Variability in lightning hazard over Indian region with respect  to El Niño–Southern Oscillation (ENSO) phases

Sreenath, Avaronthan Veettil; Abhilash, Sukumarapillai; Vijaykumar, Pattathil

doi:https://doi.org/10.5194/nhess-21-2597-2021

Articles | Volume 21, issue 8

https://doi.org/10.5194/nhess-21-2597-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/nhess-21-2597-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 8

Research article

|

26 Aug 2021

Research article |

| 26 Aug 2021

Variability in lightning hazard over Indian region with respect to El Niño–Southern Oscillation (ENSO) phases

Avaronthan Veettil Sreenath, Sukumarapillai Abhilash, and Pattathil Vijaykumar

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Final revised paper (published on 26 Aug 2021)
Preprint (discussion started on 16 Nov 2020)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Earth & Atmospheric Science', Anonymous Referee #1, 06 Dec 2020
- SC1: 'Response to the referee comments', Sreenath A V, 13 Dec 2020
- AC1: 'Reply on RC1', Abhilash. S., 08 Feb 2021
RC2: 'Review', Anonymous Referee #2, 21 Jan 2021
- SC2: 'Reply on RC2', Sreenath A V, 30 Jan 2021
- AC2: 'Reply on RC2', Abhilash. S., 08 Feb 2021

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by editor and referees) (09 Feb 2021) by Vassiliki Kotroni

AR by Abhilash. S. on behalf of the Authors (20 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (24 Mar 2021) by Vassiliki Kotroni

RR by Anonymous Referee #2 (13 Apr 2021)

Suggestions for revision or reasons for rejection

Second Review of the paper: “Variability of lightning hazard over Indian region with respect to ENSO Phases”, by Sreenath A V, Abhilash S, and Vijaykumar P
The authors change many things in the paper after the first reviews. They make detailed responses to my comments. I thank them for the work. The study is interesting but maybe not easy to fully appreciate because some lacks of information and interpretations that have to be more quantitative and closer to reality. The authors explain how is calculated the anomaly and it now requires a new approach of the results for the reviewer. According to the definition of the anomaly, the sum of the three anomalies (one for each ENSO phase) has to be zero for a given parameter and a given location. For example for LFR anomalies (figure 2), for the graupel anomalies (figure 4) etc.. It is not the case for each graph of for each graph of figure 4, figure 5 for example. I would like to understand if there is a reason or a wrong calculation. The discussion must take into account the quantitative aspect of the anomalies and to make clearly the difference between the values of the parameters and the values of the anomalies (indeed, a negative anomaly does not mean a “suppression” as it is indicated for example for the LFR (see details below). I think the authors have to clarify many comments and interpretation of the values they consider, especially for the anomalies of most parameters.

Major comments:
I use the numbering lines from the version of the paper with tracked changes.
One of the change concerns figure 1 for the LFR values. Apparently, there was an error in the plot, especially in the phase La-Nina. The LFR is now much weaker. Of course, it clarifies the comments, but is is a little surprising to have made comments that were not consistent with the figure.
Another change is the colored scale with a degraded resolution. It is not easy to appreciate some low values difference although the authors made comments about low values as for example in the case of post-monsoon period. The Indian peninsula at that moment is concerned by very weak lightning activity and it is difficult to see a difference between the different regions and the different ENSO phases.
We can also wonder why the authors choose to plot such a large area for the maps of the LFR since they make comments and analysis about India? It is especially true for the south part of the maps and for the western part too. With a reduced area, the visibility should be better?
The first comment in the abstract at line 10 about three hotspots: “three hotspots of LFR over the Indian land region became more prominent in the last decade of the monsoon season” is not obvious. I do not see three hotspots?
Lines 150-155: about the values of ice particle concentration, the value range is wide but for convective clouds we can suppose large values within the range are more probable. The range is presented with this interval [10-4 – 1 g m-3] which corresponds with values measured during a campaign. My feeling is that most values are in the upper part of the interval. Thus, as I noted in the first review, the values for the anomalies in figures 4 and 5 are < 0.0005 g m-3. Again, I do not understand such low values when the concentration is close to 1 g m-3. What does it mean? Are these values valuable for the convective clouds? They are issued from the NCEP/NCAR database with a resolution of 0.5°x0.5° but at which time do they correspond? How are these values representative of the convective clouds when they occur? For the case of the NNWI region and pre-monsoon season, the LH anomaly is < 0.01 °/hr, it is also very low values..
Line 163, the authors write: “the cold ENSO phase suppresses LFR over NEI and SPI with enhanced LFR over CI (Figure 2 (b))”. It is in contradiction with line 109, when they wrote “Irrespective of ENSO phases, the LFR peak is located over northeast India (NEI) during the pre-monsoon season:” They cannot say the LFR is suppressed during the pre-monsoon season and the cold ENSO phase, by looking at Figure 1, even if the anomaly is negative! The LFR is displayed in Figure 1. The LFR in NEI is between 0.08 and 0.12 according to Figure 1b for the cold phase and the anomaly according to Figure 2 is between -0.01 and -0.014, it is about 10% of the LFR value. They cannot talk about “suppress” it is only lower than the average between the three ENSO phases if I understand well.
Lines 162-168: For the comparison of different ENSO phases the mirror image effect is not surprising since the anomaly is calculated by the difference with the average value. If one phase involves a decrease another (or both others) has to involve an increase according the definition of the anomaly. Again, at line 168, they cannot say “that the cold phase suppresses the LFR over NEI” since it is not suppressed. Anyway, if they talk about an increase or a decrease, they have to quantify it to discuss the relative variation.
Line 169: Figure 4a shows the anomaly of graupel concentration in NEI and during the pre-monsoon season. According to the definition of the anomaly as a difference to the mean value for each phase, the sum of the anomaly values must be zero. Apparently, it is not the case for this graupel concentration. The same comment can be made for other panels of Figure 2: d, e, h, l and the same for Figure 5 and Figure 6. Can the authors explain these results? Anyway, for the parameters of microphysics issued from re-analysis, the description added in the new version of the paper is insufficient to understand the signification of these concentrations. Are they average and for which time and location are they representative?
For section 3.3, it is a little the same problem with the comparison of region NNWI during the different phases. They cannot use “suppress” for the LFR and again, a quantitative analysis could be made.

Minor comments:
I said in my first review the parameter LFR could be LFD as lightning flash density since it is a density (km-2 day-1). It is a daily density. Is it more consistent to talk about density? As in Albrecht et al. (2016) a combination is used when the double scale (time and space) is used for the flash count: for example “The TRMM LIS total lightning flash rate density (FRD – fl km-2 yr-1)” is generally used at the scale of the year. Ref Albrecht, R., Goodman, S., Buechler, D., Blakeslee, R., and Christian, H.: Where are the lightning hotspots on Earth?, Bull. Amer. Meteor. Soc., 97, 2051-2068, doi:10.1175/bams-d-14-00193.1, 2016.
It is also the case in Christian et al. (2003): in the abstract: “The Congo basin, which stands out year-round, shows a peak mean annual flash density of 80 fl km-2 yr-1 in Rwanda, and includes an area of over 3 million km2 exhibiting flash densities greater than 30 fl km-2 yr-1 (the flash density of central Florida).” It sounds better with “density”, but if the authors prefer “rate” it is also possible, some authors use it, as Cecil et al. for example.

Line 20-22: the annual death rate has to be 2,266 with a total of 31,725 in 14 years?
Line 23: “they find” and not “they finds”
Line 77: the power numbers at exponent for the units of flash rates
Line 83: LRMTS
Line 104: Write “If the ONI value is above (below) +0.5° (-0.5°) C…”
Line 137: Is it possible to talk about three hotspots? That in the southern part of Indian Peninsula is not very visible and the LFR does not reach high values there. It was not clear in the initial maps with a better color resolution (figure 1 of the previous version), it seems there is an effect of amplifying with the new color scale.
Line 141: The comment is about the values of LFR that are low during the pre-monsoon, therefore the figure for reference is Figure 1 that displays directly the LFR values. Figure 2 displays the anomaly that is a comparison with other phases of ENSO. Even if the anomaly is negative (positive) it does not mean the LFR is low (large).
Line 142: Since the anomaly is the comparison between the different ENSO phases for a given season, a negative anomaly in a region for one phase implies a positive anomaly for another phase. Therefore, why to say “however” at the beginning of the sentence since it is an evidence?
Lines 142-144: the sentence needs to be referred to the figure 3 and to say at which region it is applied.
Line 189: “analyzing”

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ED: Reconsider after major revisions (further review by editor and referees) (20 May 2021) by Vassiliki Kotroni

AR by Abhilash. S. on behalf of the Authors (18 Jul 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (19 Jul 2021) by Vassiliki Kotroni

RR by Anonymous Referee #2 (22 Jul 2021)

ED: Publish as is (22 Jul 2021) by Vassiliki Kotroni

Short summary

Lightning is a multifaceted hazard with widespread negative consequences for the environment and society. We explore how El Niño–Southern Oscillation (ENSO) phases impact the lightning over India by modulating the deep convection and associated atmospheric thermodynamics. Results show that ENSO phases directly influence lightning during monsoon and postmonsoon seasons by pushing the mean position of subtropical westerlies southward.