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Spring 2001
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Introduction
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Research Activity
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ICAE Spring 2001 News Letter
RESEARCH ACTIVITY
by Organization
* * *
AIRBORNE RESEARCH ASSOCIATES (Weston, MA)
During the summer and fall of 2000 Ralph Markson continued
development of the ATLAS single sensor total lightning mapping system using the
ARA TurboBaron aircraft to study storms in Florida and with ground based ATLAS
systems. A newly developed wave visualization system with 10 ns sampling showed
details of the initial breakdown which had not been observed previously.
Initial results with the new system supports the concept of using the initial
breakdown amplitude as an invariant strength signal which will allow the first
accurate range estimation from a single sensor. Additional work is required
including acquiring more data and automation of the system.
The second project done at ARA was full time-lag analysis of the
ionospheric potential variation, obtained from balloon soundings, compared to
temperature variation over Africa and South America. In agreement with earlier
preliminary reports (e.g., ICAE/AE Conference, Guntersville, 1999) it was found
that there was a positive correlation using morning temperature but shielding
of solar radiation by cloudiness created by the initial thunderstorms in late
morning and early afternoon decreases temperature in the mid and late afternoon
causing an inverse correlation. A paper discussing the relationship of the
global circuit to global warming is being prepared for publication.
THE UNIVERSITY OF ARIZONA (Tucson, Arizona, USA)
Natalie Murray and E. P. Krider are collaborating with John
Willett on a re-examination of the submicrosecond structure of dE/dt and E
waveforms radiated during the onset of first return strokes in cloud-to-ground
lightning. We have found that most strokes produce multiple pulses in dE/dt
during the onset of the slow front and/or the fast transition in E, and that
there are very narrow peaks and considerable structure in the associated E
signatures. Natalie is also measuring the spatial and temporal coherence of
space charge generated within or near the surf zone at the NASA Kennedy Space
Center (KSC). This summer Natalie will measure the surface electric field over
water and over land using a mobile sensor to support an aircraft campaign being
conducted by Hugh Christian and Jim Dye at KSC.
Nathan Parker is extending William Valine’s work on the
luminous development of lightning and the multiplicity of attachment points in
cloud-to-ground discharges. Nicole Kempf is continuing Bruce Gungle’s
study of the relationships between lightning and convective rainfall. William
Koshak and E. P. Krider are studying the response of the NASA Lightning Imaging
Sensor (LIS) when lightning occurs over or near the KSC and is within the LIS
field of view. An effort is also being made to determine if the total light
output from lightning flashes, as recorded by LIS, is proportional to the total
charge in the flash or any other electrical parameter. Charles Weidman is
developing and testing optical sensors that elementary, high school, and
college students can use to help validate the performance of satellite
lightning sensors. Charles is being assisted in this work by Gary Wallace and
Peter Lewis.
COLORADO STATE UNIVERSITY (Fort Collins, Colorado, USA)
- RADAR METEOROLOGY GROUP
Severe Thunderstorm,
Electrification and Precipitation Study (STEPS)
Preliminary activities include attempts to quantify the
climatological difference between positive and negative lightning-producing
storms. Comparisons are made based on polarity, percent positive, flash
density, and geography. In addition to better understanding the physics of
these storms, these measurements may provide insight into whether operational
forecasters will be able to "nowcast" severe weather formation through the use
of lightning data.
1) 11-12 June, 2000-0200 UTC: Bow-echo MCS with predominately
positive CG lightning-producing convection, and a trailing region of stratiform
precipitation that also produced a few positive CG's. Interestingly, convection
on the south side of the MCS produced predominately negative CG lightning
(coincident with positive CG lightning on the north end of the system) during
initial stages of the lifecycle. This storm was classified as severe based on
reports of 3/4 inch hail, but was apparently non-tornadic. The LMA noted
horizontally propagating lightning into the trailing stratiform region. We are
at the initial stage of analysis for this case and will focus on dual-Doppler
derived kinematics and polarimetric retrieval of relevant microphysics. These
results will subsequently be compared to EFM (balloon), LMA, and aircraft data,
all of which gathered robust data samples in the convective and stratiform
regions of the MCS.
2) 29-30 June: 20:30-03:00 UTC: Kyle Wiens is conducting
initial analyses of NEXRAD and LMA data that show two distinct cells which
developed near the KS-CO-NE border with nearly identical electrical
characteristics in their early stages. Both cells appeared to be inverted
electrically, with negative charge overlying positive and IC lightning between
the two. One cell weakened and moved off while the other underwent a dramatic
change in a matter minutes. This second cell showed explosive vertical
development and drastic changes in its electrical activity; it became a
supercell and later produced a tornado. There was excellent coverage by nearly
all STEPS instrumentation during this time. There are plans to include more
data sets to try to determine why these two cells exhibited such drastically
different behavior. Review is underway to find similar cases that occurred
during the STEPS campaign.
3) Manuscript preparation has begun for two STEPS related
studies. The first study is a ten-year climatological comparison between severe
storm reports and cloud-to-ground lightning characteristics that was used in
the scientific and logistical planning for STEPS. (Carey, L. D., S. A.
Rutledge, and W. A Petersen, 2001: The Relationship between Severe Storm
Reports and Predominate Positive Cloud-to-ground Lightning in the Contiguous
United States from 1989 - 1998. Mon. Wea. Rev., to be submitted.).
The second is a case study of the Spencer F4 tornadic
supercell on 30 May 1998 that produced predominately positive polarity
cloud-to-ground lightning for most of its lifecycle. The results from this case
study will help direct further investigation in more detailed case studies from
the unique STEPS data set. (Carey, L. D., W. A. Petersen, and S. A. Rutledge,
2001: Radar and Cloud-to-ground Lightning Characteristics of the Spencer F4
Tornadic Supercell of 30 May 1998. Mon. Wea. Rev., to be submitted.)
Electrification and
Lightning
Jesse Ryan is tying electrification and lightning to the
microphysics of the Goddard Cumulus Ensemble model. He will be using the model
to investigate the relationship between latent heating profiles and lightning
flash rates.
- COOPERATIVE INSTITUTE FOR RESEARCH IN THE ATMOSPHERE
(CIRA)
The Virtual Institute for Satellite Integration Training
(VISIT) is offering training on remote sensing topics such as lightning to
National Weather Service forecasters. Training is delivered using a
distance-learning application called VISITview and a conference phone call.
VISITview allows a slide show to be viewed by multiple users using Java-Applet
scripts and an Internet connection. Capabilities of VISITview include
animation, annotation, overlays, etc. VISIT training sessions on lightning are
described below.
"Lightning Meteorology I: Electrification and Lightning
Activity by Storm Scale" is the training session currently offered. It examines
thunderstorm electrification and cloud-to-ground (CG) lightning activity in
isolated storms and mesoscale convective systems (MCSs). The session balances
theory and application by first introducing theoretical concepts and then
presenting four case studies that demonstrate consistency between theory and
observation.
"Lightning Meteorology II: Advanced Electrification and
Anomalous Lightning Behaviors" is planned for release in early summer 2001. It
examines electrification at a more detailed level than Lightning Meteorology I
in order to offer explanations for anomalous lightning behaviors found in a
small fraction of severe storms and in many winter storms.
"CONUS CG Lightning Activity" was presented from July
1999–January 2000. It describes the operation and performance of the
National Lightning Detection Network and examines the spatial and temporal
(annual and diurnal) distributions of CG lightning over the contiguous United
States.
The VISIT web site is located at:
www.cira.colostate.edu/visit. The point-of-contact for VISIT lightning training
is Bard Zajac at: zajac@cira.colostate.edu.
COMMUNICATION AND SPACE SCIENCE LABORATORY, PENN STATE UNIVERSITY
(University Park, Pennsylvania, USA)
Les Hale (LesW3LH@aol.com) reports:
I have previously reported on slow tail measurements, but this is
about a clearly coded "mystery" signal that I am trying to identify and could
use some help. Slow tail measurements have been frequently unsatisfactory,
usually because of high ELF noise levels, inadequate preamp impedance or
bandwidth, or all of these. Perhaps one of the best efforts was one of the
earliest, when Lee Tepley of UCLA went to a quiet location away from power
lines in Hawaii (JGR, 1959). Subsequent high quality measurements were made in
Hawaii by Hughes (but only of earth currents), David Llanwyn Jones on
occasional trips to rural Wales, and Lee Marshall from the woods of
Pennsylvania. The consensus confirms Tepley, that most lightning launches
relatively uniform "millisecond" slow tails which propagate many thousands of
km before substantial dispersion (not to be confuseed with the generally
longer, less uniform, and weaker "continuing currents").
There is nothing mysterious about these phenomena: the slow tails
are required to satisfy the post lightning stroke boundary conditions, as
demonstrated by Mike Baginski (Nature 329,614, 1987). Just to have some nice
slides I took a two meter whip on top of my minivan to Aguirre Springs State
Park, NM, which turned out to be very quiet. Using an op-amp follower and a
Fluke 123 digitizing voltmeter, I was able to make some nice pictures. They
confirmed the "millisecond" slow tail concept.
But I observed something else which I would like help in
understanding. I see sequences of coded groups, obviously man made, whether
they are in blue (Navy), in black (spooks), or little green men. The "default"
pulse group is ten pulses spaced by precisely one millisecond, and of about one
quarter millisecond duration. Variable amplitude and some fading indicate that
it is not a local source. Pulses are omitted and some have reversed polarity,
with a potential of 59,049 different codes.
Some of the data I took is shown in a Figure, which I wikll FAX to
anyone who is interested. The lower right panel shows lightning flashes
followed by unipolar millisecond "slow tails," as expected from Tepley's data
(later confirmed by David Llanwyn Jones of England). The other data shows
samples of the coded groups.
I cannot find anyone who knows the source of these coded signals,
which I admit are probably not of extra-terrestrial origin, unless another
source cannot be identified. The top panel appears to be a "default" code with
ten pulses spaced by precisely one millisecond. Pulses can be omitted or of
opposite polarity, giving 59.049 different messages, counting a flat line,
according to my son Trevor. The variable amplitude indicates the source is not
local. Check it out yourself. Very easy to do.
I would suspect that this signal is not of extraterrestrail
origin. For one thing, precisely one millisecond-spaced pulses would be quite
coincidental. But it got me to thinking, that because of the extremely
effective penetrating capabilities of longitudinal electrostatic waves, ELF and
below just might be a good place to look for LGM.
UNIVERSITY OF FLORIDA (Gainesville, Florida, USA)
Triggered-lightning experiments will continue in Summer 2000 (for
the ninth year) at the International Center for Lightning Research and Testing
(ICLRT) at Camp Blanding, Florida. A number of experiments are planned
including (1) continued multiple-station measurements of electric and magnetic
fields due to both natural and triggered lightning, (2) continued studies of
the interaction of lightning with power distribution lines (both direct and
induced effects), and (3) measurement of electric fields in the immediate
vicinity of the lightning channel using Pockels sensors (jointly with CRIEPI,
Japan).
Carlos Mata defended his Ph.D. dissertation titled "Interaction of
Lightning with Power Distribution Lines". He is presently with the NASA Kennedy
Space Center.
Vladimir Rakov, David Crawford (presently with the NASA Kennedy
Space Center), Keith Rambo, George Schnetzer, Martin Uman, and Rajeev
Thottappillil (University of Uppsala, Sweden) authored a paper submitted to
JGR, titled "M-Component Mode of Charge Transfer to Ground in Lightning
Discharges". The M-component mode of charge transfer to ground is examined
using multiple-station measurements of electric and magnetic fields at
distances ranging from 5 to about 500 m from the triggered-lightning channel.
The corresponding currents at the channel base were also measured. Data have
been obtained in 1997, 1999, and 2000 at the International Center for Lightning
Research and Testing at Camp Blanding, Florida for (1) "classical" M-components
that occur during continuing currents following return strokes and (2)
impulsive processes that occur during the initial stage of rocket-triggered
lightning and are similar to the "classical" M components. All lightning events
considered in the paper effectively transported negative charge to ground. For
one triggered-lightning event, in addition to the current and close fields, the
electric field 45 km from the lightning channel was measured. The measured
close electric and magnetic fields are generally consistent with the
guided-wave mechanism of the lightning M-component. Specifically, the
M-component electric field peaks exhibited a logarithmic distance dependence,
ln(kr-1), which is indicative of a line charge density that is zero
at ground and increases with height. Such a charge density distribution is
distinctly different from the more or less uniform charge density distribution
inferred from close electric field measurements to be characteristic of
subsequent leaders in triggered lightning. The M-component magnetic field peaks
exhibited a distance dependence close to an inverse proportionality
(r-1), consistent with a more or less uniform distribution of
current within the lowest kilometer or so of the channel. The M-component
electric field at 45 km appeared as a bipolar microsecond-scale pulse that
began prior to the onset of the M-component current waveform at the channel
base. The microsecond-scale pulse is probably associated with establishing the
contact between an in-cloud leader and the current-carrying channel to ground.
This contact results in the launching of the initial, downward-moving M-wave,
which subsequently reflects off ground. M-component-type processes can produce
acoustic shock waves with peak pressure values of the same order of magnitude
as those for leader/return stroke sequences in triggered lightning.
Martin Uman, Jens Schoene, Vladimir Rakov, Keith Rambo, and George
Schnetzer authored a paper, submitted to the JGR, titled "Correlated Time
Derivatives of Current, Electric Field Intensity, and Magnetic Flux Density for
Triggered Lighting at 15 m". The authors present measured current and its time
derivative correlated with the corresponding electric field intensity and
magnetic flux density and their time derivatives measured at 15 m for two
lightning return strokes triggered in 1999 at Camp Blanding, Florida. Lightning
was triggered to a vertical 2 m rod mounted at the center of a 70 m x 70 m
buried metallic grid. The rocket launching system was located underground at
the center of the grid. The experiment was designed to minimize any influence
of either the strike object or a finite-conducting Earth (propagation effects)
on the fields and field derivatives. The measured current derivative, magnetic
field derivative, and electric field derivative waveforms associated with
return strokes are observed to be unipolar pulses that have similar wave shapes
for the first 150 ns or so, including the initial rising portion, the peak, and
about 50 ns after the peak. The current and magnetic field derivative
waveshapes are essentially identical for their total duration and both decay to
near zero about 200 ns after the peak derivative is reached. The electric field
derivative decays more slowly than the current derivative after about 150 ns,
taking about 500 ns to decay to near zero. The transmission-line model is used
to calculate the return-stroke field derivatives given the measured current
derivative as a model input with the return stroke speed as an adjustable
parameter. A reasonable match between calculated and measured fields for stroke
S9934-6 is achieved for an assumed return stroke speed of 1.7 x 108
m s-1, and for stroke S9934-7 for a speed of 1.5 x 108 m
s-1, but there are clearly aspects of the physics of the return
stroke of which the relatively simple transmission-line model does not take
adequate account. Although the field derivatives and the current derivative
have similar waveshapes for about 150 ns, which might appear to be consistent
with the hypothesis that the peak is dominated by the radiation field
component, transmission line model calculations show that at the electric field
derivative peak of both strokes about 40 percent of the total derivative is
electrostatic field, about 40 percent induction field, and about 20 percent
radiation field; while for the magnetic field derivative peak of S9934-6 about
60 percent is induction field and about 40 percent is radiation field and for
S9934-7 about 70 percent is induction field and 30 percent is radiation field.
If one assumes that the measured electric field derivatives are purely
radiation field, which apparently is not the case, and applies the transmission
line formula for a radiation field source near ground level, a return stroke
speed near the speed of light is calculated, consistent with the results of
previous close measurements and similar theory. Measured electric field
derivative waveshapes at 15 m and at 30 m are observed to be similar, which
also might appear to be consistent with the hypothesis that the derivatives are
dominated by the radiation field component, but, according to transmission line
model calculations, while the calculated total field derivative waveshapes are
similar at 15 and 30 m, the mix of field components at these two distances is
quite different.
Rajeev Thottappillil (University of Uppsala, Sweden) and Vladimir
Rakov authored a JGR paper titled "On Different Approaches to Calculating
Lightning Electric Fields". Three different approaches to the computation of
lightning electric and magnetic fields are compared and discussed. These
approaches are the traditional dipole (Lorentz condition) technique and two
versions of the monopole (continuity equation) technique. The latter two
techniques are based on two different formulations of the continuity equation,
one used by Thottappillil et al. (1997) and the other by Thomson (1999), the
difference between the formulations being related to different treatments of
retardation effects. The three approaches involve the same expression for the
vector potential but different expressions for the scalar potential. It is
analytically shown that the three different expressions for the scalar
potential are equivalent and satisfy the Lorentz condition. Further, the three
approaches yield the same total fields and the same Poynting vectors. However,
expressions for the individual electric field components in the time domain in
the three approaches, traditionally identified by their distance dependence as
electrostatic, induction, and radiation terms, are different, suggesting that
explicit distance dependence is not an adequate identifier. It is shown that
the so identified individual field components in the electric field equation in
terms of charge density derived by Thottappillil et al. (1997) are equivalent
to the corresponding field components in the traditional equation for electric
field in terms of current based on the dipole technique. However, the
individual field components in the electric field equation based on
Thomson’s (1999) approach are not equivalent to their counterparts in the
traditional dipole-technique equation. Further, in Thottappillil et al.’s
(1997) technique and in the traditional dipole technique, the gradient of
scalar potential contributes to all three electric field components, while in
Thomson’s (1999) technique only to the electrostatic and induction
components (the radiation component is determined by the time derivative of
vector potential only). Calculations of electric fields at different distances
from the lightning channel show that the differences between the corresponding
field components identified by their distance dependence in different
techniques are considerable at close ranges (tens of meters from the channel),
but become negligible at far ranges (of the order of 100 km). Expressions for
the individual magnetic field components in the three techniques are the same
since they are derived from the same expression for the vector potential.
FMA RESEARCH INC. (Fort Collins, Colorado)
Walter A. Lyons reports:
FMA Research, Inc. is preparing for the ninth consecutive summer
of sprite observations from the Yucca Ridge Field Station (Walt Lyons and Tom
Nelson). Since 1993, over 7500 transient luminous events (TLEs), including
sprites, halos, trolls, elves, and blue starters have been imaged from Yucca
Ridge. This year’s activities will be scaled back somewhat from past
efforts. Primary emphasis will be placed on observing TLEs above storms in
Oklahoma, near the new Lightning Mapping Array (LMA), during balloon missions
of Bill Beasley (OSU) and Ken Each (NM Tech).
The main focus this year will be to analyze the vast amount of
data acquired during the 2000 STEPS campaign (under NSF Support). Over 160
sprites were imaged in or near the coverage area of the NM Tech 3-D LMA. In
addition, ELF measurements were obtained by Earle Williams (MIT), Colin Price
(Tel Aviv University), Martin Fullekrug (Germany) and Steve Cummer (Duke
University). Charge moments have been computed by Williams and Cummer for
several dozen sprites from the storms on 18 and 19 July 2000. Initial evidence
suggests that, as expected, large charge moments (> 300 C*km) were
associated with the +CG discharges that resulted in optically detected sprites.
ELF/ULF signals were also obtained at the Syowa Antarctic station operated by
Tohoku University (H. Fukunishi). Excellent signatures of High Plains sprites
were monitored on 4 July 2000 at Syowa. Among the more interesting results from
STEPS were the first known ground-level videos of what appear to be blue
starters emerging from the top of an electrically active supercellular
thunderstorm about 75 km from Yucca Ridge. A new GEN III blue extended imager
was employed which may have aided in this observation. The same storm produce
numerous (several dozen) very small (1-2 pixel), short (1 video frame) and very
bright flashes of light or "dots" on the outer surface of the convective
overshooting dome of the storm. These events were generally not associated with
in-cloud lightning or VLF emissions. They may have represented immature "blue
starters" or perhaps yet another new phenomenon.
Walt Lyons will make a presentation on the imaging and visual
observations of sprites at the upcoming NCAR Workshop on Atmospheric Optics in
June in Boulder, CO.
GLOBAL ATMOSPHERICS INC.
We have recently begun full operation of a VHF time-of-arrival
network using a research version of our LDAR-II sensor. The network of seven
sensors located around the Dallas-Fort Worth International Airport has
collected complete data sets for several storms during spring of 2001. The LDAR
II system is a commercial extension of New Mexico Tech’s Lightning Mapping
Array. The operation of this test network is a major step in the development of
the commercial LDAR-II VHF system and is also important for on-going work to
understand the importance of cloud lightning information in general and the
altitude information provided by VHF mapping systems in particular. The
assessment of the value of altitude information is an evolution from a joint
study between GAI and MIT Lincoln Laboratory (Earle Williams, Bob Boldi, Mark
Weber, Anne Matlin) that involved examining altitude information in addition to
discharge rate in relation to severe storms in Florida observed by the original
NASA LDAR system.
Our efforts to understand further the importance of cloud
discharges are also motivated by a growing interest among operational
meteorologists in having cloud plus cloud-to-ground [CG] lightning information.
Lightning detection networks that employ GAI’s new IMPACT-ESP sensor,
which can detect and report both cloud and CG discharges, have recently been
installed by the Danish Meteorological Institute (DMI), the New Zealand
Meteorological Service, and the Korean Meteorological Administration (KMA). The
KMA has also purchased an LDAR-II VHF system that is designed to provide cloud
flash information with high detection efficiency over all of South Korea to
complement the high-efficiency CG detection of the IMPACT-ESP network. Finally,
a recent paper by Dennis Boccippio (NASA-MSFC), Ken Cummins, Hugh Christian
(NASA-MSFC) and Steve Goodman (NASA-MSFC) describes the combination of total
lightning observations by the NASA Optical Transient Detector with CG data from
the U.S. National Lightning Detection Network to estimate the long-term ratio
of cloud lightning to CG lightning over the continental U.S. (Monthly
Weather Review, vol. 129, pp. 108-122).
In November, 2000, GAI hosted the 2000 International Lightning
Detection Conference (ILDC) in Tucson Arizona, and was attended by more than
160 attendees from 25 countries. Forty-eight (48) papers were presented. Major
topics included technologies for total lightning detection using both
ground-based and space-based systems, the applications of total lightning
information in meteorology, and thunderstorm forecasting and safety. A complete
list of papers presented and links to the abstracts/papers can be found at
www.glatmos.com/news/ildc_schedule.htm.
For further information, contact : mmurphy@glatmos.com,
kcummins@glatmos.com, or rholle@glatmos.com
INDIAN INSTITUTE OF TROPICAL METEOROLOGY – PHYSICAL
METEOROLOGY AND AEROLOGY DIVISION (Pune, India)
The Indian Institute of Tropical Meteorology (IITM) functions as a
national centre for basic and applied research in monsoon meteorology of the
tropics in general with special reference to monsoon meteorology of India and
neighbourhood. Its primary functions are to promote, guide and conduct research
in the field of meteorology in all its aspects. IITM has made significant
contributions in the challenging areas of the Meteorology and Atmospheric
Sciences like Weather Forecasting, Climatology and Global Change,
Hydrometeorology, Monsoon, Climate Modelling, Cloud Physics, Weather
Modification, Atmospheric Chemistry and Atmospheric Electricity.
Studies in Atmospheric Electricity is one of the projects of
Physical Meteorology and Aerology Division of the IITM. Under this project the
continuous observations of different electrical parameters such as electric
field, point discharge current, drop charge etc. were taken since the 1970 at
this station (Pune) during fair and disturbed weather conditions. From the
atmospheric electricity point of view the study of thunderstorms is one of the
important topic as it controls the global electrical system. With this view, in
the present study the authors have examined the occurrence of nature's
important phenomenon thunderstorm, by using the statistical model viz. the
Markov Chain Models and present the results derived thereof.
Markov Chain Models for the
pre-monsoon season thunderstorms over Pune
M. K. Kulkarni , S. S. Kandalgaonkar and M.I.R.
Tinmaker
Thunderstorm is an important weather phenomenon to understand many
issues relating to the atmospheric electricity and weather. The
occurrence/non-occurrence of thunderstorm on a given day is a simple
meteorological example and sequence of their daily observations at a particular
location constitutes the time series of that variable. The time series analysis
is one of the statistical method used to forecast the thunderstorm occurrence.
The thunderstorms have a tendency to cluster and form a sequence of
thunderstorm day or a non-thunderstorm day. Such a tendency can be well
explained by Markov Chain Models of a particular order of conditional
dependence of a physical process. The present study deals with the application
of Markov Chain Models to the thunderstorm events during the pre-monsoon season
over the Pune region (180 32' N ,730 51' E, 559 amsl ).
The Markov Chain is the most common class of the model to
represent the time series of discrete variable. It consists of a system and a
set of transitional states. The principle of Markov Chain is the probability of
a thunderstorm on any day depends only upon whether there was a thunderstorm or
not on the previous day. In this short contribution, the daily thunderstorm
data for Pune station for a period of 11 years (1970-80 ) during pre-monsoon
season is utilised and subjected to Markov Chain Models.
The data for each year is considered as a separate sample of a
time series of a particular year. Using conditional frequencies, transition
probabilities for the first, second and third order Markov Chain Model have
been calculated. The parameter estimates of the Markov Chains of different
order have been estimated separately for each sample and then overall estimates
are obtained by combining suitably the estimates of all samples. Instead of
conventional Chi-Square test a decision making procedure based on the extension
of the maximum likelihood principle was used. The proper order of Markov Chain
for modelling the time series of thunderstorm occurrence is assessed by using
the Akaike's Information Criterion. The overall study suggested that the data
series under investigation was best explained by the first order Markov Chain
Model. The analysis of n-step probability distribution of thunderstorm activity
over Pune region reveals that from 5th step onwards the thunderstorm
phenomenon becomes independent irrespective of its initial state. The overall
stationary or climatological probability of pre-monsoon thunderstorm recurrence
activity over Pune region is very less (0.12). The observed and theoretical
values of mean recurrence times for thunderstorm day and non-thunderstorm days
realistically matched. The results narrated in the present study appeared to be
consistent with the availability of the data. Further investigations are needed
to confirm the results obtained.
INSTITUTE OF ATMOSPHERIC SCIENCES, SOUTH DAKOTA SCHOOL OF MINES
AND TECHNOLOGY (Rapid City, South Dakota 57701, USA)
Andy Detwiler (Andrew.Detwiler@sdsmt.edu)
reports:
John Helsdon continues to work on modelling lightning discharges
with student Inna Suz. He also works with PhD candidate Xingjun Zhang modelling
the effects of lightning on cloud chemistry. Zhang is comparing their model
results with lightning and chemical observations from the STERAO field
program.
Andy Detwiler, Qixu Mo, and Donna Kliche continue to organize and
analyse observations from last summer's STEPS field program. Preliminary
results are posted at http://www.ias.sdsmt.edu/institute/t28/index.htm .
The SDSMT armored T-28 is being outfitted with a replacement
engine. It will be flying in the Rapid City area this summer for a series of
instrument development tests. Ken Eack, NMIMT, and Bill Beasley, OU, will be
testing their equipment for observing X-rays, and the SDSMT group will be
working on several of their own instrument projects. The aircraft has no
commitments for the summer of 2002 and we are looking for researchers who are
interested in incorporating in situ measurements in convective storms into
their research plans. If you have such interest, please contact Andy Detwiler
by email at andy@ias.sdsmt.edu, or by phone at 605-394-2291.
INSTITUTE FOR PROBLEMS IN MECHANICS (Moscow, Russia),
KRZHIZHANOVSKY POWER ENGINEERING INSTITUTE (Moscow, Russia),
LIGHTNING ELIMINATORS & CONSULTANTS, INC. (Boulder, Colorado,
USA),
MOSCOW INSTITUTE OF PHYSICS & TECHNOLOGY (Dolgoprudny,
Russia)
Nickolay Aleksandrov (MIPT, alek@neq.mipt.ru), Edvard Bazelyan
(KPEI), Roy Carpenter (LEC), Mark Drabkin (LEC) and Yuri Raizer (IPM) have
recently begun a new study of the effect of corona on lightning discharge under
thundercloud conditions.
The purpose of this work is to numerically simulate corona
discharge near a high grounded object in an atmospheric electric field and to
estimate the effect of the injected space charge on the initiation and the
development of upward leader and counterleader. A simulation model of
non-stationary corona near the electrodes of different geometry has been
developed. This model was used to calculate the volt-ampere characteristic of
the discharge, the distribution of the injected space charge in the
cloud-to-ground gap and the evolution in time of the electric field near the
tip of the object. A model for describing the initiation and the development of
upward leader and counterleader in the cloud of space charge has been
suggested. It was shown that a strong redistribution of electric field by the
injected space charge can retard and even eliminate the initiation and
development of upward leader in the thundercloud electric field. The effect
becomes more pronounced for multi-center (with numerous needles) electrodes of
large radius that have been suggested by Lightning Eliminators &
Consultants, Inc.
The next step of this work is to analyze the development
conditions for the stepped leader of downward lightning and the way a lightning
chooses a point to strike. Focus will be on the study of the leader process in
the completing phase when the leader tip propagates in the space charge layer
close to the ground. The peculiarities of the development of downward leader
under conditions of an extremely extended charged layer (~ 1 km2 and larger) created by a large number
of specially mounted grounded electrodes will also be considered.
The applied aim of this work is to develop new efficient methods
to protect large-dimension engineering objects against direct lightning
strokes.
LF*EM RESEARCH (Dunedin, New Zealand)
17 Dunedin/Wtt Highway, PINE HILL 9001 Dunedin, NZ
Richard L Dowden, James B Brundell, and Craig J Rodger report
on global lightning location by VLF:
Current methods of radio location of lightning by timing, such as
LPATS, measure the time of arrival (TOA) of the leading edge of the lightning
impulse or "sferic". Using bandwidths extending to a few megahertz, the leading
edge can be determined to within 1 microsecond or better. This in turn allows
ground strike location to within a few hundred meters. To avoid reception of
the skywave, receiver sites must be less than few hundred km apart.
In the VLF band (3-30 kHz) lightning sferics can be detected some
10,000 km away. The catch is that the sferics from such distant lightning are
strongly dispersed. They have a duration of several milliseconds instead of
tens of microseconds. More importantly, there is no sharp onset and so no
definite TOA. Instead, the amplitude of the sferic waveform increases from the
noise background over several tens of microseconds to a rather blunt maximum
before decreasing over a few milliseconds.
One way of getting around this is to cross-correlate the sferic
waveforms received at a pair of spaced receivers to find the arrival time
difference. This uses the amplitude spectrum of the sferics from the discrete
Fourier transform (DFT) of the data. Noting that the Omega Navigation System,
using only 8 transmitteres world-wide at frequencies of ~10 -14 kHz achieved
location accuracies of 1-2 km by phase measurement, we use the progression of
phase versus frequency at the time of triggering. The latter can be determined
from the GPS pulse-per-second (PPS) to well within 1 microsecond.
In a "perfect" (Dirac delta) pulse, all frequency components have
the same phase at the pulse instant so the progression of phase versus
frequency is zero. In a dispersed pulse such as a lightning sferic this is no
longer true. However, by restricting our phase measurement to the frequency
range 6-20 kHz, which contains most to the sferic energy and largely avoids the
"tweeks" at the Earth-ionosphere cutoffs, we find the delay to the "Time Of
Group Arrival" (TOGA) from the average (from a regression line) progression of
phase versus frequency at the trigger time. Omega measurement of such
progression of phase from 10.2 to 13.6 kHz could also have been used for
location. In fact, TOGA is a sort of "inverse-Omega" where precisely located
receivers are used to locate a multitude of "VLF transmitters" (lightning).
As in any radio location of lightning by timing, only the arrival
time differences at pairs of stations is relevant. However, only the TOGAs need
to be compared instead of the full waveforms in the cross-correlation method.
Since calculation of the TOGA is derived from the phase spectrum of the DFT of
the data, we hope to get location accuracies similar to that of Omega, and
eventual global coverage with a similar number (~10) of receivers.
At this stage of our research we have only 3 receivers, spaced a
few thousand km apart. We need more to establish accuracy and efficiency.
MASSACHUSETTS INSTITUTE OF TECHNOLOGY (Lincoln Laboratory,
Lexington, Massachusetts, USA)
Mark Weber and Earle Williams are involved in a new project on
oceanic convective weather in collaboration with NCAR, NRL and ARINC, and
sponsored by the Federal Aviation Agency. NASA TRMM data (radar,
visible/infrared, and the Lightning Imaging Sensor) will be used to interpret
more intelligently the GOES satellite imagery for convective weather hazard to
aviation. The use of DoD non-imaging satellite assets is also planned to
develop a climatology for oceanic mesoscale lightning, and as a possible
monitor for the Madden-Julian Oscillation which strongly modulates oceanic
convective weather.
MASSACHUSETTS INSTITUTE OF TECHNOLOGY (Parsons Laboratory,
Cambridge, Massachusetts 02139, USA)
Correlated variations of rainfall and lightning over the African
continent on a 4-5 day time scale are now understood in the context of a global
5-day planetary wave. The integrated mesoscale lightning activity is documented
with Schumann resonance observations from Rhode Island. The daily African
rainfall is provided in datasets from NOAA (John Janowiak and Pingping Xie) and
NASA (Bob Adler and George Huffman). The global wave is revealed in global
observations of surface air pressure that show a westward moving wavenumber-one
disturbance (as in Madden and Julian (1972)), with a strongly declining
pressure over Africa on days with maximum mesoscale lightning. Graduate student
Akash Patel is documenting these results in a Master’s thesis to be
completed this summer.
Observations carried out in the TRMM (Tropical Rainfall Measuring
Mission) LBA field experiment in Rondonia, Brazil have been submitted for
publication in the LBA Special Issue of the Journal of Geophysical Research
with numerous coauthors from NASA and from Brazil. During the westerly wind
regime in Brazil, equivalent to the monsoon regime in India and northern
Australia, convection over the Amazon (disclosed with NASA TOGA radar
observations) showed a distinct maritime characteristic (clean boundary layer,
weakly developed mixed phase region, and low lightning activity). Accordingly,
this regime over the Amazon rainforest has been named ‘green ocean’.
Collaboration with Daniel Rosenfeld has been very valuable in the documentation
of a strong influence of aerosol in suppressing warm rain coalescence through a
deep zone during the highly polluted early premonsoon regime when smoke from
biomass burning is prevalent.
A review article on sprites has recently been prepared for Physics
Today. Numerous images of sprites, elves and haloes were generously provided by
many researchers in this field. This article emphasizes the early contributions
from spectroscopy and gaseous electronics (in work by Lord Rayleigh, J.J.
Thomson, C.T.R. Wilson and Irving Langmuir) to the present understanding of the
phenomenon.
In part to prepare for the writing of this review article,
laboratory experiments were carried out (with Bob Golka, Dave Williams, Stan
Heckman and Russ Armstrong) with air-filled DC-excited glow discharge tubes of
various sizes, at pressures representative of sprite altitudes in the
mesosphere. Integrated spectroscopic observations of the positive column of the
discharge showed, as with integrated observations in the main body of sprites,
abundant evidence for (red) nitrogen first positive emission but an absence of
(blue) first negative emission. These results will be discussed at the IAGA
meeting in Hanoi, Vietnam in August.
NATIONAL LIGHTNING SAFETY INSTITUTE, NLSI (Louisville, Colorado,
USA)
www.lightningsafety.com
- We continue our Subject Matter Expert two day intensive
education seminars, primarily directed to US Department of Defense and US
Department of Energy management/supervisory persons. During the past six months
five such workshops were conducted at Los Alamos NM (2), Washington DC (2), and
Charleston SC (1).
- A new one day workshop, intended for field electricians and
facility inspectors, is called "Inspection, Maintenance and Testing of the
NFPA-780 Lightning Protection System." Graduates of this class are certified by
NLSI to verify that existing NFPA-780 lightning protection systems are in
as-specified working condition. Already this training has been provided for
DoD, DOE, and US Navy personnel.
- Site inspections of interest included: A) Shortwave radio
transmission facility at Bella Vista, Costa Rica. Bonding and surge suppression
issues were examined. B) Vestas wind turbine farm near El Paso TX.. A 8.5 ohms
earth electrode subsystem was developed in dry rocky conditions where
background soils were measuring 155 ohms.
- A new Transfer Impedance Measurement Instrumentation System
(TIMIS) is available to characterize the lightning response of sensitive assets
and facilities. Injection of low currents into the LPS and measurement of very
low conducted or induced voltages or electric fields are used to determine
transfer impedances into building steel, AC power lines, signal and data
wiring, copper water pipes, etc. The transfer impedances are used to determine
lightning voltages and currents in critical systems or components within the
facility. TIMIS is particularly useful for the very sensitive transfer
impedance measurements required to characterize Faraday cage LPSs. An extensive
set of verification and validation tests on TIMIS was successfully completed
recently by Sandia National Laboratories. The TIMIS is now being commercialized
by BOLT, Inc. under the direction of its President, Dr. Marvin Morris, who was
formerly the manager of Sandia National Laboratories Electromagnetic Analysis
and Test Department. NLSI is collaborating in the effort to predict lightning
behavior and effects upon high risk structures.
- In response to continuing vacillation by NFPA regarding their
"Standard for the Installation of Lightning Protection Systems NFPA-780", both
the US Dept Defense and the US Dept Energy are reviewing and updating their
respecting lightning protection documents. NLSI is a contributing member to
both review panels. A NLSI article in the Jan. 2001 issue of Quality Power
Assurance outlines our comprehensive, systematic approach to lightning safety.
This paper can be reviewed at:
www.lightningsafety.com/nlsi_lhm/explosives.html
- NLSI continues to broadcast the lightning safety message with
written presentations and public speaking engagements, recently including: US
Weather Broadcasting Meteorologists Assn.; Science Insight; Colorado State
Parks Assn.; Sports Turf Mgrs. Assoc. Mtg.; International Lightning Detection
Conference; Michigan Sports Turf Managers Assn.; DOE Consequence Assessment and
Protective Actions Subcommittee (SCAPA); City of Westminster; Colorado Public
Risk Assessment Org.; WABC Channel 7 TV – New York City; "Safety and
Supervisor" magazine; "Athletic Turf" magazine; Network of the World (London),
etc.
- NOAA/NWS has declared June 18-23 "National Lightning Safety
Awareness Week."
NLSI is participating in this effort.
NEW MEXICO TECH – LIGHTNING MAPPING GROUP (Socorro, New
Mexico, USA)
Paul Krehbiel, Bill Rison, and Ron Thomas report:
New Mexico Tech's Lightning Mapping Array (LMA) was operated in
the Severe Thunderstorm Electrification and Precipitation Study (STEPS) between
May 24and August 10, 2000. A network of 13 mapping stations was deployed and
provided excellent observations of numerous predominantly positive CG storms
and several tornadic storms. The +CG storms were commonly found to produce
inverted polarity intracloud discharges, namely discharges between mid-level
positive charge in the storm and upper-level negative charge, or between lower
positive and mid-level negative charge. Lightning ‘holes’ were again
observed in several tornadic and supercell storms, and appear to be a
characteristic feature of such storms.
We are in the process of documenting and evaluating the huge
dataset collected during STEPS in collaboration with the other investigators.
All of the lightning mapping data have been processed in decimated form and are
available on the web, at www.lightning.nmt.edu. On the website, visit
‘STEPS 2000 Observations’ for a description of the program and an
initial posting of results, or ‘LMA STEPS data server’/‘Download
STEPS LMA data’ to look at complete sets of data images and web
animations. (Some specific animation examples are June 22 2200-2400 and June 23
0000-0400, or July 21 0000-0600.) The full, non-decimated data are currently
being processed during important storm times.
TEL AVIV UNIVERSITY, DEPARTMENT OF GEOPHYSICS AND PLANETARY
SCIENCES (Tel Aviv, Israël)
The team led by Zev Levin, Colin Price and Yoav Yair will try and
obtain high-resolution images of sprites from space during the MEDIEX campaign,
and correlate them with ground-based ELF-VLF measurements. The present launch
date for STS-107 (the space shuttle Columbia) is April 2002, for a 16-day
mission at 39 degrees inclination. The payload consists of a multi-spectral
Xybion IMC201 camera that will be operated by an Israeli astronaut in
cooperation with a ground team located at NASA/GSFC. Images will be recorded on
digital VCRs in the crew-cabin and downlinked to the ground. Observational runs
would consist of continuous recording of the Earth’s limb from the
direction of the dusk terminator towards the night side, preferably before
midnight local time at the observed area. In order to enhance the success
probability, as many thunderstorms as possible would be targeted. The
observation areas would cover an area that extends from 39S to 39N, along the
shuttle orbit. The most (active) desired areas will be tropical South America,
North-Australia and Indonesia, South-East Asia, China, Sea of Japan,
Continental USA and the Gulf of Mexico. Several groups have expressed interest
in the MEDIEX-Sprite campaign and will collect electromagnetic and optical data
during the mission. These include Earle Williams (MIT), Umran Inan (Stanford),
Walt Lyons (FMA Research Inc.), Marcelo Saba (Brazil), Zen Kawasaki (University
of Osaka, Japan) and Martin Fullekrug (Frankfurt, Germany).
Orit Altaratz, Zev Levin and Yoav Yair continue the study of the
properties of winter thunderstorms along the coast of Israel, with special
emphasis on the differences between the areas near Tel-Aviv and Haifa. The
objective is to understand the role of different parameters, such as
topography, sea-land temperature difference and aerosol particles concentration
in affecting the dynamical and microphysical characteristics of thunderclouds
in this region. Part of this study is carried out by analyzing data from
lightning detection systems (LPATS, CGR3 and LIS) and data from the Tel Aviv
University radar. In addition, a numerical study is being carried out by using
the RAMS model to simulate the evolution of clouds, including electrical charge
separation and electric field build-up, as they move from the Mediterranean Sea
toward the coast.
Colin Price, together with graduate student Mustafa Asfur, has
analysed part of the Israeli ELF/VLF data collected during the STEPS2000 field
campaign. Using a higher sampling frequency than previously used for the ELF (1
kHz) allowed a better estimate of the distance from our station of the positive
lightning that produces sprites. Furthermore, using the VLF for direction
finding, we were able to considerably improve our location of the positive
lightnings that produced sprites, a distance of 11,000 km away from our
observing station.
Colin Price and graduate student Moshe Blum published a paper in
Earth, Moon and Planets (November, 2000) describing the VLF pulses produced by
meteors entering the atmosphere. We have found a close link between the
frequency of meteors during the Leonid ’99 meteor shower and the frequency
of VLF pulses identified with the meteors. We have found a unique spectrum
related to the meteors, very different to the normal lightning discharge
spectrum, hence allowing us to differentiate between the two.
Since November 2000, Martin Fullekrug from the University of
Frankfurt has been working with Colin Price at Tel Aviv University on the
relationship between large positive lightning discharges over African storms
and the cloud characteristics of these storms. It was found that the maximum
development of the African thunderstorms occurs around 1800 UT, while the
maximum frequency of large positive discharges, that likely produce sprites,
occurs 4 hours later. It is suggested that observations of sprites from Mt.
Cameroon may provide an average of 70 sprites per night.
THE UNIVERSITY OF UTAH (Salt Lake City, Utah 84112-0110,
USA)
Ed Zipser and one or more students will participate with many
colleagues in this community in the NASA and U.S. Weather Research Program
supported Convection and Moisture Experiment (CAMEX-4) in August-September
2001. The program will include coordinated flights in tropical cyclones by the
NASA ER-2 and DC-8, one or more NOAA WP-3Ds, and other aircraft. One of the
goals will be to watch for opportunities for detailed observations of
convective bursts in hurricane eyewalls, seeking clues whether lightning and
other remote sensing data can help anticipate rapid intensification of the
storm.
Ongoing research in the tropical convection group at the
University of Utah includes systematic analysis of the 3-year TRMM (Tropical
Rain Measuring Mission) database, and data from previous TRMM validation field
programs. A number of papers are in press, but a sample of the database and
research approach can be found in Nesbitt, S.W., E. J. Zipser, and D.J. Cecil,
2000: A census of precipitation features in the tropics using TRMM: Radar, ice
scattering, and lightning observations. J. Climate, 13 (23), 4087-4106.
Zipser will present some recent results from the TRMM data
analysis at the IAMAS meeting (Innsbruck, July) and the AMS Radar Conference in
Munich the following week. The IAMAS paper will feature recent work of Nesbitt
on the diurnal cycle of precipitation, demonstrating that rain from MCSs and
from smaller storms peaks at different times. The Radar Conference paper by
Yorty, Zipser, and Nesbitt may be of particular interest to the AE community,
because it highlights the most extreme storms observed by TRMM during the 3
years. Many of these storms have correspondingly extreme lightning "flash"
rates. As an exercise for the reader, where would you expect these "greatest
storms on earth" to be found?
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