VHF Scintillation and Drift Studied Using Spaced Receivers in Southern Taiwan

A statistical study of the occurrence and drift characteristics of Very High Frequency (VHF) amplitude scintillations during 2015–2017 based on the observations of recently installed spaced receiver system at Pingtung in Southern Taiwan is presented in this paper. Drift characteristics during quiet periods have been examined in details and compared with the drift recorded during 08 September 2017 geomagnetic storm. Analysis of the recorded observations indicated a strong dependence of VHF scintillation on the solar activity level. Equinoctial asymmetry in the occurrence of VHF scintillation was seen in 2015 and 2016. However, such asymmetry was not apparent in 2017 (low solar flux). Quiet period spaced receiver drift indicated a gradual reduction in the zonal drift of irregularities between postsunset and postmidnight period. Intriguingly, the average quiet period drift of irregularities was found to be independent of solar activity level. A few investigations in recent past have already reported similar observations and can be generally attributed to the polarization process inside equatorial plasma bubbles; however, a definite explanation for this behavior is not available. During the active phase of the 08 September 2017 geomagnetic storm, a complex interplay of disturbance dynamo and prompt penetration electric field was observed in the spaced receiver derived drift velocity of ionospheric irregularities. Approximately −200% deviation from quiet period drift was observed during this moderate storm. A significant enhancement to the spaced receiver derived characteristic random velocity, V_c, was also seen during the active phase of storm, which indicates that the drift of irregularities was highly turbulent.