Ubiquitous Occurrences of Multiscale Layers of Magnetic Reconnection across a Solar Wind Stream Interaction Region at 1 au

We present a first record of significantly enhanced occurrences of magnetic reconnection exhausts as measured by the Wind satellite across a stream interaction region (SIR) at 1 au from 2019 January 4 10:11:20 UT to 2019 January 5 09:58:00 UT. The activity is clustered in a slow wind compression regime ahead of the SIR interface with a deflected, compressed fast wind. The 43 exhausts of this 1 day SIR dominate a distribution of 71 exhausts as obtained by a multiwindow sliding technique application to the 8 day period on 2019 January 1–9. Active current sheets inside the SIR are associated with normal directions mostly near the ecliptic plane and a more azimuthal-than-Parker magnetic field direction at 1 au. We find that exhausts wider than 500 ion inertial lengths are typically present just upstream and inside this SIR rather than within unperturbed slow and fast winds beyond a shocked solar wind. The observations suggest that plasma and field compressions may be crucial elements in driving a breakup of large-scale current sheets embedded in SIRs into smaller, multilayered current sheet segments through magnetic reconnection.