the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Nov 2024
Leaping and vortex motion of the shock aurora toward the late evening sector observed on 26 February 2023
Abstract. On 26 February 2023, a shock aurora triggered by an interplanetary shock (IP shock) was observed in northern Scandinavia at 21 MLT. Previously, ground-based observations of shock auroras have primarily been conducted on the dayside, where IP shocks hit. However, this study successfully observed the shock aurora on the nightside at 21 MLT. This is the first time the morphology of a shock aurora has been observed on the nightside using ground-based cameras. We introduce the observational results by four ground-based cameras and a magnetometer network in the northern hemisphere. Previous observations have shown that shock auroras consist of two types of optical signatures, i.e., diffuse and discrete auroras, with a few minutes of separation. In this study, three distinct signatures were observed with a few minutes lags: (1) a luminosity enhancement of an arc-shaped green aurora, (2) the appearance of red auroras, and (3) leaping of discrete auroras towards the nightside (antisunward) with a vortex-like structure. While red emissions have been previously observed in shock auroras, this is the first time undulating and jumping structures have been discovered. Comparison with equivalent currents estimated from the magnetometer network showed that the first luminosity enhancement occurred within one minute after the onset of the geomagnetic variation induced by the IP shock, so-called geomagnetic sudden commencement (SC), and the red aurora observed after the formation of upward field-aligned currents over northern Scandinavia. Furthermore, the propagation speed of the aurora in (3) had the same order as the solar wind speed in interplanetary space, as reported in previous studies. These newly identified morphological features of the shock aurora provide valuable insights into how current systems associated with SC propagate towards the nightside.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Annales Geophysicae. The peer-review pro- cess was guided by an independent editor, and the authors also have no other competing interests to declare.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.-
Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-3277', David Knudsen, 04 Jan 2025
Shock aurora is scientifically interesting because it results from a very specific driving impulse in the solar wind. While primary effects appear on the dayside of the Earth, this paper documents nightside signatures, which are rare and difficult to detect. The information gained is useful in understanding the magnetospheric mechanisms involved in the generation of shock aurora. This paper is a clear presentation of relevant observations including some newly-discovered phenomena. I believe it will be a valuable contribution to the literature. I have only a few minor technical/grammatical comments:
line 7: "lag" instead of "lags"
line 18: "Solar wind conditions are one of the most crucial parameters...". Suggest "...among the most crucial..." (since "conditions" is plural and inconsistent with "one of".)
line 86: "Only photometer observations with a narrow and zonal field of view". Suggest you remove "and"; I believe you mean a FOV which is narrow in the zonal direction, i.e. a narrow zonal FoV.
line 150: "initially appeared aurora": suggest "aurora which appeared initially"
line 289: "stational folding": not sure what's meant here. Do you mean spatial folding?
Citation: https://doi.org/10.5194/egusphere-2024-3277-RC1 -
AC1: 'Reply on RC1', Sota Nanjo, 07 Jan 2025
Thank you very much for reviewing and evaluating our manuscript. We appreciate your thoughtful comments and suggestions for improvement. We will address all the technical and grammatical issues you pointed out, including clarifying "stational folding" as "spatial folding."
Your feedback has been very helpful, and we believe it will enhance the clarity and quality of our paper.
Citation: https://doi.org/10.5194/egusphere-2024-3277-AC1
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AC1: 'Reply on RC1', Sota Nanjo, 07 Jan 2025
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RC2: 'Comment on egusphere-2024-3277', Anonymous Referee #2, 04 Mar 2025
This paper examines a shock aurora event on 26 February 2023 in northern Scandinavia, marking the first time such nightside auroral features have been captured by ground-based cameras. Using high-resolution all-sky imagery and magnetometer data, the study identifies three distinct auroral forms—a pre-existing green arc, a red diffuse aurora, and a secondary discrete arc exhibiting unique leaping and vortex-like motions. These observations are correlated with geomagnetic sudden commencement and field-aligned current signatures, offering new insights into solar wind interactions with the nightside ionosphere. The manuscript is well written and is recommended for prompt publication after minor suggested changes.
Apart from the suggestions from Reviewer 1, I recommend that the authors provide an introduction to ionospheric equivalent currents, as these are crucial for the analyses in Figures 5 and 6. An explanation of how equivalent currents relate to field-aligned currents (in terms of strength and direction, for example) would enhance the clarity of the discussion.
A minor question on Figure 1: the negative Bz and sudden increase in Pdyn appear roughly 50 minutes before the SC, as shown in the H component. Does this time difference arise from the solar wind’s propagation from L1 to Earth? Normally, a propagation algorithm is used to remove for that delay.
Citation: https://doi.org/10.5194/egusphere-2024-3277-RC2 -
AC2: 'Reply on RC2', Sota Nanjo, 04 Mar 2025
Thank you for your constructive feedback on the manuscript. I fully acknowledge your suggestions and will revise the paper accordingly.
Regarding the explanation of equivalent currents, I will add a detailed description to clarify their relevance to the analyses presented in Figures 5 and 6. Specifically, I will explain how equivalent currents are related to field-aligned currents to improve the connection to the discussion.
In response to your question about the time difference between the solar wind data and ground-based data in Figure 1, I will revise the manuscript to emphasize that this delay is due to the fact that the DSCOVR satellite at L1 observes the solar wind, and the corresponding effects on the Earth's magnetic field are observed at the ground with a time delay. The time difference has been preserved in the plot by using the data provided by the NOAA's website in order to avoid any potential misunderstanding that could arise from altering the data.
Thank you once again for your valuable suggestions.
Citation: https://doi.org/10.5194/egusphere-2024-3277-AC2
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AC2: 'Reply on RC2', Sota Nanjo, 04 Mar 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-3277', David Knudsen, 04 Jan 2025
Shock aurora is scientifically interesting because it results from a very specific driving impulse in the solar wind. While primary effects appear on the dayside of the Earth, this paper documents nightside signatures, which are rare and difficult to detect. The information gained is useful in understanding the magnetospheric mechanisms involved in the generation of shock aurora. This paper is a clear presentation of relevant observations including some newly-discovered phenomena. I believe it will be a valuable contribution to the literature. I have only a few minor technical/grammatical comments:
line 7: "lag" instead of "lags"
line 18: "Solar wind conditions are one of the most crucial parameters...". Suggest "...among the most crucial..." (since "conditions" is plural and inconsistent with "one of".)
line 86: "Only photometer observations with a narrow and zonal field of view". Suggest you remove "and"; I believe you mean a FOV which is narrow in the zonal direction, i.e. a narrow zonal FoV.
line 150: "initially appeared aurora": suggest "aurora which appeared initially"
line 289: "stational folding": not sure what's meant here. Do you mean spatial folding?
Citation: https://doi.org/10.5194/egusphere-2024-3277-RC1 -
AC1: 'Reply on RC1', Sota Nanjo, 07 Jan 2025
Thank you very much for reviewing and evaluating our manuscript. We appreciate your thoughtful comments and suggestions for improvement. We will address all the technical and grammatical issues you pointed out, including clarifying "stational folding" as "spatial folding."
Your feedback has been very helpful, and we believe it will enhance the clarity and quality of our paper.
Citation: https://doi.org/10.5194/egusphere-2024-3277-AC1
-
AC1: 'Reply on RC1', Sota Nanjo, 07 Jan 2025
-
RC2: 'Comment on egusphere-2024-3277', Anonymous Referee #2, 04 Mar 2025
This paper examines a shock aurora event on 26 February 2023 in northern Scandinavia, marking the first time such nightside auroral features have been captured by ground-based cameras. Using high-resolution all-sky imagery and magnetometer data, the study identifies three distinct auroral forms—a pre-existing green arc, a red diffuse aurora, and a secondary discrete arc exhibiting unique leaping and vortex-like motions. These observations are correlated with geomagnetic sudden commencement and field-aligned current signatures, offering new insights into solar wind interactions with the nightside ionosphere. The manuscript is well written and is recommended for prompt publication after minor suggested changes.
Apart from the suggestions from Reviewer 1, I recommend that the authors provide an introduction to ionospheric equivalent currents, as these are crucial for the analyses in Figures 5 and 6. An explanation of how equivalent currents relate to field-aligned currents (in terms of strength and direction, for example) would enhance the clarity of the discussion.
A minor question on Figure 1: the negative Bz and sudden increase in Pdyn appear roughly 50 minutes before the SC, as shown in the H component. Does this time difference arise from the solar wind’s propagation from L1 to Earth? Normally, a propagation algorithm is used to remove for that delay.
Citation: https://doi.org/10.5194/egusphere-2024-3277-RC2 -
AC2: 'Reply on RC2', Sota Nanjo, 04 Mar 2025
Thank you for your constructive feedback on the manuscript. I fully acknowledge your suggestions and will revise the paper accordingly.
Regarding the explanation of equivalent currents, I will add a detailed description to clarify their relevance to the analyses presented in Figures 5 and 6. Specifically, I will explain how equivalent currents are related to field-aligned currents to improve the connection to the discussion.
In response to your question about the time difference between the solar wind data and ground-based data in Figure 1, I will revise the manuscript to emphasize that this delay is due to the fact that the DSCOVR satellite at L1 observes the solar wind, and the corresponding effects on the Earth's magnetic field are observed at the ground with a time delay. The time difference has been preserved in the plot by using the data provided by the NOAA's website in order to avoid any potential misunderstanding that could arise from altering the data.
Thank you once again for your valuable suggestions.
Citation: https://doi.org/10.5194/egusphere-2024-3277-AC2
-
AC2: 'Reply on RC2', Sota Nanjo, 04 Mar 2025
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Masatoshi Yamauchi
Magnar Gullikstad Johnsen
Yoshihiro Yokoyama
Urban Brändström
Yasunobu Ogawa
Anna Naemi Willer
Keisuke Hosokawa
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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