中文摘要：

2011年3月11日日本东北海域发生了9.0级大地震。根据国际GPS服务和日本国土地理院公布的GPS连续观测数据,得到地震前20天震区附近上空的电离层垂直总电子含量（Vertical Total Electron Content,VTEC）的时间序列,并利用滑动四分位法（前15天滑动）分析电离层异常。同时采集COSMIC（Constellation Observing System for Meteorology Ionosphere＆Climate）掩星资料,分析震前地震上空的电子密度廓线,研究F2层峰值密度和高度的变化。初步研究表明,从地震前一周开始,电离层参量变化出现明显的增高。结合太阳和地磁活动参数分析,电离层参量的这种异常变化有可能是地震前兆异常。

英文摘要：

A 9.0-magnitude（MW） earthquake struck off the coast of northeast Japan on 11 March 2011.On the basis of the GPS data from IGS（International GPS Service） and Japan′s GPS observation networks,we got the 20 days′ time series of the ionosphere vertical total electron content（VTEC） over the epicenter before this earthquake.To detect abnormal signal of TEC variation,a sliding quartile-based（before 15 days） process is performed.Meanwhile occultation data from FORMOSAT3/COSMIC are used in order to analyze the pre-earthquake profile of electron density and understand the variations of the F2 peak electron density（NmF2） and the peak height（hmF2）.Preliminary results demonstrate that ionospheric parameters begin to increase a week before the earthquake.Combined with the solar and Geo-magnetic activities,we suggest that the abnormal variation of the ionospheric parameters may result from the earthquake.