the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Jul 2025
First results from the equatorial geomagnetic station at Entoto Observatory and Research Center
Abstract. This paper presents the initial results from the newly deployed Entoto Magnetometer Station near Addis Ababa, Ethiopia, a collaborative project involving the South African National Space Agency (SANSA), the Space Science and Geospatial Institute (SSGI) in Ethiopia, and the German Centre for Geosciences (GFZ). The station, equipped with a LEMI-025 fluxgate magnetometer and a GSM-90 Overhauser sensor, aims to monitor geomagnetic field variations and enhance space weather research in the African sector. This deployment is a significant step in SANSA’s efforts to establish a comprehensive geomagnetic network across Africa, contributing to global space weather models. This is of particular importance, as the ENTOTO station is, to our knowledge, the only currently operational magnetic observatory near the dip equator in the African region, positioning the ENTOTO Observatory and Research Center at SSGI as a key contributor to regional and global geomagnetic research. Early observations show a good characterization of geomagnetic disturbances, with observed field changes aligning closely with the Dst index variations, which has important implications for space weather forecasting. The station also generates local K-index data for this region, providing valuable insights into ionospheric variability and its effects on technological systems. This paper details the station’s setup, data processing methodologies, and initial scientific results, laying the foundation for future research and collaboration in this critical area of space science.
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Status: closed
- RC1: 'Comment on egusphere-2025-2565', Anonymous Referee #1, 14 Jul 2025
-
RC2: 'Comment on egusphere-2025-2565', Chris Turbitt, 29 Jul 2025
Referee report: First results from the equatorial geomagnetic station at Entoto Observatory and Research Center, A. Nel1, N. Giday, M. Da Silva, D. Chekole, J. Matzka, Z. Isaacs, O. Bronkala, and L. Mogasa
Summary:
The authors have described a newly established geomagnetic variation station located close to the city of Addis Ababa, Ethiopia, designed to address the lack of ground-monitoring for space weather research in the region of North and East Africa. The authors have provided some analysis of initial data sets to show the sensitivity of the station to the local influence of the Equatorial Electroject and the station's representation of global geomagnetic disturbance. The paper is well presented, defining the aims of the new station, its detail and its application to the wider understanding of the impacts of space weather.
Referee Comment:
Line 48: Note INTERMAGNET does not operate observatories but rather enables exchange of data. The stations mentioned are (or were) operated by IPGP (AAE, MBO, SOK) and IPGP & CRAAG (TAM)
Figure 1. Error in caption. Longitude should read 38°48′24.1”E
Figure 1 suggests high magnetic gradients (up to 20nT/m) compared to the accepted recommendation of 1nT/m for a typical geomagnetic observatory (Jankowski & Sucksdorff, 1996). However, that recommendation is typically applied to absolute magnetic observatories, so may not be significant if this observatory is primarily designed for space weather monitoring. Can this be commented on, particularly given the statement in Line 90 on static disturbances?
Line 75 The definition of L9 is made further on in the paper but can it be included here as 'lower K = 9 limit'?
Line 58,84 Can these statements on the importance of an East African, equatorial station be strengthened by citation to literature on the requirement for regional space weather monitoring?
Line 113 Does the specification here of '1-second resolution' refer to direction or time? Could this be clarified?
Line 124 The term 'geomagnetic coordinate system' would be more accurately described as 'geodetic coordinate system' or 'geographic coordinate system' given the definition of the XYZ co-ordinate system
Line 131 Is the fact that the data are sampled at one-minute intervals contradictory to the 1-second resolution referred to in Line 124? Are the data down sampled or filtered to one-minute? If so, can this process be defined i.e. is a specific filter used?
Line 172 What are the sources of non-geomagnetic noise in this frequency band (> 2-minute period) and can these be filtered without attenuating the signal of interest in the same band?
Figures 9 & 10 The fitting of the mean daily maximum EEJ amplitude in the figures is close to the median daily maximum. If the daily maximum is normally distributed for both quiet and storm conditions, then the mean and the median will, of course, be equal but can it be confirmed that the plots show the mean and not the median?
Given the noted operational difficulties in maintaining long-term magnetic stations in the region, can the authors comment further on measures taken to ensure the ENTOTO station will continue to operate in the long-term? For example, are there formal long-term agreements in place between the institutes collaborating on this project?
Jankowski, J. and Sucksdorff, C. 1996. Manual on Magnetic Measurements and Observatory Practice, International Association of Geomagnetism and Aeronomy, Boulder, Co., 235 p. ISBN: 0-9650686-2-5, Chapter 3.1 Requirements for the observatory site
Citation: https://doi.org/10.5194/egusphere-2025-2565-RC2 -
EC1: 'Comment on egusphere-2025-2565', Anne Neska, 21 Aug 2025
Dear Authors,
Thank you for your submitted manuscript. We got reports from two referees now who agree that it treats a very valuable subject and is written well. They have only some questions and remarks mostly concerning clarity of the description. Therefore my decision is that your work qualifies as in need for just minor revision.
Please provide a revised version of your manuscript that clarifies the questions raised by the referees and takes into account their suggestions. Also. please provide them with an answer acknowledging their constructive and friendly feedback.
Best regards,
Anne Neska
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC1 -
AC1: 'Comment on egusphere-2025-2565', Amoré Nel, 10 Sep 2025
We thank the reviewers for their constructive and thoughtful comments. We have addressed each point and revised he manuscript accordingly. Please see detailed reponses in the document attached.
Citation: https://doi.org/10.5194/egusphere-2025-2565-AC1 -
EC2: 'Reply on AC1', Anne Neska, 10 Sep 2025
Dear Amoré Nel,
Thank you for your answer. However, it does not appear to contain any attached file. Can you check this?
Best regards,
Anne Neska
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC2 -
AC2: 'Reply on EC2', Amoré Nel, 11 Sep 2025
-
EC3: 'Reply on AC2', Anne Neska, 11 Sep 2025
Dear Amore Nel,
Thank you for uploading your answers on reviewers' comments. They seem constructive, complete, and convincing to me which is good.
Can you please also upload the revised version of your manuscript for final assessment and hopefully acceptation.
Thank you in advance,
Anne
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC3 -
AC3: 'Reply on EC3', Amoré Nel, 11 Sep 2025
-
AC4: 'Reply on AC3', Amoré Nel, 11 Sep 2025
And clean manuscript. Both sets along with response to reviewers were also uploaded on the MS Records platform.
-
EC4: 'Reply on AC4', Anne Neska, 11 Sep 2025
Thanks. I have read it and will accept it. Nevertheless, here some remarks for consideration:
1) In the Reference list, all upper case letters in publication titles are lower case - I am not sure if the journal's production department will fix this.
2) Please consider commenting on general accessibility of Entoto station data. As you said, an Intermagnet status (which would solve the data distribution problem) is not aimed at, but data of one of not many EEJ stations would be very valuable for a broader scientific community.
3) In the discussion during the editorial process an argument appeared which I have objections to (which, however, does not affect the manuscript itself). Somebody said that a magnetic gradient beneath an observatory would be problematic for the induction it caused. Please note that disturbing magnetic fields caused by electromagnetic induction are a consequence of the conductivity or resistivity (this is, the electrical properties) of underlying crustal rocks, whereas the magnetic gradient is caused by their magnetic properties. So these refer to two different physical properties which are not readily connected to each other. For the sake of scientific correctness I ask for a more precise wording also in a discussion. Thank you :-)
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC4 -
AC5: 'Reply on EC4', Amoré Nel, 12 Sep 2025
We thank the Editor for the valuable suggestions. Please find responses to the three remarks below;
1. We have now corrected the BibTeX `.bib` file accordingly by enclosing capitalised terms in braces to preserve formatting (e.g. `{Geomagnetic}`, `{EEJ}`, `{INTERMAGNET}`) and verified that the journal style file now renders them correctly in the reference list.
2. We thank the Editor for this excellent suggestion. In the revised manuscript, we have now included the following sentence at the end of the Data Availability section:
"The Entoto Magnetometer Station is not part of the INTERMAGNET network; however, we recognise the scientific value of sharing data from this equatorial variometer station. As such, the Entoto Magnetometer Station data are available for non-commercial scientific use upon request to the corresponding author. As a condition of use, users must cite this publication to acknowledge the source of the data and the contributions of the SANSA–SSGI–GFZ collaboration. Future steps may include integration into broader African or global networks via open-data agreements."
3. We fully agree with the Editor and appreciate the opportunity to clarify this point. We previously stated that
"These elevated gradients can give rise to small-scale induction effects, especially during geomagnetic storms, due to variations in subsurface conductivity."
We now realise this wording may misleadingly imply that the magnetic gradient causes the induction. We have revised that paragraph as follows:
"The gradient survey revealed localised crustal anomalies with values exceeding 10 nT/m in some areas. These elevated gradients are indicative of the magnetic properties of the underlying crustal rocks and do not, by themselves, imply enhanced electromagnetic induction. Induction effects, when present, arise from contrasts in subsurface electrical conductivity rather than from magnetic gradients. Both phenomena may coexist in complex geological settings and could introduce non-geomagnetic signals during storm times. However, since the Entoto Magnetometer Station operates as a variometer (rather than a full absolute observatory), its primary role is to capture temporal variations in the geomagnetic field. Any induction-related variability is therefore not expected to compromise the station’s scientific objectives, which focus on monitoring dynamic current systems such as the Equatorial Electrojet (EEJ) and storm-time magnetospheric responses."
Please let us know if further clarification is required. We are grateful for the constructive editorial process.
Kind regards
-
EC5: 'Reply on AC5', Anne Neska, 12 Sep 2025
Thank you very much for your excellent response. A further explanation is not required. Best wishes
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC5
-
EC5: 'Reply on AC5', Anne Neska, 12 Sep 2025
-
AC5: 'Reply on EC4', Amoré Nel, 12 Sep 2025
-
EC4: 'Reply on AC4', Anne Neska, 11 Sep 2025
-
AC4: 'Reply on AC3', Amoré Nel, 11 Sep 2025
-
AC3: 'Reply on EC3', Amoré Nel, 11 Sep 2025
-
EC3: 'Reply on AC2', Anne Neska, 11 Sep 2025
-
AC2: 'Reply on EC2', Amoré Nel, 11 Sep 2025
-
EC2: 'Reply on AC1', Anne Neska, 10 Sep 2025
Status: closed
- RC1: 'Comment on egusphere-2025-2565', Anonymous Referee #1, 14 Jul 2025
-
RC2: 'Comment on egusphere-2025-2565', Chris Turbitt, 29 Jul 2025
Referee report: First results from the equatorial geomagnetic station at Entoto Observatory and Research Center, A. Nel1, N. Giday, M. Da Silva, D. Chekole, J. Matzka, Z. Isaacs, O. Bronkala, and L. Mogasa
Summary:
The authors have described a newly established geomagnetic variation station located close to the city of Addis Ababa, Ethiopia, designed to address the lack of ground-monitoring for space weather research in the region of North and East Africa. The authors have provided some analysis of initial data sets to show the sensitivity of the station to the local influence of the Equatorial Electroject and the station's representation of global geomagnetic disturbance. The paper is well presented, defining the aims of the new station, its detail and its application to the wider understanding of the impacts of space weather.
Referee Comment:
Line 48: Note INTERMAGNET does not operate observatories but rather enables exchange of data. The stations mentioned are (or were) operated by IPGP (AAE, MBO, SOK) and IPGP & CRAAG (TAM)
Figure 1. Error in caption. Longitude should read 38°48′24.1”E
Figure 1 suggests high magnetic gradients (up to 20nT/m) compared to the accepted recommendation of 1nT/m for a typical geomagnetic observatory (Jankowski & Sucksdorff, 1996). However, that recommendation is typically applied to absolute magnetic observatories, so may not be significant if this observatory is primarily designed for space weather monitoring. Can this be commented on, particularly given the statement in Line 90 on static disturbances?
Line 75 The definition of L9 is made further on in the paper but can it be included here as 'lower K = 9 limit'?
Line 58,84 Can these statements on the importance of an East African, equatorial station be strengthened by citation to literature on the requirement for regional space weather monitoring?
Line 113 Does the specification here of '1-second resolution' refer to direction or time? Could this be clarified?
Line 124 The term 'geomagnetic coordinate system' would be more accurately described as 'geodetic coordinate system' or 'geographic coordinate system' given the definition of the XYZ co-ordinate system
Line 131 Is the fact that the data are sampled at one-minute intervals contradictory to the 1-second resolution referred to in Line 124? Are the data down sampled or filtered to one-minute? If so, can this process be defined i.e. is a specific filter used?
Line 172 What are the sources of non-geomagnetic noise in this frequency band (> 2-minute period) and can these be filtered without attenuating the signal of interest in the same band?
Figures 9 & 10 The fitting of the mean daily maximum EEJ amplitude in the figures is close to the median daily maximum. If the daily maximum is normally distributed for both quiet and storm conditions, then the mean and the median will, of course, be equal but can it be confirmed that the plots show the mean and not the median?
Given the noted operational difficulties in maintaining long-term magnetic stations in the region, can the authors comment further on measures taken to ensure the ENTOTO station will continue to operate in the long-term? For example, are there formal long-term agreements in place between the institutes collaborating on this project?
Jankowski, J. and Sucksdorff, C. 1996. Manual on Magnetic Measurements and Observatory Practice, International Association of Geomagnetism and Aeronomy, Boulder, Co., 235 p. ISBN: 0-9650686-2-5, Chapter 3.1 Requirements for the observatory site
Citation: https://doi.org/10.5194/egusphere-2025-2565-RC2 -
EC1: 'Comment on egusphere-2025-2565', Anne Neska, 21 Aug 2025
Dear Authors,
Thank you for your submitted manuscript. We got reports from two referees now who agree that it treats a very valuable subject and is written well. They have only some questions and remarks mostly concerning clarity of the description. Therefore my decision is that your work qualifies as in need for just minor revision.
Please provide a revised version of your manuscript that clarifies the questions raised by the referees and takes into account their suggestions. Also. please provide them with an answer acknowledging their constructive and friendly feedback.
Best regards,
Anne Neska
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC1 -
AC1: 'Comment on egusphere-2025-2565', Amoré Nel, 10 Sep 2025
We thank the reviewers for their constructive and thoughtful comments. We have addressed each point and revised he manuscript accordingly. Please see detailed reponses in the document attached.
Citation: https://doi.org/10.5194/egusphere-2025-2565-AC1 -
EC2: 'Reply on AC1', Anne Neska, 10 Sep 2025
Dear Amoré Nel,
Thank you for your answer. However, it does not appear to contain any attached file. Can you check this?
Best regards,
Anne Neska
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC2 -
AC2: 'Reply on EC2', Amoré Nel, 11 Sep 2025
-
EC3: 'Reply on AC2', Anne Neska, 11 Sep 2025
Dear Amore Nel,
Thank you for uploading your answers on reviewers' comments. They seem constructive, complete, and convincing to me which is good.
Can you please also upload the revised version of your manuscript for final assessment and hopefully acceptation.
Thank you in advance,
Anne
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC3 -
AC3: 'Reply on EC3', Amoré Nel, 11 Sep 2025
-
AC4: 'Reply on AC3', Amoré Nel, 11 Sep 2025
And clean manuscript. Both sets along with response to reviewers were also uploaded on the MS Records platform.
-
EC4: 'Reply on AC4', Anne Neska, 11 Sep 2025
Thanks. I have read it and will accept it. Nevertheless, here some remarks for consideration:
1) In the Reference list, all upper case letters in publication titles are lower case - I am not sure if the journal's production department will fix this.
2) Please consider commenting on general accessibility of Entoto station data. As you said, an Intermagnet status (which would solve the data distribution problem) is not aimed at, but data of one of not many EEJ stations would be very valuable for a broader scientific community.
3) In the discussion during the editorial process an argument appeared which I have objections to (which, however, does not affect the manuscript itself). Somebody said that a magnetic gradient beneath an observatory would be problematic for the induction it caused. Please note that disturbing magnetic fields caused by electromagnetic induction are a consequence of the conductivity or resistivity (this is, the electrical properties) of underlying crustal rocks, whereas the magnetic gradient is caused by their magnetic properties. So these refer to two different physical properties which are not readily connected to each other. For the sake of scientific correctness I ask for a more precise wording also in a discussion. Thank you :-)
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC4 -
AC5: 'Reply on EC4', Amoré Nel, 12 Sep 2025
We thank the Editor for the valuable suggestions. Please find responses to the three remarks below;
1. We have now corrected the BibTeX `.bib` file accordingly by enclosing capitalised terms in braces to preserve formatting (e.g. `{Geomagnetic}`, `{EEJ}`, `{INTERMAGNET}`) and verified that the journal style file now renders them correctly in the reference list.
2. We thank the Editor for this excellent suggestion. In the revised manuscript, we have now included the following sentence at the end of the Data Availability section:
"The Entoto Magnetometer Station is not part of the INTERMAGNET network; however, we recognise the scientific value of sharing data from this equatorial variometer station. As such, the Entoto Magnetometer Station data are available for non-commercial scientific use upon request to the corresponding author. As a condition of use, users must cite this publication to acknowledge the source of the data and the contributions of the SANSA–SSGI–GFZ collaboration. Future steps may include integration into broader African or global networks via open-data agreements."
3. We fully agree with the Editor and appreciate the opportunity to clarify this point. We previously stated that
"These elevated gradients can give rise to small-scale induction effects, especially during geomagnetic storms, due to variations in subsurface conductivity."
We now realise this wording may misleadingly imply that the magnetic gradient causes the induction. We have revised that paragraph as follows:
"The gradient survey revealed localised crustal anomalies with values exceeding 10 nT/m in some areas. These elevated gradients are indicative of the magnetic properties of the underlying crustal rocks and do not, by themselves, imply enhanced electromagnetic induction. Induction effects, when present, arise from contrasts in subsurface electrical conductivity rather than from magnetic gradients. Both phenomena may coexist in complex geological settings and could introduce non-geomagnetic signals during storm times. However, since the Entoto Magnetometer Station operates as a variometer (rather than a full absolute observatory), its primary role is to capture temporal variations in the geomagnetic field. Any induction-related variability is therefore not expected to compromise the station’s scientific objectives, which focus on monitoring dynamic current systems such as the Equatorial Electrojet (EEJ) and storm-time magnetospheric responses."
Please let us know if further clarification is required. We are grateful for the constructive editorial process.
Kind regards
-
EC5: 'Reply on AC5', Anne Neska, 12 Sep 2025
Thank you very much for your excellent response. A further explanation is not required. Best wishes
Citation: https://doi.org/10.5194/egusphere-2025-2565-EC5
-
EC5: 'Reply on AC5', Anne Neska, 12 Sep 2025
-
AC5: 'Reply on EC4', Amoré Nel, 12 Sep 2025
-
EC4: 'Reply on AC4', Anne Neska, 11 Sep 2025
-
AC4: 'Reply on AC3', Amoré Nel, 11 Sep 2025
-
AC3: 'Reply on EC3', Amoré Nel, 11 Sep 2025
-
EC3: 'Reply on AC2', Anne Neska, 11 Sep 2025
-
AC2: 'Reply on EC2', Amoré Nel, 11 Sep 2025
-
EC2: 'Reply on AC1', Anne Neska, 10 Sep 2025
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This is a well-written manuscript that can be recommended for publication after some re-writing has been done to address certain questions and concerns.