et al, 2002;Tinsley, 2008), which may be crucially important as an indirect factor affecting the climate. However, it is still a subject of intensive debates (Kulmala et al, 2010;Usoskin et al, 2010b;Calogovic et al, 2010).…”

Solar wind-atmospheric electricity-cloud microphysics connections to weather and climate

“…Recently, empirical evidence has been produced for a possible effect of the ionization associated with an extreme SEP event on stratospheric aerosols (Mironova et al, 2012a). Significant simultaneous changes in aerosol properties were found in the polar stratosphere (11-25 km) of both hemispheres.…”

Cosmic Rays, Solar Activity and the Climate

“…Mironova et al [19] observed an increase in the stratospheric aerosol production in a limited region of the Northern hemisphere a few days after the large ground level event (GLE) of 20 January 2005. However, the observed effect is at too high an altitude to influence the climate.…”