Global Ionospheric Structure Imaged by FORMOSAT-3/COSMIC: Early Results

Abstract

A new era of studying the ionospheric space weather effects has come after launch of the innovative satellite constellation, named as Formosa Satellite 3 or Constellation Observing System for Meteorology, Ionosphere, and Climate (abbreviated as FORMOSAT-3/COSMTC or F3/C in short), performing a radio occultation experiment capable of observing the global ionosphere three-dimensionally. This is the first time that a satellite constellation provides instantaneously both the lower and upper parts of the ionospheric electron density up to the satellite altitude. With more than 2500 soundings of the ionospheric vertical electron density profiles every day, ionospheric plasma structures over many continents and most of oceans, where ground-based observation is limited, are now observed continuously. Important ionospheric research topics, such as space weather effects to the ionosphere, variations of ionospheric plasma structure and dynamics produced by solar outputs, and atmosphere-ionosphere coupling processes, can be widely studied and modeled based on the three-dimensional ionospheric images constructed by the F3/C observations. After one year in orbit, a great amount of radio occultation soundings allow us to construct global ionospheric maps to study the ionospheric seasonal effects and atmosphere-ionosphere interactions. Taking advantage of the uniqueness of dense global coverage, the major physical mechanisms of the two studies are given. For study of the seasonal variation during solstice, electron density images of the mid- and low-latitude ionosphere show a clear north-to-south asymmetry which may be affected by the summer-to-winter neutral wind. Meanwhile a significant longitudinal variation at midnight is also seen in the solstitial season. Another interesting result is the four stronger equatorial ionization anomaly (ETA) regions located at different longitudes. This four-peaked ETA structure may result from upward propagating nonmigrating tides originated from troposphere. F3/C's observation of the daytime four-peaked structure provides an important evidence to support the proposed forming mechanism.