Decay length of slow magnetoacoustic waves in the solar corona using SDO/AIA and SolO/EUI-HRIEUV.

Slow magnetoacoustic waves have been observed in the solar corona for decades; yet, existing theories do not fully explain the wide range of observed decay lengths, and measurements from different instruments frequently disagree. We present two events with simultaneous Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) and Solar Orbiter/EUI-HRIEUV observations of slow waves in sunspot-anchored coronal fan feathers. In Event 1, the lines of sight (LoS) are separated by 16.2∘, while in Event 2, they are almost parallel. Using time-distance analysis, we identify waves with periods in the 3-minute band and quantify wave decay using the exponential folding length. For non-parallel LoS, the ratio of decay lengths measured by the two instruments, λratio=λAIA/λEUI, varies widely, with both λratio>1 and λratio<1 observed. However, when the LoS are almost parallel, the decay lengths agree with one another, and λratio≈1. These results show that the angle between the LoS and the wave propagation direction is key to determining the apparent decay of slow waves, a factor that has not yet been systematically accounted for. Since statistical studies of decay lengths constrain coronal energy-loss mechanisms, observational effects beyond simple projection must be corrected to reliably infer the underlying physical dissipation processes. This article is part of the theme issue 'Transferable mechanisms in the oscillatory processes of solar and stellar flares'.