Atmospheric transparency changes associated with solar wind-induced atmospheric electricity variations

Variations in atmospheric transmission of several percent in nominally clear air are found to accompany solar wind events associated with variations on the day-to-day timescale in the flow of vertical current density ( J z ) in the global electric circuit. The effect has been observed only for stations at high latitudes (>55°N). Increases in transmission are present when inferred J z decreases occurred without changes in tropospheric ion production. These events occurred when there was a high loading of stratospheric aerosols. Responses of opposite sign, i.e., decreases in transmission, are present when Forbush decreases of galactic cosmic ray flux occur, but only during periods of low stratospheric aerosol loading. Forbush decreases are associated with both tropospheric ion production decreases and J z decreases. Similar effects are present on the 11-year solar cycle, with climate consequences that have yet to be analyzed. The mechanisms for these phenomena are not understood, but the nature of the observations suggests that explanations should be sought in terms of theories of the effects of electric charge on the formation of aerosols, and/or effects of charged aerosols on the microphysics of vapor–water–ice conversions.