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Fall 1999
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ICAE Fall 1999 News Letter
RESEARCH ACTIVITY
by Organization
* * *
AIRBORNE RESEARCH ASSOCIATES (Weston, MA)
This summer and fall ARA has concentrated on field testing its
new ATLAS (Aircraft Total Lightning Advisory System) single station lightning
mapping system that has been under development for four years. This system is
unique for a single sensor system because it can accurately determine the
distance to IC and CG flashes. This is done through measurement of only the
initial breakdown into virgin air of the "first pulse" of lightning. This novel
patented approach is based on the principle that the first electrical breakdown
("first pulse") of all lightning is essentially invariant in amplitude and
vertical -- thus distance is proportional to 1/amplitude and there is no
polarization error arising from variations in the relative orientation of the
sensor and radiating dipole. For the first time accurate estimates of distance
can be obtained with a single sensor, this is possible for IC and CG flashes,
and these can be identified.
The initial vertical breakdown occurs where electric field
intensity maximizes, either at the bottom or top of the horizontal negative
charge layer that occupies the middle height range of thunderclouds. Discharges
at the bottom of this layer (near 5 km), where the sign of the "first pulse"
discharge is positive, occur at the initiation of the downward propagating
leader of cloud-to-ground lightning. Similarly, the "first pulse" at the top of
the negative layer (near 8 km) is negative, propagates upward, and initiates
intracloud discharges.
Previous aircraft lightning detectors operate in the VLF range
and mostly detect intense CG discharges. The characteristic "radial spread"
phenomena in the displays of these systems (a series of dots along a radial
line extending outward from the aircraft position at the center of the display)
is caused by detection of the series of return strokes in most CG flashes. They
have different intensities and are interpreted as being at different distances.
The ATLAS system, which detects only first pulses about 1% as intense as return
strokes, only shows one dot per flash at a relatively accurate range. Azimuth
is determined through conventional crossed loop/ferrite coil technology, but
through detection of only the first pulse. Because an accurate geographic
location can be determined for each flash, they can be shown realistically on a
GPS/moving map aircraft navigation system. Trying to display lightning flashes
with the "radial spread" characteristic from moving aircraft will result in a
smear of dots across the screen -- the geographic position will not be known
and the cloud of dots can obscure other information on the screen.
With support from NASA, an ATLAS system installed on the ARA
TurboBaron aircraft as well as two systems installed on the ground are being
tested in Florida. Results show good correlation of ATLAS with NLDN, the KSC
LDAR, and radar imagery. Tests are continuing and future plans call for digital
signal processing to improve performance. Those interested in the new first
pulse total lightning positioning technology, which includes ATLAS and a
multistation time-of-arrival system called LASI, should contact Ralph Markson
(rmarkson@totallightning.com). Additional details on these systems are in the
Proceedings of the 11th International Conference on Atmospheric Electricity,
NASA/Marshall Space Flight Center, AL, June1999, p.188.
AIR FORCE RESEARCH LAB (Boston, MA)
John Willett (Air Force Research Lab, Boston, MA), Dan Davis
(State University of New York at Albany), and Pierre Laroche (ONERA,
France)continue analysis of their 1996 triggered-lightning/sounding-rocket
experiment at Camp Blanding, FL. The vector, electrostatic-field profiles from
the sounding rockets have been "navigated" into an Earth-fixed coordinate
system and are being compared with radar data from the Jacksonville NEXRAD. The
current and field-change data from the triggered lightning are being analyzed
to estimate the propagation velocities of the upward positive leaders that
initiated the discharges. Electrostatic models of the corona sheath around
these leaders are also being developed to relate leader current and
ambient-potential profile to propagation velocity. Anne Bondiou-Clergerie and
Philippe Lalande (ONERA, France) are using the experimental data to validate
and improve their theoretical model of long positive leaders.
The University of Arizona (Tucson, AZ)
E. P. Krider and M. J. Murphy are continuing to compare the
locations and magnitudes of intracloud (IC) and cloud-to-ground (CG) lightning,
as detected by the Lightning Detection and Ranging (LDAR) system, the field
mill network, and the Cloud-to-Ground Lightning Surveillance System that
operate at the NASA Kennedy Space Center (KSC) and Air Force Eastern Range
(ER). The results show that when there is active convection, most CG flashes
begin on the lower side of the negative charge region with an initial discharge
that propagates downward toward a lower positive charge center (LPCC) near the
melting level. Currently, the causes of the LPCCs appear to be both a cloud
charging process and IC discharges that effectively deposit positive charge at
low altitudes. During the onset of electrification, the LPCC typically appears
first at field mill sites that are close to or under the storm.
E. P. Krider and W. J. Koshak are continuing to study the
response of the NASA Lightning Imaging Sensor (LIS) when lightning flashes
occur over or near the KSC-ER and are within the LIS field of view. Bruce
Gungle is examining the relationships between lightning and surface rainfall at
the KSC-ER. Scott Handel is studying the behavior of the surface electric field
during the onset of isolated thunderstorms and also the surface field just
before large, horizontal flashes propagate into the KSC-ER area from distant
storms. In the future, an effort will be made to determine if the total light
output produced by CG and IC flashes, as inferred from ground and satellite
measurements, is proportional to the total charge deposited by the flash.
Cloud Physics Department of Voeikov Main Geophysical Observatory
(MGO, St. Petersburg, Russia)
The group (Dr.Stepanenko V. D., Ponomarev Yu.Ph., Dr.Dovgaluk
Ju.A., Pershina T.A) headed by Dr.Sinkevich Andrei had carried out laboratory
experiments on studying the influence of electrical discharges on spectrum of
fog particles.
Experiments were carried out during the last 5 years. 3 cloud
chambers of different volumes were used - 65 m3, 1 m3,
0.01 m3. A Tesla transformer was used to produce electrical
discharges in the 65 m3 cloud chamber. Voltage was equal to 7500000
V. A 3 kV source was used to produce discharges in the 1 and 0.01 m3
cloud chambers. The results of experiments in the 65 m3 cloud
chamber have shown that there is an increase of cloud particles and electrical
field strength due to electrical discharges. Electrical field strength
increases to the order of magnitude due to the increase of volume charge.
Electrical discharges in the 1 m3 cloud chamber influence crystal
forms which appear in the chamber. Crystals with complex forms appear after
discharges. Electrical discharges in the 0.01 m3 cloud chamber lead
to drops freezing at temperature –4 to -6 °C.
Electrical discharges lead to increase of volume charge and hence
favorable conditions for further discharges appear. This mechanism of positive
feedback can play a significant role in lightning formation. Results of
experiments were presented in MGO collection of articles to the 150 anniversary
of MGO.
Acknowledgement. We would like to thank Dr Stasenko V.N for his
help in transformer Tesla installation in cloud chamber.
COLORADO STATE UNIVERSITY (Fort Collins, CO)
Department of Atmospheric Science
Timothy Lang and Steven Rutledge are utilizing dual-Doppler and
multiparameter radar data, along with electric field change meter and
cloud-to-ground lightning detection network data, to examine a broad spectrum
of thunderstorm types and intensities. The goal is to better understand how
storm kinematic and microphysical structure affect lightning production. Ten
case studies have been identified: five mid-latitude thunderstorms observed in
northeast Colorado in 1998, and five tropical thunderstorms observed during the
TRMM/LBA project, which occurred in early 1999 in the western Amazon of Brazil.
These storms vary from weak air mass and monsoonal thunderstorms to intense
squall lines and supercells. By examining how variations in lightning patterns
and production correlate to variations in the kinematic and microphysical
structures within this diverse array of storms, we hope to gain new insights
into how storm kinematics and microphysics affect lightning production.
The Frequency and Distribution of Severe Storms That Produce
Predominately Positive Cloud-to-ground Lightning in the Contiguous United
States
Although the polarity of most cloud-to-ground (CG) lightning is
negative, the ground flashes beneath severe storms are sometimes predominately
positive (i.e., > 50%). Occasionally, the +CG lightning flash density is
very high (i.e., >=0.01 km-2 h-1). The existence of
predominately positive cloud-to-ground (PPCG) lightning in severe storms evokes
fundamental questions regarding thunderstorm electrification mechanisms and
raises the possibility of nowcasting severe storms with CG lightning data.
Despite their intriguing nature, the regional frequency and % of severe storms
dominated by +CG lightning in the contiguous U.S. are not well understood. In
addition, little is known about the magnitude of positive peak currents in
these storms.
To address this issue, Lawrence D. Carey and Steven A. Rutledge
determined the %, flash density, and mean peak current of +CG lightning within
the vicinity of every large hail and tornado report during a ten year period
(1989 - 1998) during the warm season (April - September). These analyses reveal
that PPCG lightning rarely occurs beneath severe storms in the contiguous U.S.
Only 15% (5%) of severe storm reports were associated with (high flash density)
PPCG lightning. However, there was significant regional variability. The
overwhelming majority of +CG lightning dominated severe storms occurred in the
central U.S. The Eastern U.S. was nearly devoid of these unique storms; only 3%
(0.5%) of severe storms produced (high flash density) PPCG lightning there. In
the Central and Northern Plains, about 41% (15%) of severe storm reports were
accompanied by (high flash density) PPCG lightning.
Broad frequency and % maxima of severe storms that generate PPCG
lightning stretched from eastern CO and the OK Panhandle northeastward through
KS and NE to the eastern Dakotas and southern MN. In this
southwest-to-northeast tilted region, typically > 30% of severe storms were
+CG dominated. Interestingly, this feature is remarkably similar in location
and shape to the region of high percentage (e.g., > 10%) of +CG lightning
found in the Great Plains and Upper Midwest when analyzing annual NLDN data
from 1989 - 1998. This region is also characterized by a relative maxima in the
median positive peak current (> 30 kA; Orville and Huffines, Proceedings of
the 11th ICAE, 412-415, 1999). Inspection of our results shows that
severe storms dominated by PPCG lightning generate a markedly different
population of positive peak currents than other severe storms. The mean
positive peak current for severe PPCG lightning events typically ranges from 35
kA to 65 kA while it ranges primarily from 10 kA to 30 kA for all other severe
storms. Based on these results, we suggest that severe storms that produce PPCG
lightning may be largely responsible for the annual maxima in both the percent
of positive CG lightning flashes and the positive peak current that is found in
the Great Plains and Upper Midwest when analyzing annual NLDN data from
1989-1998. Additional information can be found at the following web site:
http://olympic.atmos.colostate.edu/ppcgsvr.html
NWS/VISIT Training Efforts on Lightning
The U.S. National Weather Service (NWS) is offering training on
lightning through the Virtual Institute for Satellite Integration Training
(VISIT; please see www.cira.colostate.edu/ramm/visit/visithome.asp). Bard Zajac
is the producer of lightning training and the point of contact
(zajac@cira.colostate.edu). Recent efforts have focused on the development and
delivery of a teletraining session on cloud-to-ground (CG) lightning activity
in the contiguous U.S. (CONUS) based on research by Zajac and Steve Rutledge at
Colorado State University.
The VISIT lightning teletraining session discusses 1) the
operation and performance of the National Lightning Detection Network and 2)
the spatial, annual, and diurnal variations in total (positive and negative
polarity) CG lightning activity over the CONUS and the forecast areas of the
participating NWS Weather Forecast Offices (WF0s). This teletraining session
takes roughly 90 minutes and is delivered to as many as six WFOs at a time.
(VISIT teletraining involves a computer slide show seen by all offices and
instructor via the Internet and a conference phone call.) Since the first
offering in late-July, the lightning session has been delivered to over 50
WFOs/200 individuals.
Current efforts are focused on the development of a second VISIT
teletraining session on lightning. This session will discuss: 1) the spatial,
annual, and diurnal variations of positive and negative CG lightning activity,
2) CG lightning activity over the northern Great Plains associated with severe
storms and mesoscale convective systems (MCSs), 3) CG lightning activity along
the Gulf Coast associated with the sea breeze and cold season baroclinic
systems, and 4) the false detection of intracloud lightning as low peak current
positive CG lightning over the southeastern U.S.
University of Florida (Gainesvill, FL)
A total of 30 flashes were initiated during the 1999
triggered-lightning campaign at the International Center for Lightning Research
and Testing (ICLRT) at Camp Blanding. Of these 30, 22 contained downward
leader/upward return stroke sequences, and 8 were composed of the initial stage
only. All triggered flashes effectively transported negative charge to ground.
Two triggering attempts under positive electric field conditions (fields at
ground were +4.2 and +7.9 kV/m) were unsuccessful, although there was a partial
wireburn at a height of about 10 m above ground in the event associated with
the higher field. A new experimental installation was used in the 1999
campaign, which included a rocket launcher placed below ground level and
surrounded by a 70 x 70 m2 metallic grid buried at a depth of a few
centimeters. This installation was used to minimize the effects of both the
triggering facility and the finite soil conductivity on measurements of close
electric and magnetic fields and their time derivatives.
Martin Uman, Vlad Rakov, George Schnetzer, Keith Rambo, Dave
Crawford, and Dick Fisher authored a paper titled "Time Derivative of the
Electric Field 10, 14, and 30 m from Triggered Lightning Strokes." The time
derivative of the electric field of triggered lightning strokes was directly
measured at distances of 10 m, 14 m, and 30 m. The data were taken in 1998 at
the ICLRT at Camp Blanding, Florida. The results were compared with those of
similar triggered-lightning measurements made previously at the Kennedy Space
Center at distances of 50 m and 5 km and in France at 50 m. A comparison was
also made with previous measurements at the Kennedy Space Center for natural
lightning strokes over the Atlantic Ocean at distances of the order of tens of
kilometers and with overland natural lightning data obtained at 0.7 to 14 km in
Germany. The Camp Blanding return-stroke electric field derivative peak values
normalized (assuming the inverse distance dependence valid for radiation
fields) to 100 km are similar to all previous measurements for both natural and
triggered lightning at distances from 50 m to 50 km, all being several tens of
volts per meter per microsecond, with the exception of the German overland peak
derivative values which are an order of magnitude lower. The 10 to 30 m field
derivative zero-to-peak risetimes at Camp Blanding are typically 50 to 100 ns
(minimum 30 ns, maximum 180 ns), and widths at half-peak value are typically
100 to 200 ns. There is essentially no difference between field derivative
waveshapes measured simultaneously at 10 m and at 30 m, with the closer
waveform being about a factor of 2 greater in amplitude. Fourier analysis of
field derivative waveforms indicates that the primary frequency content of the
electric field derivative waveforms is below about 20 MHz. The Camp Blanding
close return stroke field derivative waveforms differ from those of
Leteinturier et al. (1990) recorded 50 m from triggered lightning at the
Kennedy Space Center in 1985 in that their derivative waveforms typically
decrease rapidly after the peak and exhibit zero-crossings. It is argued that
the differences between the KSC and Camp Blanding waveforms are related to the
relatively large rocket-launching structure used at KSC in 1985. The mean
return stroke speed computed from the electric field derivative and current
derivative data using the transmission-line model is 2.5 x 108 m
s –1 with a standard deviation of 1 x 108 m s
–1. Some of the Camp Blanding return stroke current waveforms
exhibit a pronounced decrease in their rate-of-rise, accompanied by a similar
feature in the associated electric field waveform, at the time that the
electric field derivative pulse exhibits a transition from a sharp initial
spike to a relatively slow tail, typically 100 to 200 ns after the beginning of
the waveform. The paper was submitted to the JGR.
Vlad Rakov in collaboration with Richard Kithil of the National
Lightning Safety Institute (NLSI) authored an article titled "Small Shelters
and Safety from Lightning." The article will be published in the Golf Course
Management magazine.
LIGHTNING, HIGH VOLTAGE & INSULATION GROUP (University of
Queensland, Dept. of Computer Science and Electrical Engineering, Brisbane,
Queensland, Australia)
Dave Mackerras and Mat Darveniza are working with the Australian
Bureau of Meteorology to produce a thunderstorm and lightning climatology for
Australia, based on historical thunderday data, lightning flash counter
records, lightning location system records, and satellite observations. An
immediate objective is to supplement an existing annual thunderday map with a
ground flash density map.
An on-going study of global lightning in cooperation with Richard
Orville (Texas A&M University), Earle Williams (MIT), and Steve Goodman
(NASA, MSFC) (JGR, Vol. 103, No. D16, pages 19,791-19,809, August, 1998) has
been extended in an attempt to model global electric circuit charging. We seek
an explanation for the differences between the diurnal variation in universal
time of global lightning and the diurnal variation in universal time of the
ionospheric potential (Proceedings of the 11th ICAE, pages 634-637, June,
1999).
Observations with CGR3 lightning flash counters in Brisbane and
Darwin are continuing. One objective is to determine negative and positive
ground flash density, cloud flash density, and total flash density for these
areas. The Brisbane CGR3 observations, made in conjunction with electric field
change observations, are being used to check earlier estimates of effective
ranges, error rates, and correction procedures, for converting CGR3
registrations to flash densities.
LOS ALAMOS NATIONAL LABORATORY (Los Alamos, NM)
- FORTE Radio-Frequency Observations of Lightning (A. Jacobson,
P. Argo)
-
FORTE's RF payload continues to function well and has just
reached the 3-million-RF-event milestone. Most of these events are VHF signals
from lightning. We are concentrating on coverage of the low latitudes, which
generate most of the lightning we see globally. A recent very encouraging
development has been the successful implementation of a geolocation (using the
CCD optical imager) for events in which the imager and the RF payloads see
temporally-overlapping events. This is now allowing global geolocation of the
RF sources.
- FORTE Optical Effort: Measurements and Modeling (D. Suszcynsky,
T. E. Light, M. Kirkland)
-
Using FORTE, we have concentrated on studying optical
lightning emissions that are simultaneously detected by both the photodiode
detector (PDD) and Lightning Location System (LLS) CCD imager. The high
temporal resolution (~15 us) of the PDD waveforms and the high spatial
resolution (~10 km) of the LLS geolocations combine to give a detailed
satellite-based picture of both the spatial and temporal evolution of
terrestrial lightning at the stroke level. Concurrently we are developing 3D
Monte Carlo simulations of cloud radiative transfer, with emphasis on deducing
the temporal structure of the emission from the structure of the
scatter-delayed and -broadened observable pulse. The model is capable of
handling a variety of cloud/pulse geometries and arbitrary spatio-temporal
pulse profiles. Simple test-cases have shown good agreement with simple PDD
wave forms, and we are now beginning to consider more realistic scenarios.
- FORTE Ground Support: The LANL Sferic Array (D. Smith, K. Eack,
J. Harlin, X. Shao)
-
During 1999 we have operated an array of electric field change
sensors that has nominally consisted of 11 stations: 5 in New Mexico/Texas, 5
in Florida, and 1 in Nebraska. We record lightning waveforms with the stations
and use cross-correlation and time-of-arrival techniques to locate discharges.
The waveforms are used to determine source heights (for intracloud discharges),
classify flashes, and determine lightning parameters such as polarity, peak
current, and dipole moment change. During the 1999 thunderstorm season, the
Florida and New Mexico arrays recorded and located nearly 5000 narrow bipolar
pulses (of both positive and negative polarities), which are thought to be
produced by compact intracloud discharges. Over 25 percent of these events were
produced in a 24 hour period by four thunderstorms over the eastern plains of
New Mexico. We are working to analyze these data in context with WSR-88D
(NEXRAD) radar and other meteorological data.
- Theoretical Work in the Atmospheric and Climate Sciences Group
(R. Roussel-Dupre, E. Symbalisty, L. McNair, H. Morris)
-
Theoretical work in EES-8 at Los Alamos is focused on both
intracloud (IC) lightning and high-altitude discharges. First principles
modeling of IC lightning has yielded predictions for the optical, radio
frequency, and gamma emissions that are in good agreement with observations.
Comparisons are made with satellite based optical measurements, ground based
slow and fast field change measurements, and aircraft based gamma measurements.
Results comparing theory with recent observations of intense bipolar pulses
will be presented at the Fall AGU. Simulations of high-altitude discharges
using a new, fully electromagnetic code and a new parent discharge model are
also yielding interesting results.
INSTITUTE OF METEOROLOGY AND GEOPHYSICS (Frankfurt, Germany)
Martin Füllekrug reports:
Three GPS synchronized measurement stations recorded horizontal
magnetic field variations in the ULF/ELF transition range 4-200 Hz at
Silberborn, Germany (51.8°N, 9.5°E), and 4-19 Hz at Hollister,
California (36.8°N, 121.4°W), and Lameroo, Australia (35.5 °N,
140.6 °E), during April 1998. The three station records exhibit
simultaneous discrete excitations of Earth-ionosphere cavity (or Schumann)
resonances which result from the constructive interference of electromagnetic
waves which propagate with little attenuation in the spherical Earth-ionosphere
waveguide (Schumann, 1952; Sentman, 1995). These Earth-ionosphere cavity
resonances are mainly excited by particularly strong lightning flashes which
can be triangulated by use of the orientation of the Poynting vector along the
great circle path of propagation.
The great circle path crossing points of the three independently
observed Poynting vector orientations determine two best fitting lightning
flash locations on the Earth. The time of arrival difference between two
stations is used to resolve the hemispheric ambiguity. The derived lightning
flash locations are validated with lightning flash locations reported by the
VLF time of arrival difference system of the British Meteorological Office
(Lee, 1986). The lightning flash location accuracy by use of Earth-ionosphere
cavity resonances is on the order of several hundred kilometers. The physical
reason for the location error is threefold (Füllekrug and Sukhorukov,
1999). First, the alignment flash bearing deviation exhibits a rotational
dependence at coastal stations as a result of the excitation of higher order
modes in the vicinity of the sharp conductivity contrast between the ocean and
the Earth’s crust. Second, the bearing deviation exhibits a diurnal
variation which results from the anisotropic contribution of the ionosphere to
the wave propagation, mainly apparent during night time conditions. This
bearing deviation ?f can be estimated: ?f=arctan
(1/2k0nEhE), where k0 is the free
space wave number, hE is the height of the ionosphere E-region
(˜ 90 km), and nE is the refractive index of the nocturnal
E-region. Third, random occurrences of sporadic D-Layer ionization patches
result in a statistical variability of the source triangulation accuracy
(Pappert, 1985).
All triangulated lightning flashed represent an estimate of the
global lightning activity. Since the horizontal magnetic field variations can
easily be monitored continuously, it is possible to determine the temporal
evolution of particularly interesting thunderstorms, for example in Central
Africa, North America, and Australia. The thunderstorms in North America and
Australia exhibit a sharp rise of the flash rate and a decay within one day,
while the high flash rate in Africa persists for 3-4 days and may be associated
with a mesoscale convective system (Laing and Fritsch, 1997) or many individual
thunderstorm cells.
University of Mississippi (University, MS)
During July and August, 1999, Tom Marshall and Maribeth
Stolzenburg conducted Studies of the Electrical Evolution of Thunderstorms
(SEET) at Langmuir Lab in New Mexico. Twenty-nine balloon soundings of electric
field and thermodynamics were acquired in six different storms, with as many as
seven soundings per storm. Terry Hock and colleagues at NCAR/ATD developed a
full-GPS system for the Vaisala dropsondes as part of SEET; this technology
greatly improved balloon tracking within the thunderstorms. Also new for this
study were narrowband transmitters for the electric field meters, provided
through NCAR/ATD, which made it possible to successfully receive data from as
many as four balloons (eight instruments) at one time. During several of the
storms studied the New Mexico Tech Lightning Mapping System of Paul Krehbiel,
Bill Rison, Ron Thomas, and colleagues detected numerous lightning flashes in
the vicinity of one of more balloons. Additional data for these storms were
collected with the Langmuir Lab 3-cm Doppler radar (Steve Hunyady and Graydon
Aulich) and with the multiparameter radar operated by Paul Krehbiel in Socorro.
The ballooning portion of this project was accomplished with the assistance of
Dave Rust (NSSL), Terry Hock, Dean Lauritsen, and Errol Korn (all of NCAR/ATD),
as well as five students from the University of Mississippi and two students
from the University of Oklahoma. Data processing and analysis are now underway.
Analysis of data from the 1998 MEaPRS experiment, based in
Oklahoma, is continuing. There are fourteen balloon soundings of electric field
in mesoscale convective systems and convective squall lines as a result of that
project, which was performed in collaboration with Dave Rust and many others at
NSSL. An additional five soundings were made into supercells and convective
storms producing a high percentage of positive cloud-to-ground flashes;
analysis of these data is continuing in collaboration with Don MacGorman, Dave
Rust, and Bill Beasley (NSSL/University of Oklahoma).
INSTITUTO NACIONAL DE PESQUISAS ESPACIAIS (INPE) (Sao José
dos Campos, Brazil)
The Lightning Triggering Experiment in Brazil (LTEB) is an
international collaboration project involving Brazil, France and Canada with
the main goal to study the physics and related technical phenomena associated
with triggering lightning. The project is the first to consider this phenomenon
in the tropical region of the world, where most lightning does occur.
The institutions involved in the project are: in Brazil, the
Instituto Nacional de Pesquisas Espaciais (National Institute of Space
Research, INPE) and the University of Campinas (UNICAMP); in France, the Centre
d’Etudes Nucléaires de Genoble (Center of Nuclear Studies of
Grenoble, CENG), the Laboratoire d’Aérologie of the University of
Toulouse, and the Company INDELEC; and in Canada the company Hydro Quebec
Utility (IREQ).
The project should be developed in the installations of INPE in
Cachoeira Paulista, São Paulo, Brazil. This site was chosen considering
the high lightning activity in the region, determined through electric field
measurements, performed using field mill, during the summer season of 1999, and
its facilities. The project is divided in two phases: in the first, to occur
between December, 1999 and March, 2000, the technique to trigger lightning with
small rockets will be used; in the second phase, one year later, the technique
of laser triggering will be also attempted. During the first phase, it will be
launched about 50 rockets in Cachoeira Paulista from the beginning of January
to the end of March 2000, using both classical and altitude techniques.
Electric field (from quasi DC to VHF) and current measurements will be
performed. For additional information, please contact in Brazil Dr. Osmar Pinto
Jr. (osmar@dge.inpe.br) and in France Dr. Serge Chauzy (chas@aero.obs-mip.fr).
National Lightning Safety Institute (NLSI) (Louisville, CO)
The NLSI High Altitude Lightning Observation Station (HALOS)
– 4083 m elevation in the Rocky Mountains – completed year one of a
five year study of comparative air terminal tip geometries. Results are posted
in Chapter 6 (NLSI Research) of the WWW site: www.lightningsafety.com Many
thanks to our mentors at New Mexico Tech for valuable guidance and suggestions.
Five Chicago hotel sites were investigated for lightning
disturbances. One electrical event caused some 130 hotel guests to check out
due to loss of the telephone system. NLSI conclusions centered mostly around
non-lightning power quality issues such as poor electrical equipment
installation practices, and defective surge protection products. Dependence
upon UPS equipment for transient protection also was noted in our
recommendations.
A site study to a lightning-initiated failure of transformer
insulators at an eastern USA nuclear power was conducted. From GAI data, we
concluded that a (low amplitude) 3.6 kA flash by-passed shield wires. Shield
wire configurations had not been upgraded to the latest IEEE recommendations
found in IEEE Std 1243-1997 "IEEE Guide for Improving Lightning Performance of
Transmission Lines" and IEEE Std 1410-1997 "IEEE Guide for Improving Lightning
Performance of Electric Power Overhead Distribution Lines." Abdul Mousa of BC
Hydro participated in the NLSI contract.
NLSI distributed more than 200 copies of its 10 minute "Lightning
Safety 101" video during the 1999 lightning season. The focus of the video is
personnel safety in both work and recreation situations.
At the 1999 ICAE Huntsville meeting NLSI presented results of a
study of annual USA lightning costs and losses. The US Gummint reports the
figure to be $35 million: NLSI has evidence the real costs are in the $5
billion plus range. See NLSI WWW site, section 3.2, for summary
information.
At two meetings (American Nuclear Society meeting in Santa Fe NM
and the Range Commanders Council, White Sands Missile Range NM), NLSI presented
results of 8 years of lightning incidents to Department of Energy facilities
around the USA. Nature of damage, type of lost equipment, and distribution of
events were discussed. Conclusions as to similar lightning consequences here
might be applied to other organizations with multiple facility locations across
the USA. The paper is at NLSI’s WWW site section 5.11.
With co-author Vlad Rakov, NLSI prepared a paper on golf course
shelters and lightning safety. It will be published in Spring 2000 in Golf
Course Management magazine.
The "Certified Lightning Safety Professional" workshop series
graduated 82 students in 1999. The intensive 2-3 day class proposes to create
subject matter experts in issues related to lightning hazard mitigation. Air
terminals, grounding, bonding, shielding, surge suppression, lightning
detection and personnel safety are some of the topics discussed. Graduates
become leaders and trainers about lightning safety issues for their
organizations. The year 2000 class schedule is posted on the WWW site in
section 2.2.3.3, and the course outline is posted in section 2.2.3.2. Note the
winter classes will be held in Breckenridge CO, a ski resort located two hours
from Denver.
*NATIONAL SEVERE STORMS LABORATORY, NOAA (Norman, Oklahoma)
Ted Mansell and Jerry Straka of the University of Oklahoma and Don
MacGorman and Conrad Ziegler of NSSL have been examining model simulations of a
spectrum of severe storms that use one of three different parameterizations of
noninductive graupel-ice charging (Takahashi 1978, Gardiner et al. 1985, and
Saunders et al. 1991) modified to use rime accretion rates), along with a
single inductive charging parameterization for graupel/hail and droplets. Most
simulations have produced appreciable lightning flash rates, including
cloud-to-ground lightning, and some have produced extremely large flash rates.
Successive model runs of the same storm simulation with the three different
noninductive parameterizations typically produce significant differences in the
magnitude and distribution of thunderstorm charge and in the resulting flash
rates of various types of lightning.
David Schultz (NSSL) authored "Lake-Effect Snowstorms in Northern
Utah and Western New York With and Without Lightning"
(http://www.nssl.noaa.gov/~schultz/light/mss.html). He found that lake-effect
snowstorms with lightning have significantly higher temperatures and dewpoints
in the lower troposphere and significantly lower lifted indices than
lake-effect snowstorms without lightning. In contrast, there is little
difference in dewpoint depressions between events with and without lightning.
Nearly all events have no convective available potential energy, regardless of
the presence of lightning. The results from this paper are then discussed in
the context of current models of storm electrification. This proposed forecast
methodology will be tested this winter during the Intermountain Precipitation
Experiment (http://www.nssl.noaa.gov/mag/ipex.shtml), a field project designed
to improve understanding of orographic and lake-effect snowfall in northern
Utah.
John Cortinas and Ron Holle have started a study that will
investigate the climatological occurrence of winter lightning across North
America. The study uses 15 years of data from the United States' and Canada's
surface observing networks, which include human reports of thunder, dry-bulb
and dewpoint temperatures, wind direction and speed, visibility, and type of
weather occurring at the observation time. Holle and Cortinas are examining
these data to learn about the meteorological conditions that typically
accompany reports of winter thunder, the frequency of thunder reports, and any
relationship between reports of thunder and precipitation intensity.
Ivy Winger (NSSL and Univ. of Oklahoma School of Meteorology) is
analyzing microphysics data from the NOAA P-3 acquired during MEaPRS 1998 for
her M.S. research. These analyses will eventually be combined with electric
field profiles (whose analysis is being led by Maribeth Stolzenburg, Univ. of
Mississippi) for an MCS observed near Russelville, Arkansas. Providing guidance
to Ivy on the microphysical data analysis are Terry Schuur (NSSL/CIMMS) and Bob
Black (Hurricane Research Division).
Don MacGorman and Dave Rust of NSSL and Tom Marshall and Maribeth
Stolzenburg of the University of Mississippi are working to finalize analysis
and interpretation of the electric field soundings they acquired from storms
that produced positive ground flashes in 1998.
Ron Holle and Raúl López of NSSL, and Christoph
Zimmermann of Global Atmospherics, Inc. published "Updated Recommendations for
Lightning Safety-1998" in the October 1999 issue of the Bulletin of the
American Meteorological Society. This article consists mainly of the text of
the recommendations developed by the Lightning Safety Group that met in
Phoenix, Arizona in January 1998.
Mary Ann Cooper of the University of Illinois at Chicago's Dept.
Of Emergency Medicine, and Ron Holle and Raúl López of NSSL
published "Recommendations for Lightning Safety" in the September 22/29, 1999
issue of the Journal of the American Medical Association. This one-page letter
summarized the recommendations developed by the Lightning Safety Group.
Raúl López retired from NSSL in April 1999 to his
new home in Simpsonville, South Carolina after 20 years with NOAA's
Environmental Research Laboratories. His colleagues continue to work with him
on a variety of lightning studies that he initiated during the six recent years
at the National Severe Storms Laboratory.
OFFICE NATIONAL D’ETUDES ET DE RECHERCHES AEROSPATIALES
– ATMOSPHERIC ENVIRONMENT RESEARCH GROUP ( Paris, France)
www.onera.fr
The preparation of ORAGES microsatellite experiment is in
progress under the effort of Anne Bondiou-Clergerie (PI of the experiment,
bondiou@onera.fr), Philippe Lalande (lalande@onera.fr) and Patrice Blanchet
(blanchet@onera.fr). ORAGES is a space VHF lightning mapper which will localize
intra-cloud and cloud-to-ground lightning flashes on the earth surface. The
antenna system is currently under definition and will be experimented on a
stratospheric balloon flight at the end of 2000. ORAGES will be a low orbiting
experiment. The "Laboratoire d’Aérologie" is collaborating on the
scientific definition of the experiment (Serge Chauzy and Franck Roux).This
experiment is funded by the French Space Agency (CNES).
Claire Théry and Pierre Laroche carry on working on the
evaluation of NOx production by lightning from total lightning observations
obtained during the European campaign EULINOX (European Lightning NOx
production) and Colorado campaign STERAO-A. Those analysis are conducted in
collaboration with Hartmut Hoeller from DLR (Germany) and Jim Dye from NCAR.
Eric Defer presented his Ph.D. memo on the total lightning mapping by VHF
interferometry in June. Those interested to get is memo can contact Claire
Théry (thery@onera.fr) or Eric (defer@ucar.edu). He is currently
achieving a post-doctoral position at NCAR with Jim Dye on a similar topic. Our
approach consists in evaluating the length of the discharge including positive
and negative leader components as well as return stroke and recoil
streamers.
A collaboration between John Willett at Air Force Research Lab,
Dan Davis at SUNYA and Pierre Laroche is in progress on the analysis of
simultaneous triggered lightning and electrostatic atmospheric field profile.
Monique Petitdidier (monique.petitdidier@cetp.ipsl.fr) from CETP,
a Ph.D. student, Eric Boyer, and Pierre Laroche are working on simultaneous
observations with an electrostatic field meter and the HF radar of Arecibo at
Porto-Rico during the storms associated with hurricane GEORGE in September
1998. The effort goes on the analysis of HF emission from lightning flash as
detected by the radar receiver and the radar detection of the plasma channel.
The study of the effects of lightning on aircraft and helicopter
is currently under investigation as one of the major goals of the Atmospheric
Environment Group. Work is on lightning effect on radome and on the sweeping
mechanism on the fuselage. Those type of studies are done within large European
Program like Fulmen DG7 and EM-Haz DG12 (http://dbs.cordis.lu).
LABORATOIRE D’AEROLOGIE, UNIVERSITE PAUL SABATIER (Toulouse,
France)
The group of Atmospheric Electricity of the Laboratoire
d’Aérologie (Serge Chauzy, chas@aero.obs-mip.fr, Sylvain Coquillat,
coqs@aero.obs-mip.fr and Serge Soula, sous@aero.obs-mip.fr) has been involved
in the MAP field experiment in Northern Italy during the months of September
and October 1999. The MAP (Mesoscale Alpine Programme) is devoted to the study
of the effects of orography on the atmospheric processes. The heavy rain caused
by thunderstorm developments is part of these processes and one of the
scientific aims is the understanding of the electrical mechanisms and their
links with microphysics and dynamics.
A few electric field soundings were performed, using a newly
designed sensor devoted to the detection of the vector electric field.
Corresponding in situ measurements of meteorological parameters (pressure,
temperature and humidity ) were carried out, associated with a GPS localization
of the system. Some soundings have been realized within structures producing
stratiform rain. Surface measurements (electric field, precipitation current,
raindrop net charge, rain size spectrum) have also been performed during
several storm events. The characteristics of the precipitation current will be
studied in relation with the thundercloud development and its evolution, as it
is described by doppler and polarimetric radars detection.
As part of the project ORAGES developed by ONERA (Anne
Bondiou-Clergerie) correlation studies between lightning and precipitation
activities are carried out (Serge Soula). The main goal consists in finding a
relevant parametrization of the correlation in order to estimate the rain
amount from lightning observations by satellite and to characterize the
specific lightning activities in strong thunderstorms for applications in flood
nowcasting. A specific aim about storm activity evolution across water/land
border is considered from these correlation studies in collaboration with Henri
Sauvageot, from the radar group of the Laboratoire d’Aérologie.
The interactions between microphysics and thunderstorm
electrification are continuously studied within the group by Sylvain Coquillat.
We focus on the natural conditions of lightning triggering. Previous numerical
studies have shown that corona emission can be emitted from raindrops falling
in a vertical electric field provided they are highly charged or when they
interact with each other. The subsequent question that arises is whether the
corona emission is favored in a horizontal field configuration since raindrop
disruption field is lowered in such a situation. In order to answer this
question, we developed a numerical modeling of the behavior of an uncharged
raindrop falling in a horizontal electric field. We simultaneously performed an
experimental study used to validate the modeling at sea level pressure. It is
found that corona emission is more easily triggered in a horizontal than in a
vertical electric field. We expect this result to be reinforced when
considering charged raindrops.
Department of Physics - University of Parma (Italy)
Albino Carbognani reports on his article entitled "An Introduction
to ball lightning", and available on the Web site:
http://www.ufodatanet.org.
Among the phenomena known to geophysicists, that of ball lightning
(BL) is one of the least understood, even though it has been studied for more
than a century and a half. Precisely because of the nature of the phenomenon,
the data gathered come exclusively from eye-witness observations. However, in
recent years the BL phenomenon has been "rediscovered" by the scientific
community, and greater efforts are being made to understand it. The article
examines the main physical properties of BL, and illustrates the results of
visual observations taken from current scientific literature. Physical
parameters are discussed, as are similarities and differences between
meteorites and BL, which can be mistaken for one another. In conclusion, the
main theories suggested to interpret the BL phenomenon are reviewed, together
with the partially successful attempts made to replicate BL in laboratories. An
extensive bibliography of recent articles published in major international
scientific journals is also given. (in italian language).
SOUTH DAKOTA SCHOOL OF MINE AND TECHNOLOGY (Rapid City, SD)
Andy Detwiller reports:
The T-28 armored aircraft research group at the South Dakota
School of Mines and Technology has been working on better arrangements of field
meters on the aircraft that will yield more robust estimates of ambient
electric field components. An analysis of this system has appeared in the
October 27, 1999, issue of Journal of Geophysical Research - Atmospheres.
General information about the T-28 can be found at
http://www.ias.sdsmt.edu/institute/t28/ .
In addition, we have recently acquired a High Volume Precipitation
Spectrometer (HVPS) probe from SPEC, Inc., which soon will be outfitted with a
particle charge-measuring sensor array developed by Bill Winn and Clifton
Murray at the New Mexico School of Mining and Technology. We are looking
forward to unique charge and image data of precipitation particles in severe
storms to be acquired with this probe during the Severe Thunderstorm
Electrification and Precipitation Study (STEPS) next season.
Arrangements for STEPS are still being made and funding is still
pending as of the beginning of November. Information about STEPS is available
at :
http://www.mmm.ucar.edu/community/field.html
STANFORD UNIVERSITY: STARLAB (Stanford, California)
The VLF Group at STAR Laboratory of Stanford University is
actively involved in experimental and theoretical work targeted on
understanding of strong upward electrodynamic coupling of tropospheric
thunderstorms to the mesospheric and lower ionospheric regions and associated
optical and electromagnetic effects.
This past summer, graduate students Elizabeth Gerken, Timothy
Chevalier and Maria Salvati fielded Stanford's optical experiments for studying
sprites and elves at the Langmuir Laboratory (New Mexico). This consisted of
the Fly's Eye photometric experiment, the Dobsonian Sprite Experiment (DSE)
telescopic imager, and a broadband VLF system. The Fly's Eye had new triggering
capabilities and was able to automatically find elves for both positive and
negative cloud to ground lightning discharges. A red-filtered photometer was
added to the DSE to allow for high temporal resolution of sprite intensities in
addition to the high spatial resolution of the telescope. Another graduate
student Robert Moore completed software to automatically capture sprite events
as a video tape is being digitized, greatly reducing the time needed to process
the sprites data. Our group collaborated with scientists at Kitt Peak to
successfully triangulate on sprites and a paper will be given under the
direction of Steve Mende (University of California, Berkeley) at the Fall 1999
meeting of American Geophysical Union (AGU). Umran Inan and Elizabeth Gerken
are working to publish a paper on the fine structure of sprites seen in the DSE
results. A paper based on the 1999 data set will be given by Elizabeth Gerken
at the Fall AGU meeting. Mike Johnson, Umran Inan, Sean Lev Tov, and Tim Bell
used simultaneous observations of early/fast Very Low Frequency (VLF) events at
nine closely spaced (similar to 65 km) sites and a numerical model of the
propagation and scattering of VLF signals in the earth-ionosphere waveguide to
directly measure the scattering pattern of associated ionospheric disturbances
(GEOPHYSICAL RESEARCH LETTERS, v. 26(#15), pp. 2363-2366, AUG 1, 1999). In
cases when the causative lightning is within 700 km of the north-south array of
observing sites, early/fast VLF events are typically observed at no more than 2
or 3 sites, which indicates a narrow beam of the scattered signal in the
forward direction. In the different cases studied, forward scattering patterns
exhibit 15 dB beamwidths of less than 30 degrees consistent with horizontal
extent of 90 +/- 30 km.
Victor Pasko, Umran Inan, and Tim Bell reported results of
quantitative two-dimensional electromagnetic modeling of mesospheric electric
field transients produced by cloud-to-ground (CG) lightning discharges with
short duration currents (<0.5 ms) (GEOPHYSICAL RESEARCH LETTERS, v. 26(#9),
pp. 1247-1250, MAY 1, 1999). The range of applicability of existing
quasi-electrostatic models of sprites and the physical conditions under which
relatively weak CG lightning discharges (thundercloud charge moment changes
less than 50Cx10 km) may initiate sprites are discussed in the context of
recent experimental findings.
Georgios Veronis, Victor Pasko, and Umran Inan employed a new
two-dimensional cylindrically symmetric electromagnetic model of the
lightning-ionosphere interaction, which includes effects of both the lightning
radiated electromagnetic pulses (EMP) and the quasi-electrostatic (QE) fields,
to study effects of lightning-ionosphere interactions on time scales ranging
from several microseconds to tens of milliseconds (JOURNAL OF GEOPHYSICAL
RESEARCH-SPACE PHYSICS, v. 104(#A6), pp. 12645-12656, JUN 1, 1999). The
temporal and spatial evolution of the electric field, lower ionospheric
electron density, and optical emissions calculated with the new model are used
to investigate theoretically the effects of the lightning return stroke current
waveform (i.e., the current rise and fall timescales) and of the observational
geometry on the optical signals observed with a photometer. For typical
lightning discharges of ~100 microsecond duration the ionospheric response is
dominated by the EMP-induced heating leading to the highly transient and
laterally expanding optical flashes known as elves. For cloud to ground
lightning discharges of ~1 ms duration removing substantial amount of charge
(i.e., ~100 C from 10 km altitude), heating and ionization changes induced by
the QE field lead to the mesospheric luminous glows with lateral extent <
100 km, referred to as sprites.
UNIVERSITY OF TEL AVIV - DEPARTMENT OF GEOPHYSICS & PLANETARY
SCIENCES (Tel Aviv Israel)
During the summer of 1999, continuous measurements were obtained
in Israel in the ELF and VLF range by Colin Price, together with graduate
student Mustafa Asfur. This was part of the SPRITES '99 campaign, and initial
analysis indicates that approximately 75% of the GPS times listed by Walt
Lyons, for optical observations in Colorado, coincide with ELF transients
observed in the Negev Desert, Israel. We have used various techniques to
calculate the location of origin of these transients, and the majority appear
to originate from thunderstorms in the midwest United States.
In collaboration with Earle Williams, Colin Price is investigating
the connection between remote measurements of the Schumann Resonances and the
integrated rainfall and lightning data from the continental United States.
Since globally the convective activity between 0000-0600 UT is primarily from
North America, and our north-south magnetic field component in Israel "sees"
lightning activity primarily in the Americas and Asia, we can look at a subset
of the Schumann Resonance signal that comes primarily from North America.
Initial analysis shows some striking resemblence between the various data
sets.
Finally, as a result of a meeting at the Huntsville ICAE
conference, Ilkka Lilja Oy of Finland has donated a lightning detection system
(Stormtracker) to Tel Aviv University, which will be used by Colin Price, Yoav
Yair and Zev Levin for studying the winter thunderstorms in the eastern
Mediterranean.
UNIVERSITY OF WASHINGTON (Seattle, WA)
A theory for the microphysical mechanisms involved in collisional
charging of ice has been developed by Greg Dash and John Wettlaufer at the
University of Washington, with Brian Mason, presently at North Carolina State
University. The model is centered around recent experimental observations of
collisional charging and mass transfer, and provides semi quantitative
explanations fore several observations made in these and earlier experiments:
(1) particles growing more rapidly from the vapor are charged positively; (2)
charge transfer is proportional to growth rate; (3) during impacts the
colliding surfaces exchange amounts of liquid-like mass, with thicknesses and
temperatures far outside the limits of equilibrium surface melting; (4) charge
transfer tends to saturate at high rates.
The theory predicts trends and amounts of charge and mass
transfer in rough agreement with measurements.
Mason, B. L., 1998. An experimental investigation of charge
transfer during ice contact interactions. PhD Thesis, University of Washington
(unpublished).
Mason, B. L., and J. G. Dash, 1999. Surface melting of ice and
thunderstorm electrification. Ice Physics and the Natural Environment, ed. J.
S. Wettlaufer, J. G. Dash, and N. Understeiner, NATO ASI Series I, v. 56,
23-38.
Mason, B. L. and J. G. Dash, 1999. An experimental investigation
of charge transfer during ice contact interactions. Proc. 11th Int.
Conf. Atmos. Elec., Guntersville, Alabama. (NASA/CP-1999-209261), 321-4.
Mason, B. L. and J. G. Dash, 1999. Charge and mass transfer in
ice-ice collisions: a mechanism for electrification of thunderstorm.
Submitted. |
