Research On Precipitation Of Ring Current Protons Caused By EMIC Waves With Multi-satellite Conjugate Observations

Detached sub-auroral proton arcs are considered as a result of the precipitation of ring current protons.The wave-particle interaction can play an important role in the loss of ring current ions from the inner magnetosphere to ionosphere.To find the observational evidence,this paper focuses on the physical mechanism of ring current ion precipitation caused by electromagnetic ion cyclotron(EMIC)waves based on multi-satellite conjugate observations.This paper displays the typical event of ring current ion precipitation caused by EMIC waves with in-situ conjugate observations of satellites in the magnetosphere and ionosphere,so as to reveal the loss process of inner magnetospheric particles into the ionosphere.The distribution of ring current protons became more isotropic during the period when RBSP B satellite observed EMIC waves in the inner magnetosphere.At ionospheric altitudes,DMSP 16 satellite and NOAA 18 satellite at the footprint of RBSP B satellite observed energetic ion precipitation in the sub-auroral region simultaneously,while the SSUSI instrument of the DMSP 16 satellite observed a detached sub-auroral proton arc in the afternoon sector.To be noted,the observed precipitating ions were just projected into the detached aurora.In addition,we demonstrate that observed EMIC waves can effectively scatter ring current protons through calculating the pitch angle diffusion coefficients for protons using quasi-linear theory.Therefore,it can be concluded that EMIC waves can scatter ring current protons into the loss cone through wave-particle interactions.As a result,these scattered ring current protons will precipitate into the ionosphere along the magnetic field lines,leading to the detached proton arc in the sub-auroral region.This research provides a direct observational evidence that the detached subauroral proton arc is caused by the precipitating ring current protons scattered by EMIC waves,which reveals the important loss mechanism of ring current ions.Our result shows a great significance for studying the formation mechanism of detached proton aurora arcs and the energy transport of particles in the ionosphere-magnetosphere coupling system.