> Referee Report   
  
> This article describes a search in EVE spectra for line emission from
> nonthermal alpha-particles that undergo charge-exchange with chromospheric
> neutral hydrogen during 10 large solar flares.  Although the main result is
> a non-detection of the expected signature, the article is worth publishing
> in ApJ.  I have the following concerns about the work in its present form.
  
> (1) It is not clear from the wording in the Abstract and elsewhere in the
> article that the authors understand what mechanism produces the signal that
> they seek.  For example, the expected radiation in the red wing of the
> Lyman-alpha line of He II at 304 A is line emission, not continuum radiation.
> This expected line emission is spread over a range of red-shifted wavelengths
> owing to the distribution of nonthermal downward speeds of the
> alpha-particles.  By contrast, recombination radiation is emitted when a free
> electron is captured; this process is less efficient by orders of magnitude
> than charge-exchange with neutal hydrogen in the chromosphere (see, e.g.,
> Canfield & Chang 1985).

Thanks, that was sloppy use of the word "continuum." We had used that to 
imply the detection proces, but recognized that it would cause confusion. 
We have fixed this incorrect usage in many places.
  
> (2) The absence of enhanced emission in the red wing of the He II 304 A line
> in EVE spectra for the 10 events presented here is consistent with previous
> investigations of this phenomenon.  Basically, previous authors who
> considered time-dependent chromospheric ionization found that more
> energetic beams would ionize the chromosphere more quickly, thereby removing
> the neutral hydrogen "food source" for the charge exchange interaction.
> See, for example, Orrall & Zirker (1976, ApJ, 208, 618, especially Appendix
> C), Canfield & Chang (1985, ApJ, 295, 275, especially Table 2), Fisher et al
> (1985, ApJ, 289, 425), Brosius & Woodgate (1999, ApJ, 514, 430, especially
> Table 1).  The only positive detection of the anticipated signature of a
> beam of nonthermal protons was reported by Woodgate et al (1992, ApJ, 397,
> L95) in the red wing of H I Lyman-alpha during a flare on AU Mic based on
> Goddard High Resolution Spectrograph observations from the Hubble Space
> Telescope, and that enhancement was observed to last only three seconds.
> Although the red wing's nonthermal intensity will be smaller for weaker
> beams (weaker flares), the signal from weaker beams might be more likely to
> survive long enough to be detected by EVE.

We thank the referee for these comments, and particularly for reminding us of
the Brosius-Woodgate (1999) paper, which discusses the problems that
need to be addressed theoretically. We have added some comments in the 
Conclusions regarding time and space scales.

> (3) The Introduction is unclear in places.  For example, the sentence "The
> particles dominate the release of flare energy from the coronal magnetic
> field" sounds like "particles" are more important than the flare energy
> that was released from the coronal magnetic field.  Further, in references
> that plot the nonthermal redshifted Lyman-alpha emission, it looks like the
> emission is displaced about 5-30 A, not 20-50 (Orrall & Zirker figures 3 & 4,
> Canfield & Chang, figures 1-3, and Brosius & Woodgate figure 2).  It is
> probably also worth mentioning expectations for He II Lyman-alpha based on
> calculations of Peter et al.

> (4) All of the figures are too small to be viewed clearly. 

We think that this may be because of the double-column format? We will request
that the multi-panel figures be put in two columns. We have redone Figures 7 
and 8 for better legibility of the lettering.

> (5) Figure 2 needs to be explained more clearly.  Did the authors integrate
> over successive EVE He II 304 A line profiles to get the integrated
> irradiance light curve in the top left, and then subtract a specific
> pre-event integrated irradiance from that curve to get the curve in the
> bottom left?  Was the line profile in the bottom right derived from that in
> the upper right by subtracting the line profile from just one exposure (at
> 01:40 UT, as in Figure 3), therefore leaving the residual brightening (in
> the bottom right) due only to the flare?  The y-axes on the right panels
> should be different from those on the left.

That's all as we intended. We have revised the figure caption and clarified
the units. We have also put some further explanation in the text.
 
> (6) CHIANTI should be referenced the first time it appears in the text.
> Acronyms (like RHESSI and SEP) should be spelled out the first time they
> appear.

Thanks, we have done that.
 
> (7) The dimensions on the y-axis of Figure 3 are incorrect.

Thanks, we have corrected that.

> (8) In the 4th paragraph of Section 2, what do the results of Share & Murphy
> (1997) have to do with the ten flares presented in this work, which were
> all observed in 2010 and 2011?  Why does weak beaming mean that "the blue
> wing may also be enhanced"?  The entire thermal line profile may be enhanced
> during a flare, with the red wing further enhanced by the nonthermal
> (charge-exchange) contribution.  It would help to expand the discussion
> regarding the three locations marked off by dotted lines in Figure 4.  Are
> these locations free of emission lines, based on CHIANTI?  Are these zones
> wider than the spectral resolution of EVE?
 
We have added text with further explanations of these points.

> (9) The blue and red curves in Figure 6 appear to overlap very closely,
> as we see only a few small patches of red near the blue curve.  Does this
> mean that the EVE spectra vary very little between the impulsive and gradual
> phases?

Yes, the EVE spectra very very little, but the variations are highly
significant because of the excellent SNR. We have added some text and
a reference.
 
> (10) The meaning of the red and blue curves in Figure 9 is not defined.

We have augmented the caption and the text to explain better.