Michigan Technological University
Department of Physics and the Remote Sensing Institute

are pleased to announce a colloquium

with

Brian A. Tinsley

University of Texas at Dallas

Solar Wind and Global Circuit
Forcing of Clouds and Climate

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, J_z, in the global electric circuit affecting microphysical
interactions in clouds. The J_z 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; 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 J_z. Ion mediated
nucleation may also occur in clear air in response to changes in the
galactic cosmic ray 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 J_z and galactic cosmic ray modulation. Scavenging of ice forming nuclei
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.

Monday, March 8, 2004

4:00 p.m., M&M 113

Refreshments will be served

MTU | Physics | Colloquium