Electron Temperature Anisotropy Effects on Alpha/Proton Instability in the Solar Wind
Round 1
Reviewer 1 Report
The article "Electron temperature anisotropy effects on alpha/proton instability in the solar wind" by Lang et al. investigate the effects of alpha beam drift and electron temperature anisotropy on kinetic instability. The authors discuss how this can potentially explain the deceleration of alpha beam in the solar wind. This is an important topic, and the paper would be impactful once published. I have some comments before I can recommend the paper for publication.
1. The authors discuss “kinetic instabilities induced by both the alpha beam and the electron temperature anisotropy”, but what about the effects of alpha temperature anisotropy (see e.g., Maruca et al. 2012 https://doi.org/10.1088/0004-637X/748/2/137)? Will that not have an effect too? Please discuss.
2. The authors should discuss the limitations of linear Vlasov theories. The solar wind is a turbulent medium, with many current sheets. These would invalidate conditions for the applicability of linear Vlasov theory. I understand that historically, it is has been used this way and it works successfully. However, the authors should discuss this issue (see e.g., Gary et al. 2021 https://doi.org/10.3847/1538-4357/abb2ac).
3. Eq. (2) the authors should discuss why bi-Maxwellian is an appropriate choice. The solar wind distribution functions are far from bi-Maxwellian.
4. The instabilities have also been observed in different planetary magnetosheaths (see e.g., Maruca et al. 2018 https://doi.org/10.3847/1538-4357/aaddfb). Please discuss how the current results would be relevant to those.
5. Line 1: “spacecrafts” should be spacecraft.
Author Response
We would like to thank the anonymous referee for his/her constructive comments and valuable suggestions. According to the referee’s comments and suggestions, we have revised the manuscript and all changes are highlighted in boldface in this revision. Our responses (in boldface) to the referee’s comments are listed in point-by-point as shown in the appendix file.Author Response File: 
Author Response.pdf
Reviewer 2 Report
Based on the linear Vlasov equation of the PDRK solver, the authors investigate the kinetic instability driven by both the alpha beam and the electron temperature anisotropy in the solar wind. The effects of the electron temperature anisotropy on plasma waves (i.e., PM/W, PAW, OA/IC, PAW, KAW) instability are discussed in detail. The results show that anisotropic electrons can decrease the velocity threshold of alpha beams instability to below the local Alfven velocity, which have potential important role in explaining the alpha beam deceleration in the solar wind. In my opinion, this work is interesting and worth publishing in Universe. However, there are a few questions need to be clarified as follows.
1. A lot of figures are presented in this paper without proper physical information. So, I suggest the authors complement descriptions or delete some figures without rich physics.
2. Figure 1 shows the variations of the real frequency, maximum growth rate, and polarization in the parallel electron beta plane and the alpha beam drift velocity vα/vA. However, the authors state “The alpha beam density and drift velocity nα = 0.05ne and vα = 1.5vA were used” in lines 96-97. I strongly propose that the authors check the whole contents to avoid the similar contradictory statements.
3. The maximum growth rates have been shown in nearly all the figures, what parameter space (i.e., wavenumber, propagation angles, etc.) the maximum growth rates corresponding to should be expressed clearly. In figures 4-6 and 11-12, the propagation angles (i.e., \theta) used should also be expressed clearly.
Author Response
We would like to thank the anonymous referee for his/her constructive comments and valuable suggestions. According to the referee’s comments and suggestions, we have revised the manuscript and all changes are highlighted in boldface in this revision. Our responses (in boldface) to the referee’s comments are listed in point-by-point in the appendix file.Author Response File: Author Response.pdf
Reviewer 3 Report
see attachment
Comments for author File: Comments.pdf
Author Response
We would like to thank the anonymous referee for his/her constructive comments and valuable suggestions. According to the referee’s comments and suggestions, we have revised the manuscript and all changes are highlighted in boldface in this revision. Our responses (in boldface) to the referee’s comments are listed in point-by-point in the appendix file.Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have sufficiently addressed all the comments. I recommend the paper for acceptance.
Reviewer 3 Report
The manuscript has been revised properly, and is now ready to be published in the present form.
