Solar wind turbulence and shear: A superposed-epoch analysis of corotating interaction regions at 1 AU

A superposed-epoch analysis of ACE and OMNI2 measurements is performed on 27 corotating interaction regions (CIRs) in 2003-2008, with the zero epoch taken to be the stream interface as determined by the maximum of the plasma vorticity. When the measurements are rotated into the local-Parker-spiral coordinate system, the shear is seen to be abrupt. Converging flows are seen; about half of the CIRs show a layer of divergent rebound flow away from the stream interface. Analysis of the turbulence across the CIRs is performed. When possible, the effects of discontinuities are removed. Fluctuation amplitudes, the Alfvenicity, and the level of Alfvenic correlations all vary smoothly across the CIR. The Alfven ratio exhibits a decrease at the shear zone of the stream interface. Fourier analysis of subintervals is performed, and the results are superposed averaged as an ensemble of realizations. The spectral slopes of the velocity, magnetic field, and total energy vary smoothly across the CIR. The total-energy spectral index is similar to 3/2 in the slow and fast wind and in the CIRs. Fourier analysis of Elsasser fluctuations shows a smooth transition across the CIR from an inward-outward balance in the slow wind to an outward dominance in the fast wind. Spreading of turbulence away from the region where it is produced is limited to similar to 10(6) km. A number of signatures of turbulence driving at the shear zone are sought (entropy change, turbulence amplitude, Alfvenicity, spectral slopes, and in-out nature): none show evidence of driving of turbulence by shear.