Difference spectrum fitting of the ion–neutral collision frequency from dual-frequency EISCAT measurements

Günzkofer, Florian; Stober, Gunter; Pokhotelov, Dimitry; Miyoshi, Yasunobu; Borries, Claudia

doi:https://doi.org/10.5194/amt-16-5897-2023

Articles | Volume 16, issue 23

https://doi.org/10.5194/amt-16-5897-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-16-5897-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 23

Research article

|

08 Dec 2023

Research article |

| 08 Dec 2023

Difference spectrum fitting of the ion–neutral collision frequency from dual-frequency EISCAT measurements

Florian Günzkofer, Gunter Stober, Dimitry Pokhotelov, Yasunobu Miyoshi, and Claudia Borries

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Final revised paper (published on 08 Dec 2023)
Preprint (discussion started on 15 Sep 2023)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-1495', Anonymous Referee #3, 16 Sep 2023

This manuscript presented the application of the difference spectrum method to analyze the EISCAT multifrequency measurements in three campaigns to directly obtain ion-neutral collision frequency profiles. The fitting results is acceptable. Due to the lack of ion-neutral collision frequency measurement in the dynamo region, the method presented here is highly valuable.
This manuscript is well structured with careful writing. And the results and conclusions presented are clear and acceptable. I recommend this manuscript to publish without further revisions.

Citation: https://doi.org/10.5194/egusphere-2023-1495-RC1
- AC1: 'Reply on RC1', Florian Günzkofer, 19 Oct 2023
  
  We thank the Referee for taking the time to read our manuscript and for their positive feedback.
  
  Citation: https://doi.org/10.5194/egusphere-2023-1495-AC1
RC2:
'Comment on egusphere-2023-1495', Anonymous Referee #2, 06 Oct 2023

The paper applied the difference spectrum method to obtain the Ion-neutral collision frequency profiles by actual measurements. The results were compared to previous measurements and models. It is a good work to verify the theory to measure collision frequency profiles by ISR. I recommend the paper to be published. Although I have some questions:
1. As you mentioned in the paper, you compare the difference of the scaling parameter β depending on the altitude. Do you analyze its change with time? What is the suitable strategy to choose the scaling parameter β?
2. If the frequency of two ISRs is close. Does the frequency difference of ISR effect the measurements?

Citation: https://doi.org/10.5194/egusphere-2023-1495-RC2
- AC2: 'Reply on RC2', Florian Günzkofer, 19 Oct 2023
  
  We thank the Referee for taking the time to review our paper. Please find the responses to your questions below.
  Referee:
  As you mentioned in the paper, you compare the difference of the scaling parameter β depending on the altitude. Do you analyze its change with time? What is the suitable strategy to choose the scaling parameter β?
  Authors:
  We determine the β parameter profile for each 60s integration window separately. The β profiles shown in Figure 4 are the median profiles of the respective campaigns. The β value does not show a significant trend over the course of one campaign (few hours) at any altitude. Since the β parameter is introduced to account for technical differences between the UHF and VHF systems, changes within a few hours are not expected. However, there are distinct outliers for some integration windows, presumably during which one of the instruments failed to measure a clear ISR spectrum allowing for analysis. Therefore, median statistics was chosen as the appropriate strategy to determine the scaling parameter β.
  
  Referee:
  If the frequency of two ISRs is close. Does the frequency difference of ISR effect the measurements?
  Authors:
  The important parameter here is not the difference of radar frequencies but their ratio ξ. As described in Equation 3, the simultaneous UHF and VHF measurements are similar to two UHF measurements at ν_in and ξν_in. This causes the difference of the two spectra. For a ξ ratio close to unity, the difference spectrum is extremely weak and overshadowed by measurement uncertainties. Inferring the ion-neutral collision frequency is therefore only possible for an ξ ratio distinctly larger than 1 (4.2 for the EISCAT systems).
  
  Citation: https://doi.org/10.5194/egusphere-2023-1495-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Florian Günzkofer on behalf of the Authors (23 Oct 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (25 Oct 2023) by Wen Yi

ED: Publish as is (14 Nov 2023) by Wen Yi

AR by Florian Günzkofer on behalf of the Authors (15 Nov 2023) Manuscript

Short summary

Electric currents in the ionosphere can impact both satellite and ground-based infrastructure. These currents depend strongly on the collisions of ions and neutral particles. Measuring ion–neutral collisions is often only possible via certain assumptions. The direct measurement of ion–neutral collision frequencies is possible with multifrequency incoherent scatter radar measurements. This paper presents one analysis method of such measurements and discusses its advantages and disadvantages.