A sixteen moment approximation based on a bi-Maxwellian that contains the stresstensor and the heat flow vector is applied to describe the ion velocity distribution which influencesthe incoherent scatter spectra.A discussion is made about the effects on the incoherent scatterspectra caused by different values of the normalized perpendicular drift velocity D,aspect angleφ between the magnetic field and the line-of-sight direction,and the ratio α of the ion-neutralcollision to ion cyclotron frequency.Numerical results show that the shifting and asymmetryof incoherent scatter spectra appear parallel to E x B and E as the normalized perpendiculardrift velocity D increases due to the ion drift velocity,the stress tensor and the heat flow vectorrespectively.However,the spectrum is always typically double-humped Maxwellian parallel toB.The ion velocity distribution is more distorted from the Maxwellian as the aspect angle φincreases from 0° to 90°,and consequently the incoherent scatter spectra is no longer typicallydouble-humped Maxwellian.As a increases,the ion velocity distribution becomes Maxwellianand the incoherent scatter spectra become typically double-humped Maxwellian even with a largevalue of the normalized perpendicular drift velocity D.It is reasonable to use the sixteen-momentapproximation to describe the non-Maxwellian plasma characterized by the large temperatureanisotropy.
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