Showing papers on "Thunderstorm published in 2004"

Smoking Rain Clouds over the Amazon

Abstract: Heavy smoke from forest fires in the Amazon was observed to reduce cloud droplet size and so delay the onset of precipitation from 1.5 kilometers above cloud base in pristine clouds to more than 5 kilometers in polluted clouds and more than 7 kilometers in pyro-clouds. Suppression of low-level rainout and aerosol washout allows transport of water and smoke to upper levels,where the clouds appear “smoking” as they detrain much of the pollution. Elevating the onset of precipitation allows invigoration of the updrafts,causing intense thunderstorms,large hail,and greater likelihood for overshooting cloud tops into the stratosphere. There,detrained pollutants and water vapor would have profound radiative impacts on the climate system. The invigorated storms release the latent heat higher in the atmosphere. This should substantially affect the regional and global circulation systems. Together,these processes affect the water cycle,the pollution burden of the atmosphere,and the dynamics of atmospheric circulation. Several hundred thousand deforestation and agricultural fires burn in Amazonia during the dry season each year, covering vast areas with dense smoke (1, 2). The smoke’s radiative impact suppresses surface heating and evaporation and stabilizes the lower troposphere. In turn, this suppresses the formation of convective clouds and precipitation and thus slows down the hydrological cycle (3). The microphysical effects of the aerosols on clouds and precipitation are no less important but have until now only been inferred from modeling and satellite observations. Convective clouds forming in smoky air show substantially reduced droplet size compared to that of similar clouds in clean air (4), with a mean satelliteretrieved effective droplet radius of 9 m in smoky clouds compared to 14 mi n clean clouds (5). This reduction of cloud droplet size by smoke is associated with an inhibition of the onset of precipitation radar echoes up to heights of 6.5 km, compared to 3 km in smoke-free clouds (6, 7). Here, we report in situ measurements for

The Severe Thunderstorm Electrification and Precipitation Study

Abstract: During May–July 2000, the Severe Thunderstorm Electrification and Precipitation Study (STEPS) occurred in the High Plains, near the Colorado–Kansas border. STEPS aimed to achieve a better understanding of the interactions between kinematics, precipitation, and electrification in severe thunderstorms. Specific scientific objectives included 1) understanding the apparent major differences in precipitation output from super-cells that have led to them being classified as low precipitation (LP), classic or medium precipitation, and high precipitation; 2) understanding lightning formation and behavior in storms, and how lightning differs among storm types, particularly to better understand the mechanisms by which storms produce predominantly positive cloud-to-ground (CG) lightning; and 3) verifying and improving microphysical interpretations from polarimetric radar. The project involved the use of a multiple-Doppler polarimetric radar network, as well as a time-of-arrival very high frequency (VHF) lig...

On the physics of lightning

Abstract: This paper discusses three issues related to lightning The first is to provide a quantitative physical explanation of the lightning stepped leader, whereby breakdown from a cloud to the ground proceeds by luminous steps about 50 m in length, with about 50 /spl mu/s separating each step The second is to explain the initiation of upward leaders from tall objects on the ground, induced by the downward leaders from the cloud Of particular importance is the concept of "critical radius," used in calculations for the effective attractive radius for the collection of lightning by lightning rods The third, is the unresolved issue of "ball lightning," where observations have been reported during thunderstorms of luminous spheres of plasma a few centimeters in diameter, moving about 1 m above the ground for periods of up to 10 s, existing inside houses and even aeroplanes Approximate quantitative calculations are given as proposed explanations of these phenomena, using numerical calculations based on the continuity equations for electrons and ions and also Poisson's Equation to account for space charge effects Also used are the two material properties of air that at 1 bar the electric field to initiate breakdown is 25 MV/m (25 kV/cm) and the field required to sustain a glow discharge is 05 MV/m (5 kV/cm)

Airborne weather radar system and radar display

Abstract: An airborne weather radar system that detects potentially hazardous weather conditions associated with storms and includes a radar display featuring visual indications of these conditions. The radar display includes a vertical situation display having iconal representations and symbolic icons indicative hazardous weather conditions and aviation hazards along the aircraft's flight path not otherwise immediately apparent or shown on standard weather radar displays. The system includes processes for detecting and predicting hazardous weather conditions such as overshooting thunderstorm tops and vaulted thunderstorm energy and serious hazards such as turbulence and hail.

Florida thunderstorms: A faucet of reactive nitrogen to the upper troposphere

Abstract: During the NASA Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) enhanced mixing ratios of nitric oxide were measured in the anvils of thunderstorms and in clear air downwind of storm systems on flights of a Wl3-57F high-altitude aircraft. Mixing ratios greater than l0 - 20 times background were readily observed over distances of 25-120 km due to lightning activity. In many of the Florida storms deposition of NO occurred up to near the tropopause but major deposition usually occurred 1 - 2 km below the tropopause, or mostly within the visible anvil volume formed prior to storm decay. Observations from two storms of very different anvil size and electrical activity allowed estimates of the total mass of NO, vented to the middle and upper troposphere. Using the cloud-to ground (CG) flash accumulations from the National Lightning Detection Network, climatological intra-cloud (IC) to CG ratios, and assuming that CG and IC flashes were of equivalent efficiency for NO production, the ranges of production per flash for a moderate-sized and a large storm were (0.51 - 1.0) x l0(exp 26) and (2.3 - 3.1) x 10(exp 26) molecules NO/flash, respectively. Using the recently determined average global flash rate of 44 8, a gross extrapolation of these two storms to represent possible global annual production rates yield 1.6 - 3.2 and 7.3 - 9.9 Tg(N)/yr, respectively. If the more usual assumption is made that IC efficiency is l/l0th that of CG activity, the ranges of production for the moderate-sized and large storm were (1.3 - 2.7) x l0(exp 26) and (6.0 - 8.1) x l0(exp 26) molecules NO/CG flash, respectively. The estimates from the large storm may be high because there is indirect evidence that the IC/CG ratio was larger than would be derived from climatology. These two storms and others studied did not have flash rates that scaled as approx. H(sup 5) where H is the cloud top altitude. The observed CG flash accumulations and NO(x) mass production estimate for the month of July over the Florida area were compared with a representative 3D global Chemistry-Transport Model (CTMJ that uses the Price et al. lightning parameterization. For two land grid points representing the Florida peninsula the model compared well with the observations: CG flash rates were low by only a factor of approx. 2. When the model grid points included the coastal regions of Florida the flash accumulations were lower than observed by a factor of 3.4 - 4.6. It is recommended that models using the Price et al. parameterization allow any global coastal grid point to maintain the land rather than the marine flash rate parameterization. The convection in this CTM underestimated the actual cloud top heights over Florida by 1 - 2 km and thus the total lightning flash rates and the altitude range of reactive nitrogen deposition. Broad scale (20 - 120 km) median mixing ratios of NO within anvils over Florida were significantly larger than in storms previously investigated over Colorado and New Mexico.

Tracing troposphere-to-stratosphere transport above a mid-latitude deep convective system

Abstract: . Within the project SPURT (trace gas measurements in the tropopause region) a variety of trace gases have been measured in situ in order to investigate the role of dynamical and chemical processes in the extra-tropical tropopause region. In this paper we report on a flight on 10 November 2001 leading from Hohn, Germany (52oN) to Faro, Portugal (37oN) through a strongly developed deep stratospheric intrusion. This streamer was associated with a large convective system over the western Mediterranean with potentially significant troposphere-to-stratosphere transport. Along major parts of the flight we measured unexpectedly high NOy mixing ratios. Also H2O mixing ratios were significantly higher than stratospheric background levels confirming the extraordinary chemical signature of the probed air masses in the interior of the streamer. Backward trajectories encompassing the streamer enable to analyze the origin and physical characteristics of the air masses and to trace troposphere-to-stratosphere transport. Near the western flank of the intrusion features caused by long range transport, such as tropospheric filaments characterized by sudden drops in the O3 and NOy mixing ratios and enhanced CO and H2O can be reconstructed in great detail using the reverse domain filling technique. These filaments indicate a high potential for subsequent mixing with the stratospheric air. At the south-western edge of the streamer a strong gradient in the NOy and the O3 mixing ratios coincides very well with a sharp gradient in potential vorticity in the ECMWF fields. In contrast, in the interior of the streamer the observed highly elevated NOy and H2O mixing ratios up to a potential temperature level of 365 K and potential vorticity values of maximum 10 PVU cannot be explained in terms of resolved troposphere-to-stratosphere transport along the backward trajectories. Also mesoscale simulations with a High Resolution Model reveal no direct evidence for convective H2O injection up to this level. Elevated H2O mixing ratios in the ECMWF and HRM model are seen only up to about tropopause height at 340 hPa and 270hPa, respectively, well below flight altitude of about 200 hPa. However, forward tracing of the convective influence as identified by satellite brightness temperature measurements and counts of lightning strokes shows that during this part of the flight the aircraft was closely following the border of an air mass which was heavily impacted by convective activity over Spain and Algeria. This is evidence that deep convection at mid-latitudes may have a large impact on the tracer distribution of the lowermost stratosphere reaching well above the thunderstorms anvils as claimed by recent studies using cloud-resolving models.

Verification of Nowcasts from the WWRP Sydney 2000 Forecast Demonstration Project

Abstract: The verification phase of the World Weather Research Programme (WWRP) Sydney 2000 Forecast Demonstration Project (FDP) was intended to measure the skill of the participating nowcast algorithms in predicting the location of convection, rainfall rate and occurrence, wind speed and direction, severe thunderstorm wind gusts, and hail location and size. An additional question of interest was whether forecasters could improve the quality of the nowcasts compared to the FDP products alone. The nowcasts were verified using a variety of statistical techniques. Observational data came from radar reflectivity and rainfall analyses, a network of rain gauges, and human (spotter) observations. The verification results showed that the cell tracking algorithms predicted the location of the strongest cells with a mean error of about 15–30 km for a 1-h forecast, and were usually more accurate than an extrapolation (Lagrangian persistence) forecast. Mean location errors for the area tracking schemes were on the ord...

New observations of sprites from the space shuttle

Abstract: [1] We present the results of space-based observations of sprites obtained during the Mediterranean Israeli Dust Experiment (MEIDEX) sprite campaign conducted on board the space shuttle Columbia during its STS-107 mission in January 2003. A total of ∼6 hours of useful data were saved from 21 different orbits, of which 1/5 contained lightning. We imaged sprites from an altitude of 280 km using a calibrated multispectral camera above thunderstorms in various geographical locations, mainly in central Africa, northern Australia, and South America, and also over the Pacific and Indian Oceans. In this paper we report on sprites observed from ranges 1600–2000 km from the shuttle, at altitudes of 40–90 km above the ground. Their brightness was in the range of 0.3–1.7 mega-Rayleighs (MR) in the 665 nm filter and 1.44–1.7 MR in the 860 nm filter. On the basis of the frequency of observed events and the number of tropical thunderstorms, we estimate the sprite rate in the tropics to be of the order of several per minute.

Model study on production and transport of lightning-produced NOx in a EULINOX supercell storm

Abstract: [1] The production of nitrogen oxides (NOx) by lightning has been investigated with a three-dimensional cloud model. For the study of the NOx transport, the lightning NOx emissions are represented by a Lagrangian particle model instead of volume emissions. The advantages of this approach are (1) the transport of NOx inside the thunderstorm can be analyzed in great detail, (2) the NOx emissions can be represented as a line source instead of a volume emission, and (3) the comparison with high-resolution aircraft measurements can be conducted. This approach is applied to the 21 July 1998 supercell storm observed during the European Lightning Nitrogen Oxides project (EULINOX). Both, parameterized and observed cloud-to-ground and intracloud flash frequencies are used in the simulation and two different lightning NOx production rates are tested. The analysis shows that the parameterization using instantaneous cloud properties can approximately reproduce the lightning activity during the early mature phase of the intensifying storm but cannot be used for the complete life cycle. The comparison of the model results with aircraft NOx measurements indicate that the NOx production rate for intracloud lightning is equivalent or higher than that for cloud-to-ground flashes. Experimentally deduced values for the cloud-to-ground lightning NOx production of 4.9 kg(N), or equivalent 2.1 × 1026 molecules NO, and a ratio between the intracloud and cloud-to-ground NOx production of 1.4 are confirmed by the model leading to an intracloud contribution to the total NOx production of up to 93%. For the applied production parameters 50% to 80% of the total lightning NOx is transported into the anvil, leading to a very pronounced “C”-shape profile. The estimated total NOx production by lightning during the lifetime of the storm is 22 t(N).

Subionospheric early VLF signal perturbations observed in one‐to‐one association with sprites

Abstract: [1] Observations on the night of 21 July 2003 of the ionospheric effects of a thunderstorm in central France are reported. From 0200 to 0315 UT, a camera system in the Pyrenees Mountains captured 28 sprites, triggered by +CG lightning as observed by the French METEORAGE lightning detection system. A narrowband VLF receiver located on Crete, at ∼2200 km southeast of the storm, observed subionospheric VLF signals from six ground-based transmitters. The amplitude of one of the VLF signals, originating at a transmitter located ∼150 km west of the storm and passing through the storm region, exhibited rapid onset perturbations occurring in a nearly one-to-one relationship with the optical sprites. These “early” VLF events are consistent with a process of narrow-angle forward scattering from a volume of enhanced ionization above the storm with lateral sizes larger than the VLF radio wavelength. The many +CG and −CG discharges that did not produce sprites were also found to not be associated with detectable VLF amplitude perturbations, even though some of these discharges reached relatively large peak currents. The rapid onsets of several of the sprite-related VLF perturbations were followed by relatively long onset durations, ranging from ∼0.5 to 2.5 s, indicating that these events were early but not “fast.” These “early/slow” events may suggest a slow process of ionization build-up in the lower ionosphere, following intense lightning discharges that also lead to sprites. A limited number of early VLF perturbation events were also associated with whistler-induced electron precipitation events, or classic Trimpi perturbations, undoubtedly produced by the precipitation of electrons due to whistler-mode waves injected into the magnetosphere by the same lightning flash that led to the production of the sprite.

Nowcasting thunderstorms in the Alpine region using a radar based adaptive thresholding scheme

Abstract: In this paper we present a new automated, radar based tool for thunderstorms nowcasting called TRT (Thun- derstorms Radar Tracking). The goal of this real-time tool is the automated detection, tracking and characterization of intense convective precipitation systems. TRT uses the re- flectivity data of the composite image of the Swiss radar net- work. The algorithm is based on an adaptive thresholding scheme, which allows the detection of convective cells at in- dividual thresholds, depending on their development phase. In this way, thunderstorms can be tracked very early during their growing phase (cells as small as a few 2◊2 km pixels) as well as in the mature stage, and trajectories are created from a sequence of radar images. The tracking is based on the method of the geographical overlapping of cells. Splits and merges are also taken into account. TRT forecasts storm movement by extrapolating the motion of individual cells up to 1 h, using the weighted cell displacement velocity. TRT is used as a nowcasting tool in a pre-operational mode at Me- teoSwiss since May 2003. on observations. The main tools in this context are remote sensing observations like radar, satellite and lightning, as well as mesonet data. Operational nowcasting systems for precipitation are mainly based on the extrapolation of radar echoes.

Nadir observations of sprites from the International Space Station

Abstract: [1] The experiment LSO (Lightning and Sprite Observations) is dedicated to the optical study, from the International Space Station, of sprites occurring in the upper atmosphere above thunderstorms. The objectives were to study these phenomena and to validate a new measurement concept for future measurements of sprites from space at the nadir. The first measurements were performed in the frame of the flight of the French Astronaut Claudie Haignere (mission Andromede) in October 2001. Observations were performed by two microcameras, one in the visible and near-infrared and the other equipped with a moderately wide band filter at 761 nm. This filter includes the most intense N2 1P emission of the sprites and partly the oxygen absorption A band of the atmosphere. The light emissions from sprites occurring in the middle and upper atmosphere are then differentiated from the emissions from lightning, occurring more deeply in the atmosphere and then more absorbed. This paper presents the first observations of sprites from space at the nadir and statistics about the respective intensities of lightning and sprites emissions as observed with this experiment.

Doppler Radar and Lightning Network Observations of a Severe Outbreak of Tropical Cyclone Tornadoes

Abstract: Data from a single WSR-88D Doppler radar and the National Lightning Detection Network are used to examine in detail the characteristics of the convective storms that produced a severe tornado outbreak within Tropical Storm Beryl's remnants on 16 August 1994. Comparison of the radar data with reports of tornadoes suggests that only 13 cells produced the 29 tornadoes that were documented in Georgia and the Carolinas on that date. Six of these cells spawned multiple tornadoes, and the radar data confirm the presence of miniature supercells. One of the cells was identifiable on radar for 11 hours, spawning tornadoes over a time period spanning approximately 6.5 hours. Several other tornadic cells also exhibited great longevity, with cell lifetimes greater than ever previously documented in a landfalling tropical cyclone tornado event, and comparable to those found in major midlatitude tornadic supercell outbreaks. Time-height analyses of the three strongest tornadic supercells are presented in order to document storm kinematic structure and to show how these storms appear at different ranges from a WSR-88D radar. In addition, cloud-to-ground (CG) lightning data are examined for the outbreak, the most intense tropical cyclone tornado event studied thus far. Although the tornadic cells were responsible for most of Beryl's CG lightning, flash rates were only weak to moderate, even in the most intense supercells, and in all the tornadic storms the lightning flashes were almost entirely negative in polarity. A few of the single-tornado storms produced no detectable CG lightning at all. In the stronger cells, there is some evidence that CG lightning rates decreased during tornadogenesis, as has been documented before in some midlatitude tornadic storms. A number of the storms spawned tornadoes just after producing their final CG lightning flashes. Surprisingly, both peak currents and positive flash percentages were larger in Beryl s nontornadic storms than in the tornadic ones. Despite some intriguing patterns, the CG lightning behavior in this outbreak remains mostly inconsistent and ambiguous, and offers only secondary value for warning guidance. The present findings argue in favor of the implementation of observing systems capable of continuous monitoring of total lightning activity in storms.

A 4-Yr Climatology of Cold-Season Bow Echoes over the Continental United States

Abstract: A search of radar mosaics and level-II Weather Surveillance Radar-1988 Doppler (WSR-88D) data revealed 51 cold-season (October–April) bow echoes that occurred in the contiguous United States from 1997–98 to 2000–01. Proximity soundings indicated mean 0–2.5-, 0–5-, and 5–10-km shear values of 14, 23, and 19 m s−1, respectively. Mean CAPE was 1366 J kg−1. Most bow echoes developed from squall lines, groups of cells, or squall lines overtaking cells that originated in the path of the squall line. Overall, cell mergers occurred just prior to the development of 34 (67%) of the 51 bow echoes, and embedded supercells were present in the mature stage of 22 (43%) bow echoes. Nine severe, long-lived bow echoes (LBEs) were identified, and seven of these had damage paths that met derecho criteria. LBEs developed in strongly forced, dynamic synoptic patterns with low to moderate instability. As in previous observational studies, proximity soundings suggested that LBEs are possible within much wider ranges of ...

Operational Measurement of Precipitation in Cold Climates

Abstract: Over the last 50 years, severe weather such as thunderstorms, squall lines, tornadoes, hurricanes, and extreme precipitation events with ensuing flash floods have dominated both scientific and operational radar meteorology (Atlas, 1990, Collier, 2001). This is natural, as one of the main benefits of weather radars is very dense sampling of precipitating systems in time and space, facilitating real-time warning and nowcasting of mesoscale severe weather which may have huge socioecomonic impacts. Also, an implication has been that some commercial radar manufacturers have paid little attention to the sensitivity of weather radar. Maximal sensitivity of a radar system is required for making snowfall measurements. Even greater sensitivity of operational radars is needed for the production of Doppler winds from clear air. The important topic of wind field estimation from Doppler measurements relates to Gekat et al. (2003), Meischner et al. (2003) and Macpherson (2003), all this book. The major proportion of the frequent boundary layer echoes found in summer, even in the north of Europe, originates from insects. For example, classification of 240 000 vertical profiles of reflectivity (VPR) from a one-year-long period in Finland revealed that 40% of all VPRs originated from clear air echoes reaching the ground, 20% from overhanging precipitation, i.e. ice crystal clouds or snowfall layers aloft, and only 40% involved precipitation reaching the ground level (Pohjola and Koistinen, 2002). The reflectivity of both nonprecipitating echo classes was typically between −20 and 5 dBZ. Both Canadian and Nordic radar networks (NORDRAD) mostly operate sensitive C-band systems. The operational Nordic radars are “standard” systems with sensitivities around −110 dBm, beamwidths of around 0.9° and pulse lengths from 0.5–2 µs. In Canada, the sensitivity requirement to detect snowfall and clear air echoes has led to the specification of a multi-pulse length capability (0.8–5 µs) and of a narrow antenna beamwidth (0.65°) (Joe and Lapczak, 2002).

Lightning charge moment changes in U.S. High Plains thunderstorms

Abstract: [1] We report measurements of impulsive (2 ms) lightning charge moment changes in more than 1000 cloud-to-ground (CG) return strokes detected by the National Lightning Detection Network in three United States High Plains storms during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) field program of 2000. The positive CG strokes (+CGs) in a mesoscale convective system exhibit an unusual charge moment distribution with a small median and long tail. Analysis suggests the presence of two different classes of +CGs in this MCS, one with small charge moment changes (≤50 C km) and the other containing larger charge moment changes (50–1400 C km). The distributions of negative cloud-to-ground stroke charge moment changes are roughly log-normal in shape with means varying from 17.7 to 36.8 C km. When combined with past measurements these means vary by a factor of 4 between storms, and there is probably not a single distribution that represents well all storms.

Thunderstorm and lightning characteristics associated with sprites in Brazil

Abstract: [1] Astudy ofthe thunderstorm andcloud-ground lightning characteristics associated with sprite events observed in Brazil is presented. The study is based on ground and aircraft sprite observations with high sensitivity intensified CCD cameras of six different thunderstorms, GOES satellite infrared images, radar and lightning network data. A total of eighteen transient optical events were recorded at three different days in 2002 and 2003, sixteen of which exhibited vertical structures typically associated with sprites. Four thunderstorms were associated with two different cold fronts, one with a Mesoscale Convective System, and one was a local isolated thunderstorm. The sprites occurred during time periods when the percentage of positive flashes was higher than the average percentage for the storm lifetime. The lightning associated with the sprite events was all positive flashes with a mean peak current higher than the mean value for all flashes in the storms. INDEX TERMS: 3304 Meteorology and Atmospheric Dynamics: Atmospheric electricity; 3314 Meteorology and Atmospheric Dynamics: Convective processes; 3324 Meteorology and Atmospheric Dynamics: Lightning; 3334 Meteorology and Atmospheric Dynamics: Middle atmosphere dynamics (0341, 0342). Citation: Pinto, O., Jr., M. M. F. Saba, I. R. C. A. Pinto, F. S. S. Tavares, K. P. Naccarato, N. N. Solorzano, M. J. Taylor, P. D. Pautet, and R. H. Holzworth (2004), Thunderstorm and lightning characteristics associated with sprites in Brazil, Geophys. Res. Lett., 31, L13103, doi:10.1029/2004GL020264.

A cloud model interpretation of jumping cirrus above storm top

Abstract: [1] A dynamically driven mechanism occurring above severe thunderstorms is described, which can explain the jumping cirrus phenomenon. A three-dimensional, non-hydrostatic cloud model is used to perform numerical simulation of a supercell that occurred in Montana in 1981. The jumping cirrus phenomenon is reproduced in the simulated storm. Analysis of the model results shows that the jumping cirrus phenomenon is produced by the breaking of the gravity waves excited by the strong convection inside the storm. The wave breaking process causes some moisture to detach from the storm cloud and jump into the stratosphere. The apparent upstream motion of the jumping cirrus is true only relative to the storm. The jumping cirrus phenomenon represents an irreversible transport mechanism of materials from the troposphere to the stratosphere.

Lightning data observed with lightning location system in Guang-Dong Province, China

Abstract: This paper presents an investigation into cloud-to-ground lightning activity data collected by a lightning detection system in the Guang-Dong Province, the southernmost in China. Annual lightning days are acquired and ground flash density maps are constructed from the database, which contains the information of more than one million flashes. The lightning days are compared with annual thunderstorm days collected by the Guang-Dong Meteorological Agency, and a weak correlation is noted. The correlation between ground flash density and thunderstorm day is studied, and an empirical formula is presented. The relationship between transmission line faults and ground flash density is discussed in this paper too. It is noted that the correlation with the faults caused by lightning is relatively high. The correlation coefficient does not significantly vary with the threshold of discharge current set for constructing the map of revised ground flash density.

The 3 November Tornadic Event during Sydney 2000: Storm Evolution and the Role of Low-Level Boundaries

Abstract: Several severe thunderstorms, including a tornadic supercell, developed on the afternoon of 3 November 2000, during the Sydney 2000 Forecast Demonstration Project. Severe weather included three tornadoes, damaging wind gusts, hail to 7-cm diameter, and heavy rain causing flash flooding. A unique dataset was collected including data from two Doppler radars, a surface mesonet, enhanced upper-air profiling, storm photography, and a storm damage survey. Synoptic-scale forcing was weak and mesoscale factors were central to the development of severe weather. In particular, low-level boundaries such as gust fronts and the sea-breeze front played critical roles in the initiation and enhancement of storms, the motion of storms, and the generation of rotation at low levels. The complex and often subtle boundary interactions that led to the development of the tornadic supercell in this case highlight the need for advanced detection and prediction tools to improve the warning capacity for such events.

The Superior, Nebraska, Supercell During BAMEX

Abstract: Two remarkable supercell storms developed on 22 June 2003 in eastern Nebraska. One of the thunderstorms, located near the town of Aurora, Nebraska, produced the largest known hailstone on record. Receiving far less attention was an adjacent supercell that was equally impressive and is referred to as the Superior, Nebraska, supercell. The two supercells formed during the Bow Echo and Mesoscale Convective Vortex (MCV) Experiment (BAMEX), operated in the spring and summer of 2003. One of the main platforms used during BAMEX was the airborne Electra Doppler Radar (ELDORA). ELDORA was deployed on the Superior supercell several hours after it initiated. Striking in one of the flybys past the storm was the characteristics of the parent circulation. The Superior supercell was associated with a mesocyclone that was the largest (~9 km in diameter) and the most intense (118ms−1 velocity differential) ever documented. Ground-based observations from a nearby Weather Surveillance Radar-1988 Doppler (WSR-88D) located in...

High‐frequency estimation of rainfall from thunderstorms via satellite infrared and a long‐range lightning network in Europe

Abstract: A rain retrieval technique called Omvrios, that combines geostationary satellite infrared (IR) observations and cloud-to-ground (CG) lightning information retrieved from a long-range lightning detection network (Zeus) in Europe, is presented. Cloud systems are defined in the IR temperature array by the 255 K isotherm. Bulk parametrizations that relate cloud top IR temperature, morphological characteristics and CG lightning information (location and flash rate) are used to discriminate rainy from non-rainy cloud systems, and to evaluate the convective and stratiform rain areas and associated area-averaged rain rates of the rainy systems. The technique's parameters were calibrated using collocated and instantaneous rain fields derived from Special Sensor Micro-wave/Imager passive microwave data. Retrieved rain estimates are aggregated to 0.1° grid resolution and 6 h temporal accumulation. The technique is validated during the warm season from May to August 2002, based on independent 6 h rain accumulation measurements from a network of 700 rain-gauges located across Europe. Statistical analysis shows high correlation with gauge rainfall data (0.88) and low overall systematic difference (∼5%). Besides direct validation against rain-gauge data, Omvrios has been compared to existing passive microwave-calibrated IR rain-retrieval techniques. It is shown that lightning information can lead to a significant (25–40%) reduction in the random error of IR retrievals and to an increase of nearly 0.3 in correlation with gauges. In terms of systematic differences (retrieval bias) Omvrios is shown to be consistent, as conditional and unconditional biases are nearly equal (within 5%), while for the other IR rain retrievals the variation between conditional and unconditional biases was significant (34–75%). Copyright © 2004 Royal Meteorological Society

Analysis of 10.7-μm Brightness Temperatures of a Simulated Thunderstorm with Two-Moment Microphysics

Abstract: A cloud-resolving model was used in conjunction with a radiative transfer (RT) modeling system to study 10.7-mm brightness temperatures computed for a simulated thunderstorm. A two-moment microphysical scheme was used that included seven hydrometeor types: pristine ice, snow, aggregates, graupel, hail, rain, and cloud water. Also, five different habits were modeled for pristine ice and snow. Hydrometeor optical properties were determined from an extended anomalous diffraction theory approach. Brightness temperatures were computed using a delta-Eddington two-stream model. Results indicate that the enhanced ‘‘V,’’ a feature sometimes seen in satellite infrared observations, may be formed through an interaction between the overshooting dome and the upstream flanking region of high pressure. This idea is contrary to one in which the overshooting dome is viewed as an obstacle to the environmental flow. As expected, the radiative effects of pristine ice particles within the anvil largely determined the brightness temperature field. Although brightness temperatures were found to be insensitive to microphysical characteristics of moderate to thick portions of the anvil, a strong relationship did exist with column-integrated pristine ice mass for cloud optical depths below about 5. Precipitation-sized hydrometeors and surface precipitation rate, on the other hand, failed to exhibit any meaningful relationship with the cloud-top brightness temperature. The combined mesoscale model and RT modeling system used in this study may also have utility in satellite product development prior to launch of a satellite and in satellite data assimilation.

Study of charge structure and radiation characteristic of intracloud discharge in thunderstorms of Qinghai-Tibet Plateau

Abstract: The comprehensive observations on lightning discharges were conducted in Naqu area of Qinghai-Tibet Plateau in summer of 2002. The electric structures of thunderstorms and the characteristics of lightning discharges at initial stage were analyzed by using the observation data. The results show that most of intracloud (IC) lightning flashes were polarities inverted in thunderstorms with tripole electric charge structure and occurred between negative charge region located in the middle of the thunderstorm and positive charge region located at the bottom of the thunderstorm. The radiation characteristics of discharge processes in cloud with longer lasting time involved in Cloud-to-Ground (CG) lightning flashes were similar to that of IC discharges. A lot of radiation pulses were produced in these discharge processes. Because the IC discharges took place at the bottom of thundercloud and were near the ground, they may produce more serious damage to equipment on the ground therefore should not be neglected in lightning protection.

The Thunderstorm Interactive Forecast System: Turning Automated Thunderstorm Tracks into Severe Weather Warnings

Abstract: The Australian Bureau of Meteorology has developed a new tool called the Thunderstorm Interactive Forecast System (TIFS; formerly known as ThunderBox) for interactively producing finished severe weather warnings and other forecasts from thunderstorm tracks, automatically diagnosed from radar data. TIFS is designed to apply recent advances in radar-based thunderstorm cell detection and tracking techniques to the efficient production of operational forecasts and warnings. The system ingests automated thunderstorm cell detections and tracks, allows graphical editing by forecasters, and produces graphical and text products from the edited data. The text generator uses a shallow, domain-specific approach. The graphical products include a map of areas that have been affected by storms, and are forecast to be affected by storms, as well as meteograms for selected locations.

Transient airglow enhancements observed from the space shuttle Columbia during the MEIDEX sprite campaign

Abstract: [1] First results of observations of ELVES during the last mission of the space shuttle Columbia by the MEIDEX (Mediterranean Israeli Dust Experiment) instrument are reported. During the eclipse parts of 25 orbits, there were observations toward the Earth's limb above the areas of active thunderstorms. Strong enhancements of the brightness of the airglow layer above lightning flashes were observed, with lateral dimensions exceeding 400 km. This phenomenon, known as ELVES, is a clear manifestation of the interaction between the electromagnetic pulse from the lightning stroke and the lower ionosphere. The observed ELVES have been produced both by vertical and horizontal discharges.