Analysis Of Magnetohydrodynamic Turbulence In Space Using Data Obtained By Multi-spacecraft Measurement

Large amplitude magnetohydrodynamic(MHD)waves and turbulence are commonly observed in space plasma environment.Using data obtained by multi-spacecraft experiments,one can separate temporal and spatial variations of measured variables.While the number of data points in the time domain can be quite large,that in the spatial domain,which is simply the number of spacecraft,is only a few at most.Therefore,such a sophisticated technique as Capon's method is often used to deal with the data in the spatial domain.Since the turbulence consists of a large number of waves,it is practically impossible to resolve it using the observed data.However,in the turbulence analysis,what we are interested in is not the separation of turbulence into all the individual waves,but is in determination of a few macroscopic physical parameters that describe the nature of the turbulence.As examples of such macroscopic parameters,we deal with the total wave power and the power-law index of the spectrum,assuming that the wave spectrum is well approximated by the power-law distribution.In this thesis,we develop a new method to determine these physical parameters using a data with a limited number of data points.We give the test turbulence data by superposing many monochromatic waves with their amplitudes be given according to the power-law spectrum and their phase distribution be specified by an external parameter that determines the coherence of the phases.The accuracy and the robustness of the proposed analysis method are examined with varying the number of observational points,spatial separation of the data points,the number of events,the phase-coherence index,among others.By carrying out the parameter survey,we found that(1)the number of waves which compose turbulence and the number of events should be large,(2)the phase-coherence index and spatial separation of data points should be small,(3)total power is underestimated by using our calculation program.The method we developed in the present thesis will be useful in dealing with actual data obtained by multi-spacecraft experiments to determine the macroscopic parameters of the MHD turbulence in space plasma.