Peer review of: Evidence for low density holes in Jupiter’s ionosphere (2019)

Reviewers' comments:  

 

Reviewer #1 (Remarks to the Author):  

 

The dispersed pulses in Jovian atmosphere should prove to be of big interest to the scientific 
community, especially if as the authors suggest they are propagating through the ionospheric 
density holes.  

In short, the paper is well-written and structured and I recommend publication after minor fixes.  

 

Below follows a list of comments and suggestions, in case the attached PDF fails.  

 

L51: A short introduction is necessary for most readers, describing why JDPs are interesting and 
what they can reveal  

 

L56: "Jovian radii" - add 1Rj=... for convenience?  

 

L66: perhaps a short recap of the modes?  

 

L71: f_pe = 40 kHz - what is the basis of this assumption?  

 

L73: phenomenology = nature?  

 

L78: what about the other 47%?  

(do they have more than 16 ms between? why not include them too?)  

 

L80: which original set?  

 

L86-88: from the figure it seems that there are actually two distributions, this is very interesting and 
should be discussed  

 

L97: this is very specific, why 300km?  

 

L108-111: this is a bias then, can it be corrected for? perhaps by filtering the longitudes with high 
auroral emissions (and then showing in an extra figure)?  

 

L112: bad start of a sentence, consider rephrasing,  

e.g., "the locations of the JDP source are.... suggesting...." or similar  

 

L128-132: Question: Is it a "trivial" knowledge that the lightnings occur all the time, but the pulses 
are seen only when an ionospheric "hole" is present allowing the wave to pass? If this is the case, I 
think it would be useful to highlight this somewhere here - using JDPs as hole detectors should prove 
useful.  



Figure 2: consider recoloring the cum. prob. axes to orange for consistency  

 

Figure 2: considering that there are no counts above 13 ms, the histograms could be "zoomed" a bit 
to make the peaks more distinguishable - unless 16 ms is somehow important?  

 

L182-183: errorbars in the figure to match these would make interpretation much easier, even if it's 
just one generic "legend" of uncertainty (i.e., for one point)  

 

Figure 3: the axis on the right plot is a bit too far from the labeled y-axis, consider adding tick values 
here as well  

 

Supplementary Figure 1: with this orientation of the figure, all of the y-axes appear upside down, 
which is a bit inconvenient to read - consider rotating the figure clockwise, or rotating the y-axes 
labels  

Supplementary Figure 2: the blue bars seems superfluous (and confusing), if the sferic events are 
detected all the time during these intervals, why not just indicate this?  

 

 

Reviewer #2 (Remarks to the Author):  

This paper presents the first detection of a new form of radio emission, Jupiter dispersed pulses. The 
authors hypothesise that these radio pulses are linked to jovian lightning bursts due to the 
coincidence of events with sferics and Whistler waves.  

 

The paper is interesting - new radio emission forms are quite exciting! - and worthy of publication 
after the following points are addressed:  

 

Line 78: Figure 2b contains only 53% of the detections as it focuses on repeating JDP pulses with a 
repetition time less than 16 ms. What about the remaining 47% of the data? Are those events single 
pulses? What is the importance of this inter-pulse spacing? Does it strengthen the case for lightning 
bursts driving the emission?  

 

Line 106 - 111: What about the region between 200 to 280 degrees where JDPs are present in the 
southern hemisphere, but neither sferics nor Whistlers are observed? There are additional locations 
where there are unique events of each type. It’s not obvious that the correlation between JDPs and 
sferics is as strong as suggested by the authors.  

 

Line 130 - 132: Is the lack of JDPs observed around the jovicentric equator an observational artefact 
due to the upper recordable frequency of the instrument? This upper limit has already been 
mentioned in line 68 as the reason that only 2% of cases are seen with frequencies above fce. 
Clarification is needed.  

 

Supplementary figure 3 and associated discussion in lines 141 - 143: Due to Juno’s orbit, 
measurements of JDPs and sferics is biased towards the terminator. The discussion should be 
tempered with respect to the local time coverage or that bias should be more explicitly stated in 
text. The phrasing “it is possible that the radio locations of JDPs observed by Juno and postulated 
ionospheric holes are both on the night side where a different recombination process from the day 
side is anticipated” is unclear.  

 

 

 

Reviewer #3 (Remarks to the Author):  

 

This reviewer found that the paper could be interesting to multidisciplinary readers but the work 
lacks strong and definitive evidence and analysis to support the conclusions.  

Major comments:  

1. The authors assumed the sources for the JDPs were produced by lightning below Juno, 
which might be correct but needs more definitive data to unambiguously support their claim. In 
figure 3 the authors compared the Juno positions when the JDPs were detected with the whistler 
and MWR (500 MHz) source positions and claimed that the JDPs were detected in the same general 
regions and inferred them as related to lightning. It is not clear from the main text and the 
supplementary material if the three types of observation were coordinated in time and space. 
Coordinated or not, the majority of the JDPs appear to be detected along different Juno orbital 
trajectories as compared to the other two observations. If they were coordinated, one should expect 
a MWR detection for each of the JDPs. The authors provided two events in Supplementary figure 2 
that appear to be detected at the same time (within 100 ms) and position by MWR. However, 2 out 
of 445 appears to be a very small fraction and the authors need to rule out the chance of random 
coincidence.  

2. The dispersion model (assuming it good enough for the ionosphere) used by the authors in 
Method is more sensitive to D than to Ne0 to fit the observed dispersion curve, therefore, one 
would expect D to have a smaller scattering range than Ne0. However, figure 2c shows the opposite 
with D scattering in ~4 orders of magnitude and Ne0 in ~2 orders of magnitude. In addition, the 
paper lacks the necessary error analysis for D, Ne0 and C, making the critical results of Ne0 less 
confident. If a Taylor expansion is used to approximate the authors’ model, one can see that the 
dispersion is proportion to the product of D and Ne0 to the first order, and therefore will naturally 
leads to the general feature of figure 2c (regardless of the scattering ranges), i.e., a smaller D will 
require a larger Ne0. So the authors’ statement in line 86 “The distribution are not random, but 
show a systematic tendency of increases in Ne0 as D decreases” does not necessarily support the 
accuracy or validity of the model.  

3. The small values of the model-fitted Ne0 are used to conclude the existence of ionosphere 
“holes”. To assure the fitted Ne0 values are reasonable, it would be beneficial to correlate the Ne0 
with the cutoff frequency of the JDPs. If a positive correlation exists between the two, the inferred 
results would be more believable, at least qualitatively. The authors have the information of the 
cutoff frequencies and should have used them.  

4. The authors claim two peaks in figure 2b for the inter-pulse time separation. A statistical 
significance analysis is needed to support the claim.  

 
Minor comments:  

1. 

Line 53. Specify the frequency range here. I found it to be 150 kHz much later in the text.  

Line 57. Suggest change “All of the pulses were detected at altitude between 9790 km and 

2. 
316,000 km above the 1 bar level.” to “All of the pulses were detected while Juno was at altitude 
between 9790 km and 316,000 km above the 1 bar level”. I first thought the radio sources were at 
these altitudes.  

Lines 57-59, sentence starts with “These…”. Why is this important? The radio propagation 

3. 
would be affected by the entire path from the source to Juno but not only the local condition at 
Juno, unless the entire path can be assumed to have the same fce and fpe.