Physics of lightning: new model approaches and prospects of the satellite observations (original) (raw)
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Chapter 13: Space- and Ground-Based Studies of Lightning Signatures
2009
This article provides a brief survey of the space-and ground-based studies of lightning performed by investigators at Los Alamos National Laboratory (LANL). The primary goal of these studies was to further understand unique lightning signatures known as Narrow Bipolar Events (NBEs). First, an overview is presented of the Fast On-orbit Recording of Transient Events (FORTE) satellite and of the ground-based Los Alamos Sferic Array (LASA). This is followed by a summary of the phenomenology, physics, and meteorological context of NBEs and NBE-related discharges. This article also discusses additional radio frequency and optical observations of lightning made by the FORTE satellite and concludes with an outlook on LANL's growing interest in the use of lightning observations in the study of severe weather and hurricane intensification.
Radio Frequency Observations of Lightning Discharges by the Forte Satellite
2002
FORTE-observed VHF signatures for different lightning discharges are presented. For in-cloud discharges, a pulse pair is typically recorded and is named a "transionospheric pulse pair" (TIPP). Many intense TIPPs are coherent and polarized, whereas initial and dart leaders do not show a recognizable degree of polarization. TIPPs are optically weaker than cloud-to-ground (CG) strokes, and stronger VHF TIPPs are optically darker. About 10% of CG strokes, mostly over seawater, produce extremely narrow, powerful VHF pulses at the very beginning of the return strokes. These narrow pulses are found to form an upward beam pattern.
A Review of Operational Lightning Detection: Comparison of Ground vs. Satellite-based Observations
Lightning generated by convective storms, and identified as a formidable hazard to life and property, results from strong storms lofting liquid-phase hydrometeors to high altitudes where freezing occurs and collisions between drops, graupel, and ice crystals lead to electrification. Among the most widely accepted theories of convective storm electrification is the " charge transfer-separation process " by which interaction (esp. collision) between ice crystals and graupel particles result in the establishment and stratification of positive and negative charge centers within the convective cloud, respectively. Differing growth processes between ice crystals (i.e. deposition of water vapor) and graupel (accretion of supercooled water) result in differing molecular structure and electron arrangement, and subsequently, favor the transfer of electrons with negative charge from an ice crystal to a graupel particle. In general, negative charge accumulates in the middle levels of the convective storm cloud, referred to as the " main negative charge " charge center, while positive charge accumulates in the upper layer and anvil (if present) region and is referred to as the " upper positive charge " center. Other secondary charge centers may develop in a convective storm, such as the " lower positive charge " center that results from falling hail, however, the main electric field built within the storm results from the separation of the main negative and upper positive charge centers. When the electric field strength (E) between the storm cloud and the ground eventually increases to the threshold value of electric breakdown potential (3 x 10 9 V/km), a stepped leader, defined as a segmented ionized channel, develops and propagates downward toward the ground in steps of 50 to 100 m length. Upon contact of the stepped leader with the ground, a bright return stroke from the ground to the cloud occurs, in which electrons flow downward from progressively higher levels in the channel. The stepped leader and return stroke comprise the lightning strike. The strike with additional return strokes, triggered by a dart leader, then comprise the cloud-to-ground (CG) lightning flash. Intracloud (IC) lightning discharge between the main negative and upper positive charge centers also results from charge separation and electrical breakdown. Ground-based and satellite-based lightning detection systems often detect both IC and CG lightning flashes, with CG strokes a stronger emitter of low frequency (LF) radiation. Lightning detection systems (LDS) have a vital role in the real-time identification of the location of lightning strokes for the purpose of public safety and weather forecasting and warning operations. Archived LDS datasets also provide support to electric utility companies to identify lightning events associated with electric power grid faults and power outages, reduce frequency and duration of power outages, and make improvements to transmission line segments susceptible to lightning damage. More importantly, flash rate and density measurements are necessary for the inference of cloud thermodynamical and microphysical processes that favor severe thunderstorm hazard phenomena including hail, tornadoes, and damaging winds (downbursts).
Coincident radio frequency and optical emissions from lightning, observed with the FORTE satellite
Journal of Geophysical Research: Atmospheres, 2001
We present long optical and radio frequency (RF) time series of lightning events observed with the FORTE satellite in January 2000. Each record contains multiple RF and optical impulses. We use the RF signatures to identify the general type of discharge for each impulse according to the discrimination techniques described by and reviewed herein. We see a large number of paired, impulsive events in the RF which allow us to study the heights within clouds of several events. We also see that the rate of RF/optical coincidence depends on the type of discharge: nearly 100% of VHF signals from first negative return strokes have an associated optical signal, whereas a mere 50% of impulsive intracloud events appear to have an optical counterpart. While the RF signals from ground strokes clearly coincide with simple optical signals in almost all cases, the intracloud lightning often shows nearly continuous, complicated RF and optical emissions which do not cleanly correlate with one another. The RF and optical pulses do not show a well-defined relationship of intensities, for any lightning type. The observed delay between the RF and optical pulses we interpret as mainly an effect of the scattering experienced by the light as it traverses the cloud. For intracloud lightning, we find no evidence of an intrinsic delay at the source between the onset of the RF and optical signals. Impulsive in-cloud RF events are seen to occur on average every 0.9 ms during a flash. This paper is not subject to U.S.
Lightning and middle atmospheric discharges in the atmosphere
Journal of Atmospheric and Solar-Terrestrial Physics, 2015
Recent development in lightning discharges including transient luminous events (TLEs) and global electric circuit are discussed. Role of solar activity, convective available potential energy, surface temperature and difference of land-ocean surfaces on convection process are discussed. Different processes of discharge initiation are discussed. Events like sprites and halos are caused by the upward quasielectrostatic fields associated with intense cloud-to-ground discharges while jets (blue starter, blue jet, gigantic jet) are caused by charge imbalance in thunderstorm during lightning discharges but they are not associated with a particular discharge flash. Elves are generated by the electromagnetic pulse radiated during lightning discharges. The present understanding of global electric circuit is also reviewed. Relation between lightning activity/global electric circuit and climate is discussed.
Characteristics of impulsive VHF lightning signals observed by the FORTE satellite
Journal of Geophysical Research Atmospheres, 2002
We study very high frequency (VHF) and optical emissions from lightning, observed by the FORTE satellite, differentiating between impulsive (transionospheric pulse pairs (TIPPs)) and nonimpulsive events. TIPPs are seen to constitute 47% of the FORTE VHF data but only 32% of the optically coincident data. The median peak optical irradiance of the optical emission associated with TIPPs is 916 μW/m2 at FORTE and for non-TIPPs is 195 μW/m2. The median effective pulse width of the optical signal from TIPPs is 658 μs, and it is 548 μs for non-TIPPs. In the VHF, both event types have similar observed peak powers (0.086 mV2/m2 and 0.089 mV2/m2, for TIPPs and non-TIPPs, respectively). The optically coincident lightning (of either type) is weaker in peak VHF emission than is the lightning that lacks coincident optical signals, although for non-TIPPs, the stronger the VHF peak, the more likely the event is to have a coincident optical signal. For TIPPs, however, this is true only for events with peak E2 < 0.1 mV2/m2. Above that threshold, TIPPs are increasingly less likely to show coincident optical emission with increasing VHF peak E2. For both TIPPs and non-TIPPs, the peak current reported by the U.S. National Lightning Detection Network™ and peak VHF power reported by FORTE are statistically proportional. The nature of the proportionality appears to depend upon the polarity of the discharge but not upon the event type. We also find that only 11% of TIPPs are associated with negative-polarity discharges, compared to 75% of non-TIPPs. Finally, we find that TIPPs arise from events with altitudes of 6-15 km, although we see optical coincidence only for those TIPPs occurring above ˜10 km.
Satellite measurements of global lightning
Quarterly Journal of the Royal Meteorological Society, 1998
The satellite-borne NASA/MSFC Optical Transient Detector provides global distributions of lightning and lightning-stroke radiance. Measurements made during the first year of its operation show that lightning activity is particularly pronounced over the tropics, much greater over land than over the oceans, and exhibits great seasonal variability. The values of lightning-stroke radiance tend to be greater over the oceans, less when lightning activity is high, and greater in the northern hemisphere winter than summer.
Journal of Geophysical Research: Space Physics, 2009
TLEs are optically observed from the U.S. Langmuir Laboratory, while ELF/VLF waveform data are simultaneously recorded on board the Centre National d'Etudes Spatiales microsatellite DEMETER and on the ground at Langmuir. Analyses of ELF/VLF measurements associated with sprite events observed on 28 July 2005 and 3 August 2005 are presented. Conditions to trace back the wave emissions from the satellite to the source region of the parent lightning discharge are discussed. The main results concern: (1) the identification from a low Earth orbit satellite of the 0+ whistler signatures of the TLE causative lightning; (2) the identification of the propagation characteristics of proton whistlers triggered by the 0+ whistlers of the causative lightning, and the potential use of those characteristics; (3) recognition of the difficulty to observe sprite-produced ELF bursts in the presence of proton-whistlers; (4) the use of geographical displays of the average power received by the DEMETER electric field antennas over the U.S. Navy transmitter North West Cape (NWC) located in Western Australia to evaluate VLF transmission cones which explain the presence (28 July events) or the absence (3 August events) of propagation links between sferics observed at ground and 0+ whistlers observed on DEMETER; and (5) owing to electron-collisions, an optimum transfer of energy from the atmosphere to the ionosphere for waves with k vectors antiparallel, or quasi-antiparallel, to Earth's magnetic field direction.
Observations of lightning in the stratosphere
Journal of Geophysical Research, 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 over the land. 1465 ning. These include the detection of gamma-ray burst of atmospheric origin [Fishman et al., 1994], lightning-induced brightening of the airglow layer [Boeck et al., 1992], and unusual tran-ionospheric pulse pair radio signals detected by the Blackbeard experiment on the ALEXIS satellite [Holden et al.,