ICAE International Commission on Atmospheric Electricity

ICAE 2003 Versailles

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Benjamin Franklin

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Tuesday 10 th June



Session A3 Storm Electrification III (poster)

  A. G. Amiranashvili and A. G. Nodia
Some Results of Investigation of IL-14 Airplane Electrization in Clouds and Atmosphere

P. Baranski, P. Bodzak, and A. Maciazek
The complex discharge lightning events observed simultaneously by the SAFIR, radar, field mill and maxwell current antenna during thunderstorms near Warsaw

W. H. Beasley, F. W. Gallagher, A. R. Bansemer, L. G. Byerley, J. A. Swenson, and I. G. Bogoev
Simulations of Spatial and Temporal Variations of Electric-Field Contours at the Surface Beneath Thunderstorms as Would Be Observed by a Network of Solar-Powered Electric-Field Meters
  A. M. Blyth and J. Latham
Corona emission thresholds for graupel-graupel collisions close to the 0C isotherm in thunderclouds
  D. E. Buechler, D. M. Mach, and R. J. Blakeslee
Relationships between Electrical and Radar Characteristics of Thunderstorms Observed During ACES
  L. M. Coleman, M. Stolzenburg, T. C. Marshall, P. R. Krehbiel, R. J. Thomas, W. Rison, and T. Hamlin
The Effects of Charge and Electrostatic Potential on Lightning Propagation
  S. Coquillat, M. P. Boussaton, S. Chauzy, S. Soula, and F. Gangneron
A new videosonde for in situ observation of precipitation particles
  A.Delannoy, A.Broc
Modeling of a Wintry Wave-forced Deep Convection over the North of Shetland Islands and Simulation of the Subsequent Cloud Electrification
  J. A. Dovgaluk, L. V. Kashelva, T. A. Pershina, Y. P. Ponomarev, A. A. Sinkevich, V. D. Stepanenko, and N. E. Veremei
Role of electrical discharges in cloud microphysics and electrical field strength changers
  T. Hamlin, P. Krehbiel, Y. Zhang, R. Thomas, W. Rison, and J. Harlin
Electrical Structure and Storm Severity Inferred by 3-D Lightning Mapping Observations During STEPS
P. H. Handel
Proof of Cloud Instability with Respect to the Formation of Several Horizontal Space Charge Layers
S. Kolev
Numerical simulations with the inductive mechanisms using some published data
  K. M. Kuhlman, E. R. Mansell, C. L. Ziegler, J.. M. Straka, and D. R. MacGorman
Dynamical, Microphysical and Electrical Simulations of the 29 June 2000 STEPS Supercell
D. MacGorman, D. Rust, O. van der Velde, M. Askelson, P. Krehbiel, and R. Thomas
Lightning Relative to Precipitation and Tornadoes in a Supercell Storm
D. M. Mach and W. J. Koshak
General Matrix Inversion Technique of the Calibration of Electric Field Sensor Arrays on Aircraft Platforms
J. Margerit and C. Nicolis
A reaction-diffusion-advection model of the early stages of cloud electrification


Some Results of Investigation of IL-14 Airplane Electrization in Clouds and Atmosphere

A.G.Amiranashvili, A.G.Nodia
Institute of Geophysics, Georgian Academy of Sciences


Data on IL-14 airplane electrization in clouds and clear atmosphere have been presented. Measurements were conducted in different regions of Georgia since 1965 to 1977. The airplane speed was approximately 250 km/hr. Flights were conducted in more than 450 convective clouds (including 25 clouds, affected by a crystallizing agent PbI2) and in 30 stratified clouds. In 40 cases, the flights were conducted in clear atmosphere. In 58 cases, there was investigated an airplane electrization in clouds of explosion of an anti-hail gear Elbrus-2, containing reagents AgI, PbI2 and NaCl. In some cases, at the same time, concentration of aerosols of over 0,7 mkm diameter was measured in a free atmosphere. Water content, concentration and size of drops were measured in clouds. A unit of an airplane charge measurement is given in 10^-6 C, omitted further for better convenience. The Table presents some data of plane electrization Q:



Flight altitude


Cloud vertical

thickness (km)

Q mean

Q max

Clear atmosphere











Cloud of

Explosion of


3.0 (PbI2)

3.0 (AgI)

3.0 (NaCl)






Convective clouds



Convective clouds

affected by


Stratified clouds










































A generalized picture of airplane electrization in different parts of a convective cloud has been presented. In particular, electrization of a plane is a maximum in the middle of a cloud at the level of 0.7 part from its vertical thickness. Empirical links of plane electrization with atmospheric aerosol content, size and cloud particle concentration, water content, ice-forming nuclei concentration, etc., have been revealed.


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The Complex Discharge Lightning Events observed Simultaneously by the SAFIR, Radar, Field Mill and Maxwell Current Antenna during Thunderstorms near Warsaw

P. Baranski
Institute of Geophysics, Polish Academy of Sciences, 01-452 Warsaw, Ks. Janusza 64, Poland

P. Bodzak, A. Maciazek
Institute of Meteorology and Water Management, 01-673 Warsaw, Podlesna 61, Poland


Special cases of c-g lightning discharges and their position in thunderclouds have been preliminary examined by means of lightning localization together with simultaneous independent electric field and Maxwell current recordings, and meteorological radar data. The nine lightning localization stations SAFIR network in Poland has started its operational functions since autumn of 2001, giving now the lightning ic and c-g discharge detections with the efficiency about 95% and their 2D localizations with the accuracy better than 1 km for the whole Poland territory (Baranski et al., 2002). The procedures of data obtaining from the new SAFIR net, especially of those connected with c-g identifications, still strongly desired (Berger, 2002), are being currently validated. They are examined using the routine SAFIR monitoring of total and local thunderstorm activity appearing inside the chosen area near Warsaw and additional detection of lightning discharges in selected thunderclouds of this region by the single point field mill and Maxwell current antenna recordings. At the first stage of this endeavour we have focused our research on observation of the occurrence of the so-called complex or bipolar flashes. Sometimes a bipolar pattern of two subsequent return strokes can appear in the same ground flash detected by the SAFIR system. It means that both positive and negative charge is neutralized by such a discharge.

On the other hand, in our sets of data we have also found not negligible number of such special cases, when the lightning discharge detected as complex one by field mill and Maxwell current antenna, is not completely recognized by the SAFIR system, i.e., one of its components (return strokes) is invisible for the SAFIR sensors. It may suggest that certain discrimination criteria which have been implemented in the software and hardware of the SAFIR system installed in Poland should be modified to achieve better efficiency for detection of that important but rather infrequent type of c-g discharges.

Additionally, by superimposing the SAFIR localizations of the detected complex flashes on the appropriate in time radio echo maps of the meteorological radar, it was possible to estimate the lightning position in relation to the position and shape of the precipitation shaft of the individual thundercloud. Such superposition of the radar pictures and ground flashes locations have also given some indications, which part of the thunderclouds are involved in generation of particular lightning discharge. Below is presented one of the examples of the studied radar and SAFIR data superposition concerning the positive part of the bipolar flash which occurred at 11:15:27 UTC during vigorous thunderstorm observed on 28-th May, 2002 near Warsaw. The left part of that illustration is the vertical cross-section radar map for the azimuth angle of the considered flash. The right part is the corresponding radar echo tops map. In both parts the arrow points out the SAFIR location of detected flash. The open circle, denoted IGF, gives the position of our measuring site with field mill and Maxwell current antenna in Warsaw. The next circle, denoted WB, shows the position of the SAFIR sensor in Warsaw.

The additional use of the LF antenna for recording the electric field changes during lightning, extends the possible insight into spatial-temporal distribution not only of the complex c-g discharges, but also of the multiple stroke flashes in relation to thundercloud development. They will be the subject of a separate report.


Baranski P., Bodzak P., Maciazek A., Some results of the SAFIR, radar and field mill observations for selected thunderstorms near Warsaw, Abstracts of the 2002'SAFIR WORKSHOP, Budapest, Hungary, 18-20 September, 2002.
Berger G., Method of evaluation of the detection performance of a network, (oral presentation during the 2002'SAFIR WORKSHOP, Budapest, Hungary, 18-20 September, 2002.)


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Simulations of Spatial and Temporal Variations of Electric-Field Contours at the Surface Beneath Thunderstorms
as Would Be Observed by a Network of Solar-Powered Electric-Field Meters

William H. Beasley, Frank W. Gallagher,
University of Oklahoma, Norman, OK 73019

Aaron R. Bansemer
National Center for Atmospheric Research, Boulder, CO 80303

Leon G. Byerley
Lightning Protection Technology, Tucson, AZ 85716

Jody A. Swenson, Ivan G. Bogoev,
Campbell Scientific, Inc.
Logan, UT 84321


Electric field meters known as "field mills" have been used for many years to measure the vertical component of the atmospheric electric field near the ground for thunderstorm research and safety purposes. Typically, the long-term reliability and maintainability of traditional field mills is limited by the connection between the rotating motor shaft and electrical ground and the degradation of electrical insulation of the sense electrodes. A new electric-field meter developed by Campbell Scientific, Inc. has eliminated both of these problems and has also reduced power requirements drastically so that the new instruments can operate on solar power. This development makes it feasible now to deploy networks of electric-field meters for many applications for which the costs would have been prohibitive in the past. In order to begin to understand how to deal with the data streams from such networks, and to develop means of displaying and interpreting the data, we have simulated the growth, decay, and advection of various simple and complex charge distributions over networks of realistically distributed electric field meters. The ultimate goals are both improved understanding of the behavior of thunderstorm electric fields at the ground and development of affordable means for improved early warning and all-clear notification with regard to the potential for lightning strikes.


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Corona Emission Thresholds for Graupel-Graupel Collisions close to the 0C Isotherm in Thunderclouds

School of Environment, University of Leeds, Leeds, UK, LS2 9JT

J. Latham,
MMM Division, NCAR, P.O. Box 3000, Boulder, CO 80307-3000, USA


Laboratory studies have been conducted of the threshold conditions under which glancing collisions between pairs of graupel pellets or small hailstones which are either melting or in wet growth, produce a corona discharge in a vertical electric field E. The observed corona is found to be emitted at the tip of an ephemeral liquid filament, of length comparable with the dimensions of the interacting hydrometeors, drawn out during each interaction. The probability f that corona was produced during an inter-action increased steadily from zero for increasing values of E above about 200kV/m, and was significantly in excess of 50% for values of E=400kV/m, which is probably about the maximum ambient value occurring in a thunderstorm. The results relate to collisions at relative velocities V characteristic of those occurring in thunderstorms. We conclude that this mechanism of corona initiation could be of importance and lead to the production of lightning in regions of a thundercloud where the temperatures are close to 0C. It thus appears that corona can be initiated from solid or liquid hydrometeors of precipitation dimensions at all temperatures at which lightning is commonly initiated.


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Relationships between Electrical and Radar Characteristics of Thunderstorms Observed During ACES

D. E Buechler and D. M Mach
University of Alabama in Huntsville, Huntsville, AL 35899, U.S.A.

R. J. Blakeslee
NASA Marshall Space Flight Center, Huntsville, AL 35812, U.S.A.


The Altus Cumulus Electrification Study (ACES) took place near Key West, Florida during August 2002. A high altitude, remotely piloted aircraft obtained optical pulse and electric field data over a number of thunderstorms during the study period. One unique aspect of the lightning measurements is that the time between successive overflights was small (~5 minutes), and the aircraft was still over the edge of the storm when it was turning around. Thus the storms were continuously monitored for a large portion of their life cycle. Radar data of these storms were obtained from the WSR-88D radar sites at Miami (KAMX)) and Key West (KBYX), Florida. Dual polarization radar measurements of some of the storms were also obtained by the NASA Polarimetric radar (NPOL) which was located on Ramrod Key beginning on 10 August 2002. In addition, data from the National Lightning Detection Network (NLDN) characterize the cloud-to-ground lightning activity from the storms, while observations from the Los Alamos four station EDOT lightning detection network provided information on the total (i.e., cloud-to-ground and intracloud) lightning. The lightning production from the storms investigated during ACES varied greatly. The variations in lightning activity between storms are studied by examining the three dimensional radar structure associated with the storms observed by the aircraft. Cross sections of radar observations along the flight track show the storm structure of the thunderstorms producing the fields. The evolution of radar structure and lightning activity are examined throughout storm period of observation.


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The Effects of Charge and Electrostatic Potential on Lightning Propagation

L. M. Coleman, M. Stolzenburg, T. C. Marshall
Department of Physics and Astronomy, University of Mississippi, University, MS, USA.

P. R. Krehbiel, R. J. Thomas, W. Rison, T. Hamlin
Geophysical Research Center, New Mexico Institute of Mining and Technology, Socorro, NM, USA.



Three-dimensional lightning mapping observations are compared to cloud charge structures and electric potential profiles inferred from balloon soundings of electric field in New Mexico mountain thunderstorms. The comparisons consistently show good agreement between the altitudes of horizontal lightning channels and the altitudes of electric potential extrema or wells. Lightning flashes appear to deposit charge of opposite polarity in relatively localized volumes within the preexisting lower positive, midlevel negative, and upper positive charge regions associated with the potential wells. The net effect of recurring lightning charge deposition at the approximate levels of potential extrema is to increase the complexity in the observed storm charge structure. The midlevel breakdown of both normal intracloud flashes and negative cloud-to-ground flashes is observed to be segregated by flash type into the upper and lower parts of the deep potential well associated with the midlevel negative charge. The segregation is consistent with perturbations observed in the bottom of the negative potential well due to embedded positive charge that was probably deposited by earlier flashes. It is also consistent with an expected tendency for vertical breakdown to begin branching horizontally before reaching the local potential minimum. The joint observations reconcile the apparent dichotomy between the complex charge structures often inferred from balloon soundings through storms and the simpler structures often inferred from lightning measurements.


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A new videosonde for in situ observation of precipitation particles

S. Coquillat, M. P. Boussaton, S. Chauzy, S. Soula, and F. Gangneron
Laboratoire dAérologie, UMR UPS/CNRS N5560, Observatoire Midi-Pyrénées,
14 avenue Edouard Belin, 31400 Toulouse, France


Several questions on discharge triggering and electrification processes in thunderclouds remain open at the present time. We still dont know which particles, with which electric charge, in which intense electric field, in which volume of intense electric field, are responsible for cloud discharges (11th ICAE, 1999). Blyth et al. (1998) showed that glancing collisions involving at least one raindrop can produce long liquid filaments at the tips of which corona - first step to a propagative discharge - is easily emitted in electric fields down to 150 kV/m. Furthermore, numerical results by Coquillat and Chauzy (1994) and Georgis et al. (1995) indicate that corona can also be triggered at realistic altitudes from stable raindrops as long as their electric charge is high, or pairs of drops interact. On the other hand, Baker (2001) proposed an alternative mechanism based on the acceleration of high energy electrons produced by cosmic rays that could lead to propagative discharges too. Further in situ observations of the microphysics involved in the high flash rate events are required for evaluating the probability of occurrence of these various mechanisms.

In order to investigate the possible relationship between microphysics and lightning flash rate, we plan to perform in-cloud soundings with free balloons carrying a meteorological radiosonde (PTU + GPS), an electric field sensor (3 components of the field), and a new videosonde, which has been designed for detecting the nature, the size, and the electric charge of precipitation particles. It is equipped with a video camera (CCD) that continually films at a rate of 25 images per second. Two halogenous lamps ensure a sufficient illumination to reduce its time of aperture and allow the determination of the particle size via the location of the induced shadows. The sensor is dimensioned to detect the particles singly with sizes ranging from about 0.5 mm to more than 1 cm and charges ranging from ± 1 to ± 400 pC. An induction cylinder mounted in the upper part of the sensor measures the electric charge. The electronic system processes the charge signal, digitizes it, and displays the charge value in binary code by an array of LED located in the lower part of the sensor in the field of view of the camera. This display is released during the time the particle is visible. It can be pointed out that uncharged particles are also detectable. The video signal that contains all the information is transmitted to ground by telemetry in real time.

The data processing involves the determination of various parameters that are also of importance for the comparison with radar and model data. The calculation takes into account the nature, the velocity, the corresponding sampling volume, and the probability to be detected by the camera of each particle, which is classified into four categories: raindrop, graupel, aggregate, and hail. In this way it is possible to evaluate the precipitation rate, the dimensional distribution N(D), the charge density , the equivalent radar reflectivity Z, and the percentage of charged particles (over the threshold). The precipitation rate calculation has been tested at the ground from the comparison between data from the videosonde and from a disdrometer. Further calibration of the charge density determination is currently carried out.

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Modeling of a Wintry Wave-forced Deep Convection over the North of Shetland Islands and Simulation of the Subsequent Cloud Electrification

Alain Delannoy and Alain Broc
92322 Châtillon Cedex France


South wind over the Shetland Islands produces a wave flux which, in winter time, triggers convective clouds over the Atlantic Ocean. Those clouds get electrified and produce isolated lightning flashes. In an attempt to describe the atmospheric electrical configuration produced by this meteorological situation, we run MESONH, a meso-scale non hydrostatic dynamical model, which delivers a 3D meso-scale description of the convective cell. Results from MESONH are consistent with the NOAA satellite observations. A microphysical and dynamical 1.5 D model is then applied to simulate the vertical electrification within the cell.

We present the first result of our simulation and discuss them in term of the atmospheric electric field produced by such convective clouds.

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Role of electrical discharges in cloud microphysics and electrical field strength changers

Dovgaluk J.A., Kashleva L.V., Pershina T.A., Ponomarev Yu.Ph., Sinkevich A.A., Stepanenko V.D., Veremei N.E.

Dr. Sinkevich A.A. Chief of Cloud Physics
Cloud Seeding and Solar Radiation Studies Department, A.I.Voeikov Main Geophysical Observatory, Karbyshev str.7, St.Petersburg, Russia, 194021


Investigations to study the effect of electric discharges of various types on fog spectra have been carried out in cloud chambers.

Corona dischargers were produced in cloud chamber and freezing temperature of drops were measured. It was obtained that corona discharges can cause a rise of freezing temperature up to -5 - -6 C. The dependence of drops freezing temperature from distance to corona discharges was also studied.

Streamers were produced in Large Volume MGO cloud chamber with the help of high voltage Tesla transformer. Data analyze clearly show that one can observe fog particles enlargement due to streamers. They also provide great increase in fog volume charge and hence electrical field strength.

Theoretical investigations of the role of corona dischargers in cloud characteristics changers have been carried out with numerical cloud model. Results of these investigations have shown that corona dischargers can play significant role in cloud electrization.


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Electrical Structure and Storm Severity Inferred by 3-D Lightning Mapping Observations During STEPS

T. Hamlin, P. Krehbiel, R. Thomas, W. Rison, and J. Harlin
New Mexico Institute of Mining and Technology, Socorro, New Mexico USA

Y. Zhang
Cold and Arid Regions Research Institute, Lanzhou, China


The Severe Thunderstorm Electrification and Precipitation Study (STEPS 2000) provided numerous examples of storms that electrified anomalously, some of which became severe. The storms were often supercells and there were several cases in which the lightning activity consisted primarily of IC flashes for substantial periods of time, only followed much later (if at all) by the onset of positive cloud-to-ground activity. Radar comparisons for the tornadic storm of June 29 and the non-severe Bird City storm of June 3 during STEPS indicate that positive charge was localized at mid-levels in the precipitation core, but the electrification also had a horizontally extensive, multilayer structure extending away from the core.

The anomalous storms often began with lightning between mid-level negative charge and lower positive charge, corresponding to the lower part of a normal tripole structure. An upper positive charge then rapidly developed that initiated more intense lightning activity and completed a normal tripolar structure, but with the important difference that the lower positive region appeared to be a dominant charge, as indicated by the complete lack of CG discharges of either polarity. With further intensification of the lightning activity the upper positive charge appeared to gradually evolve downward in altitude to become the dominant mid-level charge, and upper level negative charge developed above this to produce an inverted dipole structure that appeared to be stable for long periods of time.

The LMA obtained observations of the total lightning activity in several tornadic storms. In each of three or four cases the initial tornado of the storm (or a funnel cloud that did not extend to ground) was accompanied by a distinctive lightning-free region, or lightning `hole', in 3-dimensional observations of the VHF lightning radiation sources. The lightning holes appear to be associated with a strong updraft on the upshear side of the storm, and the tornados occurred on the western edge of the holes. The occurrence of the lightning holes in these and other severe supercell storms was accompanied by upward moving, high-altitude lightning events indicative of strong convective surges in the storm. The F1 tornado on June 29, 2000 of STEPS was preceded by a sequence of three such convective surges at 10 to 15 minute intervals extending up to 15-16 km altitude MSL. Each surge was accompanied by a successively stronger lightning hole, with the third surge initiating the tornado. The observations appear to be characteristic of tornadic storms, or of storms having the potential for becoming tornadic, and could provide an additional means of nowcasting tornadic occurrences.



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Proof of Cloud Instability with Respect to the Formation of Several Horizontal Space Charge Layers

Peter H. Handel
Department of Physics and Astronomy, Univ. of Missouri St. Louis, MO 63121, USA


For the first time we present a rigorous proof of the instability of clouds containing small ice crystals, or sufficiently small H2O aggregates in general, to the spontaneous formation of several horizontal polarization layers and space charge layers. Our investigation was inspired by the balloon observations (Fig. 1) of many horizontal space charge layers in the more quiescent conditions of the trailing region of Mesoscale Convective Systems (MCS). The method used by us was suggested by the success of the author's polarization catastrophe approach to cloud and thundercloud electrification, which proved to be applicable also in the rings of Saturn.

Our proof contains two parts. In the first part we evaluate the dipole moment of a single ice crystallite, and then derive the expression of the free energy of a cloud of such crystallites. We then prove that the free energy of a uniform cloud with sufficient ice crystallite concentration is lowered by the spontaneous formation of layers of polarization and polarization charge, partially compensated by real masking charges. Let us denote by a the polarizability.

The free energy is given by the integral from the cloud base to clod top, of n/a-n2/3e0, where n=n(z) is the initially constant concentration of ice crystallites as a function of height z. The condition requiring a sufficient concentration of crystallites is usually satisfied.

In the second part, starting from a cloud-lagrangian incorporating among other contributions also the free energy contributions derived before, we show that an arbitrarily small sinusoidal perturbation of the cloud concentration will grow exponentially, indicating the presence of the instability that had to be proven. ( = vacuum permittivity)


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Numerical Simulations with the Inductive Mechanisms using some published Data

Staytcho Kolev
National Institute of Meteorology and Hydrology-BAS, Blvd. Tzarigradsko Shaussee 66, 1784 - Sofia, Bulgaria
Email: stayko.kolev@meteo.bg


There are a lot of laboratory experiments in the last 10-15 years dealing with thunderstorm elecrification processes. One of the most important result is the laboratory evidences of the main role which play the non-inductive mechanisms in the thundercloud charging processes and especially in the the primary stage establiging enough electrical charges to provoke the first lightning stroke. Futher laboratory studies in UMIST (Brooks and Saunders 1994) have shown that the experimental results are broadly in line with the predictions of the inductive theory, as presented by Mason [1988], although it seems likely that he may have overestimated the number of droplets that rebound from the rimer. It seems more likely that the inductive mechanisms acts as a contributory mechanism in the later stages of electrification although there is disagreement between thundercloud models which include it in this capacity [Dye et al.,1986;Heldson and Farley, 1987;Ziegler et al., 1991]. . According to Brooks and Saunders [1994] the significance of the mechanism to thunderstorm electrification is still open to question and further is argued that a better understanding of the detailed nature of droplet-graupel interactions in clouds is required in order to assess properly the contribution of the inductive mechanism to cloud electrification.

Having in mind the importance of of the 2-mm diameter graupel particles and cloud droplets contents, it has been calculated the expected lightning frequences on a base of the inductive mechanism.



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Dynamical, Microphysical and Electrical Simulations of the 29 June 2000 STEPS Supercell

Kristin Kuhlman
Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, c/o National Severe Storms Laboratory, 1313 Halley Circle, Norman, Oklahoma 73069 USA
Phone: (405) 366-0413
Fax: (405) 366-0472

Edward R. Mansell, Conrad L. Ziegler, Jerry. M. Straka, and Donald R. MacGorman


The Severe Thunderstorm Electrification and Precipitation Study (STEPS) provided one of the most comprehensive data sets ever obtained on electrification and lightning in severe storms. Numerical simulations of the storms from STEPS can assist the improved understanding of relationships between kinematics, microphysics and electrification. The OU-NSSL three-dimensional dynamic cloud model was used to simulate the first three hours of the life cycle of the 29 June 2000 tornadic supercell from STEPS. This study compares radar-observed and numerically modeled structure of the storm. We also examine the sensitivity of simulated charge structure and lightning due to changes in the charge separation parameterizations; comparisons of simulated electrical structure and lightning characteristics are made with electrical observations using balloon-borne electric field soundings and the Lightning Mapping Array (LMA).


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Lightning Relative to Precipitation and Tornadoes in a Supercell Storm

Don MacGorman, Dave Rust,
National Severe Storms Laboratory, Norman, OK, USA

Oscar van der Velde, Mark Askelson,
CIMMS/University of Oklahoma, Norman, OK, USA

Paul Krehbiel, and Ron Thomas
New Mexico Institute of Mining and Technology, Socorro, NM, USA


To examine relationships of lightning activity to tornadoes and precipitation formation, we have analyzed a supercell storm that occurred in the central United States on 13 June 1998. Data were provided by the National Severe Storm Laboratory's 10-cm polarimetric radar and by New Mexico Institute's lightning mapping array. The storm was positioned well for observation for roughly one hour, during which it produced tornadoes and large hail.

Trends in the number of VHF radiation sources near the mixed phase region were similar to the trends of mass and volume of graupel in this region. Trends in graupel mass at still higher altitudes appeared unrelated. The rate of VHF sources produced by lightning channels tended to increase at middle levels of the storm prior to tornadoes. Furthermore, the maximum height of VHF sources tended to increase before severe weather, in a pattern suggestive of updrafts penetrating the equilibrium level. Trends were consistent with the hypothesis that increases in lightning lead severe weather, but increases in flash rates were neither as prominent nor as clearly associated with severe weather as those reported for Florida storms, possibly because flash rates were very large (>100 per minute) throughout the period.

Cloud-to-ground flash rates averaged less than 1 per minute for the first 40 minutes of our analysis, but then increased to several per minute. This increase began a few minutes after a strong sustained updraft that caused wet growth of hail. During the increase, almost all cloud-to-ground flashes were positive, and the polarity of cloud flashes appeared inverted from normal. Though wet growth was not likely itself responsible, we hypothesize that unusually large liquid water content in the updraft caused graupel to gain positive charge in regions in which it normally gains negative charge, thereby inverting the electrical structure of the storm.


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General Matrix Inversion Technique of the Calibration of Electric Field Sensor Arrays on Aircraft Platforms

D. M. Mach
University of Alabama in Huntsville, Huntsville, AL 3599, U.S.A.

W. J. Koshak
NASA Marshall Space Flight Center, Huntsville, AL 35812, U.S.A.


We have measured the vector electric field in and around thunderstorms and other clouds with several aircraft (e.g., ER-2, DC-8, Citation, Altus) using sets of rotating vane electric field mills. One of the most critical steps in using the electric field data from these sensors is determining the relationship between the mill outputs and the external vector electric field. We have developed a generalized calibration method that works with all of the different aircraft/mill combinations. Our method is based on the determination of the matrix that represents the individual mill responses to the external electric field. Given a field mill and aircraft configuration, this matrix is always unique. This matrix can then be inverted to determine the external electric field from the mill outputs. A distinct advantage of the method is that if one or more mills need to be taken out of the equation (for example, due to a mill malfunction), it is a simple matter to reinvert the matrix without the bad mill. Our method starts by estimating the responses of each mill to the external electric field components. We then produce a first estimate of the external electric field. The external field estimate is then "correct" using any known properties of the external field (i.e., roll/pitch maneuvers in fair weather fields) and used to re-estimate the responses of the mills to the external fields. We correct the new estimates of the mill responses based on our knowledge of the mill conditions (i.e., mill symmetry and placement) and continue to iterate between the mill responses and field values correcting each one until the values converged. The results of this calibration method are shown for four different aircraft.  


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