Authors: Yuliang Ding(EPSS, UCLA), Chen Shi(EPSS, UCLA), Marco Velli(EPSS, UCLA), Zesen Huang(EPSS, UCLA), Nikos Sioulas(JPL)

We carry out a superposed-epoch analysis of WIND measurements of over 200 corotating interaction regions (CIRs)/stream interaction regions (SIRs), with zero epoch determined using minimum variance analysis(MVA). We can clearly see a velocity shear zone where the velocity increases rapidly accompanied by strong compression with an increase of proton density in the slow wind side ahead of the interface. Analysis of the turbulence is carried out by calculating the normalized cross helicity (σ_c, which measures the ratio of energy in outwardly propagating Alfvénic fluctuations to that of Sun-ward fluctuations), and normalized residual energy (σ_r,  which measures the ratio of kinetic energy to magnetic energy in fluctuations). We use wavelet transform to obtain the fluctuation energy within certain frequency ranges. The results show that across the slow wind-fast wind interface, σ_c increases from around 0.25 to 0.75, and σ_r increases from around -0.6 to -0.4, indicating enhanced outward dominance and weakened magnetic dominance in the fast solar wind. Drops of both σc and σr at zero epoch are observed, caused by a sharp increase of energy in both the inward Alfvénic fluctuations and magnetic fluctuations. A smooth increase of σc inside the slow wind toward the interface is also observed. One possible cause might be the presence of the heliospheric current sheet in the slow wind, where the inward-outward ratio tends to balance.