Magnetohydrodynamic Turbulence in the Solar Wind

The fluctuations in magnetic field and plasma velocity in the solar wind possess many features expected of fully developed magnetohydrodynamic turbulence. Understanding this nonlinear system is complicated by the dynamical effects of velocity shear between fast and slow solar wind streams, by the spherical expansion of the solar wind, and by its compressibility. Direct spacecraft observations from 0.3 to over 20 AU, radio scintillation observations of plasmas near the Sun, numerical simulations, and various models provide complementary methods that have shown convincingly that the fluctuations in the wind parameters undergo significant dynamical evolution independent of whatever turbulence might exist in the solar photosphere and corona. This rich area of study allows one to test theories of turbulence against direct observation, and to use observations to guide and motivate development of turbulence theories. The solar wind thus provides an excellent laboratory for studying many fundamental questions about turbulent plasmas.