We report on a terrestrial gamma ray flash (TGF) that occurred on 15 August 2014 coincident with an altitude‐triggered lightning at the International Center for Lightning Research and Testing (ICLRT) ...in North Central Florida. The TGF was observed by a ground‐level network of gamma ray, close electric field, distant magnetic field, Lightning Mapping Array (LMA), optical, and radar measurements. Simultaneous gamma ray and LMA data indicate that the upward positive leader of the triggered lightning flash induced relativistic runaway electron avalanches when the leader tip was at about 3.5 km altitude, resulting in the observed TGF. Channel luminosity and electric field data show that there was an initial continuous current (ICC) pulse in the lightning channel to ground during the time of the TGF. Modeling of the observed ICC pulse electric fields measured at close range (100–200 m) indicates that the ICC pulse current had both a slow and fast component (full widths at half maximum of 235 μs and 59 μs) and that the fast component was more or less coincident with the TGF, suggesting a physical association between the relativistic runaway electron avalanches and the ICC pulse observed at ground. Our ICC pulse model reproduces moderately well the measured close electric fields at the ICLRT as well as three independent magnetic field measurements made about 250 km away. Radar and LMA data suggest that there was negative charge near the region in which the TGF was initiated.
Key Points
Best documented TGF observed at ground
Second TGF induced by triggered lightning
An ICC pulse occurred simultaneously (within 20 μs) of the TGF
To calculate the burden of 2009 pandemic influenza A (pH1N1) in the United States, we extrapolated from the Centers for Disease Control and Prevention's Emerging Infections Program ...laboratory-confirmed hospitalizations across the entire United States, and then corrected for underreporting. From 12 April 2009 to 10 April 2010, we estimate that approximately 60.8 million cases (range: 43.3-89.3 million), 274 304 hospitalizations (195 086—402 719), and 12 469 deaths (8868-18 306) occurred in the United States due to pH1N1. Eighty-seven percent of deaths occurred in those under 65 years of age with children and working adults having risks of hospitalization and death 4 to 7 times and 8 to 12 times greater, respectively, than estimates of impact due to seasonal influenza covering the years 1976—2001. In our study, adults 65 years of age or older were found to have rates of hospitalization and death that were up to 75% and 81%, respectively, lower than seasonal influenza. These results confirm the necessity of a concerted public health response to pH1N1.
Previous studies of lightning in anvil clouds have reported that flashes began in or near the storm core and propagated downwind into the anvil. It had been thought that flashes could not be ...initiated far downwind in the anvil, because anvil charge was thought to be produced mainly in the storm's deep updraft and to decrease with distance into the anvil. Here we report observations of the in‐cloud development of lightning flashes in the anvils of two supercell storms, including the first observations of flashes that began in the anvil 30–100 km from the cores of the storms and propagated upwind back toward the cores. Interaction between charge regions in the two converging anvils of adjoining storms appeared to cause some of the distant flash initiations, but a local charging mechanism in the anvil likely also contributed to the flash initiations. All flashes that struck ground beneath the distant anvil transferred negative charge to ground instead of the positive charge usually transferred to ground there, an apparent consequence of the parent storm having an inverted‐polarity electrical structure.
We have developed semi-independent methods for determining CH2O scavenging efficiencies (SEs) during strong midlatitude convection over the western, south-central Great Plains, and southeastern ...regions of the United States during the 2012 Deep Convective Clouds and Chemistry (DC3) Study. The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) was employed to simulate one DC3 case to provide an independent approach of estimating SEs and the opportunity to study CH2O retention in ice when liquid drops freeze. Measurements of CH2O in storm inflow and outflow were acquired on board the NASA DC-8 and the NSF/National Center for Atmospheric Research Gulfstream V (GV) aircraft employing cross-calibrated infrared absorption spectrometers. This study also relied heavily on the nonreactive tracers i-/n-butane and i-/n-pentane measured on both aircraft in determining lateral entrainment rates during convection as well as their ratios to ensure that inflow and outflow air masses did not have different origins. Of the five storm cases studied, the various tracer measurements showed that the inflow and outflow from four storms were coherently related. The combined average of the various approaches from these storms yield remarkably consistent CH2O scavenging efficiency percentages of: 54%±3% for 29 May; 54%±6% for 6 June; 58%±13% for 11 June; and 41±4% for 22 June. The WRF-Chem SE result of 53% for 29 May was achieved only when assuming complete CH2O degassing from ice. Further analysis indicated that proper selection of corresponding inflow and outflow time segments is more important than the particular mixing model employed. Key Points Obtained remarkably consistent CH2O scavenging efficiencies of 41 to 58% in all but one storm Six of seven different methods produced the same result on one storm within a 7% range Erroneous scavenging efficiencies result when inflow and outflow are not coherently related
This study examines coordinated storm and triggered lightning observations made in July–August 2013 at the International Center for Lightning Research and Testing to determine why triggered flashes ...in Florida typically transition from an upward vertical channel entering the cloud to horizontal structure near the storm's melting level. Data from a balloon‐borne electric field meter, a mobile 5 cm wavelength radar, and a small‐baseline VHF Lightning Mapping Array acquired during a period in which three flashes were triggered on 1 August confirmed the hypothesis that the transition to horizontal lightning structure just above the melting level occurred in a layer of negative charge. This experiment was the first to provide vertical profiles of the electric field in Florida storms, from which their vertical charge distribution could be inferred. Three dissipating storms observed on different days all had negative charge near the melting level, but a growing mature storm had positive charge there.
Key Points
Florida triggered flashes propagate through negative charge near the melting layer
Negative charge is just above the melting layer of dissipating Florida storms
Charge distributions are more complex in mature than in dissipating storms
Unique in situ measurements of CO, O3, SO2, CH4, NO, NOx, NOy, VOC, CN, and rBC were carried out with the German Deutsches Zentrum für Luft‐ und Raumfahrt (DLR)‐Falcon aircraft in the central U.S. ...thunderstorms during the Deep Convective Clouds and Chemistry experiment in summer 2012. Fresh and aged anvil outflow (9–12 km) from supercells, mesoscale convective systems, mesoscale convective complexes, and squall lines were probed over Oklahoma, Texas, Colorado, and Kansas. For three case studies (30 May and 8 and 12 June) a combination of trace species, radar, lightning, and satellite information, as well as model results, were used to analyze and design schematics of major trace gas transport pathways within and in the vicinity of the probed thunderstorms. The impact of thunderstorms on the O3 composition in the upper troposphere/lower stratosphere (LS) region was analyzed. Overshooting cloud tops injected high amounts of biomass burning and lightning‐produced NOx emissions into the LS, in addition to low O3 mixing ratios from the lower troposphere. As a dynamical response, O3‐rich air from the LS was transported downward into the anvil and also surrounded the outflow. The ΔO3/ΔCO ratio was determined in the anvil outflow region. A pronounced in‐mixing of O3‐rich stratospheric air masses was observed in the outflow indicated by highly positive or even negative ΔO3/ΔCO ratios (+1.4 down to −3.9). Photochemical O3 production (ΔO3/ΔCO = +0.1) was found to be minor in the recently lofted pollution plumes. O3 mixing ratios within the aged anvil outflow were mainly enhanced due to dynamical processes.
Key Points
Overshooting of the central U.S. severe thunderstorms probed in situ by aircraft
ΔO3/ΔCO ratios were determined for fresh and aged (~12–24 h) anvil outflow
O3 enhanced (~20–50 nmol mol−1) in the aged anvil outflow mainly due to dynamical processes
During the Deep Convective Clouds and Chemistry (DC3) experiment in summer 2012, airborne measurements were performed in the anvil inflow/outflow of thunderstorms over the Central U.S. by three ...research aircraft. A general overview of Deutsches Zentrum für Luft‐ und Raumfahrt (DLR)‐Falcon in situ measurements (CO, O3, SO2, CH4, NO, NOx, and black carbon) is presented. In addition, a joint flight on 29 May 2012 in a convective line of isolated supercell storms over Oklahoma is described based on Falcon, National Science Foundation/National Center for Atmospheric Research Gulfstream‐V (NSF/NCAR‐GV), and NASA‐DC8 trace species in situ and lidar measurements. During DC3 some of the largest and most destructive wildfires in New Mexico and Colorado state's history were burning, which strongly influenced air quality in the DC3 thunderstorm inflow and outflow region. Lofted biomass burning (BB) plumes were frequently observed in the mid‐ and upper troposphere (UT) in the vicinity of deep convection. The impact of lightning‐produced NOx (LNOx) and BB emissions was analyzed on the basis of mean vertical profiles and tracer‐tracer correlations (CO‐NOx and O3‐NO). On a regular basis DC3 thunderstorms penetrated the tropopause and injected large amounts of LNOx into the lower stratosphere (LS). Inside convection, low O3 air (~80 nmol mol−1) from the lower troposphere was rapidly transported to the UT/LS region. Simultaneously, O3‐rich stratospheric air masses (~100–200 nmol mol−1) were present around and below the thunderstorm outflow and enhanced UT‐O3 mixing ratios significantly. A 10 year global climatology of H2O data from the Aura Microwave Limb Sounder confirmed that the Central U.S. is a preferred region for convective injection into the LS.
Key Points
Severe overshooting Central U.S. thunderstorms probed in situ by three aircraft
Highly variable NOx and O3 mixing ratios in the anvil outflow region
Mixing of lightning‐produced NOx and O3‐rich stratospheric air masses
Correlated Lightning Mapping Array and vertical‐scan radar images are presented for three rocket‐and‐wire triggered lightning flashes that occurred sequentially within 17 min in the presence of a ...decaying multicellular convective storm system over north‐central Florida. The initial stage (IS) of each flash propagated generally vertically to the altitude of the 0°C melting level, about 5 km, and then subsequently propagated for many kilometers horizontally along the melting level contour. Radar images suggest that the propagation paths of the IS channels below and above the melting level were heavily influenced by precipitation gradients. Flash UF 11‐24 exhibited a 12.6 km unbranched IS channel, the longest unbranched channel observed in the study by a factor of three. During flash UF 11‐25 (119 ms following the cessation of the measured IS current at ground and prior to the first return stroke), a natural cloud‐to‐ground discharge, perhaps induced by the IS, initiated between 2.5 and 4 km altitude and struck ground 5 to 7 km from the launching facility. The IS of flash UF 11‐26 propagated upward through a descending precipitation packet and apparently induced a naturally appearing bi‐level intracloud discharge via an upward‐negative leader that initiated within the IS breakdown region 3.5 km from the launching facility. The upward‐negative leader propagated from 5.6 to 9.3 km altitude in a time of 11 ms. The electrical current measured at ground during the IS of flash UF 11‐26 exhibited a 57 ms polarity reversal, transferring 19 C of positive charge to ground.
Key Points
Correlated LMA and vertical‐scan radar images of Florida triggered lightning
Correlation of IS breakdown path with radar‐determined precipitation gradients
Rocket‐and‐wire triggering of a naturally appearing bi‐level IC discharge
Stable isotopic composition of water vapor in the tropics Lawrence, James Robert; Gedzelman, Stanley David; Dexheimer, Darielle ...
Journal of Geophysical Research - Atmospheres,
27 March 2004, Letnik:
109, Številka:
D6
Journal Article
Recenzirano
Water vapor samples collected during tropical field experiments at Puerto Escondido, Mexico, near Kwajalein (KWAJEX), and near Key West, Florida (CAMEX 4), were analyzed for their stable isotope ...contents, 1H218O:1H216O and 2H1H16O:1H216O. Highest δ18O values approached isotopic equilibrium with seawater during quiescent weather or in regions of isolated or disorganized convection. Lowest δ18O values occurred in or downwind from regions of organized mesoscale weather disturbances and ranged as low as 15‰ below isotopic equilibrium with seawater. The mean δ18O value of vapor over the sea surface therefore decreases as storm activity and organization increases.
Eighteen lightning flash rate parameterization schemes (FRPSs) were investigated in a Weather Research and Forecasting model coupled with chemistry cloud‐resolved simulation of the 29–30 May 2012 ...supercell storm system observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. Most of the observed storm's meteorological conditions were well represented when the model simulation included both convective damping and lightning data assimilation techniques. Newly‐developed FRPSs based on DC3 radar observations and Lightning Mapping Array data are implemented in the model, along with previously developed schemes from the literature. The schemes are based on relationships between lightning and various kinematic, structural, and microphysical thunderstorm characteristics (e.g., cloud top height, hydrometeors, reflectivity, and vertical velocity) available in the model. The results suggest the model‐simulated graupel and snow/ice hydrometeors require scaling factors to more closely represent proxy observations. The model‐simulated lightning flash trends and total flashes generated by each scheme over the simulation period are compared with observations from the central Oklahoma Lightning Mapping Array. For this supercell system, 13 of the 18 schemes overpredicted flashes by >100% with the group of FRPSs based on storm kinematics and structure (particularly updraft volume) performing slightly better than the hydrometeor‐based schemes. During the storm's first 4 hr, the upward cloud ice flux FRPS, which is based on the combination of vertical velocity and hydrometeors, well represents the observed total flashes and flash rate trend; while, the updraft volume scheme well represents the observed flash rate peak and subsequent sharp decline in flash rate.
Plain Language Summary
Accurate lightning forecasts are important for daily activities. They are also important because lightning produces nitrogen oxide, which affects the distribution of atmospheric trace gases that have significant roles in influencing our climate (e.g., ozone). Lightning is recreated in weather models using already determined relationships between observed lightning and thunderstorm characteristics (e.g., hydrometeors and vertical velocity). Lightning prediction is also highly dependent on how well the model represents current conditions, like thunderstorm location and strength. Eighteen lightning‐thunderstorm relationships, or schemes, were investigated in a cloud‐resolved Weather Research and Forecasting model coupled with chemistry to simulate the 29–30 May 2012 supercell storm system observed during the Deep Convective Clouds and Chemistry (DC3) field campaign and to identify the best scheme associated with the event. Modifications to the model‐simulation were first required to better represent the observed convection before comparing the observed and model‐simulated lightning. Generally, the schemes based on storm kinematics and structure perform slightly better for this case study than the microphysical schemes. Two schemes (i.e., upward cloud ice flux and updraft volume) well represent the supercell system's lightning activity. The upward cloud ice flux scheme was used in follow‐on lightning chemistry and trace gas analyses.
Key Points
Thirteen of eighteen flash rate parameterization schemes overestimated the observed number of flashes by more than 100%
Upward cloud ice flux and updraft volume schemes well represent lightning activity in the early and later stages of the storm, respectively
Flash rate prediction is highly dependent on how schemes are applied in cloud‐resolved models and on accurate simulation of storm variables
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