We thank the reviewer for their critical assessment of our paper. We
have addressed all the points, as detailed below. We have enumerated
their points in consecutive order. The resulting modifications to the
manuscript are marked in blue.

> 1. First, the Vasil paper is first mentioned at the end of a list
> (Balbus & Hawley 1994; Urpin 1996; Masada 2011; Kagan & Wheeler 2014;
> Wheeler et al. 2015; Vasil et al. 2024). However, neither Balbus &
> Hawley 1994 nor Urpin 1996 contain the words "sun" or "solar".
> They talk about stars. It’s fine to mention that, but it’s
> misleading to include Balbus & Hawley and Urpin in that list.

We have now placed the reference to Vasil+24 more prominently in the
beginning and address earlier applications to the Sun and other stars
after that. In the second paragraph, we now also indicate what the
authors of those papers did.

> 2. Also notable, the Masada and Wheeler et al. papers only considered
> local WKB analyses, which involve solving local polynomials for
> the local growth rate. These kinds of results are only relevant for
> fine-scale MRI turbulence. The Vasil work is completely different,
> using full-spherical calculations for global modes. It’s important to
> mention this.

This has now been mentioned this in the new text mentioned above.

> 3. It only becomes clear on the 2nd page that the Vasil et al. paper
> is the target, with the passage that begins "One approach is to ignore
> convection, but to retain some of its secondary effects, i.e., the NSSL
> with ∂Ω/∂ϖ < 0 and magnetic fields produced by convection; see the
> discussion by Vasil et al. (2024) and an appraisal by Zweibel (2024):.
> The part about “i.e., the NSSL with ∂Ω/∂ϖ < 0” makes sense -
> that seems to be exactly the approach in the Vasil et al. paper.
> The statement “and magnetic fields produced by convection” is very
> misleading. The Vasil et al. paper did include a large-scale background
> poloidal field (as part of the instability problem). However, the
> authors never said the field was "produced by convection". It's hard to
> see how they could. The large-scale field is part of the global dynamo,
> and the Vasil et al. paper only assumed it is present at the start of
> the solar cycle. It's important to make this distinction clear.

We have now skipped "produced by convection".

> In contrast, the authors go on to say "Furthermore, correlations
> among different components of the fluctuating parts of the turbulent
> velocity and magnetic fields emerge that are parameterized in terms of
> (i) diffusive contributions, such as turbulent viscosity and turbulent
> magnetic diffusion, and (ii) non-diffusive contributions such as Λ and
> α effects". This all seems reasonable.
> However, I'm far from okay with the claims that "... which are
> chiefly responsible for producing differential rotation and large-scale
> magnetic fields in the Sun (Rudiger & Hollerbach 2004). These effects
> explain in a self-consistent way the NSSL and the largescale magnetic
> field by solving the averaged equations (Pipin 2017); see Brandenburg
> et al. (2023) for a review.". There is nothing "self-consistent" about
> making up Greekletter terms and saying that are "chiefly responsible"
> for so many observed phenomena. Making a model is reasonable, but the
> wording (as though it's fully settled) is highly misleading.

We have rephrased that part of the text and included references to papers that
do not share the view that mean-field theory is useful. Regarding
"self-consistent", we have now added "In practice, of course, the use
of approximations compromises this goal."

> 4. Later in the paper, the authors claim “Note that the
> turbulent magnetic diffusivity was ignored in the work of
> Vasil et al. (2024)”. This statement is also false or highly
> overstated. Searching the paper finds “The momentum and magnetic
> Reynolds numbers are Re = Rm ≈ 1.5 × 10^3. These values are vastly
> more dissipative than the microphysical properties of solar plasma
> (that is, Re ∼ 10^12), and the microphysical Pm ≪ 1, implying that Rm
> <<Re. The studies conducted here find relative independence in the MRI
> on the choices of Re within a modest range.” It’s reasonable if the
> authors disagree with the specific details of the turbulent dissipation
> in Vasil et al. However, it appears that the two papers incorporate
> this in similar ways.

We agree with the referee and have now replaced "ignored" by "strongly
underestimated". In addition, at the end of the first paragraph of
Section 3.7 on page 11, we have added some explanation that their
values for the turbulent magnetic Reynolds number of 1500 correspond to
a turbulent magnetic diffusion rate that is 500 times below our blue
line in our Figure 10.  This would strongly underestimate the actual
turbulent diffusion.

> 5. The authors also have the statement "This value of the magnetic
> field strength is also what was considered by Brandenburg (2005b), and
> it is compatible with what was assumed by Vasil et al.(2024)". I'm
> also surprised that the authors didn't mention the Brandenburg
> (2005b) paper in the introduction. This paper is about “The Case for
> a Distributed Solar Dynamo Shaped by Near-Surface Shear ”. While this
> work didn't mention the MRI, it seems the authors were, at one point,
> more interested in the NSSL for the dynamo. Given the agreement with
> Vasil et al. for the magnetic field strength, the authors should do
> more to mention this sooner as part of the discussion.

We have now mentioned both papers after we wrote "Using for the mean
field of the Sun Brms=300G, ..."; see page 11.

> 6. Finally, the authors seem to miss the Vasil et al. discussion

We apologize if we did. We were primarily interested in the role of the
magnetorotational instability in a solar near-surface mean-field dynamo.

> Second, after the stage-setting in relation to the Vasil et al. paper,
> I have a fair bit of scepticism regarding the heavy reliance on
> mean-field modeling in the current paper.

We have now added a paragraph at the end of the conclusions where we
emphasize the need for direct three-dimensional turbulence simulations
where no reliance to mean-field modeling is needed.

> 7. For example, in a recent review of mean-field electrodynamics,
> Hughes (2018), elaborates on several "tribulations". In particular
> * In general, α and β are tensor quantities. Simplifying these to
> scalar parameters seems dubious in the highly anisotropic NSSL.
> * Even more general, α and β are fully non-local integral operators,
> which would likely be the case in the NSSL. I know Occam’s razor
> should prevent including too many moving parts. But perhaps tuned
> and nonlinear “quenched” α and β are already a bit too far is
> simplicity is the point.
> * Crucially, Hughes (2018) points out that the coefficients for
> these tensors are "derived under assumptions that are not applicable
> in astrophysical turbulence" which is characterized by "extremely high
> values of Rm".
> * Hughes also notes the "wide variability" and "incoherence of the
> e.m.f.," implying that its “mean magnitude is determined by diffusive
> rather than dynamic processes”. This directly impacts the reliability
> of mean-field parameters.
> * Hughes also discusses the "catastrophic quenching" of the
> α-effect by even "very weak large-scale magnetic field" at high
> Rm, which "presents a major problem in explaining observed large-scale
> magnetic fields" if α is the dominant dynamo process.
> – While Brandenburg et al. paper acknowledges that their ηT estimates
> are "somewhat uncertain", their conclusion that turbulent magnetic
> diffusivity "may be too large for the MRI to be excited" relies
> heavily on these mean-field parameters, whose fundamental derivation
> and behavior in realistic astrophysical turbulence are a subject of
> significant theoretical debate and uncertainty. Finally, thank whoever
> that we actually *see* a perfectly healthy global magnetic field. So
> we know it’s not catastrophically quenched.  But perhaps this is
> just another hint that a turbulent α effect is off track. I would
> like to see much more circumspection about the parameterizations.

These are certainly important points that need to be addressed. We have
now mentioned this in our new last paragraph of the conclusions.

> The authors explicitly refer to the "Malkus–Proctor mechanism"
> as "macrophysical feedback" stemming from the Lorentz force of the
> large-scale magnetic field (J × B). They observe that when the MRI
> is excited (for CΩ < 0), the work done by the Lorentz force and the
> magnetic dissipation rate are "always much larger" than in cases where
> MRI does not operate.

Yes, but we also mention that this simple rule might not apply to dynamos
in spheres, where other dynamo properties are known to be sensitive to
the sign of the shear parameter.

> 8. While the authors acknowledge this macro-dynamical feedback and
> its association with enhanced dissipation, their primary conclusion for
> the Sun's NSSL leans towards the suppression of MRI due to turbulent
> magnetic diffusivity and α-quenching (feedback from the Lorentz force
> of the small-scale field) limiting the magnetic field strength. This
> framing might be seen as subtly shifting the emphasis from the
> fundamental role of induced large-scale flows and ohmic dissipation
> (i.e., Malkus & Proctor) to the parameterized effects of small-scale
> turbulence within the mean-field framework.

We recall that we invoke alpha quenching in Section 3.5 solely "to
facilitate dynamo saturation at a lower magnetic field strength" allowing
us therefore access to "a regime with C_Omega <0 without MRI"; see the
beginning of the second paragraph of Section 3.5 on page 9. This was
the last section before we address the comparison with earlier work in
Section 3.6 and estimates for the Sun in Section 3.7. We agree that this
can be regarded as a shift in emphasis, but given our clear motivation,
it can hardly be regarded as subtle.

> 9. The Vasil et al. paper also seems to point the large-scale feedbacks,
> "As the cycle progresses, the toroidal field can undergo several
> possible MHD instabilities contributing to poloidal-field regeneration,
> for example, the helical MRI, non-axis-symmetric MRI, the clamshell
> instability and several more, including a surface Babcock–Leighton
> process". The Brandenburg et al. authors appear to make α and β
> parameterization seem like the only option. The abstract is a prime
> example of this. What the paper shows only relates to a very specific
> parameterization and the implicit assumptions behind those. That said,
> if we want to go for mean-field assumptions, I would have also liked
> to see a Babcock–Leighton effect. It might be poorly understood how
> it occurs, but it’s clearly observed.

We have now mentioned the possible dynamo effect from the decay of active
regions in the newly introduced third paragraph of the introduction on
page 2.

> 10. However, in support of large-scale feedbacks (as opposed to
> mean-field parameterizations), the authors fail to mention anything
> about Solar Active Longitudes. In particular (e.g.) Berdyugina &
> Usoskin (2003) mention "persistent active longitudes separated by 180
> degrees". Long-lived large-scale structures points to the importance
> of macrophysical effects. It seems the perhaps most compelling thing
> the authors have done is put constraints on the size of the diffusion,
> not the magnetic field. They should mention this as a possibility.

The study of active longitudes is an exciting topic. There are many
different attempts in the literature trying to model this phenomenon,
which is also seen on other stars. However, even the observational
reality of this phenomenon is being disputed. To our knowledge, a possible
relation to the MRI has not yet been proposed. Therefore we have refrained
from entering into this discussion in our paper.

> For more minor issues, I have several questions about the model setup
> and results.

> 11. The fully compressible equations are appropriate. But it's not
> clear how the simulations can run long enough for a full dynamo cycle
> with extreme time-stepping restrictions. I assume they've used a
> reduced sound speed but it's not clear by how much.

Yes, we forgot to specify the value of the sound speed. We have now
done this at the end of the first paragraph of Section 2.2.

> 12. In general, I find the heavy reliance on non-dimensional parameters
> obscures how the simulations relate to the known properties of the
> sun. Perhaps a table translating into solar equivalents would be good.

???

> 13. The authors state ”In all of our cases, we consider q = ±3/2
> For the solar NSSL, however, we have q = 1”. I suppose q = 3/2 gives
> the shear more of a chance. But it's not clear why the authors would
> choose q = 3/2 when it would have been trivial to use q = 1.

[I have now submitted a version of Run A for q=1.]

> 14. Moreover, in the section "Estimates for the Sun" the authors
> say "For the MRI to be excited, √ the Alfven frequency, ωA = vA k
> must not exceed the rotational shear frequency, 2qΩ, where q = −∂
> ln Ω/∂ϖ is the local nondimensional shear parameter. For the solar
> NSSL, we have q = 1". This is extremely misleading if they didn't
> actually use q = 1 in their models.

???

> 15. Also, the "Estimates for the Sun" section is very close
to beginning of the Vasil et al. paper. The authors should mention this
and make comparisons to the estimates in the previous paper.

???

> 16. The CΩ parameter is essentially a shear Reynolds number. As
> mentioned before, the Vasil et al. paper used values that are probably
> about 1000 in the current scaling. Figure 3 seems a lot more optimistic
> than the written words. I think most solar modelers would be comfortable
> if turbulent Reynolds numbers needed to be only a few factors of 10.
> The Vasil et al. paper say explicitly "We compute sample simulations
> down to Re ≈ 50 with qualitatively similar results". Arguing about
> anything much smaller than this seems highly academic.

???

> 17. Statements like the following plague paper throughout: "We see
> that, regardless of the boundary conditions, the cases with negative
> shear, where the MRI is possible, all have less magnetic energy than the
> cases with positive shear. Thus, the action of the MRI always diminishes
> dynamo action". I have no idea of the intention of the authors. But,
> seriously? "Thus, the action of the MRI always diminishes dynamo
> action" It's a fact to say "in all of our simulations the MRI
> always diminished dynamo action". But claiming something **always
> diminishes** else leaves no room for anything else. The "Thus,..."
> is also problematic. It's not clear to me that comparing negative and
> positive shear in an NSSL-like simulation implies anything other than
> the output of the simulation changed. It doesn't make much sense
> to consider positive shear in the NSSL because the NSSL has negative
> shear. The rest of the sun has positive shear, fair enough. But the
> setup (especially Cartesian) is completely different from everywhere
> else in the sun.

Our intention is to find out whether the MRI is active in our model.
To clarify this point, we have now added some more explanation in the
beginning of Section 3.2. Regarding the referee's comment that the last
sentence of that first paragraph "leaves no room for anything else",
we have now rephrased it to talk more specifically about "our Cartesian
shearing-periodic mean-field models" and write "Thus, the action of
the MRI is to diminish dynamo action in our Cartesian shearing-periodic
mean-field models."

> Overall, I have no objections to recommending a paper like this,
> i.e. trying to cast doubt on a previous result. But it comes off as
> an extremely weak attempt to neutrally add to the record information
> that others can use to judge for themselves. The authors can complain
> the Vasil et al. paper overstated claims, but I'm not reviewing
> that paper. It's part of the record and the authors should follow
> up as constructively as possible. I cannot recommend this paper
> until the authors do a lot more to tone down the overstatement and
> misrepresentations. They also have used a system of parameters that
> allows readers to easily tell what's happening in relation to the sun
> and other work.

We hope that our responses above are satisfactory to the referee.
Our intention was to provide a first study of the effects of the MRI
for a dynamo-generated magnetic field. Earlier models either used an
initial magnetic field (as is the case in Vasil et al.) or they were
too complex to address this question (e.g., Brandenburg+92, Pipin17).