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.

Bankov L., R. Heelis, M. Parrot, J.-J. Berthelier, P. Marinov, and A. Vassileva (2009), WN4 effect on longitudinal distribution of different ion species in the topside ionosphere at low latitudes by means of DEMETER, DMSP-F13 and DMSP-F15 data, Annales Geophysicae, 27, 2893–2902 doi: 10.5194/angeo-27-2893-2009
Chang, F. Y., Liu, J. Y., Fang, T. W., Rajesh, P. K., & Lin, C. H. (2020). Plasma depletion bays in the equatorial ionosphere observed by FORMOSAT‐3/COSMIC during 2007–2014. Journal of Geophysical Research: Space Physics, 125, e2019JA027501. https://doi.org/10.1029/2019JA027501
Chao, C.-K., Su, S.-Y., & Liu, C. H. (2020). Initial nighttime ionospheric observations with advanced ionospheric probe onboard FORMOSAT-5. Advances in Space Research, 65, 2405– 2411.
England S. L., S. Maus, T. J. Immel, and S. B. Mende (2006), Longitudinal variation of the Eregion electric fields caused by atmospheric tides, Geophysical Research Letters, VOL. 33, L21105, doi:10.1029/2006GL027465
Fejer B. G., J. W. Jensen, and S. Y. Su (2008), Quiet time equatorial F region vertical plasma drift model derived from ROCSAT-1 observations, Journal of Geophysical Research, VOL. 113, A05304, doi:10.1029/2007JA012801
Fejer, B. G., Tracy, B. D., & Pfaff, R. F. (2013). Equatorial zonal plasma drifts measured by the C/NOFS satellite during the 2008–2011 solar minimum. Journal of Geophysical Research, 118, 3891– 3897
Hagan M. E. and Forbes J. M. (2003), Migrating and nonmigrating semidiurnal tides in the upper atmosphere excited by tropospheric latent heat release, Journal of Geophysical Research. Space Physics, VOL. 108, NO. A2, 1062, doi:10.1029/2002JA009466
Hagan, M. E., Maute, A., Roble, R. G., Richmond, A. D., Immel, T. J., & England, S. L. (2007). Connections between deep tropical clouds and the Earth’s ionosphere. Geophysical Research Letters, 34, L20109.
Hartman W. A. and Heelis R. A. (2007), Longitudinal variations in the equatorial vertical drift in the topside ionosphere, Journal of Geophysical Research Space Physics, VOL. 112, A03305, doi:10.1029/2006JA011773
Hawkins, J. M., and P. C. Anderson (2017), WN4 variability in DMSP ion densities across season, solar cycle, and local time, Journal of Geophysical Research. Space Physics, 122, 8755–8769, doi:10.1002/ 2017JA024065.
Henderson, S. B., C. M. Swenson, A. B. Christensen, and L. J. Paxton (2005), Morphology of the equatorial anomaly and equatorial plasma bubbles using image subspace analysis of Global Ultraviolet Imager data, Journal of Geophysical Research, 110, A11306, doi:10.1029/2005JA011080
Immel T. J., E. Sagawa, S. L. England, S. B. Henderson, M. E. Hagan, S. B. Mende, H. U. Frey, C. M. Swenson, and L. J. Paxton (2006), Control of equatorial ionospheric morphology by atmospheric tides, Geophysical Research Letters, VOL. 33, L15108, doi:10.1029/2006GL026161
Jin, H., Miyoshi, Y., Fujiwara, H., and Shinagawa, H. (2008), Electrodynamics of the formation of ionospheric wave number 4 longitudinal structure, Journal of Geophysical Research., 113, A09307, doi:10.1029/2008JA013301.
Kil H., S.-J. Oh, M. C. Kelley, L. J. Paxton, S. L. England, E. Talaat, K.-W. Min, and S.-Y. Su (2007), Longitudinal structure of the vertical E x B drift and ion density seen from ROCSAT-1, Geophysical Research Letters, VOL. 34, L14110, doi:10.1029/2007GL030018
Kil H., E. R. Talaat, S.-J. Oh, L. J. Paxton, S. L. England, and S.-Y. Su, Wave structures of the plasma density and vertical E × B drift in low-latitude F region (2008), Journal of Geophysical Research., VOL. 113, A09312, doi:10.1029/2008JA013106
Lin, C. H., W. Wang, M. E. Hagan, C. C. Hsiao, T. J. Immel, M. L. Hsu, J. Y. Liu, L. J. Paxton, T. W. Fang, and C. H. Liu (2007a), Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT‐3/COSMIC: Three‐dimensional electron density structures, Geophys. Res. Lett., 34, L11112, doi:10.1029/2007GL029265
Lin C. H., C. C. Hsiao, J. Y. Liu, and C. H. Liu (2007b), Longitudinal structure of the equatorial ionosphere: Time evolution of the four-peaked EIA structure, Journal of Geophysical Research, 112, A12305, doi:10.1029/2007JA012455
Lin, C. H., Hsiao, C. C., Liu, J. Y., and Liu, C. H. ( 2007c): Longitudinal structure of the equatorial ionosphere: Time evolution of the four-peaked EIA structure, Journal of Geophysical Research s., 112, A12305, https://doi.org/10.1029/2007JA012455
Lin, C. H., Liu, J. Y., Hsiao, C. C., Liu, C. H., Cheng, C. Z., Chang, P. Y., Tsai, H. F., Fang, T. W., Chen, C. H., and Hsu, M. L. (2009): Global ionospheric structure imaged by FORMOSAT3/COSMIC: early results, Terr. Atmos. Ocean. Sci., 20, 171–179, https://doi.org/10.3319/TAO.2008.01.18.01(F3C)
Lin, C. H., Hsiao, C. C., Liu, J. Y., & Liu, C. H. (2007). Longitudinal structure of the equatorial ionosphere: Time evolution of the four‐peaked EIA structure. Journal of Geophysical Research, 112, A12305. https://doi.org/10.1029/2007JA012455
Liu, G., Immel, T. J., England, S. L., Kumar, K. K., and Ramkumar, G.: Temporal modulations of the longitudinal structure in F2 peak height in the equatorial ionosphere as observed by COSMIC, Journal of Geophysical Research., 115, A04303, https://doi.org/10.1029/2009JA014829, 2010
Liu, H., and S. Watanabe (2008), Seasonal variation of the longitudinal structure of the equatorial ionosphere: Does it reflect tidal influences from below? Journal of Geophysical Research., 113, A08315, doi:10.1029/2008JA013027.

Lühr H, Hausler K, Stolle C (2007) Longitudinal variation of F region electron density and thermospheric zonal wind caused by atmospheric tides. Geophysical Research Letters 34: L16102.
Pavlov, A. V. (2006), The role of the zonal E × B plasma drift in the low-latitude ionosphere at high solar activity near equinox from a new three-dimensional theoretical model, Ann. Geophys., 34, 2553– 2572.
Sagawa E., T. J. Immel, H. U. Frey, and S. B. Mende, Longitudinal structure of the equatorial anomaly in the nighttime ionosphere observed by IMAGE/FUV (2005), Journal of Geophysical Research, VOL. 110, A11302, doi:10.1029/2004JA010848