Temporal And Spatial Distributions Of TEC Depletions And Multi-instruments Observation Of Irregularities Over South China

The South China subcontinent is located in the northern crest of equatorial anomaly region where ionosphere scintillation and TEC depletions occurs frequent. This paper presents the temporal and spatial distributions of TEC depletions over South China, based on the simultaneously observations of GPS L-band scintillation and GPS-TEC, at Shenzhen station. Simultaneously, utilizing several measurements, the observations of ionospheric irregularities during December over South China are presented. In addition, this paper also reveals the reasons for the occurrence of irregularities. The main research contents and results are as follows:1, This paper presents the temporal and spatial distributions of TEC depletions over South China, based on the data observed at Shenzhen station, located under the northern crest of equatorial anomaly, from 2011 to 2012. Our results reveal that the characteristics of TEC depletions vary with local time(LT), latitude and longitude. Deeper TEC depletions(approximately 20 TECU) well coincide with the occurrences of intense scintillations(S4≥0.5). But in post-midnight or at the north edge of equatorial anomaly over South China, some shallow TEC depletions(<10 TECU) were recorded along with the absence of scintillations(S4<0.2). TEC depletions also showed seasonal variations. They occurred mainly in the vernal and autumnal equinox period during 2011 and 2012, with depth in the ranges of 1- 20 TECU, and durations in the range of 16- 30 minutes. Our results also suggest that most TEC depletions occurred between 20:30 and 23:30 LT, and gradually disappeared after 23:30 LT to local midnight.2, Statistical analysis of TEC depletions show that the depth of TEC depletions related to solar activity level. High levels of solar activity may be associated with an increase in the depth of TEC depletions and vice versa. The plasma bubbles in low latitude region are drifted from equatorial region. The lower the latitude, the earlier the TEC depletions onset and the longer the duration of TEC depletions last. The plasma bubbles have a tendency to disappear when they drift into the north edge of equatorial anomaly over South China.3, Utilizing GPS scintillation receiver observations over Guangzhou, and the Digisonde and VHF radar measurements at Fuke, the occurrence of ionospheric irregularities during December for the year 2011, 2012 and 2013 over South China are investigated. Observational results show that irregularities were only recorded on 13 December 2013. On this day, intense scintillations were observed by GPS scintillation receiver at Guangzhou station, and F-region irregularities echoes and intense spread-F were recorded by VHF radar and Digisonde at Fuke station. Moreover, this article attempts to explain the reasons for the occurrence of irregularities that day. Our results show that there is no geomagnetic storm to trigger or inhibited the post-sunset scintillation occurrence, the vertical plasma drift velocity provided favorable conditions, and the irregularity generation is controlled by the F2-layer height increase. In addition, seed perturbation of atmospheric gravity waves may play an important role in the generation of irregularities.