Transverse magnetohydrodynamic (MHD) waves have been shown to be ubiquitous
in the solar atmosphere and can in principle carry sufficient energy to
generate and maintain the Sun's million-degree outer atmosphere or corona.
However, direct evidence of the dissipation process of these waves and
subsequent heating has not yet been directly observed. Here we report on high
spatial, temporal, and spectral resolution observations of a solar prominence
that show a compelling signature of so-called resonant absorption, a long
hypothesized mechanism to efficiently convert and dissipate transverse wave
energy into heat. Aside from coherence in the transverse direction, our
observations show telltale phase differences around 180 degrees between
transverse motions in the plane-of-sky and line-of-sight velocities of the
oscillating fine structures or threads, and also suggest significant heating
from chromospheric to higher temperatures. Comparison with advanced numerical
simulations support a scenario in which transverse oscillations trigger a
Kelvin-Helmholtz instability (KHI) at the boundaries of oscillating threads via
resonant absorption. This instability leads to numerous thin current sheets in
which wave energy is dissipated and plasma is heated. Our results provide
direct evidence for wave-related heating in action, one of the candidate
coronal heating mechanisms.Comment: 28 pages, 9 figures, accepted for publication in ApJ. Part II by
Patrick Antolin et al. will appear soo