[Loops] new paper on IRIS diagnostics for coronal heating and accelerated particles

[judge]

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




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