Apparent tropospheric response to MeV‐GeV particle flux variations: A connection via electrofreezing of supercooled water in high‐level clouds?

Abstract

The ionization production by MeV‐GeV particles (mostly galactic cosmic rays) in the lower atmosphere has‐well defined variations on a day‐to‐day time scale related to solar activity, and on the decadal time scale related to the sunspot cycle. New results based on an analysis of 33 years of northern hemisphere meteorological data show clear correlations of winter cyclone intensity (measured as the changes in the area in which vorticity is above a certain threshold) with day‐to‐day changes in the cosmic ray flux. Similar correlations are also present between winter cyclone intensity, the related storm track latitude shifts, and cosmic ray flux changes on the decadal time scale. These point to a mechanism in which atmospheric electrical processes affect tropospheric thermodynamics, with a requirement for energy amplification by a factor of about 10 7 and a time scale of hours. A process is hypothesized in which ionization affects the nucleation and/or growth rate of ice crystals in high‐level clouds by enhancing the rate of freezing of thermodynamically unstable supercooled water droplets which are known to be present at the tops of high clouds. The electrofreezing increases the flux of ice crystals that can glaciate midlevel clouds. In warm core winter cyclones the consequent release of latent heat intensifies convection and extracts energy from the baroclinic instability to further intensify the cyclone. As a result, the general circulation in winter is affected in a way consistent with observed variations on the interannual/decadal time scale. The effects on particle concentration and size distributions in high‐level clouds may also influence circulation via radiative forcing.