Can periodicity in low altitude cloud cover be induced by cosmic ray variability in the extragalactic shock model?

TL;DR

This paper explores whether cosmic ray variability, linked to galactic oscillations, could induce periodic changes in low altitude cloud cover, potentially affecting Earth's climate and biodiversity over 62 million-year cycles.

Contribution

It proposes a mechanism connecting cosmic ray flux oscillations with low altitude cloud cover changes via atmospheric ionization, supported by modeling calculations.

Findings

Cosmic ray flux oscillations can increase atmospheric ionization at low altitudes.

Enhanced ionization may lead to increased cloud condensation nuclei formation.

Potential climate impact includes increased albedo and reduced global temperature.

Abstract

Variation in high energy cosmic rays (HECRs) has been proposed to explain a 62 My periodicity in terrestrial fossil biodiversity. It has been suggested that the infall of our galaxy toward the Virgo cluster could generate an extragalactic shock, accelerating charged particles and exposing the earth to a flux of high energy cosmic rays (HECRs). The oscillation of the Sun perpendicular to the galactic plane could induce 62 My periodicity in the HECR flux on the Earth, with a magnitude much higher than the Galactic cosmic ray change we see in a solar cycle. This mechanism could potentially explain the observed 62 My periodicity in terrestrial biodiversity over the past 500 My. In addition to direct effects on life from secondaries, HECRs induced air showers ionize the atmosphere leading to changes in atmospheric chemistry and microphysical processes that can lead to cloud formation including low altitude cloud cover. An increase in ionization changes the global electric circuit which could enhance the formation of cloud condensation nuclei (CCN) through microphysical processes such as electroscavenging and ion mediated nucleation, leading to an increase in the cloud cover. This could increase the albedo and reduce the solar flux reaching the ground, reducing the global temperature. Using an existing model, we have calculated the enhancement in atmospheric ionization at low altitudes resulting from exposure to HECRs. We use a conservative model to estimate the change in low altitude cloud cover from this increased ionization.