Interpretation of Short-Term Solar Variability Effects in the Troposphere

Abstract

Among possible external forcing agents for tropospheric response to solar variability, the variation of MeV-GeV particle fluxes, resulting in changes in stratosphere-troposphere ionization and electric fields, is a plausible candidate. The MeV-GeV particle hypothesis fits reported correlations of geopotential heights, temperatures and vorticity area index (VAT) on the one hand with solar proton events, high-speed solar wind plasma streams, magnetic storms and Forbush decreases of galactic cosmic rays on the other hand. Both solar wind magnetic structures and changes in the terrestrial magnetosphere modulate the incoming particle fluxes. The day-to-day correlations are strongest in winter.Mechanisms linking MeV-GeV flux changes with tropospheric changes are speculative. Among a number of processes to be investigated, one not previously considered involves the electrofreezing of supercooled water droplets in high clouds of cyclones; their growth by the Wegener-Bergeron instability; sedimentation to lower level supercooled clouds where they enhance freezing and latent heat release; the intensification of convection; and in warm core winter cyclones the extraction of energy from the baroclinic instability to further intensify the cyclone; leading to changes in the general circulation. On a longer time scale changes in water/ice ratio in cirrus may lead to changes in cloud radiative forcing and also to changes in the general circulation.