中文摘要：

基于低纬（海南）台站（19．5°N，109．1°E）电离层测高仪在2004年观测到的偶发E层（Es）临界频率（，0E）和虚高（h’Es）数据，利用谱分析方法，给出了中国低纬地区Es层在全年和不同季节内的短周期变化特性．对全年数据谱分析表明，Es层除具有非常强的24h周期外，还具有显著的12h和8h周期．对不同季节内两个参数的谱分析进一步表明，8h周期主要出现在，0匠参数的春秋分季和夏末及在h’Es参数的几乎所有季节；6h周期主要出现在，0E。参数的11—12月．海南低纬Es层中具有显著的6h和8h周期特性，特别是这两个周期还能同时出现在冬季，这是以往研究中不曾发现的新结果．初步分析认为，Es层的6h和8h周期极可能是分别由1／4日和1／3日潮汐所造成的．

英文摘要：

The time series of the ionospheric Sporadic E （Es） critical frequency （foEs） and its virtual height （hiEs） were performed on a large database of DPS-4 ionograms recorded at Hainan station （19.5°N, 109.1°E） in 2004 to investigate the features of tidelike periodicity variations in low latitude. On yearly spectra, there was pronounced 8-hour periodicity in low latitude Es in addition to the well known 24- and 12-hour tidal variations. The yearly average phases of 24-, 12-, and 8-hour periodicities for foEs （h＇Es） were at 13：00LT （13：00LT）, 11：00LT （09：00LT）, and 09：30LT （09：30LT）. On every two-month spectra, the results showed that （1） the 24-hour periodicity in Es was the most pronounced in each season; （2） The 12-hour periodicity in Es was outstanding in each season except in January-February months; （3） The 8-hour periodicity was remarkable in equinoxesand July-August months for foes, and it was notable in almost each season for h＇Es; （4） The 6-hour periodicity mainly occurred in November and December for foes, whereas for hies it appeared more in summer and winter, and weakly in equinox months. It is clearly distinct from previous results by the fact that the 6- and 8-hour periodicities in Es layer at Hainan station can occur in winter or other seasons. The 6- and 8-hour periodicities in Es layer most probably are caused by the quarter- diurnal and terdiurnal tide components, which needs to be investigated further by combining the observations and modeling of local tide.