Prediction and understanding of the north-south displacement of the heliospheric current sheet

Based on WSO observations of the photospheric magnetic field and the potential field-source surface (PFSS) model, we compare the solid angles occupied by the positive source surface field with that of the negative. We develop an algorithm to quantitatively estimate and understand the positive-negative displacement of the heliospheric current sheet (HCS) about Sun’s magnetic dipole equator and the north-south displacement of the HCS about the heliographic equator. The north-south HCS displacement predicted using the algorithm quantitatively agrees with that observed by Ulysses and WIND in 1994-1995. The predicted positive-negative and north-south HCS displacement for 362 Carrington rotations between 1976 and 2001 show that in addition to the two long southward HCS displacement intervals that are consistent with earlier observations and statistical results, there are several short north-south HCS displacement intervals in the rising and early declining solar activity phases. All the positive-negative HCS displacements about the Sun’s magnetic dipole equator determined for the 25 years can be understood using the positive-negative asymmetry in the characteristics of coronal holes or open field regions between two hemispheres, such as the area, field strength or the outward expansion factor of the coronal holes. To understand the north-south HCS displacement about the heliographic equator, the effect of the Sun’s magnetic dipole tilt angle relative to the Sun’s rotation axis must be taken into consideration as well.