This document is very clear in its description of valuable measurements made from a Portuguese ship in the Atlanic Ocean. Important "clean" data sets are provided. I congratulate the authors, and I hope that their observations will be further used for research purposes.

I only found one error; on line 222, "dully "should be replaced by "duly".

Review of “The SAIL dataset of marine atmospheric electric field observations over the Atlantic Ocean” by Susana Barbosa et al.

Susana Barbosa has devoted valuable attention to making scientific observations from a Portuguese Navy ship.  I this work the emphasis lies with the measurement of the fair-weather electric field.  At a time of resurging interest in the monitoring of the global electric circuits, these efforts are most welcome.  The work definitely deserves to be published, but some suggestions come to mind for improving the final submission.  These substantive issues are followed by detailed comments/edits on the text.

Summary:  Publish after major revision

Substantive Issues:

• Sources for the DC global circuit

Thunderstorms are given emphasis (page 1, line 14) as the source for the global circuit, but recent work by Mach et al. (2009, 2010) have substantiated the prescient suggestions of CTR Wilson (1921), a paper cited by the authors, that electrified shower clouds may play an equally important role.  It is recommended that the authors study the relevant sections of Wilson (1921) and then modify their Introduction slightly.

• Absolute calibration of electric field

The one aspect of this work in most need of additional attention is the absolute calibration.  And this is never a trivial task.  The E field magnitudes in Figures 5, 6, 8 and 9 are low.  The Carnegie Curve” field is low by roughly a factor of two. This reviewer needs clarification of procedure.  The very best thing to have done is to place the second sensor “on shore” but perhaps more rigorously than what is reported in line 136 on page 6, to mount the CS-110 flush-mounted on a large planar surface on the dock and well out of influence of the mast and rigging of the ship.  (If flush-mounted the makers of the CS-110 have a sound procedure for absolute calibration.)  Then one makes simultaneous recordings on shore (i.e., the flat dock) and on the ship mast in fair weather conditions to get the best form-factor for the ship’s installation.  The shore measurement is the absolute reference.

The procedure described above is exactly what members of the Carnegie Institution did with the calibration of the E field on the Maude, though instead of using a flat dock, they used the flat Arctic ice sheet in the vicinity of the ship, when it was locked in the ice.

Now if this rigorous procedure has not been undertaken, I am not quite sure what to suggest.  One could adjust the mean value in Figure 6 to match the Carnegie ship measurements, or more recent ones undertaken by Wilson and Cummins (2021) on measurements made (also with CS-110 instruments) on buoys at sea off the coast of Florida.

Wilson, J. G., & Cummins, K. L. (2021). Thunderstorm and fair-weather quasi-static electric fields over land and ocean. Atmospheric Research, 257, 105618. https://doi.org/10.1016/j.atmosres.2021.105618

 Neither adjustment may be appealing to the authors, so I am hoping the more rigorous treatment has been pursued, or could still be pursued.  The mean values of 119 V/m reported in line 140 (page 7) is close to the Carnegie mean value of 130 V/m and in Figure 7 I see an eyeball mean near 120 V/m.  So now I wonder if this normalization was applied to the analysis in Figure 9, why isn’t the mean value roughly twice what is shown here?

I do think something can be done to improve the situation overall.

• Spikes in Figure 6

Isn’t it likely that the spikes in Figure 6 in the purple record for the pier are due to cultural activity on the pier near the CS-110 that could not be completely suppressed?

• Selection of common time series for two scenarios

I think data plots of the kind shown in Figure 6 transformed to a scatterplot in Figure 7 is a a good way to calibrate one field recording against another.  I would suggest however the calculation of a formal correlation coefficient between the two records as further quantitative evidence that you are measuring (mostly) a common E field imposed on both instruments.

• Confusion about data “while navigating” and “in port”

Here I cited line 70 on page 3 and line 86 on page 4.  In Figure 2, does the “land” flag mean being in port and not under sail (“navigating”.   Please clarify all in the text.

• Energy bandwidth of gamma ray source

The information provided in line 63 on page 3 is relevant to an earlier interest on the reviewer’s part in seeing whether electron runaway may have been occurring during precipitation events at sea.  However, the rather low min value for gamma ray energy (475 keV) will allow for radon daughter products and that could dominate any event.  To be more certain about real electron runaway, this lower threshold would be need to be substantially higher.  See also Chilingarian (2018).

Chilingarian, A. (2018). Long lasting low energy thunderstorm ground enhancements and possible Rn-222 daughter isotopes contamination. Physics Review D, 98, 022007. https://doi.org/10.1103/physrevd.98.022007

Detailed comments/edits on the text:

Page 1

Line 14   Add “and electrified shower clouds”

Line 22 “variation of global thunderstorm activity”

Page 23 delete “throughout the Earth”

Page 2

Line 24   change “at the end of the day” to “late in the day”

Line 27 “came to be known”

Line 28  Can also cite Markson (BAMS, 2007)

Line 31  “The need for such observations…”

Line 34  Interesting.  I had forgotten about this.  That should be checked again sometime, maybe by this group.

Line 41  The inclusion of a photo of the ship with mast and rigging would be helpful here.

Line 44   “arrived in Lisbon”

Line 48   Why is the microsecond precision so important for your endeavors here?

Line 53  Suggest change from “rotating” to “oscillating”

Line 53  “at a height”; No problem of E field shielded by conductive rigging?

Line 56  I think you need more details about “radon gas progeny” (the same suggestion I made for your other recent manuscript).

Page 3

Lines 59-61  Think you need to tie together better the visibility variable and the conductivity variable, with aerosol being the key physical linkage.

Line 65   Clarify why “pointing upwards”?

Line 68  Is the outgoing also shortwave, or rather longwave radiation?

Page 4

line 74  change “voids” to “missing segments”

line 78 “to foster their reuse”

line 86  This seems contradictory with line 70 on the previous page.

Figure 2 caption should tell what total time was involved.

Line 94  2 meter height over flat terrain? (Your procedure is not entirely clear to me.)

Page 5

Lines 102-103   Your procedure is not completely clear to me

Line 106   4 V/m is a small fraction of typical fair weather fields

Figure 3: minor DC offsets

Figure 4:  only Campbell (CS-110) people will know how to interpret these results (and me!)

Page 6

Line 112   Suggest adding: “The electric field is downward-directed in fair weather conditions”

Line 118  “applying these procedures to the raw data”

Line 133  This suggests that only height is included but it is more complicated than that I think.

Lines 135-136  Use of photos here would be helpful.

Line 138  Calculation of correlation coefficient would be helpful here.

Page 7

Line 141 Quantify the correlation.

Figure 6 caption:  Add a statement about the weather condition for this short period of data.

Page 8

Figure 7   What is the origin of the points beneath the main linear scatter?  It would be useful to give the overall correlation coefficient.

Line 150  What are the details of the height-corrected data?

Line 156  “as a fully-ocean day”

Page 9

Line 162  Are “marine observations” all ocean days?

Line 166  Add a sentence about the quantitative comparison: the Carnegie curve amplitude variation is +/- 15% as I recall.

Figure 9 is a very valuable result, but it would be nice if the absolute field were more accurate (see earlier remarks in item (2) above.

Line 172  This reminds me of the spike in Figure 6 (top record).  What do you attribute that to?

Line 174  What is the “jupyter notebook”?

Page 10

Line 175  “what is “Zenodo”?

Figure 10  What do you think causes the spikes?   Could they be chunks of radioactivity coming over?  The first author is well-suited to answering this question.

Line 184 “are consistently high”   They are constant.   Discuss that limit (40 km) (see line 67 on page 3)

Page 11

Figures 11 and 12  Why not show solar radiation for the same two days shown for visibility?  This would help point up the internal consistency of the overall data archive.

Line 204  “jupyter notebook”???

Page 12

Line 213 “include”

Line 222 “duly” ???

Section 5   Should this follow the Conclusions, or rather appear in an Appendix?

Page 14

What did the Portuguese Navy get out of the useful project?

End review

Earle Williams

This data paper presents and summarises the data obtained during the SAIL voyage. As the authors indicate, this dataset is important for long term monitoring of atmospheric electricity which, in turn, is important for long term environmental change. The data and how they were obtained are described fully and carefully, though I have added some minor suggestions below that I hope could improve clarity.

As the authors suggest, the electric field measurements appear reliable, but look likely to have been influenced by the ship’s geometry.  The field mills are calibrated in that they give readings in Volts per metre, and the relative variations in the data are still valid, for example the Carnegie-like curve in figure 9. However, without some sort of quantification of the reduction factor to account for the geometrical screening from the ship, comparisons of the absolute values are almost impossible. There seem to be two ways to work out the geometric factor to “reduce” the data to an idealised situation. The first approach would be to carry out more measurements with the sensors on the ship, which is probably no longer possible. Another approach, which may be more suited to retrospective analysis, is to use an electrostatic model of the ship geometry to work out the distortion at the position of the sensors.

This paper is worthy of publication without this reduction factor, which may take some time to evolve (as I believe it did for the original Carnegie voyages), but the authors do need to discuss this issue more than they do in the manuscript I saw.

Minor comments

L 24 clarify that the timings are in local time

L30 might be good to spell out what you mean by these (eg aerosol) since you talk about pollution later

L82 please add a brief description of what the logging errors were and how they were corrected so the reader does not have to refer to the reference

Figure 2 please spell out the colour scheme again so the figure can be understood without looking at Figure 1

L95 it isn’t clear what you mean about the “default value of the sensor” when they were at different heights, please reword.

Figs 3 and 4 please define box, whisker and outlier criteria

Fig 5 please label plots (a) (b) etc and refer to them in the text. It looks like 12 is missing from the y axis of the E2 plot bottom left.

Fig 6 list date and location of these measurements in caption for completeness

Fig 8 Is the daily median difference plot a Gaussian distribution? I would expect it to be, but the plot suggests it might be a little skewed. Could the authors please do a statistical test for “normality” and discuss the origin of any “non normality”? Or repotting the histogram so that data looks more Gaussian might also help.

L190 is it not more rigorous to replace any negative values with NA rather than assuming they are zero?

Table 1 should be “dry bulb” and “wet bulb” temperature

COMMENTS TO THE AUTHOR(S)

The preprint manuscript detailing the SAIL dataset of marine atmospheric electric field observations over the Atlantic Ocean is a significant contribution to the field of atmospheric science. It provides a comprehensive dataset that is well-documented and made publicly available, which is a strength of the study. The authors have taken care to ensure the traceability and reproducibility of the data curation chain, which is essential for such datasets to be useful in the scientific community. The manuscript is well-structured, and the findings are presented clearly, making the paper accessible to a broad audience. The interdisciplinary relevance of the dataset, spanning atmospheric electricity, climate variability, and space-Earth interactions, is well-articulated.

But I am concerned about the following points：

Major:

1. Data Interpretation and Context: While the dataset is extensive and valuable, the manuscript could benefit from a more detailed discussion on the implications of the observed diurnal variability of the atmospheric electric field. Specifically, how do these observations compare with existing models of the global atmospheric electric circuit, and what new insights do they provide regarding the influence of thunderstorm activity on this circuit?
2. Ancillary Data Analysis: The manuscript mentions ancillary measurements such as gamma radiation, visibility, and solar radiation. It would be beneficial to include a more detailed analysis of these variables in relation to the electric field data. For instance, are there any correlations between gamma radiation spikes and changes in the atmospheric electric field, and if so, what might be the atmospheric or climatic implications?
3. Comparison with Other Studies: The paper references previous studies and observations, such as the Carnegie curve. It would enhance the manuscript if the authors could include a comparison of their findings with these historical data, discussing any deviations and potential reasons for them.

Minor:

1. Consistency in Units: There appears to be an inconsistency in the use of units for gamma radiation measurements. The manuscript should be reviewed to ensure that all units are used consistently and are clearly defined.
2. Grammerly: Some sentences are structurally complex, which may hinder understanding. The authors are encouraged to simplify these sentences to make the article more accessible.