Further considerations of cosmic ray modulation of infra-red radiation in the atmosphere

Abstract

Understanding effects of ionisation in the lower atmosphere is a new interdisciplinary area, crossing traditionally distinct scientific boundaries. Following the paper of Erlykin et al. (Astropart. Phys. 57--58 (2014) 26--29) we develop the interpretation of observed changes in long-wave (LW) radiation (Aplin and Lockwood, Env. Res. Letts. 8, 015026 (2013)), by taking account of cosmic ray ionisation yields and atmospheric radiative transfer. To demonstrate this, we show that the thermal structure of the whole atmosphere needs to be considered along with the vertical profile of ionisation. Allowing for ionisation by all components of a cosmic ray shower and not just by the muons, reveals that the effect we have detected is certainly not inconsistent with laboratory observations of the LW absorption cross section. The analysis presented here, although very different from that of Erlykin et al., does come to the same conclusion that the events detected were not caused by individual cosmic ray primaries -- not because it is impossible on energetic grounds, but because events of the required energy are too infrequent for the 12/hr rate at which they were seen by the AL experiment. The present paper numerically models the effect of three different scenario changes to the primary GCR spectrum which all reproduce the required magnitude of the observed effect. However, they cannot solely explain the observed delay in the peak effect which, if confirmed, would appear to open up a whole new and interesting area in the study of water oligomers and their effects on LW radiation. We argue that a technical artefact in the earlier experiment is highly unlikely and that our initial observations merit both follow-up experiments and more rigorous, self-consistent, three-dimensional radiative transfer modelling.