Abstract: Using Ne(electron density) and Te(electron temperature) data of Langmuir Probe onboard DEMETER(Detection of Electro-magnetic Emissions Transmitted from Earthquake Regions) satellite,the paper studies the variations of electron density and electron temperature associated with strong earthquakes.The specific scientific objectives of Langmuir Probe are to map the bulk plasma parameters and to study their variations associated with seismic activity,volcanism and human activity and other sources of perturbations.Langmuir probe sweeps in voltage allow to obtain a current-voltage(Ⅰ-Ⅴ) characteristic every second.Bulk plasma parameters are obtained from the analysis of the Ⅰ-Ⅴ characteristics.The work principle,data format of Langmuir Probe onboard DEMETER is briefly introduced.We mainly studied the 2006 M_W 7.9 Tonga earthquake and the M_W 7.1 Taiwan earthquake in this paper.For each earthquake,we choose the orbits which passed over the area about 2000km around epicenter,including four months data before and two months data after the earthquakes.There are mainly three steps to reprocess the raw data,in order to avoid disturbances resulting from solar activities and geomagnetic activities.The result on the M_W 7.9 Tonga earthquake shows that at the equatorial region the electron density was relatively low before 28 April,while it began to increase from 28 April,and got the highest at 2 May one day before the earthquake.Until 4 May after the main shock,Ne began to decline.Based on comparison between revisited orbits,the orbit 097681(before shock) and 098721(after shock) observed certain disturbance.To further investigate the features of the preearthquake ionospheric anomalies,using 5 days as time window and 1 day as step size,we examined the temporal and spatial evolution of electron density within the area of 2000km around epicenter.Results show that the normal distribution of Ne kept at a relatively high level,except a relatively sharp reduction of Ne from 29 April to 2 May.The result on the M_W 7.1Taiwan earthquake shows that Ne changed randomly,while Te kept at a relatively high level,but dropped gradually before the quake.Currently we have no evidence to conclude that these changes are the results from the seismic activity,but based on data reprocessing,we can exclude the disturbances induced by solar activity and magnetic field at certain degree.If these changes of Ne/Te really resulted from earthquake,we may prudently conclude that ionospheric disturbance associated with seismic activity may possibly occur in a short time impending an earthquake with a short duration.

Key words: Langmiur, DEMETER, electron density(Ne), electron temperature(Te), Tonga earthquake, Taiwan earthquake

摘要： 文中介绍了Langmiur探针的观测原理,并利用电子浓度(Ne)和电子温度(Te)数据研究了2006年5月3日M_W7.9汤加地震和2006年12月16日M_W7.1台湾地震。结果发现汤加地震前2～5d电子浓度连续4d降低,电子温度变化不明显。台湾地震前后电子浓度的变化不明显,但电子温度在地震当天及后续3d出现了低值。目前没有直接的证据表明这些变化是由地震活动引发的,但在数据处理过程中选择了当地22时至次日3时的观测数据,并且剔除了Dst≤-30nT,Kp≥3,AE≥200nT时的记录数据,在一定程度上排除了太阳、地磁等因素引起的电离层异常情况。

关键词: Langmiur探针, DEMETER, 电子浓度, 电子温度, 汤加地震, 台湾地震