Influence of the Solar Magnetic Field on Tropospheric Circulation

Abstract

The solar and interplanetary magnetic sector structure has its source in a large-scale photospheric magnetic field structure that is carried away from the Sun by the solar wind to form a warped equatorial current sheet in the heliosphere. A complete rotation of this current sheet is carried past the Earth by the solar wind every 27 days, and several terrestrial effects result. The area of wintertime troughs in the northern hemisphere as measured using the vorticity area index (VAI) reaches a minimum about one day after the current sheet passes the Earth (a sector boundary). The percentage depth of this minimum is larger for the areas with the most intense tropospheric circulation. Certain passages of the current sheet that are observed in the interplanetary medium to be particularly active have an influence on the trough area that is twice as large as the average effect. A quantitative analysis indicates that forecasting using the Limited Area Fine Mesh grid is significantly less accurate during the two days following the passage of the current sheet. Individual troughs crossing 180° longitude when the interplanetary magnetic field is directed away from the Sun (i.e., at the present time the current sheet is south of the Earth) are significantly larger than troughs crossing 180° longitude when the field is toward the Sun. Possible physical mechanisms include a solar phasing influence on planetary waves leading to constructive or destructive interference, an observed influence of the heliospheric current sheet on the vertical electric field in the troposphere, and sector-related changes in solar EUV intensity which may influence O₃ concentrations and the reaction rates of atmospheric chemical processes.