标题：Implication of kinetic Alfven waves to magnetic field turbulence spectra: Earth's magnetosheath
作者：Dwivedi, N. K.; Kumar, S.; Kovacs, P.; Yordanova, E.; Echim, M.; Sharma, R. P.; Khodachenko, M. L.; Sasunov, Y.
作者机构：[Dwivedi, N. K.; Khodachenko, M. L.; Sasunov, Y.] Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria.; [Kumar, S.] Kyung Hee Uni 更多
通讯作者地址：[Dwivedi, NK]Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria.
来源：ASTROPHYSICS AND SPACE SCIENCE
关键词：Turbulence; Magnetic field spectra; Spectralslope; Kinetic Alfven wave;; Nonlinearity
摘要：In the present paper, we investigate the power-law behaviour of the magnetic field spectra in the Earth's magnetosheath region using Cluster spacecraft data under solar minimum condition. The power spectral density of the magnetic field data and spectral slopes at various frequencies are analysed. Propagation angle, kB, and compressibility, R vertical bar, are used to test the nature of turbulent fluctuations. The magnetic field spectra have the spectral slopes, , between -1.5 to 0 down to spatial scales of 20i (where i is ion gyroradius), and show clear evidence of a transition to steeper spectra for small scales with a second power-law, having between -2.6 to -1.8. At low frequencies, fsc<0.3fci (where fci is ion gyro-frequency), kB approximate to 90 degrees to the mean magnetic field, B0, and R vertical bar shows a broad distribution, 0.1R vertical bar 0.9. On the other hand at fsc>10fci, kB exhibits a broad range, 30 degrees kB90 degrees, while R vertical bar has a small variation: 0.2R vertical bar 0.5. We conjecture that at high frequencies, the perpendicularly propagating Alfven waves could partly explain the statistical analysis of spectra. To support our prediction of kinetic Alfven wave dominated spectral slope behaviour at high frequency, we also present a theoretical model and simulate the magnetic field turbulence spectra due to nonlinear evolution of kinetic Alfven waves. The present study also shows the analogy between the observational and simulated spectra.