中纬度电离层f_oF_2潮汐的变化特性

Tidal variations of the ionospheric f_oF_2 in mid-latitude ionosphere

本文通过对1960年以来全球磁纬度40°N至50°N内测高仪台站的观测数据进行研究,提取了电离层F2层临界频率(foF2)的潮汐,揭示了其变化特征及可能的形成原因.研究发现,周日和半日的迁移潮汐分量(即DW1和SW2)强度最大,并且显示出明显的年变化和半年变化.周日潮汐的3波分量(即DE3)作为典型的非迁移潮汐分量,相对较弱,显示出微弱的半年变化.在冬季,DW1和SW2与太阳活动指数(F107)呈现正相关性,其相关系数分别大于0.88和0.65.相反,在夏季,DW1和SW2与太阳活动指数呈现负相关性,特别是SW2,其相关系数在6月份达到-0.72.在相对于纬向均值的归一化处理之后,上述潮汐强度和太阳活动指数之间的正/负相关性被显著增强/削弱.其中,归一化后的夏季DW1和SW2与太阳活动指数的相关系数达到-0.8.更加深入的讨论显示出上传的大气潮汐波动可能是电离层潮汐除了太阳辐射之外的重要驱动源,并且这种驱动机制在SW2中更加强烈.

Ionospheric tidal features of the critical frequency of ionospheric F2 layer （foF2） and their possible causes are revealed based on the ionosonde observation from global stations between magnetic latitudes of 40N and 50N since 1960. It is found that the diurnal and semidiurnal migrating tidal components （DW1 and SW2） are the strongest and exhibit obvious annual and semiannual variations. The typical non-migrating tidal component, the diurnal tidal component with wavenumber 3 （DE3） is relatively weak and shows some semiannual variation. Both DW1 and SW2 are observed to have a positive correlation with solar activity index in winter, with the correlation coefficients mostly larger than 0.88 and 0.65 respectively. On contrast, summer DW1 and SW2 are found to show a negative correlation with solar activity index, especially SW2, in which the correlation coefficient reaches -0.72 in June. The positive/negative correlations between tidal strength and solar activity are significantly weakened/enhanced by the normalization （relative to the zonal mean values）. The negative correlation coefficients reduce to -0.80 in both summer DW1 and SW2 by this method. Further discussion revealed that the upward atmospheric tides are confirmed to be the driving source of the ionospheric tides besides the solar radiation. Besides, this driven mechanism between atmospheric tides and ionospheric tides is particularly strong in ionospheric SW2.