| Solar wind turbulence focuses on determining the origin, characteristics, and dynamic evolution of fluctuating solar wind parameters, such as the interplanetary magnetic field, solar wind velocity, and plasma density. The full three-dimensional power spectral tensor, and its Fourier transform, the correlation tensor, serve as one of the most important theoretical and observational tools in the study of solar wind turbulence. In-situ magnetometer measurements of magnetic turbulence in space plasmas yield only a one-dimensional spectrum of the turbulence corresponding to fluctuations sampled along the solar wind flow direction. This reduced spectrum cannot adequately characterize the potentially rich three-dimensional structure of the turbulence. However, cosmic rays impacting a spacecraft have already passed through and interacted with the turbulent field surrounding the spacecraft, and they, in some sense, carry information on the detailed structure of the turbulence. In particular, the simple unlagged correlation between the magnetic fluctuations and fluctuations of the cosmic ray flux, ⟨δBδf⟩, first discussed by Bieber [1987a], can potentially provide unique information on the detailed nature of interplanetary magnetic turbulence.; We derive a theoretical expression for the particle-field correlation. The theoretical development of ⟨δBδ f⟩, which starts with the Vlasov equation, subject to the usual quasilinear approximations, describes the leading-order approximation of the particle-field correlation for a general turbulent geometry, including non-axisymmetric turbulence, in a plasma flowing in an arbitrary direction with respect to the average magnetic field.; We also present the first measurements of the particle-field correlation using neutron monitor data from Spaceship Earth and in-situ solar wind data archived at the OMNI database. The data analysis covers a three year period during solar minimum from 1995–1997. Preliminary data analysis does not support the simplest solar wind turbulence model of mirror-symmetric magnetostatic slab geometry. |
