Geostationary magnetic field response to solar wind pressure variations: Time delay and local time variation

Abstract

The relationship between solar wind dynamic pressure changes and geosynchronous magnetic field response is studied using 15 years of OMNI2 and GOES data at 1‐minute resolution. Significant magnetospheric response to solar wind‐forcing is found to be most frequent near noon (30% of all intervals), and virtually absent on the night‐side. The strongest response occurs when IMF Bz is strongly northward and the effect of reducing IMF Bz is most pronounced in the dusk sector. Approximately 25% of dayside Bz variance for related intervals can be attributed to direct response from solar wind dynamic pressure forcing. Time lag between changes in the solar wind at the bow shock nose and similar fluctuations in the magnetosphere at geosynchronous orbit (6.6 Re) is typically 2 to 4 minutes, with responses occurring first in the post‐noon sector and approximately 2 minutes later near dawn. The OMNI2 HRO time‐shifting algorithm appears to be quite effective, with a slight (2 minute) systematic increase in lag and no increased scatter for the most distant upstream solar wind satellite location.