Day-to-day Variability of Ionosphere Electron Density During Solar Minimum Derived from FORMOSAT-7/COSMIC-2 Measurements

P. K. Rajesh, Charles C.H. Lin, J. T. Lin, C. Y. Lin, Jia Yue, T. Matsuo, S. P. Chen, C. H. Chen

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6 Citations (Scopus)


This study examines the day-to-day variability of low-latitude ionosphere using global ionospheric specification (GIS) electron density profiles derived from FORMOSAT-7/COSMIC-2 radio occultation measurements during a deep solar minimum period of August 2019 to July 2020. The measurements reveal significant daily variations over dayside low latitudes, yielding about 10-20% standard deviation in equinoxes, 20-30% in solstices, reaching 40-50% in winter. The nighttime deviations could be 30-60%, being largest in solstices. Day-to-day variations are also observed in the longitudinal wave-4 structures. The period mostly remained geomagnetically quiet except for some moderate disturbances on a few days. Tidal decomposition of the GIS electron density shows that in-situ forced migrating diurnal (DW1) terdiurnal (TW3) oscillations and the background zonal mean yield only ~25% of the daily variations despite accounting for almost 75-90% of the observed electron density. Thus, forcing from lower atmosphere dominates the contribution (~75%) to the observed daily variations. Only about one third of this lower atmospheric forcing comes from the migrating semidiurnal SW2 and the usually investigated non-migrating diurnal eastward DE2, DE3, stationary planetary wave SPW3, SPW4, and semidiurnal eastward SE1, and SE2 components. The residual tides other than those mentioned above, including secondary waves through non-linear interactions and other planetary waves, thus significantly influence the day-to-day variations in electron density and modify the longitudinal wave structures.

Original languageEnglish
JournalTerrestrial, Atmospheric and Oceanic Sciences
Issue number6
Publication statusPublished - 2021 Dec

All Science Journal Classification (ASJC) codes

  • Oceanography
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)


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