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