低纬地磁Z分量的半年变化

利用武汉、广州、泉州和琼中等4个低纬地磁站连续多年的地磁资料，计算了各月5个磁静日Z分量日均值与中午1100---1300时段平均值之差(Dz)，对每年12个Dz采用多元回归分析方法，得到各年的半年变化幅度和相位．结果表明：4个站的Dz每年都有半年变化现象；半年变化幅度与太阳活动有关，一般来说，太阳活动高年Dz半年变化幅度明显大于太阳活动低年；太阳活动本身的半年变化，对Dz半年变化幅度有显著的调制作用；Dz半年变化的相位在3—4月(或9—10月)，即极大值出现在分季；低纬地区地磁Z分量存在显著的半年变化，能够反映赤道电急流也有明显的半年变化，这再一次证明，赤道电急流幅度的半年变化，通过“喷泉效应”使得电离层，f0F2产生半年变化，其是产生，f0F2半年变化的一个主要因素．

SEMIANNUAL VARIATION OF GEOMAGNETIC Z COMPONENT AT LOW LATITUDE

Using the data collected in 4 geomagnetic stations located separately at Wuhan, Guangzhou, Quanzhou and Qiongzhong in the low latitude, the difference of geomagnetic Z component (Dz) between the diurnal average value and the average value of 1100-1300 LT at 5 quiet-day in every month have calculated. The amplitude and phase of semiannual variation in every year have obtained by analyzing the 12 Dz with multiple regression method. The result shows that Dz of 4 stations all have semiannual variation in every year. The amplitude of semiannual variation is related to the solar activity, and in general, the amplitude of semiannual variation of Dz in solar maximum is obviously greater than that in solar minimum. The semiannual variation of solar activity modulates the amplitude of semiannual variation of Dz obviously. The phase of semiannual variation of Dz is in March- April (or September-October), so the maximum of Dz appears in Equinox. The semiannual variation of geomagnetic Z component at low latitude indicates that the equato-rial electrojet have semiannual variation as well. The semiannual variation of the equatorial electrojet causes the f0F2 of ionosphere to appear semiannual variation by fountain effect. And this is a reasonable mechanism to produce semiannual variation of f0F2.