  Here we present the study of a compact emission source during an X1.3 flare
on 2022-March-30. Within a $\sim41$~s period (17:34:48 UT to 17:35:29 UT), IRIS
observations show spectral lines of Mg II, C II and Si IV with extremely
broadened, asymmetric red-wings. This source of interest (SOI) is compact,
$\sim$ 1\arcsec.6, and is located in the wake of a passing ribbon. Two methods
were applied to measure the Doppler velocities associated with these red wings:
spectral moments and multi-Gaussian fits. The spectral moments method considers
the averaged shift of the lines, which are 85 km s$^{-1}$, 125 km s$^{-1}$ and
115 km s$^{-1}$ for the Mg II, C II and Si IV lines respectively. The red-most
Gaussian fit suggests a Doppler velocity up to $\sim$160 km s$^{-1}$ in all of
the three lines. Downward mass motions with such high speeds are very atypical,
with most chromospheric downflows in flares on the order 10-100 km s$^{-1}$.
Furthermore, EUV emission is strong within flaring loops connecting two flare
ribbons located mainly to the east of the central flare region. The EUV loops
that connect the SOI and its counterpart source in the opposite field are much
less brightened, indicating that the density and/or temperature is
comparatively low. These observations suggest a very fast downflowing plasma in
transition region and upper chromosphere, that decelerates rapidly since there
is no equivalently strong shift of the O I chromospheric lines. This unusual
observation presents a challenge that models of the solar atmosphere's response
to flares must be able to explain.
