Solar Wind and Global Circuit Forcing of Clouds and Climate Prof. Brian A. Tinsley, University of Texas at Dallas.

Observed correlations of changes in atmospheric dynamics, in cloud cover, and in atmospheric transparency with solar wind changes on the day-to-day timescale point to mechanisms involving changes in the vertical current density, Jz, in the global electric circuit affecting microphysical interactions in clouds. The Jz changes can result from changes in cosmic ray flux, relativistic electron precipitation, solar proton fluxes or electrical coupling between the solar wind and the polar ionosphere.
There are two proposed mechanisms for such electrical effects; electroscavenging of both charged cloud condensation nuclei (CCN) and ice forming nuclei (IFN); and ion-mediated nucleation of ultrafine particles that may grow into CCN. Both mechanisms are responsive to changes in space charge at the tops and bottoms of clouds, caused by changes in Jz. Ion mediated nucleation may also occur in clear air in response to changes in the GCR flux. There are at least two ways that clouds, if responding to the proposed microphysical mechanisms, may affect climate. Changes in CCN concentration lead to changes in cloud cover by the indirect aerosol effect, and this modulates incoming solar and outgoing longwave radiation. These may affect zonal circulation because of latitudinal gradients in the cloud cover responses caused by latitudinal variations in the Jz and GCR modulation. Scavenging of IFN enhances contact ice nucleation and precipitation efficiency, and in winter storms may affect cyclogenesis through latent heat transfer, with cumulative effects on regional winter circulation.