the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Oct 2023
Solar cycle signatures in lightning activity
Ronald Langer
Ivana Kolmašová
Ondřej Lhotka
Jan Rusz
Igor Strhárský
Abstract. The cross-correlation between lightning occurrence and cosmic ray intensity, solar activity and solar wind is examined on a global scale using data from the World Wide Lightning Location Network (WWLLN) for the period 2009 to 2022. The cross-correlation coefficients vary depending on the position on the globe. Positive cross-correlation between lightning occurrence and Sun spot number is found in most of Africa, South and Central America, while in parts of Europe and Southeast Asia the cross-correlation is negative. Positive cross-correlation between lightning occurrence and By component of heliospheric magnetic field is found for Southern part of South America, part of Europe, and northwestern Asia. Possible mechanisms are discussed. Although local weather and climate play a dominant role in lightning occurrence, observations suggest that changes in solar UV radiation during the solar cycle, together with global circulation and atmospheric waves, may modulate lightning occurrence in tropical and subtropical regions, while the polarity of the heliospheric magnetic field, atmospheric circulation and waves affect lightning occurrence more in mid- and high-latitude regions. The observed changes in cosmic ray intensity play an insignificant role in the global occurrence of lightning.
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Jaroslav Chum et al.
Status: open (extended)
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RC1: 'Comment on egusphere-2023-2124', Earle Williams, 26 Nov 2023
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Review of Solar Cycle Signatures in Lightning Activity, by J. Chum, R. Langer, I. Kolmasova, O. Lhotka, J. Rusz and I. Strharsky
This study revisits an important area of research with a very mixed collection of findings in earlier work. The initiative to work with lightning strokes rather than thunder days (the traditional approach) may represent an improvement, but the selection of the WWLLN data set to do the stroke test over a single solar cycle has notable limitations. Apparent contradictions with earlier findings need to be addressed, and broader attention to the literature on this topic, and especially in the realm of the global circuit of atmospheric electricity, is needed. Substantial improvements will be needed to move this work to publication.
Summary: Consider for publication after major revision
- Comments on main findings in Figure 2a
At the outset, the results in Figure 2a, the most important figure in the manuscript, are rather amazing in showing such large and coherent positive correlation coefficients over two of three major lightning zones. My first reaction; if this is a meaningful indication of a positive relationship between the sunspot representation of solar activity and lightning activity on the 11-year time scale, why hasn’t this been exposed in earlier studies? By ‘earlier’ studies I can be more specific in sections 2 and 7 below.
I have some questions about general procedure. Why were quadratic fits implemented? How do they affect the results? Normalizing the data can affect the amplitude and the cross correlation. This should be considered. (You did not show the raw data for Figure 3.) No information is included here about statistical significance. The availability of a single solar cycle in the analysis should have an impact on significance. What about p values? What about lag results in the important context of phase, and see further below. No frequency analysis is included.
The generality “correlation does not guarantee causality” is also deserving of discussion, when confidence limits are placed on the main correlation findings. To be sure the correlation coefficients are large, but how confident are we, given a single 11-year wavelet and with ENSO also involved dead center?
- Pinto et al 2013
In this reviewer’s opinion, the strongest single published result on lightning response (via thunder days) to the solar cycle was Pinto et al 2013. Why? Because multiple 11-year solar cycles were examined and because half a dozen recording stations in Brazil were analyzed, and finally because the details of the correlation calculations were shown, unlike earlier works by Brooks (1934) and Kleymenova (2006). The main problem here, not addressed by the authors, is that contrary to the inferred results in Figure 2a, an anti-phase behavior was found, with greater numbers of thunder days at solar minimum. The region of Brazil analyzed by Pinto et al. (2013) lies within the region of strong positive correlation coefficients in Figure 2a. Aren’t these apparently contradictory findings troubling? If the authors are of the view that stroke counts make a dramatic improvement in the analysis, they need to show the evidence for that.
- The selected analysis period 2009-2022
Only a single solar cycle is represented by the 13-year period of WWLLN data available in this study. The fact that the period begins near solar min and ends near solar min, but is centered on the largest ENSO event if this century is not mentioned. The period 2014/15 was a Super El Nino event (Williams et al., 2021). Yes, the authors have taken averaging steps to suppress annual and ENSO cycles (lines 118 to 120) but nowhere do the authors suggest a possible aliasing by ENSO for the selected time interval. Enhance lightning in the phase of El Nino (and in the transition from cold to warm phase) is now well substantiated.
- The WWLLN data record
The authors have elected to do their solar cycle analysis on a lightning data record that has definite shortcomings. The authors are aware of the non-uniformity of the data (in space and in time) but are not sharing the quantitative details with readers. It would be valuable to see the history of number of available recording stations and the global stroke rates over the full 2009-2022 time interval. If trends are removed with quadratic fits, and that procedure leads to enhanced correlation coefficients, then we should be able to see how the data are treated as that impacts the findings. Traditionally, the Asian region is best represented with WWLLN because the network developed out of R. Dowden in New Zealand, and Africa is least well represented because sensors there are fewer in number (mostly due to high internet costs). Figure 1 does provide evidence for 3-chimney lightning dominance, but not with a ranking that is consistent with present knowledge (with Asia/Maritime Continent typically in third place).
- Reference to ‘atmospheric electricity’
The controversial solar cycle- lightning issue has been around for a long time, and has been addressed in multiple publications involving the global electrical circuit that are neither cited nor critically addressed. Lightning remains today a legitimate source term in the DC global circuit, and a solar influence has been considered more than once. For example, Markson (1978) found evidence for solar modulation of the global circuit (though J. Willett had reservations). Markson and Muir (1980) found evidence for solar wind influence on the global circuit. Still later, Markson (1981) found evidence for positive correlation between ionospheric potential and cosmic rays. The present study contends that cosmic rays are not influencing lightning intensity (and by inference, the DC global circuit). Muhleisen (1977, follow on to Garmisch ICAE), in :”The global circuit and its parameters” found evidence for a solar cycle modulation of ionospheric potential. The authors should be addressing these earlier findings in light of the results found in the present work. In general, where the authors refer to “changes in the global electric circuit” (line 67), they need to expand the discussion.
- Quantification of correlation coefficients in the text.
The correlation coefficient is the primary metric in this paper to characterize the solar cycle impact on lightning. As such, more effort should be devoted to quantifying the numbers in the text wherever they are mentioned. Specific examples of such places are lines 12, 14, 27-28, 40, 57-58, 169, 175, 193, 229, 232-234, 251, 257, 270-271 and 289. Other works for which correlation coefficients are needed for comparison are Schlegel, Brooks and Ansol.
- Earlier thunder day analyses
In addition to the earlier study by Brooks (1934), another study by Kleymenova (1967), cited by Pinto et al 2013, is overlooked. Brooks is here characterized as “thorough”, and in that respect this study follows up on the classic investigation of thunder days (Brooks, 1925) which is indeed thorough, but in 1934 falls short in not showing actual data used in the correlation analysis. Brooks (1934) also found exceptional correlation in Siberia, which is not followed up here. Kleymenova (2006) found a mixture of phase in her solar cycle studies, and phase clearly deserves more attention here. Most importantly, if the present authors have evidence that stroke counts (with WWLLN) are improving on thunder days for this kind of analysis, that should be elaborated. At the same time, the value of the thunder day observation should be critically discussed, given a consistent practice by meteorological observers since the late 19th century. Modern lightning network data is limited in addressing climate issues on long time scales (like the present one).
- Temperature variations on the 11-year solar cycle
The global temperature is larger at solar max than at solar min, on account of the greater total energy received by the Sun at solar max. The global temperature variation (of the order of 0.1 C peak-to-peak over 11 years) has been documented (Camp and Tung, 2007; Zhou and Tung, 2-13). Nickolaenko (2015) had earlier suggested that a solar cycle in lightning activity and Schumann resonance intensity could be explained in this way. Williams (2015) raised objections, but at least this in-phase relationship is consistent with the present findings and not consistent with Pinto et al. 2013, for example. It is difficult for this reviewer to see how this physics is going to help explain positive correlation in only two of three lightning chimneys.
- Solar ultraviolet radiation
The leading explanation for a positive phase relationship here, and one in keeping with item (8) above, involves heating by solar UV. Surely some numerical models have been run to treat this additional energy source, and it would be helpful to the paper if the authors could chase the linkage from the heated stratosphere to the existence of enhanced upward motion in the troposphere, recognized as necessary to enhance the global lightning activity. More attention needs to be given to connecting the UV with the air motions that influence lightning.
- Planetary wave mechanisms
If the global lightning is the be enhanced by any kind of planetary wave activity. Of relevance here are Anyamba et al JAS, and works on the Madden Julian Oscillation by U.S. authors Rutledge and coauthors and by Russian authors N. Slyunyaev, E. Mareev, Kozlova then it would be helpful to cite several works in which lightning is modulated by planetary waves and others. Additional info can be found in a review chapter on Schumann resonances in a book by Hans Betz in 2009.
- Heliosphere Magnetic Field impact
Four pages of this 13-page paper are devoted to correlation checks on this mechanism. Given the space devoted, some additional explanation of the physical mechanism(s) suggested beyond what is stated in lines 64-67 on page 3 and at the bottom of page 8. “Changes in atmospheric electricity” is not sufficient here. Brian Tinsley is invested in a chain of events (including cloud microphysics) in this context but many of these links have yet to be verified.
- Work by G. Satori on solar cycle time scale
Satori et al (2005) showed evidence for modification of the Schumann resonances on the 11-year time scale by virtue of the dramatic changes in solar X-radiation on the upper characteristic (i.e., magnetic) height of the Schumann cavity. These changes were shown to affect the modal frequencies and Q factors, but with smaller effects on intensities. Later Bozoki et al. (2021) demonstrated changes in Q factors by both changes in X-radiation and energetic electron precipitation, with corresponding increases in magnetic intensity that they linked with the Q factor increases. No changes in the lightning source on the 11-year time scale were inferred. The Kulak group in Poland also has a publication showing effects of solar X-radiation on cavity Q-factors on short time scales. This is a research area presently in a state of flux, with a recent article on SR measurements in China in JGR (Han et al., 2023).
Sátori (2011) also showed that the lightning area at high NH latitudes increases around solar maximum while it exhibits opposite behavior in the tropical/subtropical belts. Additional references are included later in this review.
- Superbolt maximum
This pertains to the discussion in lines 264-269. I have been intrigued along with the third author about this important issue. How can changes in the ionospheric medium so strongly change the detectability of superbolts? Are we expected to have another superbolt maximum as solar maximum comes on again? Is the buildup to the 2014 El Nino responsible? One small detail here: the authors choose to remove seasonality in their correlation analysis, but this superbolt issue is definitely a seasonal issue. So what data are they pointing to in this work from boreal winter to substantiate this link?
Detailed Comments/Edits on the text:
Page 1
Abstract:
line 12 What are typical numbers?
lines 20-21 Note possible inconsistency with Markson (1981)
Page 2
Introduction
line 26 “thorough” is debatable. See item (7) above. Brooks also deserves more discussion.
lines 34-35 The marked inconsistency between this work and Pinto et al 2013 is not noted and discussed.
line 35 “thunder day data”
lines 38-40 Were Schlegel’s findings consistent or inconsistent with the present results, for the regions he investigated?
line 40 What was a “significant cross correlation” by the authors’ reckoning?
line 41-44 Why did the authors not come back to this point in the Discussion?
line 49 The authors are assuming here that correlation is causality, without further discussion.
lines 51-52 Need to get discussion of Markson (1981) in here somehow.
Page 3
lines 61-62 We need much more elaboration here, to see how the stratospheric warming will increase the vertical motions in the troposphere, known to affect lightning activity.
line 67 Elaboration on mechanism would also be useful here.
line 72 See discussion of solar proton events in Markson (1978)
lines 82-83 Need references for evidence here. None of the suggested mechanisms link with CAPE and atmospheric instability, known ingredients for lightning activity,
Page 4
line 97 “data are obtained”
Lines 97-104 The authors give no justification here for the selection of the WWLLN lightning data set to undertake this study. A 30% detection efficiency for a 30 kA peak current threshold tells you right away that WWLLN is essentially an inefficient detector for CG lightning and with little access to the more dominant IC lightning.
line 108 More info is needed here about trends, and especially because a major ENSO event is occurring in the middle of the selected data window.
Line 115 If normalized variables are used then a short table is needed that shows the mean values and the standard deviations.
line 118 The authors are aware of ENSO, but not facing up to its central presence in the selected data window. More critical assessment is needed here.
line 119 “cross correlation coefficients” You need to include the equations you use to produce the results.
Page 5
line 123 Yes the 3-year running mean will reduce the impact of ENSO will bill not eliminate it. Too little discussion of “preparation” of the data is given here.
line 145 Why is this so? Elaborate for non-experts. What did you do with it?
line 152 change “can be” to “are readily verified”
line 153 Add a sentence: “The continental lightning dominates the oceanic lightning by more than an order of magnitude”.
Page 6
line 160 Suggest repeating the entire period here.
line 161 These numbers should be compared with state-of-the art results from LIS and GLD360 for numbers of strokes one gets with detection systems with much larger DE.
line 164 In light of apparently contradictory Pinto et al (2013) finding, the discussion on correlation phase needs to be expanded.
line 174 The text should tell what continent the selected bin is located and better yet, show the grid point on one of your maps. It would also be helpful to see a selection of samples from bins not exhibiting maximum correlation.
Page 7
Figure 2 caption, add “number of lightning strokes…”
lines 186-187 “and atmospheric electricity” reference shows disinterest in details here, and references
line 190 No mention is made of the South Atlantic Anomaly region, often addressed in studies of this kind.
Page 8
Figure 3 caption should say where this region is located and why it was selected.
Figure 3: clearly more lightning at solar maximum, and not what Pinto et al (2013) with thunder day analysis.
Line 201 “changes of atmospheric electricity” Here again it sounds like atmospheric electricity is some nebulous subject not being addressed by the authors. We need to hear the details here.
Page 10
line 229 Quantify “large values”
Page 11
line 237 Here the authors seem concerned with phase. GOOD.
Page 12
line 251 Quantify the values.
lines 255-257 This sounds hand-wavy and unreferenced. It would be valuable to look at the literature and see where planetary wave activity (i.e., MJO) is affecting lightning activity.
Page 13
Line 258 Here the authors are attentive to phase.
line 259 The monsoon trough is not a productive region for thunderstorms (see Williams et al., JAS, 1991), and it is not clear that a different mechanism is operating in the so-called break period between monsoon trough visitations. This is an unconvincing explanation for the different correlation behavior in the third chimney.
Line 263 Early in the paper the authors indicated they were removing seasonal behavior by appropriate filtering. What then are they pointing to to show results for boreal winter?
lines 270 to 272 What is the physical basis here?
line 274 to 277 This is quite hand-wavy. Needs further substantiation.
lines 278-280 The authors need to square their findings with Markson (1981).
Line 279 I do not understand the point here about “suitable weather conditions”
lines 284 to 286 Why is this the case? The authors need to greatly beef up the comparative results using thunder days and using measured strokes.
line 286 “a solar rotation period signal in lightning occurrence”? Please clarify. See also Satori references below. See also Anyamba et al (2000) reference.
line 291 The authors need to be more specific about the diverse mechanisms for the occurrence of thunderstorms and how that relates to the present study.
Page 14
Line 294 Yes, analysis of a single solar cycle has definite limitations.
References to add and discuss in this paper:
Anyamba et al JAS 2000
Beloglasev and Akhmetov (2010) Geomagnetism and Aeronomy
Girish and Eapon JASTP 2008.
Kleymenova (2006) (citation is in Pinto et al. 2013)
Kozlova, A.V., N.N. Slyunyaeva, N.V. Ilina, F. G. Sarafanova, and A. V. Frank-Kamenetsky, The effect of the Madden–Julian Oscillation on the global electric circuit, Atmospheric Research, (in press), Dec 2022.
Markson (1978)
Markson and Muir (1980)
Markson (1981)
Muhleisen (1977)
Nickolaenko, A. Sun and Geosphere, (2015).
Satori, G. doctoral thesis work (2011) : real-d.mtak.hu/512/
and on the solar rotation period see: Sátori, G ; Zieger, B
Areal Variations of the Worldwide Thunderstorm Activity on Different Time Scales as Shown by Schumann Resonances
In: Serge, Chauzy; Pierre, Laroche (szerk.) Proceeding of the 12th ICAE, Global Lightning and Climate
(2003) pp. 1-4. , 4 p.- Willett comments on Markson (1978)
Williams, E., Sun and Geosphere, (2015)
End review
Earle Williams
November 26, 2023
Citation: https://doi.org/10.5194/egusphere-2023-2124-RC1
Jaroslav Chum et al.
Jaroslav Chum et al.
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