A Study Of The Electron Number Density Fluctuations Near The Plasmapause Based On VAN Allen Probes Observations

The plasmasphere is located in the earth’s inner magnetosphere and is an important area between the ionosphere and magnetosphere.The precipitation of high-energy particles caused by wave-particle interaction in the inner magnetosphere.Wave-particle interaction in the plasmasphere is the main research content of the magnetosphere-ionosphere coupling system.Almost all regions of the Sun and Earth system are filled with plasma.Plasma fluctuations play an important role in the exchange of matter and energy in the system,which is a characteristic phenomenon in the plasma:(1)the plasma wave itself carries energy and can propagate across regions in various regions;(2)plasma fluctuations can absorb particle energy to grow themselves,and can transfer energy to the charged particles in the Earth’ s magnetosphere,which causes the flux of charged particles in the Earth’ s radiation belt to increase or decrease,and possible damage to detector instruments.Understanding and predicting the dynamic evolution of charged particles in the inner magnetosphere requires futher understanding of the global spatial and temporal distribution of plasma waves and their generation mechanism.Using the observation data of the Van Allen Probes(VAPs),the background cold plasma density is calculated,the position of the plasmapause is determined according to the density gradient and the plasmapause electron number density fluctuation events were selected one by one.Each densit fluctuation event is then matches with the corresponding geomagnetic activity Kp index and Dst index according to its observation time,compiling a complete plasmapause electron number density fluctuation database.Through the above described methods,the data from September 2012 to December 2015 from VAP satellite are statistical analyzed,and 584 cases of fluctuation events were collected.The statistical analysis shows that the electron number density fluctuation events of the plasmapause mainly occurs in the dusk sectors and the global spatial and temporal distribution has a significant correlation with the magnetic local time(MLT)and geomagnetic activity.The Fast Fourier transform(FFT)is used to analyze the power spectrum of the selected electron number density fluctuation event data,and the power spectrum under differentmagnetic locations(MLT),geomagnetic activities(Kp and Dst)and magnetic shell value(L)are averaged to obtain the average power spectrum of the plasmapause electron number density fluctuation.The average power spectrum calculated by the FFT shows that the average power spectrum of the plasmapause electron number density fluctuation events within the range of1-100 m Hz has a slope close to-5/3,which has characteristics similar to the Kolmogorov spectrum,indicating the presence of well-developed two-dimensional magnetohydrodynamic turbulence.Several reasons why this turbulence may occur are finally given in this invetigation.The research work in this thesis provides an important basis content for the subsequent study of the physical mechanism,particles transport and impact on the coupling of the magnetosphere and ionosphere caused by the electron number density fluctuation of the plasmapause,and also provides an important basis for further study of magnetosphere-ionosphere space weather and more accurate prediction of space weather.