Solar Cycle Dependence of Solar Wind Geoeffectiveness

Details Solar Cycle Dependence of Solar Wind Geoeffectiveness Solar Cycle Dependence of Solar Wind Geoeffectiveness

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsh24a..04l&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SH24A-04

Physics

2784 Solar Wind/Magnetosphere Interactions, 3270 Time Series Analysis (1872, 4277, 4475), 7536 Solar Activity Cycle (2162), 7954 Magnetic Storms (2788)

Scientific paper

We find clear solar cycle dependence of the specific ways in which different physical properties of the solar wind (SW) couple to different aspects of geomagnetic activity. Geomagnetic activity is described by orthogonalized versions Kp, PC/Kp, and Dst/Kp/PC of the familiar indices. These represent, respectively, geomagnetic activity measured at mid-latitudes, geomagnetic activity measured in the (North) polar region and forced to be linearly independent of Kp, and finally geomagnetic activity measured at low latitudes and forced to be independent of both Kp and PC. Solar wind inputs are hourly averages of the SW plasma beta, dynamical pressure, the imposed duskward electric field, and a derived parameter related to nonthermally fast SW structures. These were measured by the Wind and ACE spacecraft from 1995 through December 2005. They were obtained from the OMNI2 data set. We connect these quantities using multivatiate factor analysis. During the active phase of Cycle 23 (1998- 2003) we find that Kp is primarily governed by SW dynamical pressure, PC/Kp almost entirely by the imposed electric field, and Dst/Kp/PC by the SW plasma beta and by nonthermal structures. This result holds separately for the rising and falling phases of the active Sun. However, during the preceding quiet Sun period (1995-1997) the nonthermal structures were unimportant. Then Dst/Kp/PC was governed by the SW plasma beta and dynamical pressure. At the same time, Kp was coupled directly to SW pressure and electric field, and negatively to plasma beta.

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