电离层的朔望月周期变化

Synodic Month Periodic Variations of Ionosphere

电离层应该存在月球引力引起的朔望月周期变化,但一直没有观察到。2004年6月29日,法国发射了地震电磁监测卫星DEMETER,它是近极地太阳同步圆轨道卫星。本文将DEMETER卫星搭载的朗缪尔探针观测数据分为日侧半轨数据和夜侧半轨数据两组,对两组数据进行重采样和缺失数据填补,组织成日侧轨间信号和夜侧轨间信号,然后分别对这两种信号进行太阳日周期变化的滤除和不同长度周期信号信噪比的计算,进而绘制这两种信号的信噪比-周期变化曲线。在日侧半轨的电子密度、离子密度和电子温度中观察到了清晰的朔望月周期变化,而在夜侧半轨的电子密度、离子密度和电子温度中却没有观察到朔望月周期变化。解释是:月球引力会引起大气的朔望月周期涨落,在日侧半轨,光电离造成电子密度、离子密度、电子温度在高度方向上产生较大的变化梯度,在同一高度太阳同步轨道上运行的DEMETER卫星自然会观测到这种涨落变化,而在夜侧,光电离停止,电子密度、离子密度、电子温度在高度方向上的变化梯度很小,DEMETER卫星自然不会观测到这种涨落变化。

Gravitational attraction of the moon might cause synodic month periodic variation in the ionosphere,but it has not been observed so far.On June 29,2004,France launched an ionospheric satellite DEMETER（Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions）,that was placed on a quasi Sun synchroneous circular orbit.In this paper,the data observed by the Langmuir probe of the DEMETER satellite are split into two groups：the data on the dayside and the data on the nightside.The two groups of data are re-sampled,with the missing data being padded,and the signals on the dayside and the signals on the nightside are generated.For the two groups of signals,the solar day periodic variations are filtered out,SNRs of a series of periods are calculated,and SNR-period curves are obtained.The synodic month periodic variations of electron density,ion density and electron temperature on the dayside are shown clearly,but those on the nightside are not observed.Why？ The gravitational attraction of the moon can cause the lunar atmospheric tide.During day time,the photoionization causes vertical variations of electron density,ion density and electron temperature,and lunar atmospheric tide can be observed by DEMETER satellite that was placed at the same altitude.At night,the photoionization stops and does not cause vertical variations of electron density,ion density and electron temperature,and the lunar atmospheric tide can not be observed by DEMETER satellite.