第23太阳活动周行星际磁场扇形结构对中低纬地磁场的影响

用特征向量分析法对第23太阳活动周天津静海磁场强度水平分量H的时均值进行研究，分析行星际磁场扇形结构的地磁效应（简称扇形效应）对中低纬地磁场H分量日变化的贡献.研究结果表明，中低纬扇形效应为3～11nT，在太阳活动高年扇形效应达到最大值（约11nT），低年达到最小值（约3nT）.太阳活动高年扇形效应引起的地磁H分量值变化与太阳活动低年的情况相反，但是扇形效应在夏季对地磁H分量的影响较小.太阳活动高年扇形效应日均值的增减与上升年的相反，与下降年相同，夏季扇形效应平均增量最小且无规律.春、夏和秋三个季节的扇形效应最大值都出现在太阳活动高年，冬季的扇形效应在太阳活动峰年两年后才出现最大值（约11nT）.在太阳活动低年（或高年），当扇形磁场背离（或指向）太阳时，夏季扇形效应白天引起地磁H分量增大（或减小），夜间导致地磁H分量减小（或增大），其他季节全天都会导致地磁H分量减小（或增大）.用特征向量推断行星际磁场扇形极性的符合率在春夏秋三个季节高达60%，在冬季为55%. 

IMF Sector Effect on Geomagnetic Field at MID and Low Latitudes during Solar Cycle 23

Geomagnetic data of Tianjing during solar cycle 23 have been analyzed by eigen vector method. The Interplanetary Magnetic Field (IMF) sector effect on the H component of geomagnetic field at mid and low latitudes has been studied. The results show that the sector effect magnitude is from 3 to 11nT at mid and low latitudes in contrast to tens nT at high latitudes. The IMF sector effect reached maximum (about 11nT) during solar activity maximum, and reached minimum (about 3nT) during solar activity minimum. The largest value of the sector effect during solar activity maximum occurred in spring, summer and autumn seasons. However, the largest sector effect occurred one year later in the winter season. In 1996 and 2007, when the IMF is away from (or toward) the Sun, the sector effect increase (or decrease) in H component at daytime and decrease (or increase) at night in summer, while the sector effect increase (or decrease) in H component at daytime during the other seasons. The sector effect causes opposite changes during solar maximum, however, it will have less effect during summer. For high solar activity years, the IMF sector effect on daily mean value variation of the geomagnetic field is the same (or opposite) with the decreasing (or increasing) phase of solar cycle. In the summer, the average increment minimum value arises, and the average increment is irregular. About 60% of the estimations are consistent with satellite observations in summer, spring and autumn months, but about 55% in winter months.