The optical characteristics of lightning (original) (raw)
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Letter to the Editor Intense oceanic lightning
Annales Geophysicae, 2002
The electrodynamic properties of intense oceanic lightning discharges are compared to intense continental lightning discharges. Particularly intense negative lightning discharges with absolute charge moments > 2 kC•km occur more often over the oceans than over the continents during April 1998. Intense continental lightning discharges, with negative and positive polarity, and intense positive oceanic lightning discharges primarily occur associated with mesoscale convection in the late evening. The number of intense negative oceanic lightning discharges increases in the early morning hours, probably associated with the resurgence of oceanic mesoscale convection in coastal areas. The dayto-day variability of intense negative oceanic lightning discharges exhibits a five day periodicity, possibly related to planetary waves.
Monthly Weather Review, 1998
A clear association between large peak current cloud-to-ground lightning flashes of positive polarity and sprites and elves in the stratosphere and mesosphere has been previously demonstrated. This paper reports on the first climatology of large peak current cloud-to-ground (LPCCG) lightning flashes compiled from the U.S. National Lightning Detection Network. Analysis of almost 60 million CG flashes from 14 summer months (1991-95) reveals distinct geographic differences in the distribution of positive and negative polarity LPCCGs, arbitrarily defined as flashes with peak currents Ն75 kA. Large peak current positive CGs (LPCϩCGs) are concentrated in the High Plains and upper Midwest, the region in which a large majority of optical sprite and elves observations have been obtained. By contrast, large peak current negative CGs (LPCϪCGs) preferentially occur over the coastal waters of the Gulf of Mexico and the southeastern United States. A total of 1.46 million LPCCGs were found, of which only 13.7% were ϩCGs. Almost 70% of the LPCϩCGs, however, occurred in the central United States (30Њ-50ЊN, 88Њ-110ЊW). The percentage of all LPCCGs that were positive approached 30% in the central United States compared to 4.5% for the remainder of the country. A ϩCG is 3.1 times more likely to exceed 75 kA than is a ϪCG flash on a national basis. Yet in terms of absolute numbers for all ranges of peak current Ն75 kA, negative CGs are clearly dominant. For peak currents Ն75 and 200 kA, negative CGs outnumbered positive CGs by ratios of 6.4 and 4.1, respectively. In the central United States, however, during evening hours the number of LPCϩCGs almost reaches parity with LPCϪCGs. Average stroke multiplicity also exhibited regional differences. Over a half million negative CGs and over 1000 positive CGs were found with multiplicity Ն10.
Observations of elevated power near the Brunt-Väisälä frequency
Journal of Geophysical Research, 2005
High-frequency peaks close to the Brunt-Väisälä frequency (N) are observed in the spectra of the nightglow brightness derived from OH Meinel airglow measurements made over the foothills of the Rocky Mountains in Boulder (40°03 0 N, 105°14 0 W), Colorado during the summer of 1999. Over a 57-day period there were 28 nights of sufficient duration and continuity to support reliable spectral analyses. Measurements for these nights yield persistently spectral features near N. The periods of the spectral peaks are in the range $5.6-5.8 min, usually appearing as a double-peaked feature. These periods are compared with values of the Brunt-Väisälä period (t N) derived from concurrent lidar soundings of the temperature of the upper mesosphere and lower thermosphere over Fort Collins (40°35 0 N, 105°03 0 W), Colorado, about 49 km distant from Boulder. Detailed comparisons of the observed periods and the profiles of N suggest that the double-peaked features in the spectra may arise because the OH M nightglow emissions is double-peaked, as observed by Evans and Llewellyn (1972) and by Llewellyn et al. (2002). Several theories are explored for the spectral enhancement. The data do not support a definitive answer, but we favor an explanation in terms of orographically excited waves related to the proximity of our airglow observations to the Rocky Mountains. A strong possibility is the parametric excitation described by Klostermeyer (1990). This explanation requires the presence of a large-amplitude low-frequency primary wave and is supported by the observed frequent occurrence of strong wave activity in the approximately hour period range.
Journal of Atmospheric and Solar-Terrestrial Physics, 2016
We propose a new technique to identify the occurrence of lightning and transient luminous events (TLEs) using multicolor photometric data obtained by space borne nadir measurements. We estimate the spectral characteristics of lightning and TLEs by converting the optical data obtained by the ISUAL limb experiment to the GLIMS nadir geometry. We find that the estimated spectral shapes of TLE-accompanied lightning are clearly different from those of pure lightning. The obtained results show that (1) the intensity of FUV signals and (2) the ratio of 337/red (609-753 nm) spectral irradiance are useful to identify the occurrence of TLEs. The occurrence probabilities of TLEs are 10%, 40%, 80%, in the case of lightning events having the 337/red spectral irradiance ratio of 0.95, 2.95, 14.79, respectively. By using the 60% criterion of the 337/red ratio and the existence of FUV emissions, we classify the 1039 GLIMSobserved lightning events into 828 pure lightning and 211 TLE-accompanied lightning. Since the GLIMS trigger level is adjusted to observe extremely-bright events, the occurrence probability of TLEs obtained here most probably reflects the characteristics of energetic lightning. The estimated global map is consistent with previously determined distributions: the highest activities of lightning and TLEs are found over the North/South American continents, African continent, and Asian maritime regions. While the absolute occurrence number of pure lightning and TLE-accompanied lightning are found to maximize in the equatorial region, the occurrence probability of TLEs possibly increase somewhat in the mid-latitude region. Since the occurrence probabilities of TLEs are higher over the ocean than over land, it is likely that the GLIMS-observed TLEs are due primarily to elves which tends to occur more frequently over the ocean. & 2016 Elsevier Ltd. All rights reserved. consist of fine-scale vertically-oriented structures of plasmas appearing at altitudes of 50-85 km after the occurrence of cloud-toground lightning discharge with a typical delay time of a few milliseconds to a few tens of milliseconds (e.g., Barrington-Leigh et al., 2001). Theoretical studies have suggested that the lightninginduced quasi-electrostatic field drives the initiation and growth of streamer-type discharges which split into many upward and downward branches, forming the overall complex structure of sprites (e.g., Pasko et al., 2000; Liu and Pasko, 2004). Elve is a Contents lists available at ScienceDirect
ISUAL far-ultraviolet events, elves, and lightning current
Journal of Geophysical Research, 2010
The Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) often recorded events that have significant far-ultraviolet (FUV) emissions in the spectrophotometer but have no discernible transient luminous events (TLEs) in the imager. These FUV events likely are dim TLEs. To confirm the conjecture, lightning emissions were simulated and proved to be completely absorbed by the atmosphere. The FUV emission of the FUV events follows the lightning OI emission within 1 ms, similar to the characteristics of elves. After analyzing the imager-N 2 1P brightness of the elves and their FUV intensity, a linear correlation was found, which is consistent with the work of Kuo et al. (2007). The intensity of the FUV events ranks among the dimmest elves and is less than 1 × 10 4 photons/cm 2. Combining all the information, the FUV events are identified as dim elves that eluded the detection of the ISUAL imager. Also from the detection limits of the ISUAL spectrophotometer (SP) and the imager, for the before-the-limb elves the detection number of SP is found to be nearly 16 times higher than that of the imager. This result is consistent with a related factor of ∼13 that was inferred from the U.S. National Lightning Detection Network (NLDN) peak current distribution for the negative cloud-to-ground lightning. Hence the ISUAL spectrophotometer can be used to perform elve survey, to infer the peak current of the elve-producing lightning, and possibly to be used to deduce other lightning parameters. Evidence is also found for the existence of multielves, which are FUV events from the M-components or the multiple strokes in lightning flashes.
The physical origin of the land–ocean contrast in lightning activity
2002
New tests and older ideas are explored to understand the origin of the pronounced contrast in lightning between land and sea. The behavior of islands as miniature continents with variable area supports the traditional thermal hypothesis over the aerosol hypothesis for lightning control. The substantial land-ocean contrast in updraft strength is supported globally by TRMM (Tropical Rainfall Measuring Mission) radar comparisons of mixed phase radar reflectivity. The land-ocean updraft contrast is grossly inconsistent with the land-ocean contrast in CAPE (Convective Available Potential Energy), from the standpoint of parcel theory. This inconsistency is resolved by the scaling of buoyant parcel size with cloud base height, as suggested by earlier investigators. Strongly electrified continental convection is then favored by a larger surface Bowen ratio, and by larger, more strongly buoyant boundary layer parcels which more efficiently transform CAPE to kinetic energy of the updraft in the moist stage of conditional instability. To cite this article: E. Williams, S. Stanfill, C. R. Physique 3 (2002) 1277-1292. 2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS aerosol / convection / islands / lightning / thermals / thunderstorm / updrafts
Estimates of lightning NO< sub> x production from GOME satellite observations
2005
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We report the results of two observation campaigns conducted during the Northern Hemisphere winters of 2005-6 and 2006-7 aiming to detect transient luminous events (TLEs) above winter thunderstorms in the vicinity of Israel and the eastern coastline of the Mediterranean Sea. In 10 out of 31 different observation nights we detected 66 events: 56 sprites and 10 Elves. The detection ranges varied from 250 to 450 km. Sprites were found to be produced by active cells with a vertical dimension of 5-9 km and cloud top temperature~−40°C, embedded in a much larger matrix of stratiform precipitating cloudiness. This configuration closely resembles the conditions for winter sprites in the Hokuriku region of Japan. Synchronized with the optical observations, ELF data were recorded at two observation stations in Israel and Hungary in order to qualify and quantify parameters of the parent lightning discharge associated with the TLEs. These stations are located 500 km and 2100 km respectively from the Eastern Mediterranean Sea, where most TLEs occur. Among the optically observed TLE events, we found that all the ELF signals were produced solely by positive cloud-to-ground flashes (+CGs), most of which were recorded in Israel (88%) and Hungary (77%). Calculation of the Charge Moment Change showed average values of 1400 ± 600 C km, with some extreme events exceeding 3500 C km. The average time delay between the ELF transient of the parent +CG and the observed sprites was 55 ms, with shorter delays for column sprites (42 ± 34 ms) compared to carrot sprites (68±34). Furthermore, based on the ELF data, there were no early identifiable precursors to TLE occurrence in the regional lightning activity. From the spatial formation of the observed columniform sprites, we propose that columniform sprites are sometimes arranged in a 3-dimensional circular pattern, thus mapping the instantaneous electric field in the mesosphere.