the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Jul 2025
The Role of Point Discharge in the Development of Atmospheric Electricity
Abstract. Point discharge, like lightning, is an atmospheric electricity process which has been observed directly and indirectly for centuries. Point discharge occurs when an electric field is enhanced at a point, causing local ionisation of the air and allowing a current to flow between the object and atmosphere. Point discharge sensors are simple instruments which measure the discharge currents caused by enhancements of the atmospheric electric field. In the early 20th Century, several milestone atmospheric electricity investigations were performed which employed the effects of naturally occurring point discharge currents and the measurements made by point discharge sensors. Point discharge was central to some of the arguments made in the proposal of the global atmospheric electric circuit, and the early evidence found to support this model. Point discharge sensors continued to be used throughout the 20th and 21st centuries, with understanding of their operations being developed further in this time.
Competing interests: At least one of the (co-)authors is a member of the editorial board of History of Geo- and Space Sciences.
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 paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 20 Aug 2025)
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RC1: 'Comment on hgss-2025-4', Michael J. Rycroft, 24 Jul 2025
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This clearly written paper provides an interesting historical review of the phenomenon of point discharge currents (PDCs) from pointed objects on the ground to the surrounding atmosphere, and their relationship to the ambient atmospheric electric field (whose magnitude is the potential gradient, but with the opposite sign).
Section 2 valuably discusses PDC observations made about a century ago. I wonder whether it would be good to use the data shown in Fig. 2 to plot a graph, having twelve points, showing PDC (y-axis) against Thunderstorms (x-axis), The correlation coefficient could be calculated, and the significance of the result assessed. Then thunderstorms having a dipole structure or a tripole structure are usefully discussed.
Section 3 considers other PDC observations, such as using radiosondes. Who was the S. Chapman mentioned (around line 200)? The eminent physicist Sydney Chapman? Aircraft, rocket and spacecraft observations are further discussed. In Fig. 4 I wonder whether Rocket nose cone would be a better term than Rocket warhead. Further, various ground-based observations and measurements using trees are also reviewed.
Section 4 presents analytical and theoretical considerations of the topic.
Sections 5 gives the Conclusions, concisely.
Here are some detailed points which, in my opinion, require attention before publication.
Line 7. .... electric circuit, and the early evidence was found to support this model. ...
28. ... its ...
Fig. 1a. It would be better to have a photograph showing a clear gap between the metal support of the point discharge instruments and the more distant tower. Fig. 1b. Is there a paper which describes this instrument? If so, please give a reference.
75. ... Earth; however, in areas ...
77. It was ...
114. ... ionosphere, and restoring ...
282. ... instruments; however, they still have ...
285. aircraft
288. It could be useful to state that this desert is in northern Mexico and southwestern USA.
308. ... understood, however, was ...
Acknowledgements. ... undertaking of BM's PhD project, ...
My answers to the 9 questions: YES to the first 8, and NO to number 9.
Thank you for the opportunity to read this useful and well written paper.
Michael Rycroft.
Citation: https://doi.org/10.5194/hgss-2025-4-RC1 -
AC1: 'Reply on RC1', Blair McGinness, 29 Jul 2025
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We thank the reviewer for considering our manuscript, and for the positive feedback.
We agree that correlation analysis of the data from Fig. 2 could be of benefit, and so will investigate this.
The two references of S. Chapman both refer to Seville Chapman.
The term “warhead” was used to align with the previous annotation, however we agree that “nose cone” is a more accurate description so will make this change.
A clearer photograph of the instruments in Fig. 1a will be obtained, showing the instruments separate from the tower in the background. Additionally, a citation to Marlton et al. 2013 will be included in the caption for Fig. 1b, as this paper describes the instrument.
Finally, we thank the reviewer for the further minor improvements suggested.
Citation: https://doi.org/10.5194/hgss-2025-4-AC1 -
RC2: 'Reply on AC1', Michael J. Rycroft, 30 Jul 2025
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Thank you, Blair, for your response, with which I am pleased.
I am pleased to know about the author, S. Chapman.
Best regards,
Michael Rycroft.
Citation: https://doi.org/10.5194/hgss-2025-4-RC2
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RC2: 'Reply on AC1', Michael J. Rycroft, 30 Jul 2025
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AC1: 'Reply on RC1', Blair McGinness, 29 Jul 2025
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EC1: 'Comment on hgss-2025-4', Kristian Schlegel, 31 Jul 2025
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This is a nice piece of work, a remarkably detailed historical account of the investigation of point discharges.
I have just a few comments:
I think the title does not reflect the historical aspect of the manuscript. Therefore the term historical may be included in the title. Something like: „The Role of Point Discharge in the historical Development…“
Perhaps it could be mentioned in section 2 that already in 1888 Elster and Geitel developed an instrument to measure the charge of raindrops:
Ueber eine Methode, die elektrische Natur der atmosphärischen Niederschläge zu bestimmen (Oktober 1887)
Meteorologische Zeitschrift, 5.Jg. März-Heft, 1888, S.95-100Isn’t it worth to mention Reinhold Reiter’s extensive work when discussing the PG investigations? Particularly his measurements at a cable car.
e.g.: Harrison and Schlegel, Hist. Geo Space. Sci., 14, 71–75, https://doi.org/10.5194/hgss-14-71-2023, 2023What means the abbreviation FFAR in the caption of Fig. 4 ?
Citation: https://doi.org/10.5194/hgss-2025-4-EC1 -
AC2: 'Reply on EC1', Blair McGinness, 06 Aug 2025
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We thank the editor for these comments.
We agree that including the term historical would make the title more appropriate.
We agree that the citations suggested are valuable, and so will include these.
The acronym FFAR means Folding-Fin Aerial Rocket. The caption of figure 4 will be edited to include this information.
Citation: https://doi.org/10.5194/hgss-2025-4-AC2 -
RC3: 'Reply on AC2', Michael J. Rycroft, 07 Aug 2025
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Citation: https://doi.org/
10.5194/hgss-2025-4-RC3
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RC3: 'Reply on AC2', Michael J. Rycroft, 07 Aug 2025
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AC2: 'Reply on EC1', Blair McGinness, 06 Aug 2025
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RC4: 'Comment on hgss-2025-4', Graeme Marlton, 11 Aug 2025
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Review of Manuscript: The Role of Point Discharge in the Development of Atmospheric
Electricity by Mcginess et al.
The manuscript is interesting, well written, and covers all the significant advances in point discharge current research within the atmosphere. It also provides historical references to the phenomena. Whilst comprehensive the end of the discussion section or beginning of the conclusions could benefit from a paragraph discussing the future potential of point discharge measurements in addition to the measurements being undertaken now. This will add to the historical context of the material already shown.
For example, It is clear McGinnes et al 2024 is using a Point Discharge sensors so a line on their research using the sensor would be useful
There are also some minor comments below which need rectification before publication.
L77 It instead of in
L127: It would be useful to define the convention of positive and negative PDC. i.e is negative PDC an outflow of electrons from the point as defined in Whipple and scrace. Furthermore it may be prudent to add the Potential gradient convention too.
L189: Consider a paragraph break here. This makes it easier to see there is a shift in discussion between the positive dipole and the lower positive dipole
L266: no r in Ksanfomality
L288: Import(ance)
L297: Bi -polar logarithmic electrometer
Equations (2, 3 and 4) Are the constants a, b and c universal values which can be used interchangeably between the equations. If not I’d suggest renaming them to different values to avoid confusion.
Citation: https://doi.org/10.5194/hgss-2025-4-RC4 -
AC3: 'Reply on RC4', Blair McGinness, 14 Aug 2025
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We thank the reviewer for considering our manuscript, and for the positive feedback given.
We agree that it would be beneficial to have some discussion of the future potential of point discharge, and so will include this.
We agree that defining a convention for the polarity of PDC (and providing a definition of PG) would improve clarity so will include these. In the example given (L127), an “outflow” of current refers to a conventional current flowing upwards (i.e a flow of negative charge downwards).
The constants a, b, c in equations 2, 3, 4 do not describe universal values - their interpretation varies across each equation. We agree that using different symbols for the constants in each equation would aid clarity, so will make this change.
We thank the reviewer for the additional minor improvements suggested.
Citation: https://doi.org/10.5194/hgss-2025-4-AC3
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AC3: 'Reply on RC4', Blair McGinness, 14 Aug 2025
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