Magnetic Rayleigh-Taylor Instability in Solar Atmosphere Downward Magnetic Flux Transport

Descending cold plasma structures are observed and are thought to result from the Magnetic Rayleigh$-$Taylor Instability (MRTI), which facilitates the downward transport of plasma toward the photosphere and contributes to the restructuring of the magnetic field. In this study, we perform 2.5D nonlinear compressible magnetohydrodynamics (MHD) simulation using the open$-$source MPI$-$AMRVAC code to investigate the role of MRTI under chromospheric$/$photospheric conditions. Our results show that the transverse magnetic field $\left(B_x\right)$ alters the MRTI growth by modifying the critical wavelength and delaying its onset, while the longitudinal component $\left(B_z\right)$ governs the buoyancy$-$driven dynamics, influencing the size and descent speed of mushroom$-$like structures. The height evolution of these structures exhibits a slow linear phase followed by a rapid quadratic phase. Upon reaching the photosphere, their interaction with the surrounding magnetic field further shapes the mushrooms. This study highlights the crucial role of MRTI in the magnetic flux drainage from the chromosphere to the photosphere and its contribution to magnetic field restructuring, impacting the evolution of active regions and the formation of penumbral structures.