A Lightning Mapping Array (LMA) maps radio pulses emitted by lightning leaders, displaying lightning flash development in the cloud in three dimensions. Since the last 10 years about a dozen of these advanced systems have become operational in the United States and in Europe, often with the purpose of severe weather monitoring or lightning research.
We introduce new methods for the analysis of complex three-dimensional lightning data produced by LMAs and illustrate them by cases of a mid-latitude severe weather producing thunderstorm and a tropical thunderstorm in Colombia. The method is based on the characteristics of bidrectional leader development as observed in LMA data (van der Velde and Montanyà, 2013, JGR-Atmospheres), where mapped positive leaders were found to propagate at characteristic speeds around 2 · 104 m s-1, while negative leaders typically propagate at speeds around 105 m s-1. Here, we determine leader speed for every 1.5 x 1.5 x 0.75 km grid box in 3 ms time steps, using two time intervals (e.g., 9 ms and 27 ms) and circles (4.5 km and 2.5 km wide) in which a robust Theil-Sen fitting of the slope is performed for fast and slow leaders. The two are then merged such that important speed characteristics are optimally maintained in negative and positive leaders, and labeled with positive or negative polarity according to the resulting velocity.
The method also counts how often leaders from a lightning flash initiate or pass through each grid box. This "local flash rate" may be used in severe thunderstorm or NOx production studies and shall be more meaningful than LMA source density which is biased by the detection efficiency. Additionally, in each grid box the median x, y and z components of the leader propagation vectors of all flashes result in a 3D vector grid which can be compared to vectors in numerical models of leader propagation in response to cloud charge structure.
Finally, the charge region altitudes, thickness and rates are summarized from vertical profiles of positive and negative leader rates where these exceed their 7-point averaged profiles. The summarized data can be used to follow charge structure evolution over time, and will be useful for climatological studies and statistical comparison against the parameters of the meteorological environment of storms.
Lopez, J.; Pineda, N.; Montaña, J.; Van Der Velde, O.; Fabro, F.; Romero, D. Atmospheric research Vol. 197, p. 255-264 DOI: 10.1016/j.atmosres.2017.06.030 Data de publicació: 2017-10-15 Article en revista
3D mapping system like the LMA - Lightning Mapping Array - are a leap forward in lightning observation. LMA measurements has lead to an improvement on the analysis of the fine structure of lightning, allowing to characterize the duration and maximum extension of the cloud fraction of a lightning flash. During several years of operation, the first LMA deployed in Europe has been providing a large amount of data which now allows a statistical approach to compute the full duration and horizontal extension of the in-cloud phase of a lightning flash. The “Ebro Lightning Mapping Array” (ELMA) is used in the present study. Summer and winter lighting were analyzed for seasonal periods (Dec–Feb and Jun–Aug). A simple method based on an ellipse fitting technique (EFT) has been used to characterize the spatio-temporal dimensions from a set of about 29,000 lightning flashes including both summer and winter events. Results show an average lightning flash duration of 440 ms (450 ms in winter) and a horizontal maximum length of 15.0 km (18.4 km in winter). The uncertainties for summer lightning lengths were about ± 1.2 km and ± 0.7 km for the mean and median values respectively. In case of winter lightning, the level of uncertainty reaches up to 1 km and 0.7 km of mean and median value. The results of the successful correlation of CG discharges with the EFT method, represent 6.9% and 35.5% of the total LMA flashes detected in summer and winter respectively. Additionally, the median value of lightning lengths calculated through this correlative method was approximately 17 km for both seasons. On the other hand, the highest median ratios of lightning length to CG discharges in both summer and winter were reported for positive CG discharges.
Since 2011 a 12-station 3D Lightning Mapping Array (LMA) has been operational in the Ebro Valley region in the south of Catalonia, covering an area over 200 km wide along the east coast of Spain. Since 2015 it has been split in two, with six stations active in the Santa Marta region of northern Colombia. These arrays map very high frequency pulses (60-66 MHz) emitted mainly by negative leader steps and recoil leader processes during lightning flashes.
It is well-established that lightning flashes initiate in the high-field regions between two oppositely charged sections of the thundercloud and then branch out bidirectionally into positive and negative charge volumes. A classic thunderstorm develops a “tripole” charge structure. However, how the thunderstorm environment (and climate) affects the details of the charge structure has been little investigated so far, as well as its evolution, because objective and automated ways to analyze large volumes of data in active storms have been unavailable in the past.
At the previous European Conference on Severe Storms (2015) we presented possible ways of automating the analysis of leader polarity. Now we have developed a 4D grid-based algorithm that performs much better. In each grid box, leader speed is determined by applying a robust t-x/y/z slope fitting method (Theil–Sen) to the sources in that box and surrounding boxes within dual time intervals (on the order of 5-10 ms for fast leaders and 20-40 ms for slow leaders). In each grid box the median x, y, and z component of the vector of all flashes result in a 3D vector grid which can be compared to vectors in numerical models of leader propagation in response to cloud charge structure.
The method also counts how often leaders from a lighting flash initiate in or pass through each grid box. This “local flash rate” in the storm may be used in severe weather studies and is expected to be a more meaningful tool than LMA source density which is biased by the detection efficiency for different leaders.
Among the first objectives is a statistical study of the properties of charge regions, leader speed and flash rates based on six years of LMA data, in relation to meteorological background conditions (temperature, humidity, convective available potential energy and vertical wind shear). The charge analysis can also improve the understanding of the emission of rare phenomena as Gigantic Jets and Terrestrial Gamma-Ray Flashes (TGF).
Gigantic Jets (GJ) are electrical discharges that start as lightning inside tropical thunderstorms and then grow upward to the ionosphere at 85-90 km altitude. These phenomena are very rarely observed in the mid latitude regions. Besides the unusual meteorological requirements for their production conditions, of great interest is the evolution of the discharge, which we know starts with lightning leaders and ends with streamers as in sprites. Exactly how this transition takes place has still not been observed. Therefore, we developed two intensified high-speed camera systems, one of which has been operated remotely on Curaçao (southern Caribbean Sea) since 2014, and the other, a slower but more portable system, has been operated from Santa Marta, Colombia during a campaign in July/August 2017.
The campaign was successful with 4 GJs recorded and 2 cases of interesting “troll” developments under sprites.
Earth’s atmospheric potential rapidly increases up to few tens of kilovolts below 200 m altitude. This potential drop will induce charge to tall objects at ground by virtue of electrostatic induction. In this work we investigate the induced electric charges in fair weather to a 1.5 MW and 5 MW wind turbines. The effect of rotation is included and the current calculated result in currents of few micro-amps. The production of point discharge and corona is investigated and some experiments are conducted by means of instrumented kites.
Lopez, J.; Montaña, J.; Van Der Velde, O.; Romero, D.; Aranguren-Fino, H.; Torres-Sanchez, H.; Taborda, J.; Martínez, J. International Conference on Lightning Protection p. 1-5 Data de presentació: 2016-09-26 Presentació treball a congrés
The first data set of VHF lightning mapping using a
Lightning Mapping Array system - LMA in a tropical region is
presented in this paper. Six sensors were installed at the north of
Colombia near Santa Marta city. Since the installation of the
LMA network in 2015, up to 7000 intra-cloud (IC) discharges
from September to November 2015 have been analyzed. The data
suggests that, the electrical charge distribution in tropical
thunderstorms shows higher vertical development reaching
Montaña, J.; Van Der Velde, O.; Romero, D.; Fabro, F.; Lopez, J.; Argemí, O.; Pineda, N.; Sola, G. Thunderstorm Effects on the Atmosphere-Ionosphere System Data de presentació: 2016-06-29 Presentació treball a congrés
After many attempts since C.T.R Wilson predicted the acceleration of electrons in thunderstorms, Moore et al.  finally reported high-energy emissions produced by natural lightning to ground. These emissions were attributed to the intense electric fields produced by negative leaders to ground (e.g. [2-3])
On the other hand, radio frequency (RF) radiation from lightning at frequencies higher than 500 MHz have been poorly investigated since the pioneering work by Takagi and Takeuti . RF radiation has been related to negative stepped leaders, dart leaders, k-changes (recoil leaders) and preliminary breakdown .
In the laboratory, investigations of X-rays from long sparks at atmospheric pressure started about ten years ago (e.g. [6-8]). Recently, Montanyà et al.  motivated by old publications (e.g.  and references therein) relating Bremsstrahlung to be the source of microwave radiation from lightning leaders, has shown how X-ray emissions are coincident with peaks of the microwave RF power.
Aimed by the positive results found at the laboratory, during summer of 2015, a high-energy detector and a microwave receiver at 2.4 GHz with 5.5 MHz of bandpass were installed at the Eagle Nest tower (2537 m ASL, northeastern Spain). With this setup, we obtained the first simultaneous measurements of X-rays and microwaves from natural lightning. The results are very similar to those obtained at the laboratory from long sparks: X-ray emissions from lightning leaders are accompanied by intense RF emissions.
In this work, we will discuss if X-rays and microwave emissions share the same Bremsstrahlung mechanism or if the RF emissions are just due to dipole radiation. A streamer model is used to investigate and give support to the hypothesis for focusing our future measurements. The results found here are not only significant for the theoretical knowledge of the energetic emissions from lightning and sparks, but are also very important for future experimental investigations form the ground, aircraft and space.
We present the first data set of VHF measurements of radio emissions of lightning leaders in Colombia (tropical region) using the Colombia Lightning Mapping Array network - COLMA, the first 3D-VHF system operating in a tropical region. This network consists of Six VHF sensors [1-4] installed at the north of Colombia on April 2015 near to Santa Marta city.
The COLMA network has been installed in the frame of ASIM (Atmosphere-Space Interactions Monitoring) ESA mission, in order to obtain several parameters associated with the electrical characteristics of the tropical storms favorable for the production of Terrestrial Gamma ray Flashes- TGF's [5-6].
In addition, information collected using the COLMA network has allowed us to analyze several parameters of tropical storms such as: lightning leader propagation and electrical charge structure. For instance, a simple analysis of ten minutes interval on 16th November 2015, revealed what we expected, the lightning leaders can propagate at high altitude with a high vertical development. In that case, frequent activity of LMA sources were located up to 15 km of height. On the other hand, the electrical charge structure presented a tripolar distribution centred at 6.5 km, 8 km and 10.5 km of height.
The information present here has many implications because, the COLMA network is the first VHF 3-D system installed in the tropical region and this information will allow us to analyze and continue investigating the electrical properties of tropical storms such as, spatial distribution, intra cloud ratio, duration, altitude of the electrical charge, lightning leader information and the conditions for TGF production (altitude, charge, potential and electric field).
Montaña, J.; Lopez, J.; Van Der Velde, O.; Romero, D.; Fabro, F. International Conference on Grounding and Earthing & International Conference on Lightning Physics and Effects p. 1-4 Data de presentació: 2016-06-06 Presentació treball a congrés
On April 2015 a Lightning Mapping Array network (COL-LMA) was installed at the north of Colombia. This network provides 3D mapping of the development of lightning leaders. For the first time such network has been setup in the tropics. That allows us to investigate the high altitude development of lightning leaders. Here we present the results of the first measurements to confirm that negative leaders at altitudes of 15 km are common in the observed thunderstorms.
Lopez, J.; Montaña, J.; Van Der Velde, O.; Romero, D.; Fabro, F.; Taborda, J.; Aranguren-Fino, H.; Torres-Sanchez, H. European Geosciences Union General Assembly p. 1 Data de presentació: 2016-04-18 Presentació treball a congrés
In April 2015 the 3D Lightning Mapping Array (COLMA) network was installed on Santa Marta area (north of Colombia). The COLMA maps VHF radio emissions of lightning leaders in three dimensions by the time-of-arrival technique (Rison et al., 1999). This array has six sensors with base lines between 5 km to 20 km. The COLMA is the first VHF 3D network operating in the tropics and it has been installed in the frame of ASIM (Atmosphere-Space Interactions Monitor) ESA’s mission in order to investigate the electrical characteristics of tropical thunderstorms favorable for the production of Terrestrial Gamma ray Flashes (TGF).
In this paper we present COLMA data of several storms. We discuss lightning activity, lightning leader altitudes and thunderstorm charge structures compared to data form our ELMA (Ebro Lightning Mapping Array) at the north-east coast of Spain.
The data confirm what we expected, lightning leaders can propagate at higher altitudes compared to mid latitude thunderstorms because the higher vertical development of tropical thunderstorms. A simple inspection of a ten minute period of the 16th of November of 2015 storm shows a tripolar electric charge structure. In that case, the midlevel negative charge region was located between 7 to 9 km. The structure presented a lower positive charge below the midlevel negative and centred at 6.5 km and an upper positive charge region extending from 9 km to slightly more than 15 km. This vertical extension of the upper positive charge where negative leaders evolve is significantly larger compared to the storms at the ELMA area in Spain. COLMA has shown frequent activity of negative leaders reaching altitudes of more than 15 km.