(a) Solar wind parameters observed by STEREO A during 2011 July 14–18. From top to bottom: pitch angle distribution of suprathermal electron (246.6 eV), magnetic field strength, azimuthal and elevation angles of field direction in RTN coordinates, proton velocity, proton density, proton temperature, and total perpendicular pressure. The gray and yellow shaded regions mark two interacting SIRs (SIR1_STA and SIR2_STA). The red shaded region indicates the heliospheric plasma sheet. The green vertical dashed line marks the stream interfaces (SI1_STA). The magenta dashed vertical line indicates the HCS crossing. (b) Fluctuations of the components of the proton velocity (δVpr, δVpt, δVpn) and the Alfvénic velocity (δVbr, δVbt, δVbn) derived from magnetic field fluctuations.