Dear Paola
thanks for pointing me to the supplementary stuff. It is a pity
this was not made
central to the paper, a casualty of choosing Science Magazine as a
vehicle.
please understand my comments below are driven by the provocative
nature of
your conclusion and my interest in understanding basic physical
processes in the
Sun's atmosphere.
OK so I have read this through and finally found your explanation,
here are my reactions, your
words are in quotes:
1. "Chromospheric
reconnection could in principle provide an alternative
explanation for
the observed chromospheric and TR variability, but we find that
the observations
support the hypothesis of beam heating. "
The moss brightenings clearly occur at
conjugate footpoints of hot loops undergoing heating, and there
is a clear correlation
between the coronal and chromospheric/TR emission, naturally
explained by beam
heating."
since "moss" (=phenomenology) is believed to be the hot
transition region heated by conduction it
should be impossible to get moss at just one footpoint. Hence
footpoint emission at both footpoints says
nothing other than conduction dominates. A clear correlation
between corona and TR is always expected
when conduction is important. The correlation between
chromosphere and corona says something else.
2. "The Si IV brightenings are strong and occur throughout the
region of the hot
loop footpoints; if they were caused by chromospheric
nanoflares, the reconnection
and energy release would have to happen in all these locations
consistently at a
specific height appropriate to yield strong (and blueshifted) Si
IV emission (i.e., if they
occurred over a range of heights, some of them would happen too
deep and would not
produce any Si IV increase). Beam heating naturally explains the
spatial and temporal
coherence of various brightenings throughout the field-of-view,
especially since the
deposition height of electron beams (through the thick-target
mechanism) naturally
occurs at the height of the IRIS
observations."
But so does reconnection in a stratified atmosphere- V_A the
Alfven speed varies with a scale height of
2H where H is the density scale height, 120 km or so. So,
reconnection (~ V_A) will always occur fastest
in the least dense upper reaches of the chromosphere for a given
magnetic field. (Another example is radiative heating from
above which reaches only to tau=1 or so).
3. "Finally, given that moss variability is
observed only at time when the overlying coronal loops are
heated, if qchromospheric
nanoflares were the source of the observed variability, the
correlation with the coronal
emission would have to be explained.
iris_moss_rev1
"
This is the same as the point 1. above. So this is I think your
major point.
Now I am very puzzled because there is a huge literature
talking of spicules that generate heating events into
the corona which is precisely what would be needed to explain your
points 1. and 3.
My conclusion: 1. science should be about refuting hypotheses not
supporting them. We already have
a "surfeit of support for hypotheses" in solar physics owing to the
non-unique interpretations that
are possible, examples are given above. 2. Your data reveal just
one essential observation to believe your
hypothesis, but it is very far removed from a direct indicator of
beam physics, and 3. Your data can be
interpreted in a reconnection-driven spicule that has been advoctaed
for very forcefully by some.
So I remain extremely puzzled and unconvinced. No doubt those
advocating both for
this process and spicules/reconnection can perform some Houdini-like
"rescuing of the
phenomena", but I must say this is all a very funny business.
Phil