Wen‐Yao Xu

Normalization of sunspot cycles and eigen mode analysis

The smoothed monthly sunspot numbers of the previous 22 complete sunspot cycles are normalized in time domain, and then an eigen mode analysis is carried out to draw the principle factors (or components) in the cycles. The results show that the main characteristics of the solar cycles can be described fairly well by the first 5 eigen modes. The obtained eigen modes are used to predict the declining phase of cycle 23 on the basis of the data prior to its maximum. The prediction indicates that cycle 23 will last for 127 months to December 2006, with the minimum of 6.2.

Investigation of the SA evolution by using the CHAOS-4 model over 1997-2013

The temporal and spatial evolution characteristics of the geomagnetic secular acceleration (SA) are investigated, based on CHAOS-4 core field model during the period of 1997–2013. The SA evolution on a short time scale is associated with the phenomenon of the geomagnetic jerk. More details of the global extent and the occurrence time of the successive jerks (the 1999, 2003, 2007, and 2011 jerks) are obtained. The location, size and reversed polarity pattern for the 1999 jerk are similar to those for the 2003 jerk in the Asian-Indian sector. While the 2007 and 2011 jerks mainly take place in the Atlantic sector. The direction and speed of the shift for the four jerks are different, identified by the occurrence time of the jerks. The zonal motions of the SA patches exhibit an oscillation pattern in the Asian-Indian sector, whereas a purely westward drifting pattern is along the equator in the Atlantic sector. It is believed that the shift of the jerks is related to the motion of SA-Br patches observed at the core-mantle boundary (CMB).

The Legendre polynomials modeling method of small-scale geomagnetic fields

Based on ground-based geomagnetic surveys, we propose a small-scale geomagnetic field modeling method using Legendre polynomials. Combined with the data preprocessing techniques and the least squared estimation, a high-degree model is constructed to describe the small-scale structure of the field and draw the geomagnetic field maps. The results of the experiments show that the average misfit of total field intensity between the predicted model and the real observations is less than 30 nT. At the same time, fine structures of the field can be predicted, and the boundary effect is effectively suppressed, which facilitate improvement of modeling of the geomagnetic field. We also discuss the advantage and shortage of this modeling technique and its application scope. It is of great significance for application of the geomagnetic field to space exploration, minerals prospecting and subsurface structure probing.

Geomagnetic responses in high latitudes during the storm of July 15—16, 2000

The ionospheric equivalent currents in the high latitudes and the auroral electrojet system during the geomagnetic storm on July 15–16, 2000 are analyzed by using geomagnetic data from IMAGE chain. The large-scale vortices of equivalent currents are observed in the storm. The vortices on the dusk side of ionosphere correspond to four-celled pattern of plasma convection associated with NBZ, region I and region II field-aligned currents. Only one vortex can be found on the dawn side of ionosphere after interplanetary magnetic field (IMF) turns southward. In the initial phase of the storm, the center of eastward electrojets tends to shift equatorward. It arrives at 58.62° latitude of corrected geomagnetic coordinates (CGM). The westward electrojets are strong in the main phase. The center of westward electrojets in this period moves equatorward and may be beyond the southernmost station (56.45°) of the chain.