HR: 0830h
AN: SM41A-08    [Abstracts]
TI: A Statistical Study of IMF Bz Generation in the Solar Wind
AU: * Lyatsky, W
EM: lyatsky@cspar.uah.edu
AF: Alabama A&M University, 4900 Meridian St., Normal, AL 35762 United States
AU: Tan, A
EM: arjun.tan@email.aamu.edu
AF: Alabama A&M University, 4900 Meridian St., Normal, AL 35762 United States
AB: It is well known that the interplanetary magnetic field (IMF) Bz component plays an important role in the generation of geomagnetic activity. The origin of IMF Bz is yet not completely understood but some simple cases of coronal mass ejections when the ambient IMF is draping the CME plasma clouds. However, IMF Bz is observed not only during CMEs but practically continuously. For this study we used correlation analysis of solar wind data near the Earth in the solar-ecliptic coordinate system. First we studied the IMF Bz generation during two minima of geomagnetic activity related to negative and positive Sun's magnetic field polarity, respectively. We found that both sign and magnitude of IMF Bz have a regular character and clearly correlate with other solar wind parameters: the IMF Bx component, IMF orientation, and Sun's magnetic field. Then we analyzed events related to all levels of solar activity for ten years from 1995 through 2004 when almost continuous series of solar wind data is available. The most interesting result is a strong dependence of IMF Bz on IMF orientation in the horizontal plane: IMF Bz tends to zero when IMF vector in the horizontal plane is along the Parker spiral and increases with the deflection of the IMF vector from Parker spiral orientation. The correlation between IMF Bz and the IMF Bn component orthogonal to the Parker spiral increases with time of averaging. Correlation coefficient for daily mean data is about 0.63. The correlation increases if we account also for IMF magnitude, B, in the horizontal plane. Correlation between IMF Bz and a combination of IMF Bn and B leads to correlation coefficient for daily mean data of about 0.71. We did not find any evident dependence of IMF Bz on solar wind speed but a strong increase in correlation with increasing solar wind speed. Thus, we have found that the "false" (non-Parker spiral) IMF orientation in the horizontal plane is an important factor for IMF Bz generation. We discuss the obtained results in terms of MHD waves and quasi-steady-state inhomogeneities moving with the solar wind.
DE: 2164 Solar wind plasma
DE: 2784 Solar wind/magnetosphere interactions
DE: 2788 Storms and substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2005 Joint Assembly