In geospace (outer space between a height of 400 km and about 10 km), there is a group of electrically charged particles called plasma.Plasma is known to generate various radio waves and change the distribution and energy of plasma itself.

 Among them, radio waves called "electromagnetic ion cyclotron waves" with a frequency of about 1 hertz are thought to affect aurora activity and radiation distribution in outer space, but until now, the moment when radio waves are generated from plasma has been observed. It wasn't caught.

 This time, an international collaborative research group led by the Institute for Space-Earth Environmental Research, Nagoya University has developed a new analysis method that identifies fluctuations in plasma distribution from the phase relationship between radio waves and plasma and seeks mutual energy transfer.Using this method, we analyzed the observation data of NASA's scientific satellite "THEMIS" and succeeded in identifying the moment when the electromagnetic ion cyclotron wave is generated.

 According to the announcement, asymmetrical holes (holes) that exist for only a few seconds are generated in the ion group that exists in the universe, and the energy of the ion group produces radio waves due to the existence of these holes.The detection of holes in a group of ions that occur and disappear in a few seconds is the first achievement in the world.

 The research group plans to apply a similar method to the analysis of various types of radio waves generated in space plasma.In particular, it is expected that by applying it to the precise observation data of the geospace exploration satellite "Arase", it will be clarified how the space radio wave "Whistler Wave Chorus", which has been a mystery for many years, is born.Furthermore, by clarifying the mutual connection between plasma and radio waves in the universe, it is expected that the mechanism by which radiation and aurora will change will be clarified and used for space weather forecasts.

Paper information:[Geophysical Research Letters] Ion hole formation and nonlinear generation of Electromagnetic Ion Cyclotron waves: THEMIS observations

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