The Diffusion Interaction Region of Dayside Magnetic Reconnection

Magnetic reconnection is a universal process that allows for the transfer and release of energy previously stored in a magnetic field configuration. At Earth, this process can occur in the boundary layer between Earth's magnetic field and the solar wind, called the magnetopause. This allows the magnetopause to act as the primary ``entry gate" for the solar wind's energy into the Earth’s magnetosphere and upper atmosphere. Along the magnetopause, magnetic reconnection is triggered inside diffusion regions: an electron diffusion region (EDR) embedded inside a larger ion diffusion region (IDR). Inside these diffusion regions, plasma decouples from the magnetic field, allowing the release of magnetic energy into the plasma. We identify a hitherto undefined region in the diffusion regions, which results from the interaction of demagnetized electrons in the EDR's reconnection current sheet and remagnetizing electrons in the IDR. We call this region the Diffusion Interaction Region (DIR). Using in situ MMS plasma data and 2.5D particle-in-cell simulations, we isolate its defining features, which includes a significant parallel current structure and regions of parallel energy conversion. Defining this important and underexplored region of magnetic reconnection helps us determine how the local diffusion regions may couple with the large-scale current structures within which they are embedded.