Direct imaging of magnetohydrodynamic wave mode conversion near a 3D null point on the sun

Pankaj Kumar; Valery M Nakariakov; Judith T Karpen; Kyung-Suk Cho

doi:10.1038/s41467-024-46736-4

Direct imaging of magnetohydrodynamic wave mode conversion near a 3D null point on the sun

Nat Commun. 2024 Mar 26;15(1):2667. doi: 10.1038/s41467-024-46736-4.

Authors

Pankaj Kumar^{1

2}, Valery M Nakariakov³, Judith T Karpen⁴, Kyung-Suk Cho^{5

6}

Affiliations

¹ Department of Physics, American University, Washington, DC, 20016, USA. pankaj.kumar@nasa.gov.
² Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA. pankaj.kumar@nasa.gov.
³ Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry, CV4 7AL, UK.
⁴ Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA.
⁵ Korea Astronomy and Space Science Institute, Daejeon, 305-348, Korea.
⁶ University of Science and Technology, Daejeon, 305-348, Korea.

Abstract

Mutual conversion of various kinds of magnetohydrodynamic (MHD) waves can have profound impacts on wave propagation, energy transfer, and heating of the solar chromosphere and corona. Mode conversion occurs when an MHD wave travels through a region where the Alfvén and sound speeds are equal (e.g., a 3D magnetic null point). Here we report the direct extreme ultraviolet (EUV) imaging of mode conversion from a fast-mode to a slow-mode MHD wave near a 3D null point using Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations. An incident fast EUV wavefront associated with an adjacent eruptive flare propagates laterally through a neighboring pseudostreamer. Shortly after the passage of the fast EUV wave through the null point, a slow-mode wave appears near the null that propagates upward along the open structures and simultaneously downward along the separatrix encompassing the fan loops of the pseudostreamer base. These observations suggest the existence of mode conversion near 3D nulls in the solar corona, as predicted by theory and MHD simulations. Moreover, we observe decaying transverse oscillations in both the open and closed structures of the pseudostreamer, along with quasiperiodic type III radio bursts indicative of repetitive episodes of electron acceleration.