福爾摩沙衛星五號自2017年8月24日發射，運行於725公里高、傾角98.3°之太陽同步軌道，其科學酬載先進電離層探測儀(Advanced Ionospheric Probe, AIP)提供夜間2230 LT高精準電離層電漿參數。福衛五號於2018至2020年間累積超過700萬筆現地量測之離子濃度及離子速度數據，是研究太陽極小期夜間低緯度電離層電漿四峰(wavenumber -4, WN4)及電漿匱乏灣(plasma depletion bay, PDB)結構與變化之利器。離子濃度逐日、月及季變化，顯示WN4主要出現在春秋分期間，其中以三和十月最為明顯。反之，三個南向與北向PDB則分別盛行於六月和十二月夏冬至期間。WN4區域離子速度大多出現下衝現象，PDB區域則正好與之相反。此外，WN4離子濃度峰與東向速度峰，以及PDB離子濃度谷和東向速度谷均一一對應，說明夜間電離層F域離子濃度峰與谷主要受到東向離子速度之影響。;FORMOSAT-5 (F5) with a sun-synchronous orbit at 725 km altitude and 98. 3° inclination was launched on 24 August 2017. A science payload of Advantage Ionosphere Probe (AIP) onboard the F5 satellite is used to observe structures and dynamics of wavenumber -4 (WN4) and plasma depletion bay (PDB) in the ion density and ion velocity in the nighttime equatorial/low-latitude ionosphere at 2230 LT (local time) during the low solar activity period from 2018-2020. The result shows that WN4 prominently appears in March and September equinoxes, while three north and south PDBs significantly occur in June and December solstices, respectively. The ion velocity tends downward (upward) at the WN4 (PDB) longitudes. A detailed study shows that for WN4 and PDB, the ion density maximum (minimum) coincides with the eastward ion velocity maximum (minimum). These indicate that the zonal plasma drift is essential to WN4 and PDB formations in the nighttime equatorial ionosphere.
