HR: 0830h
AN: SH21B-0148    [PDF]
TI: Effect of Sun's Magnetic Field Polarity on Interplanetary Magnetic Field Bz
AU: * Lyatsky, W
EM: lyatsky@cspar.uah.edu
AF: Alabama A&M University, 4900 Meridian St, Huntsville, AL 35762 United States
AU: Tan, A
EM: atan@aamu.edu
AF: Alabama A&M University, 4900 Meridian St, Huntsville, AL 35762 United States
AU: Lyatskaya, S
EM: lyatsky@cspar.uah.edu
AF: Alabama A&M University, 4900 Meridian St, Huntsville, AL 35762 United States
AB: The results of a statistical study of IMF Bz are presented for two minima of solar activity for the periods of 1985-1987 and 1995-1997, related to negative and positive polarity of the Sun's magnetic field, respectively. We found that IMF Bz is dependent on the magnitude of IMF horizontal (Bx) component, IMF orientation, and Sun's magnetic field polarity. 1) The correlation between IMF Bz and Bx is positive for positive polarity and negative for negative polarity. 2) Positive and negative IMF Bz tends to occur predominantly during IMF orientations significantly different from the Parker spiral: for positive polarity, positive IMF Bz tends to occur around f less than 40 degree and negative IMF Bz around f =-60 degree where f is the minimal angle measured counterclockwise from Parker spiral direction to IMF vector in the horizontal plane. For negative polarity, IMF Bz has the opposite behavior. 3) The effect of Sun's magnetic field polarity is especially evident for IMF Bx more than 4 nT. In this case, IMF Bz are predominantly negative for negative polarity and positive for positive polarity, and the difference between average IMF Bz for positive and negative Sun's magnetic field polarities is about 2 nT. Correlation coefficient characterizing the dependence of IMF Bz on Sun's magnetic field polarity is about 0.5 and increases with increasing IMF Bx. The observed features of IMF Bz may be caused by decreasing solar wind speed near the HCS. As a result, portions of disturbed magnetic field lines slow down while approaching the HCS. This leads to the rotation of IMF vector in the vertical and horizontal planes. The observed dependences of IMF Bz on IMF Bx, IMF orientation, and Sun's magnetic field polarity are qualitatively consistent with this hypothesis.
DE: 2149 MHD waves and turbulence
DE: 2162 Solar cycle variations (7536)
DE: 2164 Solar wind plasma
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting