Showing papers on "Thunderstorm published in 1995"
TL;DR: In this article, three algorithms extract information on precipitation type, structure, and amount from operational radar and rain gauge data, and statistically summarize the vertical structure of the radar echoes, and determine precipitation rates and amounts on high spatial resolution.
Abstract: Three algorithms extract information on precipitation type, structure, and amount from operational radar and rain gauge data. Tests on one month of data from one site show that the algorithms perform accurately and provide products that characterize the essential features of the precipitation climatology. Input to the algorithms are the operationally executed volume scans of a radar and the data from a surrounding rain gauge network. The algorithms separate the radar echoes into convective and stratiform regions, statistically summarize the vertical structure of the radar echoes, and determine precipitation rates and amounts on high spatial resolution. The convective and stratiform regions are separated on the basis of the intensity and sharpness of the peaks of echo intensity. The peaks indicate the centers of the convective region. Precipitation not identified as convective is stratiform. This method avoids the problem of underestimating the stratiform precipitation. The separation criteria are...
953 citations
TL;DR: In this paper, high-resolution radar data collected in Florida during the Convection and Precipitation/Electrification Experiment are used to elucidate the microphysical and kinematic processes occurring during the transition of a multicellular storm from convective to stratiform stages.
Abstract: High-resolution radar data collected in Florida during the Convection and Precipitation/Electrification Experiment are used to elucidate the microphysical and kinematic processes occurring during the transition of a multicellular storm from convective to stratiform stages. A statistical technique is employed to examine the evolving properties of the ensemble small-scale variability of radar reflectivity, vertical velocity, and differential reflectivity over the entire storm. Differential radar reflectivity data indicate that the precipitation at upper levels was nearly glaciated early in the storm's lifetime. Dual-Doppler radar data show that throughout the storm's lifetime both updrafts and down-drafts were present at all altitudes and that most of the volume of the radar echo contained vertical velocities incapable of supporting precipitation-size particles. Thus, the ensemble microphysical properties of the storm were increasingly dominated by particles falling in an environment of weak vertic...
638 citations
01 Jan 1995
TL;DR: In this paper, the rate of atmospheric NO production and its effect on telecommunication system performance are discussed. But the authors do not consider the effect of atmospheric noise on the performance of telecommunication systems.
Abstract: Ion Chemistry and Composition of the Atmosphere, A.A. Viggiano and F. Arnold Meteorologic Aspects of Thunderstorms, E.R. Williams Thunderstorm Electrification, C.P.R. Saunders Lightning Currents, T. Ogawa Lightning Detection from Ground and Space, R.E. Orville Artificially Triggered Lightning, K. Horii and M. Nakano Ball Lightning, H. Kikuchi Lightning and Atmospheric Chemistry: The Rate of Atmospheric NO Production, M.G. Lawrence, W.L. Chameides, P.S. Kasibhatla, H.Levy II, and W. Moxim Lightning Within Planetary Atmospheres, K. Rinnert Quasistatic Electromagnetic Phenomena in the Atmosphere and Ionosphere, R.H. Holzworth Schumann Resonances, D.D. Sentman Low-Frequency Radio Noise, A.C. Frazer-Smith Radio Noise Above 300 kHz due to Natural Causes, D.E. Proctor Atmospheric Noise and Its Effects of Telecommunication System Performance, A.D. Spaulding
367 citations
TL;DR: The first observations of a newly documented type of optical emission above thunderstorms are reported in this paper, which is called "blue jets" or narrowly collimated beams of blue light that appear to propagate upwards from the tops of thunderstorms, were recorded on B/W and color video cameras for the first time during the Sprites94 aircraft campaign, June-July 1994.
Abstract: Initial observations of a newly documented type of optical emission above thunderstorms are reported. 'Blue jets', or narrowly collimated beams of blue light that appear to propagate upwards from the tops of thunderstorms, were recorded on B/W and color video cameras for the first time during the Sprites94 aircraft campaign, June-July, 1994. The jets appear to propagate upward at speeds of about 100 km/s and reach terminal altitudes of 40-50 m. Fifty six examples were recorded during a 22 minute interval during a storm over Arkansas. We examine some possible mechanisms, but have no satisfactory theory of this phenomenon.
351 citations
Book•
29 Aug 1995
TL;DR: The history of satellite meteorology can be found in this paper, where the authors present an overview of the history of the field of meteorology and its application in satellite data collection.
Abstract: Introduction: History of Satellite Meteorology. Scope of The Book. Orbits and Navigation: Newton's Laws. Keplerian Orbits. Orbit Perturbations. Meteorological Satellite Orbits. Satellite Positioning, Tracking and Navigation. Space-Time Sampling. Launch Vehicles and Profiles. Radiative Transfer: Basic Quantities. Blackbody Radiation. The Radiative Transfer Equation. Gaseous Absorption. Scattering. Surface Reflection. Solar Radiation. Meteorological SatelliteInstrumentation: Operational Polar-Orbiting Satellites. Operational Geostationary Satellites. Other Satellite Instruments. Satellite Data Archives. Image Interpretation: Satellite Imagery. Spectral Properties. Image Enhancement Techniques. Geolocation and Calibration. Atmospheric and Surface Phenomena. A Final Note.Temperature and Trace Gases: Sounding Theory. Retrieval Methods. Operational Retrievals. Limb Sounding Retrievals. Ozone and Other Gases. The Split-Window Technique. Winds: Cloud and Vapor Tracking. Winds from Soundings. Ocean Surface Winds. Doppler Wind Measurements. Clouds and Aerosols: Clouds from Sounders. Clouds from Imagers. Clouds from Microwave Radiometry. Stratospheric Aerosols. Tropospheric Aerosols. Precipitation: Visible and Infrared Techniques. Passive Microwave Techniques. Radar. Severe Thunderstorms. Earth Radiation Budget: The Solar Constant. Top of the Atmosphere Radiation Budget. Surface Radiation Budget. The Future: NOAA K, L, M.Mission to Planet Earth. Other Possibilities. A Final Comment. Appendixes: List of Meteorological Satellites. Abbreviations. Principal Symbols. Systeme International Units. Physical Constants. Subject Index.
264 citations
TL;DR: In this paper, a fully compressible, nonlinear, numerical, two-dimensional simulation of a midlatitude squall line was used to study vertically propagating waves generated by deep convection.
Abstract: High-frequency gravity waves generated by convective storms likely play an important role in the general circulation of the middle atmosphere. Yet little is known about waves from this source. This work utilizes a fully compressible, nonlinear, numerical, two-dimensional simulation of a midlatitude squall line to study vertically propagating waves generated by deep convection. The model includes a deep stratosphere layer with high enough resolution to characterize the wave motions at these altitudes. A spectral analysis of the stratospheric waves provides an understanding of the necessary characteristics of the spectrum for future studies of their effects on the middle atmosphere in realistic mean wind scenarios. The wave spectrum also displays specific characteristics that point to the physical mechanisms within the storm responsible for their forcing. Understanding these forcing mechanisms and the properties of the storm and atmosphere that control them are crucial first steps toward developing a parameterization of waves from this source. The simulation also provides a description of some observable signatures of convectively generated waves, which may promote observational verification of these results and help tie any such observations to their convective source.
260 citations
TL;DR: In this paper, the authors show that the electric field inside storms tends to be limited to magnitudes less than or equal to the breakeven field, which may explain why electric field magnitudes greater than 150 kV m−1 are rarely found inside thunderstorms.
Abstract: Lightning may be initiated via an electron avalanche that may occur when energetic electrons (∼1 MeV) are accelerated by thunderstorm electric fields to velocities sufficient to produce new energetic electrons during ionizing collisions with nitrogen or oxygen molecules. For the avalanche to occur, the thunderstorm electric field must exceed a critical value called the breakeven field. At any altitude the breakeven field is substantially less than the field usually thought necessary either for dielectric breakdown or for streamer propagation. We show that 23 electric field soundings through thunderstorms seem to confirm that lightning occurs when the electric field exceeds the breakeven field. The soundings also show that the electric field inside storms tends to be limited to magnitudes less than or equal to the breakeven field. This breakeven mechanism may explain why electric field magnitudes greater than 150 kV m−1 are rarely found inside thunderstorms. It may also help explain the initiation of lightning and other types of discharges that either propagate upward from the tops of thunderstorms or occur above them.
249 citations
TL;DR: In this article, the authors analyzed cloud-to-ground lightning flash data collected by the National Lightning Detection Network in and around 16 central U.S. cities for the period 198992.
Abstract: Cloud-to-ground lightning flash data collected by the National Lightning Detection Network were analysed in and around 16 central U.S. cities for the period 198992. Lightning data are well suited to study storm activity in and around large urban areas since their continuity and coverage in space and time is superior to historical, spatially limited records of thunderstorm activity. Frequency of cloud-to-ground lightning flashes (of negative and positive polarity) in the area immediately upwind, within, and immediately downwind of the cities were compared. An enhancement of lightning frequency on the order of 40%85% was found over and downwind of many of these cities. A number of possible urban-related causal factors were examined including effects of increased urban concentrations of cloud condensation nuclei, urban population and size, and the presence of distinct topographic features in and around the cities. Various factors, physical and anthropogenic, appeared to interact in diverse ways to...
139 citations
TL;DR: In this article, the authors reviewed observational and modeling studies of cloud venting by a wide variety of cloud types ranging from ordinary cumuli, to ordinary cumulonimbi, mesoscale convective systems and tropical and extratropical cyclones.
134 citations
TL;DR: In this article, ship reports of present weather obtained from the Comprehensive Ocean-Atmosphere Data Set are analyzed for the period 1958-91 in order to elucidate regional and seasonal variations in the climatological frequency, phase, intensity, and character of oceanic precipitation.
Abstract: Ship reports of present weather obtained from the Comprehensive Ocean-Atmosphere Data Set are analyzed for the period 1958-91 in order to elucidate regional and seasonal variations in the climatological frequency, phase, intensity, and character of oceanic precipitation. Specific findings of note include the following: 1) The frequency of thunderstorm reports, relative to all precipitation reports, is a strong function of location, with thunderstorm activity being favored within 1000-3000 km of major tropical and subtropical land masses, while being quite rare at other locations, even within the intertropical convergence zone. 2) The latitudinal frequency of precipitation over the southern oceans increases steadily toward the Antarctic continent and shows relatively little seasonal variation. The frequency of convective activity, however, shows considerable seasonal variability, with sharp winter maxima occurring near 38 deg. latitude in both hemispheres. 3) Drizzle is the preferred form of precipitation in a number of regions, most of which coincide with known regions of persistent marine stratus and stratocumulus in the subtropical highs. Less well documented is the high relative frequency of drizzle in the vicinity of the equatorial sea surface temperature front in the eastern Pacific. 4) Regional differences in the temporal scale of precipitation events (e.g., transient showers versus steady precipitation) are clearly depicted by way of the ratio of the frequency of precipitation at the observation time to the frequency of all precipitation reports, including precipitation during the previous hour. The results of this study suggest that many current satellite rainfall estimation techniques may substantially underestimate the fractional coverage or frequency of precipitation poleward of 50 deg. latitude and in the subtropical dry zones. They also draw attention to the need to carefully account for regional differences in the physical and spatial properties of rainfall when developing calibration relationships for satellite algorithms.
117 citations
TL;DR: In this paper, the physical processes leading to sprites also alter the conductivity of the lower ionosphere, and the data constitutes the first evidence that the physical process leading to the sprites also alters the conductivities of the ionosphere.
Abstract: VLF perturbations on signals propagating along great-circle-paths (GCP) through electrically active midwest thunderstorms are associated with luminous high altitude glows (referred to as sprites) observed from aircraft or ground. The data constitutes the first evidence that the physical processes leading to sprites also alter the conductivity of the lower ionosphere.
TL;DR: In this paper, the synoptic conditions associated with 27 severe thunderstorm events that occurred in central Arizona during the summer monsoon have been examined systematically and compared to long-term mean July conditions.
Abstract: Severe thunderstorms are relatively rare over Arizona and occur most frequently during the summer monsoon period, that is, July, August, and early September. Forecasting in Arizona during the summertime is quite difficult and skill scores are low for both precipitation and severe thunderstorm watches and warnings. In the past, due to the sparse population of Arizona, severe thunderstorms usually impacted few people and were considered relatively insignificant events. However, over the last 20 years, the population of central Arizona has grown dramatically, and the impact of severe thunderstorm and flash flood occurrences has also increased. Synoptic conditions associated with 27 severe thunderstorm events that occurred in central Arizona during the summer monsoon have been examined systematically and compared to long-term mean July conditions. The period of study covered 1978 to 1990, and cases selected were limited to the high population area of central Arizona. McCollum subjectively identified ...
TL;DR: In this article, 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.
Abstract: 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.
TL;DR: In this article, the principal observational characteristics of sprites and jets are presented, and several proposed production mechanisms are reviewed, as well as the proposed production mechanism for sprites and jet emissions.
Abstract: Recent low light level monochrome television observations obtained from the ground and from the space shuttle, and low light level color and monochrome television images obtained from aboard jet aircraft, have shown that intense lightning in mesoscale thunderstorm systems may excite at least two distinct types of optical emissions that together span the space between the tops of some thunderstorms and the ionosphere. The first of these emissions, dubbed ‘‘sprites,’’ are luminous red structures that typically span the altitude range 60–90 km, often with faint bluish tendrils dangling below. A second, rarer, type of luminous emission are ‘‘blue jets’’ that appear to spurt upward out of the anvil top in narrow cones to altitudes of 40–50 km at speeds of ∼100 km/s. In this paper the principal observational characteristics of sprites and jets are presented, and several proposed production mechanisms are reviewed.
TL;DR: In this paper, a statistical technique is employed to examine the evolving properties of the ensemble small-scale variability of high-resolution radar data collected in a multicellular Florida thunderstorm and synthesize these observations with results from the first two parts of the study into a selfconsistent conceptual model that describes the convective-to-stratiform transition of the storm.
Abstract: A statistical technique is employed to examine the evolving properties of the ensemble small-scale variability of high-resolution radar data collected in a multicellular Florida thunderstorm. This paper examines vertical mass transport and mass divergence and synthesizes these observations with results from the first two parts of the study into a self-consistent conceptual model that describes the convective-to-stratiform transition of the storm. Vertical mass transport distributions indicate that the more numerous weak and moderate-strength upward and downward velocities, not the few strongest, accomplished most of the vertical mass transport in the storm. Hence, most of the mass of precipitation is condensed outside the areas of intense upward motion. These data thus suggest a change in the way we think about convection. Although the few regions of strongest vertical motion play a part in the overall storm evolution by dispersing particles throughout the depth of the storm, it is the more preva...
TL;DR: In this paper, a series of papers dealing with operational weather forecasting within the Central Region of the National Weather Service is presented, focusing on the primary Central Region warm season weather producer, the thunderstorm.
Abstract: This paper is one of a series of papers dealing with operational weather forecasting within the Central Region of the National Weather Service. It focuses on the primary Central Region warm season weather producer, the thunderstorm. Some of the unique aspects of Central Region thunderstorms are highlighted. Techniques used to answer four questions routinely posed by forecasters are described. These questions are the following: 1) Will thunderstorms occur that will affect my area of forecast responsibility? 2) If thunderstorms develop, will these thunderstorms reach severe intensity? 3) If these thunderstorms reach severe intensity, what types of severe phenomena are likely with these storms? and 4) If thunderstorms occur, what storm type is most likely to be observed? A case from 14 May 1990 is used to illustrate the application of some of the techniques.
TL;DR: In this article, the authors acquired 11 balloon soundings of the electric field and thermodynamics in large and sometimes severe and tornadic thunderstorms over the southern Great Plains over the last decade.
Abstract: We have acquired 11 balloon soundings of the electric field and thermodynamics in large and sometimes severe and tornadic thunderstorms over the southern Great Plains. The ascent rates of the balloons were used to divide the soundings into weak and strong updrafts. All 11 soundings had magnitudes of charge densities and thicknesses of charge regions similar to those reported previously in small thunderstorms. The five weak-updraft soundings had complex charge structures of 7–9 charge regions below 10 km altitude. The magnitude of the maximum measured electric field in these soundings was 100–150 k V m−1. The four soundings in strong updrafts had balloon ascent rates of at least 15 m s−1 for at least 1 km. These soundings had simpler electrical structures of 3–5 charge regions below 10 km altitude. Their maximum measured electric fields ranged from 85 to 130 kV m−1. The data may support an earlier hypothesis that charge is elevated in strong updrafts. In addition, the data may suggest that simpler charge structures are associated with proximity to strong updrafts rather than with different storm types.
TL;DR: In this paper, two-dimensional and three-dimensional simulations of a midlatitude squall line with a high-resolution non-hydrostatic model suggest that the multicellular structure of the storm may be associated with gravity waves generated by convection.
Abstract: Two-dimensional and three-dimensional simulations of a midlatitude squall line with a high-resolution non-hydrostatic model suggest that the multicellular structure of the storm may be associated with gravity waves generated by convection. Time-lapse display of model output demonstrates that the commonly described “cut-off” process is actually a gravity wave phenomenon. The convective cells arise as gravity waves, which are forced by continuous strong low-level convergence at the storm's gust front. The waves propagate to both sides of the gust front. The stronger westward (front to rear) mode dominates at the mature stage of the squall line. Continuous low-level updraft is generated at the nose of the cold pool, which propagates at the speed of a density current. Updraft cells periodically break away from this persistent low-level gust-front updraft and move at phase speeds of their associated gravity waves, not at the surrounding airflow speeds as implied by the traditional multicell model. Lin...
TL;DR: A mesoscale convective system (MCS) developed over central Arizona during the late evening and early morning of 23-24 July 1990 and produced widespread heavy rain, strong winds, and damage to buildings, vehicles, power poles, and trees across northern sections of the Phoenix metropolitan area as mentioned in this paper.
Abstract: A mesoscale convective system (MCS) developed over central Arizona during the late evening and early morning of 23–24 July 1990 and produced widespread heavy rain, strong winds, and damage to buildings, vehicles, power poles, and trees across northern sections of the Phoenix metropolitan area. Although forecasters from both the National Weather Service and National Severe Storms Laboratory, working together in the 1990 SouthWest Area Monsoon Project (SWAMP), did not expect thunderstorms to develop, severe thunderstorm and flash flood warnings were issued for central Arizona between 0300 and 0500 local standard time. This study examines the precursor and supportive environment of the mesoscale convective system, drawing upon routine synoptic data and special observations gathered during SWAMP. During the evening of 23 July and the early morning of 24 July, low-level southwesterly flow developed and advected moisture present over southwest Arizona across south-central Arizona into the foothills and...
TL;DR: In this article, the authors present a physical model of the process of high altitude optical flash, correlated with the presence of giant thunderstorms in the atmosphere below, based on low frequency RF break-down of the upper atmosphere, ignited by the upward prop- agating electromagnetic pulses due to conventional low-altitude lightning.
Abstract: Past and recent observations indicate the presence of lightning at altitudes in excess of 30 kin. The phenome- non is manifested as a high altitude optical flash, correlated with the presence of giant thunderstorms in the atmosphere below. This letter presents the first physical model of the process. The model is based on low frequency RF break- down of the upper atmosphere, ignited by the upward prop- agating electromagnetic pulses due to conventional low alti- tude lightning. Horizontal intercloud lightning strokes form the optimal configuration. Horizontal lightning discharges with cloud-to-cloud moment charge ~ 6,000 -- 8,000 C-kin account for the observed level of optical emissions.
TL;DR: In this paper, two different instruments (one carried by a rocket and one carried by balloon) were launched on two occasions into thunderstorms and the soundings were similar, which gives us some confidence in both instruments.
Abstract: Instruments that measure the intense electric field strengths in thunderclouds (∼100 kV m−1) are designed to minimize the production of ions by small electrical discharges (coronas) emanating from the instruments themselves. The nearby charge of these ions would unpredictably disturb the natural field of the cloud. In an attempt to assess this disturbance, two different instruments (one carried by a rocket and one carried by a balloon) were launched on two occasions into thunderstorms. In spite of differing trajectories, the soundings were similar, which gives us some confidence in both instruments. In addition, the measurements revealed some interesting features of the two storms. Each storm appeared to have six significant and distinct regions of charge. The balloon soundings also revealed that lightning flashes temporarily increased the electric field strength above the thunderclouds (at altitudes from 9.7 to 14.3 km) by amounts up to 10 kV m−1, after which the fields decayed away in 50 to 125 s. One pair of ascent and descent rocket soundings, separated in time by a maximum of 60 s and horizontally by 1 to 3 km, showed little change in the thunderstorm electric field between ground and 7.5 km altitude.
Patent•
03 Apr 1995
TL;DR: In this paper, a user aircraft transmits, via cellular telephone equipment or direct radio link, a request for information together with a user identification number, where a microcomputer processes the weather data to correct for the aircraft's position and heading, then displays storm locations relative to the aircraft.
Abstract: Electromagnetic radiation from lightning is detected at a ground station which is part of a cellular network of stations; a computer determines a position of a thunderstorm associated with the lightning, then compiles and stores the storm location data. A user aircraft transmits, via cellular telephone equipment or direct radio link, a request for information together with a user identification number. After validation of the user number weather data is transmitted to the aircraft where a microcomputer processes the weather data to correct for the aircraft's position and heading, then displays storm locations relative to the aircraft. The display may incorporate radar data and satellite photographs of cloud formations. In-flight weather notices are transmitted in addition to the storm location data.
01 Jan 1995
TL;DR: In this paper, the authors developed algorithms relating lightning and precipitation quantity and used lightning location to determine rainfall depth and distribution for areas in New Mexico and found that there was a significant correlation between rain-gauge measured precipitation and lightning within a 3-km radius of the rain gauge location, with best predictions occurring from regressions that included lightning strikes and relative humidity.
Abstract: Typically, 50-70% of the total annual precipitation in New Mexico can be produced by convective thunderstorms during the period June through September. These thunderstorms are accompanied by intense lightning and characteristically produce heavy, localized rainfall resulting in high spatial variation in precipitation inputs. During other months precipitation over the entire Sevilleta (105 ha) often occurs from broad-scale storm systems and is much less spatially variable on a per-storm basis. Summer precipitation is a primary factor driving plant productivity as well as influencing nutrient cycling, herbivore activity, and detritivore activity. Knowledge of the timing, location, and amounts of pre- cipitation is important in planning or monitoring research activities and spatial modeling of the dynamics in this semiarid region. Technology exists for locating cloud-to-ground lightning strikes that has the potential to locate these intense precipitation events, quantify the volume of water associated with them, and document the spatial and temporal variability of this phenomenon over large areas. Near real-time analysis capability can identify areas receiving precipitation that will experience rapid vegetation growth in this semiarid region. This study developed algorithms relating lightning and precipitation quantity and used lightning location to determine rainfall depth and distribution for areas in New Mexico. There was a significant correlation between rain-gauge measured precipitation and lightning within a 3-km radius of the gauge location, with best predictions occurring from regressions that included lightning strikes and relative humidity. Average precipitation volume per cloud-to-ground lightning strike averaged 36 190 m3 for the 3 km radius circle, resulting in an average rainfall depth of 1.3 mm per lightning strike. Lightning location technology, combined with a Geographic Information System (GIS), defined the spatial and temporal resolution of these intense, summer precipitation patterns and provided a more detailed estimate of total precipitation and precipitation distribution than was provided by the sparse network of precipitation gauges. Combining this information with satellite sensing of veg- etation growth (e.g., greenness index) can identify causal mechanisms for temporal and spatial patterns in short-term vegetation processes (e.g., primary production) and long-term vegetation dynamics for this area.
TL;DR: In this article, a 3-mm-wavelength (95 GHz) pulsed Doppler radar was installed in a van and operated in the Southern Plains of the United States during May and early June of 1993 and 1994.
Abstract: An experiment whose objective was to determine the wind and reflectivity substructure of severe convective storms is detailed. A 3-mm-wavelength (95 GHz) pulsed Doppler radar was installed in a van and operated in the Southern Plains of the United States during May and early June of 1993 and 1994. Using a narrow-beam antenna with computer-controlled scanning and positioning the van several kilometers from targets in severe thunderstorms, the authors were able to achieve 30-m spatial resolution and also obtain video documentation. A dual-polarization pulse-pair technique was used to realize a maximum unambiguous velocity of ±80 m s−1. Analyses of data collected in a mesocyclone near the intersection of two squall lines, in a low-precipitation storm, and in a hook echo in a supercell are discussed. A strategy to achieve 10-m spatial resolution and obtain analyses of the internal structure of tornadoes is proposed.
TL;DR: In this paper, a deep convective storm observed during the Central Equatorial Pacific Experiment (CEPEX) has been simulated using the two-dimensional version of a three-dimensional cloud dynamics, microphysics, and chemistry model.
Abstract: A deep convective storm observed during the Central Equatorial Pacific Experiment (CEPEX) has been simulated using the two-dimensional version of a three-dimensional cloud dynamics, microphysics, and chemistry model. The simulated storm is characterized by the penetration of the cloud tower into the lower stratosphere and by a widespread cloud anvil. Clear evidence of vertical transport of water vapor through the convective turret to the upper troposphere has been found. A large amount of small ice crystals formed in the cloud top and in the anvil together with graupels induced by frozen raindrops. Intense mixing of boundary layer air into the cloud caused by the deep convection can result in low ozone area inside the cloud turret and inside the anvil. However, simultaneously, stratospheric air with high ozone volume mixing ratio was brought into the cloud region in the troposphere, especially in the upper part of the anvil, which could play a significant role in the tropical tropospheric O 3 budget. Due to the deep convection, a significant fraction of boundary layer dimethyl sulfide (DMS) or other ocean-derived chemicals is also transferred to the free troposphere, but we find no evidence for significant transport to the stratosphere.
TL;DR: More than 150 luminous cloud-ionosphere discharges (CIs) were observed above a thunderstorm complex moving SE across the state of Iowa during the night of 9-10 August 1993 as discussed by the authors.
Abstract: During the night of 9–10 August 1993 more than 150 luminous cloud-ionosphere discharges (CIs) were observed above a thunderstorm complex moving SE across the state of Iowa. Images of the CIs were obtained through clear air by intensified CCD TV cameras at the O'Brien Observatory of the University of Minnesota located about 60 km NE of Minneapolis and 250–500 km from the storm center. The discharges consisted of bright vertical striations extending from 50–80 km altitude, often covering tens of kilometers laterally, with tendrils of decreasing intensity visible for the brighter events down to cloud tops below 20 km altitude. All the more intense CIs were coincident with a VLF sferic in the 300Hz–12kHz range, but small events often did not yield a detectable sferic. There is no unambiguous evidence that CIs were sources of sferics. Some of the CIs were observed to be coincident with a cloud brightening and with a cloud-ground stroke recorded by the National Lightning Detection Network. The duration of the images was generally less than one TV field (< 16.7 ms). Many of these discharges have now been observed by the space shuttle, by aircraft-borne TV cameras and a large number by a ground-based camera observations in Colorado. The present results are compared with these observations and recent theoretical ideas related to the CI events are discussed. It is proposed that CIs arise from intense bursts of cloud electrification and may follow the preexisting paths of cloud-to-ionosphere thunderstorm currents.
TL;DR: This study developed algorithms relating lightning and precipitation quantity and used lightning location to determine rainfall depth and distribution for areas in New Mexico, providing a more detailed estimate of total precipitation and precipitation distribution than was provided by the sparse network of precipitation gauges.
Abstract: Typically, 50-70% of the total annual precipitation in New Mexico can be produced by convective thunderstorms during the period June through September. These thunderstorms are accompanied by intense lightning and characteristically produce heavy, localized rainfall resulting in high spatial variation in precipitation inputs. During other months precipitation over the entire Sevilleta (105 ha) often occurs from broad-scale storm systems and is much less spatially variable on a per-storm basis. Summer precipitation is a primary factor driving plant productivity as well as influencing nutrient cycling, herbivore activity, and detritivore activity. Knowledge of the timing, location, and amounts of precipitation is important in planning or monitoring research activities and spatial modeling of the dynamics in this semiarid region. Technology exists for locating cloud-to-ground lightning strikes that has the potential to locate these intense precipitation events, quantify the volume of water associated with them, and document the spatial and temporal variability of this phenomenon over large areas. Near real-time analysis capability can identify areas receiving precipitation that will experience rapid vegetation growth in this semiarid region. This study developed algorithms relating lightning and precipitation quantity and used lightning location to determine rainfall depth and distribution for areas in New Mexico. There was a significant correlation between rain-gauge measured precipitation and lightning within a 3-km radius of the gauge location, with best predictions occurring from regressions that included lightning strikes and relative humidity. Average precipitation volume per cloud-to-ground lightning strike averaged 36 190 m3 for the 3 km radius circle, resulting in an average rainfall depth of 1.3 mm per lightning strike. Lightning location technology, combined with a Geographic Information System (GIS), defined the spatial and temporal resolution of these intense, summer precipitation patterns and provided a more detailed estimate of total precipitation and precipitation distribution than was provided by the sparse network of precipitation gauges. Combining this information with satellite sensing of vegetation growth (e.g., greenness index) can identify causal mechanisms for temporal and spatial patterns in short-term vegetation processes (e.g., primary production) and long-term vegetation dynamics for this area.
TL;DR: In this article, three-dimensional numerical simulations were performed to understand the cause of the observed ozone drop and water vapor increase in the anvil of a severe, isolated thunderstorm.
Abstract: During the cloud dynamics and chemistry field experiment CLEOPATRA in the summer of 1992 in southern Germany, the Deutsche Forschungsanstalt fur Luft- und Raumfahrt (DLR) (German Aerospace Research Establishment) research aircraft Falcon traversed four times the anvil of a severe, isolated thunderstorm. The first two traverses were at 8 km altitude and close to the anvil cloud base, while the second two traverses were at 10 km. During the 8-km traverse, measured ozone mixing ratios dropped by 13 parts per billion by volume (ppbv) from the ambient cloud free environment to the anvil cloud, while water vapor increased by 0.3 g kg−1. At the 10-km traverses, ozone dropped by 25 ppbv, while water vapor increased by 0.18 g kg−1. Three-dimensional numerical thunderstorm simulations were performed to understand the cause of these changes. The simulations included the transport of two chemical inert tracers. Ozone was assumed to be one of them. The initial ozone profile was composed from an ozone routine sounding and the in situ Falcon measurements prior to the thunderstorm development. The second tracer is typical for a surface released pollutant with a nonzero, constant value in the boundary layer but zero above it. The redistribution of both tracers by the storm is calculated and compared with the observations. For the anvil penetration at 10 km, the calculated difference in ozone mixing ratios is 21 ppbv, while for water vapor an increase of 0.25 g kg−1 was found, in good agreement with the observations. To validate the model results, the radar reflectivity was calculated from simulated fields of cloud water, rain, graupel, hail, and snow and ice crystals and compared with observed values. With respect to maximum reflectivity values and spatial scales, again, excellent agreement was achieved. It is concluded that the rapid transport from the boundary layer directly into the anvil level is the most likely cause of the observed ozone decrease and water vapor increase. Entrainment of ozone-rich environmental air into the anvil cloud occurred but left a protected core with undiluted boundary layer air in the anvil cloud even at a distance of 120 km from the main updraft. Processes such as production of O3 by electrical discharges, chemical reactions of ozone with boundary layer-released or lightning-produced nitrogen compounds, scavenging by hydrometeors, and heterogeneous reactions at the surface of ice crystals may occur, but on the timescale of 0.5–1 hour seem to have a negligible influence on the observed ozone drop.
TL;DR: In this paper, the unique combination of synoptic-scale and mesoscale weather conditions and topographic factors that contribute to and enhance convectively produced flash flooding and river flooding are described and categorized.
Abstract: Heavy rain and flooding are of particular concern to forecasters throughout the eastern and southeastern United States. In this paper, the unique combination of synoptic-scale and mesoscale weather conditions and topographic factors that contribute to and enhance convectively produced flash flooding and river flooding are described and categorized. A classification system for synoptic-scale flooding events is developed, which is then used to identify the distribution (by month and synoptic-scale weather system) of major floods in the region of interest. Also, examples of flooding caused by synoptic-scale weather systems are presented. Characteristics of mesoscale heavy-rain events that result in flooding are discussed. Topographical and geographical factors in the region, which play a role in these events, are described, along with examples of mesoscale, flash flood events. Finally, floods produced by warm-top thunderstorms, which pose a unique and challenging forecast problem throughout the east...
TL;DR: The WSR-88D algorithm as discussed by the authors identifies individual thunderstorm cells within radar imagery and yields an index proportional to the probability that the cell will shortly produce damaging surface winds, large hail, or tornadoes.
Abstract: The WSR-88D severe weather potential (SWP) algorithm is an automated procedure for the detection of severe local storms. The algorithm identifies individual thunderstorm cells within radar imagery and, for each cell, yields an index proportional to the probability that the cell will shortly produce damaging surface winds, large hail, or tornadoes. This index is a statistically derived function of the storm's maximum vertically integrated liquid (VIL) and horizontal areal extent. The correlation between these storm characteristics and severe weather occurrence was first documented in the 1970s. Several National Weather Service field offices in the central plains and Northeast regions of the United States have successfully used VIL as a discriminator between severe and nonsevere thunderstorms. This paper describes the observational data and statistical methodology employed in the development of the SWP algorithm, and regional and seasonal variations in the SWP/severe weather relationship. The expec...