研究中低緯度電離層不穩定性與電動力學和縱向電漿結構(2/3)

Ionosphere, which was discovered more than a century ago, still continues to be actively studied. Ionospheric research is one of the major objectives of high profile space missions like the recent COSMIC-2 or FORMOSAT-7 satellite constellation. Ionospheric research is not only driven by scientific curiosity but also is vital for modern day space based navigation/communication. Ionospheric irregularities can result in severe errors in the positioning accuracy in navigation using Global Navigation Satellite System (GNSS) like the American Global Positioning System (GPS). Intermediate scale irregularities in the ionosphere can cause random fluctuations in the amplitude of GPS signals, commonly known as ionospheric scintillation. Severe ionospheric scintillation can result in receiverloss of lock and signal outage, which can disrupt the navigation using GPS. The proposed plan will investigate the behavior of ionospheric irregularities occurring over low and mid-latitudes and the longitudinal structure of the ionosphere driven by coupled atmosphere-ionosphere dynamics. Generation mechanism of Equatorial Plasma Bubble (EPB) which is also a pre-requisite for strong ionospheric scintillation, will be studied. Some of the unresolved issues that have been lingering around are the seeding mechanism of EPB, the role of E region conductivity and the formation of Large Scale Wave Structure (LSWS). Thus a coordinated investigation utilizing the VHF scintillation receivers installed at Pingtung, Taiwan, Equatorial Atmosphere Radar (EAR) operated from Kototabang, Indonesia and GNSS Radio Occultation (RO) onboard FORMOSAT- 7 will be carried out to understand the background conditions and electro- dynamical processes responsible for the formation of EPB. Over mid-latitudes, Meso-Scale Travelling Ionospheric Disturbances (MSTIDs) can result in navigation errors, whose forecast is extremely important for the reliability of GPS navigation. The causative mechanisms and also the low-latitude boundary till which MSTIDs can propagate, is still an open subject of investigation. Whether the MSTIDs are associated with gravity wave related structuring of plasma or it is associated with Perkins plasma instability is the pertinent issue that needs to be further understood. A coordinated investigation of MSTIDs utilizing airglow imaging (low latitude from Hanle, India; Mid-latitude from Yonaguni/Ishigaki/Shigaraki, Japan), incoherent scatter measurements with MU radar, vertical profiling of MSTIDs using FORMOSAT-7 RO and in-situ measurement by SWARM constellation is required to further our understanding of the processes that are responsible for its formation. Apart from these, global scale longitudinal processes like the formation of wave number 4 structure will be studied using the unprecedented global profiling by FORMOSAT-7. The impact of wave number 4 structure of global local time EIA on other ionospheric processes needs to be studied. For example, reminiscent of EIA are generally observed in the post-sunset hours after the reversal of zonal electric field. Thus, the role of wave number 4 structure on the nighttime scintillation S4 needs to be evaluated.