中文摘要：

F-lacuna是高纬极区电离层测高仪频高图上经常出现的一种F层回波描迹部分或全部消失的现象,直接影响电离层参数的标定,其表征的电离层物理过程尚未定论.利用南极中山站测高仪频高图数据,本文统计分析了Flacuna在不同太阳风速度水平下的发生频率,主要对2012年2月15日一次F2-lacuna观测实例的粒子沉降及电离层特性进行了分析.观测特征表明,F2-lacuna发生期间,电离层电子总含量TEC明显减小,昭和站SuperDARN高频雷达观测到的中山站上空电离层Bragg后向散射增强,但对应来自磁层的电子和离子沉降并不明显.这可能是由磁层亚暴引起的极区电离层电流体系扰动,触发电离层F-B不稳定性,产生沿场向排列的小尺度不规则体,其热效应导致F2层密度减小,F2-lacuna出现.

英文摘要：

As a typical phenomenon on ionograms observed at high latitudes,F-lacuna usually occurs in summer daytime.It manifests itself as partial or total disappearance of normal ionogram traces,which usually prevents the determination of ionospheric parameters from ionograms.Due to the sparse data in polar region,its mechanism is still controversial.The ionograms recorded by Zhongshan Digisonde 4D were used to carry out this study.According to the missing traces concerning either F1 region,F2region,or the whole F region,the F-lacuna can be classified intothree types,i.e.,F1-lacuna,F2-lacuna and total lacuna,respectively.This paper concentrated on F2-lacuna mechanism.Based on the F-lacuna events with manual judgments,we studied all three types of F-lacuna occurrence rate in different solar wind velocity conditions,then focused on the simultaneous observations from GPS TEC,HF radar and DMSP satellite,during a F2-lacuna case.The statistical on the daily F-lacuna occurrence frequency relation to averaged solar wind velocity indicates that F2-lacuan occurs more frequent with solar wind velocity increasing.The observations show that a substorm occurred during the F2-lacuna period.In the mean time,the in-situ TEC decreases,Bragg back scattering of Super DARN HF radar enhances,but the particle precipitation is not obvious.Through the statistical and case study,we analyzed F2-lacuna occurrence mechanism.On one hand,the heating effect from F-B instability triggered by substorm enhances the O＋recombination rate of upper F region,leading to the decreased electron density of F2 region and subsequently the decreased TEC.On the other hand,the F-B instability disturbance produces small-scale irregularities along the field aligned observed by SuperDARN HF radar.