Understanding observational characteristics of solar flare current sheets

Context. The elongated bright structures above solar flare loops are suggested to be current sheets, where magnetic reconnection takes place. Observations have revealed various characteristics of the current sheet; however, their physical origin remains to be ascertained. Aims. In this study we aim to reveal the relations of observational characteristics of current sheets with the fundamental processes of magnetic reconnection. Methods. Using high-resolution 3D magnetohydrodynamic simulations of turbulent magnetic reconnection within a solar flare current sheet, we synthesized the remote-sensing observations of the current sheet and determined their physical properties. Results. Turbulent magnetic reconnection can significantly broaden the apparent width of the current sheet, which is much larger than the realistic physical width because of the superposition effect. The differential emission measures of the current sheet have two peaks; the high-temperature component is spatially related to confirmed small-scale reconnection sites, showing that the current sheet is directly heated by reconnection. Moreover, we demonstrate that strong turbulence can cause the nonthermal broadening of spectral lines at both the current sheet and flare loop-top regions. A strong correlation between them in time is also observed. Conclusions. Our 3D turbulent magnetic reconnection flare model can be used to interpret primary observational characteristics of the elongated bright current sheets of solar flares.