CMAG: A Mission to Study and Monitor the Inner Corona Magnetic Field

Round 1

Reviewer 1 Report

The article describes the Coronal Magnetograph mission, proposed in response to the ESA’s call 400 for “Fast” mission opportunity. It is well written, concise and understandable by a non-solar audience. I have only a few minor comments:

1. With the exception of lines 417-419, little information is given about the external oculter; the authors may wish to expand on that.

2. The authors failed to mention that coronal magnetic fields can and have been measured in the radio range (see the recent review by Alissanrakis & Gary, 2021; doi: 10.3389/fspas.2020.591075). A senctence ar two should be added in Section 1.2

3. lines 28-29: "maintaining a relatively constant level further out."; the pressure certainly decreases smoothly above the Transition Region.

Author Response

Thanks a lot for the comments. We have taken them into account. We are aware of the radio observations, so thanks for telling us we were missing that info in the paper. It is important. Furthermore, we have also added some more information regarding the occulter disk size in the main text.

Best,

David

Reviewer 2 Report

The CMAG mission introduced in this manuscript may provide an excellent opportunity for the solar physics and space weather communities to extend the current knowledge of the coronal magnetic field, which is of great importance. In the meantime, the manuscript is well-written, providing sufficient technical and management information. Therefore, I believe the manuscript can be accepted as it is.

Author Response

Thanks for reviewing the CMAG paper. 

Best,

David

Reviewer 3 Report

In the paper, the authors proposed a mission, namely CMAG, to study the vector magnetic fields and velocities of the inner corona. By providing the magnetic field and velocity data, CMAG mission aims to address some of the most important scientific questions in solar physics: coronal heating, flare and CME formation, and the generation and energy transport of waves. To achieve it, the authors proposed an imaging spectropolarimeter as the sole instrument to measure the Stokes parameters of selected coronal spectral lines: Fe XIV 530 nm, Fe XI 789 nm, and Fe XIII 1074 nm. To achieve coronagraphic observations, an external occulter installed on another spacecraft is needed. The authors found that a formation flight distance of 430 meters between the coronagraph and the occulter will reduce the scattered light significantly and therefore increase the polarimetric sensitivity. In the paper, the authors present the mission concept, including the payload concept, data products, mission operations baseline and spacecraft concept.

Overall the paper is well written and the space mission focus on one of the most important problems in solar physics: the measurement of magnetic fields in the solar corona, which is responsible for coronal heating, solar wind acceleration, and solar activity events. As such, the topic is very relevant to aerospace and to the whole community. Therefore I recommend it for publication in Aerospace. There are two points the authors may want to consider before the final publication.

1. The Visible Emission Line Coronagraph (VELC) on board Aditya-L1 mission may need to be mentioned since it also aims for coronal magnetic field measurement with the help of spectropolarimetric observations of Fe XIII 1074 nm line.

2. The mission aims to observe the innor corona magnetic filed from 1.02-2.5 solar radii. In the height range of, say >1.7 solar radii, the magentic field will be very weak, lower than 1 G, and stokes V/I smaller than 10^-4 and the density much smaller. How can CMAG achieve to measure the magnetic field in these regions?

Author Response

Thanks for the useful comments. We certainly have implemented them. We should not forget Aditya-L1. Furthermore, we have added some more info in the text regarding the low field strengths. Of course, in those circumstances we need to integrate more photons and try to keep the S/C stability during longer period of times. 

Best,

David