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The space science team at Central University has discovered that the moon is causing huge ups and downs in the global ionosphere. Photo by Lin Yen-Tsen

Professor Liu Jann-Yenq, Dr. Wu Tsung-Yu, Dr. Lin Chi-Yen, and Professor Chang Chi-Wei published the article “The Three-dimensional Plasma Structures and Flows of the Earth’s Upper Atmosphere Due to the Moon’s Gravitational Force” on the world’s top journal Scientific Reports. They fully utilized the data of radio occultation collected by the satellites FORMOSAT-3 and FORMOSAT-7 for the past 15 years, analyzing the three-dimensional structures of the global ionosphere and the lunar tide effect cast upon it by the moon’s gravitational force. Their discovery was unprecedented.

For thousands of years, humans have known the rise and fall of sea levels, and such a natural phenomenon is called the tide, which is caused by lunar gravity. The research team led by Professor Liu Jann-Yenq further discovered that the amplitude of the ionosphere also has such high and low tides. The team collected the radio occultation data from FORMOSAT-3 and FORMOSAT-7 satellites and analyzed the three-dimensional structures of the ionosphere. They discovered that the moon’s pull can cause the amplitude of the global ionosphere to fluctuate between 3 and 5 km, and the amplitude of the ionospheric tides can be a thousand times larger than that of the sea tides. Sea tides on the Earth can be constrained by geographical landscapes; the features of high and low tides in different regions thus vary. However, distinct from sea tides, the lunar tides observed in the ionosphere clearly demonstrate the moon’s gravitational force, which is closer to the original theory of lunar tides.

“FORMOSAT-3 and FORMOSAT-7 are the satellites developed in the collaborative research project by Taiwan and the United States, aiming to build a highly reliable mission-oriented meteorological satellite system. By receiving signals from the Global Navigation Satellite System (GNSS), the satellites can collect data on atmospheric pressure, temperature, humidity, and the vertical distribution of the ionosphere's electron density. The observation range covers the whole world. Thanks to the densely accumulated observation data; we could thus successfully discover the three-dimensional tidal phenomenon of the global ionosphere,” said Professor Liu Jann-Yenq.

NCU’s research team publishes its research on ionospheric amplitude change caused by the moon’s gravitational force. Figures on the left are data from the satellites FORMOSAT-3 and FORMOSAT-7. Figures on the right demonstrate how the amplitude of the ionosphere is affected by the moon’s gravitational force. Photo courtesy of Professor Liu Jann-Yenq