- Boccippio, D.J., K. Driscoll, W. Koshak, R. Blakeslee, W. Boeck, D. Mach, H.J.
- Christian and S.J. Goodman, 1997: Cross-sensor validation of the Optical
Transient Detector(OTD).
Lightning data from the U.S. National Lightning Detection Network
(NLDN) is used to perform preliminary validation of the satellite-based
Optical Transient Detector (OTD). Sensor precision, accuracy,
detection efficiency and biases of the deployed instrument are
considered. We estimate the sensor to have, on average, better than
30 km spatial and 100 ms temporal accuracy. The detection efficiency
for cloud-to-ground lightning is about 45-70%, slightly higher for
intracloud lightning. There are only marginal day/night biases in the
dataset, although 55 day averaging is required to remove
sampling-based diurnal lighting cycle biases. The sensor detects
statistically significant differences in the optical characteristics of
intracloud, negative cloud-to-ground and positive cloud-to-ground
lightning, although it cannot a priori determine flash types.
- Boccippio, D.J., 1996: The electrification of stratiform anvils. PhD Dissertation,
- Massachusetts Institute of Technology.
Stratiform precipitation regions accompany convective activity on many spatial scales.
The electrification of these regions is anomalous in a number of ways. Surface and
above-cloud fields are often ``inverted'' from normal thunderstorm conditions.
Unusually large, bright, horizontal ``spider'' lightning and high current and charge
transfer positive cloud-to-ground (CG) lightning dominates in these regions.
Mesospheric ``red sprite'' emissions have to date been observed exclusively over
stratiform cloud shields.
We postulate that a dominant ``inverted dipole'' charge structure may account for this
anomalous electrification. This is based upon laboratory observations of charge
separation which show that in low liquid water content (LWC) environments, or dry but
ice-supersaturated environments, precipitation ice tends to charge positively (instead
of negatively) upon collision with smaller crystals. Under typical stratiform cloud
conditions, liquid water should be depleted and this charging regime favored. An
inverted dipole would be the natural consequence of large-scale charge separation
(net flux divergence of charged ice), given typical hydrometeor profiles.
The inverted dipole hypothesis is tested using radar and electrical observations of four
weakly organized, late-stage systems in Orlando, Albuquerque and the Western
Pacific. Time-evolving, area-average vertical velocity profiles are inferred from single
Doppler radar data. These profiles provide the forcing for a 1-D steady state
microphysical retrieval, which yields vertical hydrometeor profiles and ice/water
saturation conditions. The retrieved microphysical parameters are then combined with
laboratory charge transfer measurements to infer the instantaneous charging behavior
of the systems.
Despite limitations in the analysis technique, the retrievals yield useful results. Total
charge transfer drops only modestly as the storm enters the late (stratiform) stage,
suggesting a continued active generator is plausible. Generator currents show an
enhanced lowermost inverted dipole charging structure, which we may infer will result
in a comparable inverted dipole charge structure, consistent with surface, in-situ and
remote observations. Fine-scale vertical variations in ice and liquid water content may
yield multipolar generator current profiles, despite unipolar charge transfer regimes.
This suggests that multipoles observed in balloon soundings may not necessarily
conflict with the simple ice-ice collisional charge separation mechanism. Overall, the
results are consistent with, but not proof of, the inverted dipole model.
- Boccippio, D.J., C. Wong, E.R. Williams, R. Boldi, H.J. Christian and S.J. Goodman,
- 1996: Global validation of single-station Schumann resonance lightning location.
Submitted to J. Atmos. Terr. Phys..
Global measurements of large, optically bright lightning events from the
Optical Transient Detector (OTD) satellite are used to validate estimates of
lightning location from single-station Schumann resonance (SR) data.
Bearing estimates are obtained through conventional magnetic
direction-finding techniques, while source range is estimated from the
range-dependent impedance spectrum of individual SR transients. An
analysis of 40 such transients suggests that single-station techniques can
locate lightning globally with an accuracy of 1-2 Mm. This is confirmed by
further validation at close ranges from flashes detected by the National
Lightning Detection Network (NLDN). Observations with both OTD and SR
systems may be useful in globally locating lightning with necessary, if not
sufficient, characteristics to trigger mesospheric "red sprites".
- Boccippio, D.J., E.R. Williams, S.L. Heckman, W.A. Lyons, I.T. Baker and R. Boldi,
- 1995: Sprites, ELF transients and Positive Ground Strokes. Science, 269,
1088-1091.
Observations of two summertime mesoscale convective systems (MCS') reveal that
mesospheric optical "sprite" phenomena are often coincident with both large amplitude
positive cloud-to-ground lightning and transient Schumann resonance excitations of the
entire earth-ionosphere cavity ("Q-bursts"). These observations, together with previous
studies of MCS electrification, are supportive of a simple electrostatic mechanism for the
triggering of sprites, following concepts originally set forth by C.T.R. Wilson, in which
the rapid removal of large quantities of positive charge from an areally extensive charge
layer stresses the mesosphere to dielectric breakdown.
- Boccippio, D.J., 1995: A diagnostic analysis of the VVP single-Doppler retrieval
- technique. J. Atmos. Oc. Tech., 12,230-248.
A diagnostic analysis of the VVP (Volume Velocity Processing) retrieval method is
presented, with emphasis on understanding the technique as a linear, multivariate
regression. Similarities and differences to the VAD/EVAD retrieval techniques are
discussed, using this framework. Conventional regression diagnostics are then employed
to quantitatively determine situations in which the VVP technique is likely to fail. An
algorithm for preparation and analysis of a robust VVP retrieval is developed, and
applied to synthetic and actual datasets with high temporal and spatial resolution.
A fundamental (but quantifiable) limitation to some forms of VVP analysis is inadequate
sampling dispersion in the n-space of the multivariate regression, manifest as a
collinearity between the basis functions of some fitted parameters. Such collinearity may
be manifest either in the definition of these basis functions or in their realization
in a given sampling configuration. This nonorthogonality may cause numerical instability,
variance inflation (decrease in robustness) and increased sensitivity to bias from neglected
wind components. It is shown that these effects prevent the application of VVP to small
azimuthal sectors of data. The behaviour of the VVP regression is further diagnosed
over a wide range of sampling constraints, and reasonable sector limits established.
- Boeck, W. L., O. H. Vaughan,Jr., R. Blakeslee, B. Vonnegut, and M. Brook,
- Lightning induced brightening in the airglow layer, Geophys. Res. Letters,
19, 99-102, 1992.
This report describes a trasient luminosity observed at the altitude of the airglow
layer (about 95 km) in coincidence with a lightning flash in a tropical oceanic
thunderstorm directory beneath it. This even provides new evidence of direct coupling
between lightning an dionospheric events. This luminous event in the ionosphere was the
only one of its kind observed during an examination of several thousand images of
lightning recorded under suitable viewing conditions with Space Shuttle cameras.
Several possible mechanisms and interpretations are discussed briefly.
- Boeck, W. L., O. H. Vaughan, R. Blakeslee, B. Vonnegut, M. Brook, and J. McKune,
- Observations of lightning in the stratosphere, accepted by J. Geophys.
Res., 1993.Document.
An examination and analysis of video images of lightning, captured
by the payload bay TV cameras of the space shuttle, provided a
variety of examples of lightning in the stratosphere above thunderstorms.
These images were obtained on several recent shuttle flights while
conducting the mesoscale lightning experiment (MLE). The images
of stratospheric lightning illustrate the variety of filamentary
and broad vertical discharges in the stratosphere that may accompany
a lightning flash. A typical event is imaged as a single or multiple
filament extending 30 to 40 km above a thunderstorm that is illuminated
by a series of lightning strokes. Examples are found in temperate
and tropical areas, over the oceans and the land.
- Boeck, W. L., O. H. Vaughan, R. Blakeslee, B. Vonnegut, and M. Brook
- The Role of the Space Shuttle Videotapes in the Discovery of Sprites, Jets and
Elves, Submitted to J. Atmos. Terr. Physics 1997.Document.
The sequence of video tape observations of the upper atmospheric
optical flashes called sprites, jets, starters, and ELVES are
described in the successsive phases of search, discovery, confirmation,
and exploration for the years before 1993. Although there were
credible eyewitness accounts from ground observers and pilots,
these reports did not inspire a systematic search for hard evidence
of such phenomena. The science community would instead wait for
serendipitous observations to move the leading edge of this science
forward. The phenomenon, now known as a sprite, was first accidently
documented on ground based videotape recordings on the night of
July 6, 1989. Video observations from the space shuttle acquired
from 1989 through 1991 provided 17 additional examples to confirm
the existence of the sprites phenomenon. Successful video observations
from a mountain ridge by Lyons, starting July 7, 1993,
and night-time aircraft video observations by Sentman and Wescott
on July 8, 1993 established the basic science of the sprite phenomena
by acquiring and analyzing data based on hundreds of new events.
The 1994 Sprites campaign and the video titled "Red Sprites
and Blue Jets" popularized the name sprite and provided a
vocabulary of terms to describe the visual attributes. Prior
to this video, investigators used a variety of vague descriptive
words to describe the individual events. Also, during the 1994
campaign, Wescott and coworkers obtained the first quantative
measurements of jets and provided the name "blue jets".
A third phenomenon was discovered in video from the STS-41 mission
(October 1990) in the lower ionosphere directly above an active
thunderstorm. It consisted of a large horizontal brightening
several hundred kilometers across at the altitude of the airglow
layer. In 1995, Lyons and associates confirmed the existence
of this type of very brief brightening which they named Emissions
of Light and Very Low Frequency Perturbations From Electromagnetic
Pulse Sources (ELVES). Because sprites, jets, and ELVES have
appeared for millennia, their discovery was inevitable. The partial
history related in this paper outlines the unsophisticated activities
using shuttle video and the dissemination of the results by video
presentations during the early phases of sprite research. This
paper does not attempt to evaluate the advances in the science
based on the measurement campaigns of Lyons, Sentman and the many
other investigators.
- Boeck, W. L., O. H. Vaughan, R. Blakeslee, B. Vonnegut, M. Brook, and J. McKune,
- Observations of lightning in the stratosphere, J. Geophys.
Res., 100, 1465-1475, 1995.
An examination and analysis of video images of lightning, captured by the
payload bay TV cameras of the space shuttle, provided a variety of examples
of lightning in the stratosphere above thunderstorms. These images were
obtained on several recent shuttle flights while conducting the mesoscale
lightning experiment (MLE). The images of stratospheric lightning illustrate
the variety of filamentary and broad vertical discharges in the stratosphere
that may accompany a lightning flash. A typical event is imaged as a single
or multiple filament extending 30 to 40 km above a thunderstorm that is
illuminated by a series of lightning strokes. Examples are found in
temperate and tropical areas, over the oceans and the land.
- Christian, H. J., R. J. Blakeslee, and S. J. Goodman, The detection of lightning
- from geostationary orbit, J. Geophys. Res., 94(D11), 13329-13337, 1989.
Lightning observations from satellites in low Earth orbit have been made over the past
25 years, producing estimates of global flash frequency by season and latitude as well
as information on diurnal variations. However, these measurements have suffered from low detection efficiencies, poor spatial resolutions, and the inability to continuously
monitor specific storms or storm systems. Using results of investigations with a high-altitude
NASA U-2 aircraft and other research, a space sensor capable of mapping both intracloud
and cloud-to-ground lightning discharges from geostationary orbit during day and night with
a spatial resolution of 10 km and a detection efficiency of 90% is currently being developed.
In addition, this sensor, which is called the Lightning Mapper Sensor (LMS), will monitor
storms on a continual basis. The combination of modern solid state mosaic focal planes
with extensive on-board signal processing in the LMS provides a powerful technique for
the detection of weak background-contaminated signals and permits the detection of
lightning during the day. The LMS has a 10.5\deg\ field of view that covers all of the continental
United States, large oceanic areas, all of Central America, much of South America
including the Andes and the Amazon Basin, and large regions of the inter-tropical convergence
zone. It is anticipated that the LMS will be flown on a GOES satellite in the mid-1990s.
The characteristics and design of the LMS are presented as well as a discussion of the
scientific research that will be possible with this instrument.
- Cifelli, R., S.A. Rutledge, D.J. Boccippio and T. Matejka, 1996: Horizontal
- divergence and vertical velocity retrievals from Doppler radar and wind
profiler observations. Atmos. Oc. Tech., 13, 948-966.
Vertical motion profiles can be diagnosed with the mass continuity equation using
horizontal divergence fields derived from various single-Doppler radar techniques such
as EVAD (extended velocity-azimuth display), CEVAD (concurrent extended velocity-azimuth
display), and VVP (volume velocity processing). These methods allow for the retrieval of
mesoscale air motions in precipitating regions when the wind field is relatively
homnogeneous. In contrast, VHF wind profiler data can provide a direct measurement of
vertical motin, albeith across a much smaller domain compared to the single-Doppler radar
techniques. In this study, we compare horizontal divergence and vertical motion patterns
derived from the various single-Doppler methods with those obtained from VHF profiler
data.
The diagnosed profiles of horizontal divergence and vertical velocity from the
single-Doppler (scanning radar) techniques are in qualitative agreement in the lower
troposphere but often exhibit large variability at higher levels. Because of less
stringent radar echo requirements, the VVP technique often analyzed data above the top
of the EVAD-CEVAD analysis domain, resulting in a deeper layer of upper-level divergence.
The CEVAD technique often produced a deeper and larger region of upward motin despite
similar profiles of divergence, probably due to the CEVAD top boundary condition
specification of particle terminal fall speed as opposed to the vertical air motion, as
well as to the adjustment procedure employed during the regression solutions.
The wind profiler data showed much larger vertical gradients and magnitudes of divergence
and vertical velocity when averaged over the same time interval required to collect data
for a single-Doppler retrieval. However, when all the available data were composited, the
high-frequency variability in the wind profiler retrievals was reduced resulting in
relatively good agrement between all analysis methods. The wind profiler usually sampled
vertical motion (divergence) several kilometers above the single-Doppler retrievals, which
the authors attribute to the stringent precipitation echo coverage requirements imposed
by the scanning radar analysis techniques, thus limiting their vertical extent near
echo top.
- Driscoll, K. T., R. J. Blakeslee, and M. L. Baginski, A modeling study of the
- time-averaged electric currents in the vicinity of isolated thunderstorms,
J. Geophys. Rev., 97, 11,535-11,551, 1992.
A thorough examination of the results of a time-dependent computer model of a dipole
thunderstorm revealed that there are numerous similarities between the time-averaged
electrical properties and the steady state properties of an active thunderstorm. Thus,
the electrical behavior of the atmosphere in the vicinity of a thunderstorm can be
determined with a formulation similar to what was first described by Holzer and Saxon
in 1952. From the Maxwell continuity equation of electric current, a simple analytical
equation was derived that expresses a thunderstorm's average current contribution to
the global electric circuit in terms of the generator current within the thundercloud,
the intracloud lightning current, the cloud-to-ground lightning current, the altitudes
of the charge centers, and the conductivity profile of the atmosphere. This equation
was found to be nearly as accurate as the more computationally expensive numerical
model, even when it is applied to a thunderstorm with a reduced conductivity thundercloud,
a time-varying generator current, a varying flash rate, and a changing lightning mix.
- Driscoll, K. T., R. J. Blakeslee, and W. J. Koshak, A time-averaged current
- analysis of a thunderstorm using ground-based measurements, accepted by J.
Geophys. Res., 1993.
The amount of upward current provided to the ionosphere by a thunderstorm that appeared
over the Kennedy Space Center (KSC) in July 11, 1978, is reexamined using an analytic
equation that describes a bipolar thunderstorm's current contribution to the global
circuit in terms of its generator current, lightning currents, the altitudes of its
charge centers, and the conductivity profile of the atmosphere. Ground-based measurements,
which were obtained from a network of electric field mills positioned at various distances
from the thunderstorm, were used to characterize the electrical activity inside the thundercloud.
The location of the lightning discharges, the type of lightning, and the amount of
charge neutralized during this thunderstorm were computed through a least-squares
inversion of the measured changes in the electric fields following each lightning
discharge. These measurements provided the information necessary to implement the
analytic equation, and consequently, a time-averaged estimate of this thunderstorm's
current contribution to the global circuit was calculated. From these results the amount
of conduction current supplied to the atmosphere by this small thunderstorm was computed
to be less than 25% of the time-averaged generator current that flowed between the two
vertically displaced charge centers.
- Koshak, W. J., R. J. Solakiewicz, D. D. Phanord, and R. J. Blakeslee, A
- diffusion model for lightning radiative transfer,accepted by J. Geophys.
Res., 1993.
A one-speed Boltzmann transport theory, with diffusion approximations, is applied to
study the radiative transfer properties of lightning in optically thick thunderclouds.
Near-infrared ($\lambda = 0.7774 \mu$m) photons associated with a prominent oxygen emission
triplet in the lighting spectrum are considered. Transient and spatially complex lightning
radiation sources are placed inside a rectangular parallelepiped thundercloud geometry
and the effects of multiple scattering are studied. The cloud is assumed to be composed
of a homogeneous collection of identical spherical water droplets, each droplet a nearly
conservative, anisotropic scatterer. Conceptually, we treat the thundercloud like a nuclear
reactor, with photons replaced by neutrons, and utilize standard one-speed neutron
diffusion techniques common in nuclear reactor analyses. Valid analytic results for
the intensity distribution (expanded in spherical harmonics) are obtained for regions
sufficiently far from sources. Model estimates of the arrival-time delay and pulse width
broadening of lightning signals radiated from within the cloud are determined and the results
are in good agreement with both experimental data and previous Monte Carlo estimates. Additional
model studies of this kind will be used to study the general information content of cloud
top lightning radiation signatures.
- Krider, E. P. and R. J. Blakeslee, The electric currents produced by
- thunderclouds, J. Electrostatics, 16, 369, 1985.
Recent measurements show that the Maxwell current densities, $\vec J_m$, produced by
thunderclouds are quasi-steady at the ground even in the presence of lightning. These
measurements also show that $\vec J_m$ is usually dominated by the displacement current
component when the electric field is close to zero; therefore, $\vec J_m$ can often be
estimated from just an electric field measurement. Maps that show the time-development
of the pattern of the average $\vec J_m$ over a relatively large area are given for one
Florida thunderstorm. These maps are in good agreement with radar echoes and the
locations of lightning charges, and can now be used in further studies of thunderstorm
electricity.
- Orville, R. E., E. J. Zipser, M. Brook, C. Weidman, G. Aulich, E. P. Krider,
- H. Christian, S. Goodman, R. Blakeslee, and K. Cummins, 1997: Lightning in
the region of the TOGA COARE, Bull. Amer. Meteor. Soc., in press.
In the fall of 1992 a lightning direction finder network was deployed in the western
Pacific Ocean in the area of Papua, New Guinea. The instruments were modified to
detect cloud-to-ground lightning out to a distance of 900 km. Data were collected from
cloud-to-ground lightning flashes for the period 26 Nov 1992--15 Jan 1994. The analyses
are presented for the period 1 Jan 1993--31 Dec 1993. In addition, a waveform recorder
was located at Kavieng to record both cloud-to-ground lightning and intracloud lightning
in order to provide an estimate of the complete lightning activity. The data from these instruments are to be analyzed in conjunction with the data from ship and airborne
radars, in-cloud microphysics, and electrical measurements from both the ER-2 and DC-8. The waveform instrumentation operated from approximately mid-January through February 1993.
Over 150,000 waveforms were recorded.
During the year, Jan--Dec 1993, the cloud-to-ground lightning location network recorded 857,000 first strokes of which 5.6% were of positive polarity. During the same period,
437,000 subsequent strokes were recorded. The peak annual flash density was measured
to be 2.0 flashes/km$^2$ centered on the western coastline of the island of New Britain,
just southwest of Rabaul. The annual peak lightning flash density over the Intensive Flux
Array of Tropical Oceans Global Atmosphere Coupled Ocean-Atmosphere Response Experiment was 0.1 flashes/km$^2$, or more than an order of magnitude less than that measured near
land. The diurnal lightning frequency peaked at 1600 UTC (0200 LT), perhaps in coincidence
with the nighttime land-breeze convergence along the coast of New Britain. Median monthly
negative peak currents are in the 20--30 kA range, with first stroke peak currents
typically exceeding subsequent peak currents. Median monthly positive peak currents
are typically 30 kA with one month (June) having a value of 60 kA.
Positive polar conductivity was measured by an ER-2 flight from 40\deg N geomagnetic
latitude to 28\deg S geomagnetic latitude. The measurements show that the air conductivity
is about a factor of 0.6 lower in the Tropics than in the midlatitudes. Consequently,
a tropical storm will produce higher field values aloft for the same rate of electrical
current generation. An ER-2 overflight of tropical cyclone Oliver on 7 Feb 1993
measured electric fields and 85-GHz brightness temperatures. The measurements reveal
electrification in the eye wall cloud region with ice, but no lightning was observed.
- Weber, M. E., H. J. Christian, A. A. Few, and M. F. Stewart, A thundercloud
- electric field sounding: Charge distribution and lightning, J. Geophys. Res.,
87, 7158, 1982.
An instrumented free balloon measured electric fields and field changes as it rose
through a thundercloud above Langmuir Laboratory, New Mexico. The variation of the electric
field with altitude implied that the cloud contained negative space charge of density
$-0.6$ to $-4$ nC/m$^3$ between 5.5 and 8.0 km MSL. The environmental temperature at
these levels ranged from $-5\deg$ to $-20\C$. Our measurements imply that the areal
extent of this negative charge center was significantly greater than that of the cloud's intense precipitation shafts. At altitudes grater than 8 km, the instrument ascended
past net positive charge. We also inferred from our measurements positive space charge
adjacent to the Earth's surface (concentration 0.6 nC/m$^3$) and in the lower portion
of the cloud (1.0 nC/m$^3$). Electric field changes from intracloud lightning were interpreted
by using a simple model for the developing streamer of the initial phase. Thunder source
reconstructions provided estimates for the orientation of lightning channels. Seven
`streamers' so analyzed propagated on the average, at $5\x 10^4$ m/s and carried a
current of 390 A. The mean charge dissipated during a flash was 30 C.
- Williams, E.R., R. Zhang and D.J. Boccippio, 1993: The microphysical growth state of
- ice particles and the large scale electrical structure of clouds. J. Geophys.
Res., 99, 10787-10792.
Cloud temperature, liquid water content, and vertical air velocity are all considered in
evaluating the microphysical growth state of ice phase precipitation particles in the
atmosphere. The large-scale observations taken together with in situ measurements indicate that
the most prevalent growth condition for large ice particles in active convection is sublimation
during riming, whereas the most prevalent growth condition in stratiform precipitation is vapor
deposition. The large-scale electrical observations lend further support to the idea that particles
warmed by riming into sublimation charge negatively and particles in vapor deposition charge
positively in collisions with small ice particles.
- Wurman, J., S. Heckman, D.J. Boccippio, 1993: A bistatic multiple Doppler radar
- network: Part I, Theory. J. Appl. Met., 32, 1802-1814.
A multiple Doppler radar network can be constructed using only one, traditional, transmitting
pencil-beam radara and one or more passive, low gain, non-transmitting receiving sites. Radiation
scattered from the pencil beam of the transmitting radar as it penetrates weather targets can be
detected at the receive-only sites as well as at the active transmitter. The Doppler shifts
of the radiation received at all the sites can be used to construct two- and three-dimensional
windfields in a manner similar to that used with traditional Doppler radar networks.
There are unique scientific advantages to a bistatic multiple Doppler network:
1.All radial velocity measurements from individual pulse volumes are collected simultaneously
since there is only one source of radiation.
2.The intensity of the obliquely scattered radiation can be compared to Rayleigh scattering
predictions and used for hail detection.
3.Rapid scanning of localized weather phenomena can be aided by elimination of the need to
scan with multiple radars.
This type of radar network also has significant economic advantages. Passive sites contain no
high voltage transmitting equipment or large rotating antennas. They require no operators and
much less maintenance. We estimate initial investment costs and subsequent operational and
maintenance costs are less than 1/30 that of conventional radars.
There are shortcomings particular to these types of networks:
1.Passive, low gain receiving sites are more sensitive to contamination from transmitter side-lobes
and to secondary scattering from weather echoes.
2.Low gain receiving sites are less sensitive to weak weather echoes.
3.Cartesian (u,v,w) windfields derived from bistatic network data exhibit about twice the expected
error as those constructed from data from traditional active networks containing equal numbers
of radars.
Multiple scattering and side-lobe contamination levels are acceptable in most situations and can be
reduced with the use of higher gain receiveing antennas. The low sensitivity and higher erros of the
bistatic networks can be ameliorated with the use of multiple passive sites, a practical solution due
to their very low cost.
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