Diagnostics of Flare Loop Parameters in Shrinkage and Ascent Stages Using Radio, X-ray, and UV Emission
Round 1
Reviewer 1 Report
The oscillations were observed during the time period in the same order of the period of the electric current oscillation. There might be some observations error for the oscilation period?
minor problem:
line 39, define variable, tau_{5000}
Author Response
//
Comments and Suggestions for Authors:
The oscillations were observed during the time period in the same order of the period of the electric current oscillation. There might be some observations error for the oscillation period?
Authors reply:
We based on the result of Li & Gan (2006, Fig.3) which shows oscillations with a period of 154 s observed in UV radiation (195) only on a time interval of 6 min. Our estimates show that the quality factor of RLC oscillations in the M2.5 flare on 2002 April 16 is quite low, ~10. Therefore, we noted in the manuscript that our estimates of the electric current magnitude at a low quality factor of oscillations, strictly speaking, should be fair in order of magnitude.
Minor problem: line 39, define variable, tau_{5000}
Authors reply:
The optical thickness τ5000 =1 for radiation with a wavelength of 5000 Å means the zero level, from which the height of solar atmosphere is measured (see, e.g. Priest, Solar MHD, Reidel, 1982). We add this explanation in the text of the manuscript (in bold).
Reviewer 2 Report
With the assumption of taking a flare loop as an equivalent electric circuit, the authors carried out diagnostics for the plasma parameters of two flare loops. This is an interesting picture, which may be useful to interpret the dynamics of flare loops, like contraction and post-contraction oscillations (with a short period). The physical picture is easy to understand, however, the assumption should first seek observational support with vector magnetograms taken by, e.g., HMI onboard SDO. The total electric current of 10^{11} Ampere contained a flare loop with a length scale of the cross-section of 3.5 x 10^6 meter means a current density of 10^{-2}A m^{-2}, which is much lower than the typical current density in solar active regions detected by HMI (>10^{-1} A m^{-2}). The authors need to explain the major discrepancy. Also, the authors need to provide observational support for the electric current model.
Author Response
Comments and Suggestions for Authors:
With the assumption of taking a flare loop as an equivalent electric circuit, the authors carried out diagnostics for the plasma parameters of two flare loops. This is an interesting picture, which may be useful to interpret the dynamics of flare loops, like contraction and post-contraction oscillations (with a short period). The physical picture is easy to understand, however, the assumption should first seek observational support with vector magnetograms taken by, e.g., HMI onboard SDO. The total electric current of 10^{11} Ampere contained a flare loop with a length scale of the cross-section of 3.5 x 10^6 meter means a current density of 10^{-2}A m^{-2}, which is much lower than the typical current density in solar active regions detected by HMI (>10^{-1} A m^{-2}). The authors need to explain the major discrepancy. Also, the authors need to provide observational support for the electric current model.
Our reply:
Models of a current-carrying flare loop (e.g. Zaitsev et al. [11]; Melrose, ApJ, 1995, 451, 391) supported by observations. For example, Hagyard (Solar Phys. 1988, 115, 107) using observations of AR 2372 on April 6,1980 with the vector magnetograph of the Marshall Space Flight Center concluded that the vertical electric current outflows from the photosphere at one loop footpoint and inflows into the photosphere at the another footpoint. In this case, the current density was of about jz ≈ 10-2 A/m2. Observational support in favor of a current-carrying loop were presented also by Tan Baolin et al. (Solar Phys. 2006, 239, 137), and Tan Baolin (Adv. Sp. Sci. 2007, 39, 1826). Flares are quite different. Gary & Demolin (ApJ, 1995, 455, 982) revealed ≈ 3×10-2 A/m2. The same values of jz inferred using the vector magnetograms of the Haleakala Stokes Polarimeter (Pevtsov et al. ApJ, 1997, 491, 973) and HMI/SDO (Sharykin & Kosovichev, ApJ, 2015, 808, 72). Zimovets et al (ApJ, 2020, 891,138) were determined in the Introduction the photospheric vertical electric currents jz ≥(1-3)×103 statampere/cm2 = (0.3-1)×10-2 A/m2 as strong enough. They concluded that data of HMI/SDO for 48 flares gave the magnitudes of jz = (103-105) statampere/cm2.
We add a part of this reply in the manuscript as item (iii) in subsection 4.1
Author Response File: 
Author Response.docx
Reviewer 3 Report
The paper presents a proposal of a diagnostic method of plasma parameters in flare loops by assuming a flare loop as an equivalent electric circuit. It shows that loop shrinkage may be due to increase of the electric current in the loop, and number density, temperature, electric current, etc. are determined for the past flare observations.
The idea is interesting and summarized concisely. The reviewer suggest the authors to check the followings as minor comments.
line 13 of page 1
What does "the dimensions" means. Please describe specifically such as loop length, height, etc.
line 42 of pare 1
line 45 of page 2
The abbreviation EMF is used only twice without explanations. It would be better to write it down without acronym.
section 4.1 of page 4-5
During the impulsive phase, accelerated electrons are transported in the loop, and they would create currents. Do they have any role on the shrinkage?
line 140 of page 4
The wavelength band of the short channel of GOES X-ray Sensor is described as 0.5-4.8 Å. Of course, the response function of the detector is not a rectangular shape, but 0.5-4.0 Å is more popular data for the description of the wavelength of the short channel. Please correct it.
Author Response
Comments and Suggestions for Authors:
The paper presents a proposal of a diagnostic method of plasma parameters in flare loops by assuming a flare loop as an equivalent electric circuit. It shows that loop shrinkage may be due to increase of the electric current in the loop, and number density, temperature, electric current, etc. are determined for the past flare observations. The idea is interesting and summarized concisely.
The reviewer suggest the authors to check the followings as minor comments:
line 13 of page 1:
What does "the dimensions" means. Please describe specifically such as loop length, height, etc.
Our reply:
We add to the Abstract more words concerning the loops characteristics obtained in the manuscript.
line 42 of page 1 and line 45 of page 2:
The abbreviation EMF is used only twice without explanations. It would be better to write it down without acronym.
Our reply:
We put in the manuscript “the electromotive force (e.m.f.)” instead of EMF.
section 4.1 of page 4-5:
During the impulsive phase, accelerated electrons are transported in the loop, and they would create currents. Do they have any role on the shrinkage?
Our reply:
With pulsed injection of accelerated electrons into the loop, they can change the total electric current in the loop during a time of loop flight (of the order of seconds), which is small compared to the oscillation period of the loop as an equivalent electric circuit. If the velocity dispersion of accelerated electrons exists, this current disappears in a few bounce-periods as the result of reflections of electrons from the loop magnetic mirrors.
We add this explanation in the text of the manuscript.
line 140 of page 4:
The wavelength band of the short channel of GOES X-ray Sensor is described as 0.5-4.8 Å. Of course, the response function of the detector is not a rectangular shape, but 0.5-4.0 Å is more popular data for the description of the wavelength of the short channel. Please correct it.
Our reply: we did this correction.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
As I reported earlier, this is an interesting paper, applying the current model to interpret the dynamics of flare loops, like contraction and post-contraction oscillations. The authors have made a revision, and I am satisfied with the interpretation and the connection with existing observations.
