Interactive comment on “ An overview of the lightning and atmospheric electricity observations collected in Southern France during the HYdrological cycle in Mediterranean EXperiment

35 36 The PEACH project (Projet en Electricité Atmosphérique pour la Campagne HyMeX -the Atmospheric 37 Electricity Project of HyMeX Program) is the Atmospheric Electricity component of the HyMeX (Hydrology 38 cycle in the Mediterranean Experiment) experiment and is dedicated to the observation of both lightning 39 activity and electrical state of continental and maritime thunderstorms in the area of the Mediterranean 40 Sea. During the HyMeX SOP1 (Special Observation Period) from 5 September to 6 November 2012, four 41 European Operational Lightning Locating Systems (OLLSs) (ATDnet, EUCLID, LINET, ZEUS) and the 42 HyMeX Lightning Mapping Array network (HyLMA) were used to locate and characterize the lightning 43 activity over the Southeastern Mediterranean at flash, storm and regional scales. Additional research 44 instruments like slow antennas, video cameras, micro-barometer and microphone arrays were also 45 operated. All these observations in conjunction with operational/research ground-based and airborne 46 radars, rain gauges and in situ microphysical records are aimed at characterizing and understanding 47 electrically active and highly precipitating events over Southeastern France that often lead to severe flash 48 floods. Simulations performed with Cloud Resolving Models like Meso-NH and WRF are used to interpret 49 the results and to investigate further the links between dynamics, microphysics, electrification and 50 lightning occurrence. Herein we present an overview of the PEACH project and its different instruments. 51 Examples are discussed to illustrate the comprehensive and unique lightning dataset, from radio52 frequency to acoustics, collected during the SOP1 for lightning phenomenology understanding, 53 instrumentation validation, storm characterization and modeling. 54 55

This is somewhat indicated in Sect. 3 L24 but could be described earlier. Response : A super site over land or the ocean gathers research instruments dedicated to the study of specific processes. We propose the following to detail a bit more the notion of super site. "Those equipments were deployed at or near super sites where dedicated research instruments are gathered to document specific atmospheric processes c." -3 The PEACH experiment: p8020 L20. Maybe one can start first with the goals of PEACH. For instance, part of Sect. 3.1. could be placed here to describe the scientific objectives. Response : We would prefer to keep the current structure of the paper as the two first paragraphs describe briefly the nature of the electrical activity in the Mediterranean Basin and the relevance of the lightning detection for storm monitoring over the Mediterranean Sea. Then we list the scientific objectives of the PEACH project and its observational/modeling strategy.
-p8023: LMA, EFM, SLA are all described in a designated subsection. However, this is not the case for INR. Therefore, the authors could consider to include a subsection explaining the main parameters of the INRs, as has been done for the other instruments. Response : The induction rings (INR) were built just before the field deployment and were not enough tested before their deployment and operation during the field campaign. They all failed due to non-reliable electronic chips. It is why we did not originally describe them in the paper. Notice that the INR measurements were aimed to provide some ground-truth on the actual electrical charges carried by the raindrops at the ground for a comparison and verification of simulated charge distribution at ground level provided by the cloud-resolving model MESO-NH. As suggested by the Reviewer we now include one section describing the principle of an induction ring as well as the explanation of the failure. Here is the text that has been inserted: " The electric charge carried by raindrops can easily be detected and measured by a simple apparatus commonly called induction ring. This sensor is constituted of a cylindrical electrode (the ring) on the inner surface of which induced electric charges appear by electrostatic influence when a charge raindrop enters the sensor. When the drop leaves the sensor, C3452 the induced charges disappear. The cylindrical electrode is connected to an electrometer and the current signal induced by the passing of a charged drop (a bipolar current impulse) is sampled at a rate of 2000 Hz. It is amplified and integrated by an electronic circuitry that directly provides the charge signal. This one appears as a single pulse with amplitude and length proportional to the charge and to the velocity of the drop, respectively. The actual charge is deduced from the calibration of the sensor. If the drop collides with the induction cylinder, the pulse signal exhibits a slow exponential decay (MacGorman and Rust, 1998) that is easily recognizable in the post data processing. In this case, the raindrop charge that is fully transferred to the induction cylinder is determined by a specific calibration. The charge measurement sensitivity ranges from about ± 2 pC to ± 400 pC. Furthermore, the charge signal duration at mid height can be used to determine the size of the charged raindrops provided the relationship between size an fall velocity in function of the actual temperature and pressure (Beard, 1976). Such measurement provides key information on the electric charge carried by the rain at the ground to validate numerical modeling. It documents the spectrum of charged drops and helps deduce the proportion of charged drops within the whole drop population by comparing its spectrum with the one measured by a disdrometer. Four induction rings were built and operated during the SOP1, mainly along the South to North axis at the foothills of the Massif Central where most of high precipitating events occur. Unfortunately, only few events passed above the sensors and in these rare cases, the main electronic component of the induction rings suffered dysfunction that were not detected during the laboratory tests, so no valuable INR data are available for the SOP1." -3.3 Operational Lightning Location Systems: The writing style of the subsections concerning the description of the OLLS is not coherent. The authors could slightly rewrite these sections in order to converge the writing style of the OLLS subsections. Response : As suggested by the Reviewer, the subsections dealing with the description of the OLLSs have been rewritten with similar information. See the different sections describing the OLLSs. C3453

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Interactive Discussion Discussion Paper -Concerning the description of all the OLLS: It would be worth to include some LA and DE values + references, if possible within the region/neighborhood of HyMeX SOP1. Response : Some numbers are now given in the different subsections describing the OLLSs. We would like to stress out that one of the objectives of the investigations performed with the HyMeX SOP1 data is to assess in the SOP1 region both DE and LA for all operational networks.
-3.5 Modeling: This section is out of the scope of this paper and no further results are presented in this paper on the modeling aspects. Maybe the authors could just make a comment concerning the modeling efforts in stead of including sect. 3.5.1 and 3.5.2 in the manuscript. For instance p8034 L22-L26 can be removed to Section 5 Prospects. Response : The Authors was discussed on that question before the submission. Our strategy is to use as much instruments as possible, and models are instruments for us, to tackle the different scientific questions investigated here. So we would like to keep the Modeling section as it is now. Some modeling exercises have already been performed, but are not discussed here. s -4.1 SOP1 Climatology: The authors should include a bit more info on the climatology during SOP1: How many thunderstorm days were observed in the region of interest (describe Fig. 2), how many flashes have been observed during SOP1?, ... Response : We have provided some additional information on the lightning climatology. Figure  2 has now one extra panel showing the number of lightning days on the yearly basis for the SOP1 duration. No reference on actual number of flashes is given due to the successive upgrade of Météorage network. Note that we performed a set of investigations on the lightning climatology based on Météorage data that were used for the definition of the HyMeX SOP1 Implementation Plan. We propose the following text now: "The year 2012 was rather weak in terms of lightning activity over the center of the SOP1 domain. The electrical activity was mainly located in the far Northern part of Cévennes-Vivarais, and was more pronounced along the Riviera coastline and over the Ligurian Sea (Fig. 2b). About 0.3% of the 5 km x 5 km pixels of the year 2012 C3454 AMTD 7, C3449-C3473, 2014 Interactive Comment

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Discussion Paper contribute to more than 20% of the 16-year climatology. Over the 500-km side domain plotted in Fig.2a and 2b, and for a period ranging from 5 September to 6 November, the total number of days with lightning activity in 2012 reached a value of 44 days, slightly below the average value for the 16 years of interest (Fig. 2c)." Minor comments and proposed editorial changes: -P8017 L8: rephrase: 'A lightning flash then consists in a multi-scale physical process' Response : We propose "A lightning flash is then constituted of a series of multi-scale physical processes".
-P8017 L9: ... over large distances of a few km or more. Response : Corrected as suggested.
-P8017 L21: rephrase: 'to provide the most comprehensive description for analyzing in details the lightning flashes', e.g.: provide the most comprehensive description in C3456 AMTD 7, C3449-C3473, 2014 Interactive Comment

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Discussion Paper order to analyze in great detail ... Response : Corrected as suggested.
-P8020 L13 & L15: two times 'autumn', the last one on L15 could therefore be removed Response : Removed as suggested.
-P8021 L15-L20: Last sentences could be split into 2 sentences to improve readability. Response : We propose now "However, further scientific investigations are required to document the links between the lightning activity and the dynamical and microphysical properties of the parent clouds in continental and maritime Mediterranean storms. In addition it is necessary to identify the key parameters derived from OLLS records alone or in combination with other meteorological observations to provide suitable proxies for a better storm tracking and monitoring over the entire Mediterranean Basin." 3.1 Scientific objectives and observational/modeling strategy: -P8021 L21: The scientific objectives, i.e. p8021 L22 -p8022 L18, could be removed and replaced at the beginning of Sect. 3. Therefore, the title could become '3.1 observational and modeling strategy'. Thus, p8022 L19 could be the new start of Sect. Response : As mentioned earlier we would prefer to keep the current structure of the paper. -P8024 L9/L10: three times 'stage' in 1 sentence is a bit too much. Make use of synonyms. Response : Sorry for the phrasing. We propose "As a result, the HyMeX SOP1 experiment is probably the first ambitious field experiment in Europe to offer such comprehensive description of lightning activity and of its parent clouds over a mountainous area from the early stage to the decaying phase of the sampled electrical storms." -P8024 L11: ... in conjunction with the operational network of Météo-France ... Response : Modified as suggested.
-P8024 L13: start a new paragraph with: 'In the following we ...'. However, this sentence is too long and could be split into 2 sentences: In the following we give some ... observations. Several other studies are underway to investigate the ...and rain patterns, as derived ... + However: 'in the following' is not true in this case: 'in the following' the instruments are described in Sect. 3.2, so text should be changed accordingly. Response : We propose "In this article we give some examples of only atmospheric electricity observations. Several studies are underway on the electrical properties of thunderstorms relatively to cloud properties like cloud structure, microphysics and rain patterns as derived from radar and satellite observations and in situ measurements. -P8027 L17/L19: orientated -> oriented Response : Corrected.
-P8027 L25: avoid "(...)" Response : We propose "The polarity of the field is positive when the field points upward and the electric field is created by negative charge overhead." 3.2.5: VFRS -P8028 L2: VRFS acronym has been already introduced earlier in the text, so no need to do this again. Response : OK. It is removed now. We propose "The VFRS instrument". The UK Met Office VLF ATDnet (Arrival Time Differencing NETwork) lightning location network takes advantage of the long propagation paths of the VLF (frequency range) sferics emitted by lightning discharges, which propagate over the horizon via interactions with the ionosphere (Gaffard et al., 2008). The ATDnet network consists of 11 that regularly contribute to the "operational network", plus sensors distributed further afield. The waveforms of VLF sferics received at the ATDnet sensors are transmitted to a central processor in Exeter, where the waveforms are compared in order to estimate arrival time differences. These arrival time differences are compared with theoretical arrival time differences for different locations, in order to estimate the most likely source location. Current ATDnet processing requires four ATDnet sensors to detect a lightning stroke in order to be able to calculate a single, unambiguous source location. ATDnet predominantly detects sferics created by CG strokes, as the energy and polarization of Sferics created by CG return strokes can travel more efficiently in the Earth-Ionosphere waveguide, and so are more likely to be detected at longer ranges than typical IC discharges. ATDnet location uncertainties within the region enclosed by the network of sensors are on the order of a few kilometers, i.e. suitable for identifying electrically active cells.

EUCLID
The EUCLID network ( sensors (oldest to newest), all operating over the same frequency range (1 kHz -350 kHz) with individually-calibrated gains and sensitivities. Data from all of these sensors are processed in real-time using a single common central processor, which also produces daily performance analyses for each of the sensors. This assures that the resulting data are as consistent as possible throughout Europe. In fact, the Europewide data produced by EUCLID is frequently of higher quality than the data produced by individual country networks, due to the implicit redundancy produced by shared sensor information. Since the beginning of the cooperation the performance of the EU-CLID network has been steadily improved, e.g. with improved location algorithms, with newer sensor technology and by adapting sensor positions because of bad sites. The flash/stroke detection efficiency (DE) of the EUCLID network in the south of France was determined to be 90%/87% for negative and 87%/84% for positive discharges but for a time period where a close sensor was out of order (Schulz et al., 2014). Therefore the values should be rated as lower limits of EUCLID DE in this region. The location accuracy was determined to be 256 m but based on 14 strokes only.

LINET
The LINET system is a modern lightning detection network in the VLF/LF domain (5 kHz -100 kHz) developed by nowcast GmbH (Betz et al., 2008, 2009. LINET Europe consists of more than 120 sensors placed in 25 countries. Each of them includes a field antenna, a GPS antenna and a field processor. The field antenna measures the magnetic flux produced by a lightning. The processor evaluates this signal and combines it with the accurate time provided by the GPS antenna. Compact data files are then sent to a central processing unit where the final stroke solutions are generated. Accurate location of strokes requires that the emitted signal is detected by many sensors. Reported strokes are based on reports from at least 5 sensors. Strokes are located using the Time-Of-Arrival (TOA) method. LINET detects also cloud strokes, and can distinguish between CG strokes and IC strokes. km between adjacent sensors, allowing very good detection efficiency, even for very weak strokes (< 10 kA), whereby an average statistical location accuracy of ∼200 m is achieved. However, in the HyMeX area in Southern France the baselines are longer and, thus, the efficiency is somewhat lower than in most other LINET network areas.

ZEUS
The ZEUS network is a long-range lightning detection system, operated by the National Observatory of Athens. ZEUS system comprises six receivers deployed in Birmingham (UK), Roskilde (Denmark), Iasi (Romania), Larnaka (Cyprus), Athens (Greece), Lisbon (Portugal), the latter being relocated to Mazagon (Spain). ZEUS detects the impulsive radio noise emitted by a lightning strike in the Very Low Frequency (VLF) spectrum between 7 and 15 kHz. At each receiver site an identification algorithm is executed that detects a probable sferics candidate, excludes weak signal and noise and is capable of capturing up to 70 sferics per second. Then the lightning location is retrieved (at the central station) using the arrival time difference technique. Further details on ZEUS network are given in Kotroni and Lagouvardos (2008). Lagouvardos et al. (2009) have compared ZEUS system with the LINET system over a major area of Central-Western Europe where the latter system presents its major efficiency and accuracy and found that the location error of ZEUS was 6.8 km and the detection efficiency 25%. These numbers are applicable also for the SOP1 domain. The authors found also that while ZEUS detects cloud-to-ground lightning it is also capable to detect strong IC lightning. At this point it should be stated that the statistical analysis showed that ZEUS is able, with high accuracy, to detect the occurrence of lightning activity although it underdetects the actual number of strokes." 3.4: Instrumentation during EOP and LOP -General comment: Maybe this section can be moved to Sect. 5 'Prospects' section, since this paper deals only with SOP1 observations Response : This section was placed here in order to show that the PEACH team is providing an expertise on lightning activity, mainly with the operational networks, for HyMeX EOP and LOP activities as others supersites are still running and C3464 AMTD 7, C3449-C3473, 2014 Interactive Comment

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Discussion Paper future local field campaigns over the Mediterranean Basin are expected. So we would like to keep that section in its current place in the paper.
-P8033 L6: '12 LMA': however, on p8029 L16: '11 stations' => make consistent Response : This is a new LMA network that has been installed in Corsica and has been operated since mid-July 2014. It is not the same network as the one operated during SOP1, which was borrowed to NASA Marshall Space Fight Center group. From the Reviewer comment, we have added the following precision in the former p8029 L16 "The 12th HyLMA station was online early beginning of September 2012".
A regular IC -P8036 L12: an example of a regular Response : Added.
-P8036 L13: What is meant with #06? Response : It is the number of the IOP event. We rephrase it as follows " Figure 3 shows an example of a regular IC flash recorded by HyLMA during SOP1 Intensive Observation Period (IOP) IOP-06 on 24 September 2012".
-P8036 L16: Do not use '(' and ')', just make it into a normal sentence. For instance: 'For more information on ... the interested reader is referred to Thomas ...' Response : We propose the following "It was composed of 2510 VHF sources as reconstructed from at least 7 HyLMA stations and chi2 < 1. For more information on the definition of the parameters associated to each LMA source the interested reader is referred to Thomas et al. (2004). The VHF sources were vertically distributed between 4 and 12 km height (Fig. 3d)." -P8036 L19: msl? => asl? Response : "asl". Corrected.
-P8036 L23: propagated faster: as evidenced from? Response : As evidenced from the actual distances traveled by the negative leaders compared to the ones traveled by the positive leaders during the same temporal gap. We inserted the previous phrase in the paper now.
-P8037 L8: at close range of about 25 km by the VRFS instruments. VFRS has been already explained, so 'FM and video camera' can be removed. Response : Modified as suggested.
-P8037 L17: rewrite a bit: ATDnet reported 7 events, whereas EUCLID identified 5 strokes ..., and LINET categorized 8 strokes as ... Response : Modified as suggested as follows "ATDnet reported 7 events, whereas EUCLID identified 5 strokes as negative ground connections, and LINET categorized 8 strokes as negative ground connections and 1 stroke as positive ground connection"    Table 1    ..'available only for EUCLID and LINET with ...': I see black stars for ZEUS as well Response : The type of strokes is only available from EUCLID and LINET. This information does not exist for ZEUS. To avoid any mis-understanding, we removed the part of the sentence "and type of detected events available only for EUCLID and LINET".