Showing papers on "Thunderstorm published in 2012"

Convective Modes for Significant Severe Thunderstorms in the Contiguous United States. Part I: Storm Classification and Climatology

Abstract: Radar-based convective modes were assigned to a sample of tornadoes and significant severe thunderstorms reported in the contiguous United States (CONUS) during 2003–11. The significant hail (≥2-in. diameter), significant wind (≥65-kt thunderstorm gusts), and tornadoes were filtered by the maximum event magnitude per hour on a 40-km Rapid Update Cycle model horizontal grid. The filtering process produced 22 901 tornado and significant severe thunderstorm events, representing 78.5% of all such reports in the CONUS during the sample period. The convective mode scheme presented herein begins with three radar-based storm categories: 1) discrete cells, 2) clusters of cells, and 3) quasi-linear convective systems (QLCSs). Volumetric radar data were examined for right-moving supercell (RM) and left-moving supercell characteristics within the three radar reflectivity designations. Additional categories included storms with marginal supercell characteristics and linear hybrids with a mix of supercell and Q...

The Atmosphere : An Introduction to Meteorology

Abstract: 1. Introduction to the Atmosphere. 2. Heating Earth's Surface and Atmosphere. 3. Temperature. 4. Moisture and Atmospheric Stability. 5. Forms of Condensation and Precipitation. 6. Air Pressure and Winds. 7. Circulation of the Atmosphere. 8. Air Masses. 9. Weather Patterns. 10. Thunderstorms and Tornadoes. 11. Hurricanes. 12. Weather Analysis and Forecasting. 13. Air Pollution. 14. The Changing Climate. 15. World Climates. 16. Optical Phenomena of the Atmosphere.

Convective Modes for Significant Severe Thunderstorms in the Contiguous United States. Part II: Supercell and QLCS Tornado Environments

Abstract: A sample of 22 901 tornado and significant severe thunderstorm events, filtered on an hourly 40-km grid, was collected for the period 2003–11 across the contiguous United States (CONUS). Convective mode was assigned to each case via manual examination of full volumetric radar data (Part I of this study), and environmental information accompanied each grid-hour event from the hourly objective analyses calculated and archived at the Storm Prediction Center (SPC). Sounding-derived parameters related to supercells and tornadoes formed the basis of this investigation owing to the dominance of right-moving supercells in tornado production and the availability of supercell-related convective parameters in the SPC environmental archive. The tornado and significant severe thunderstorm events were stratified by convective mode and season. Measures of buoyancy discriminated most strongly between supercell and quasi-linear convective system (QLCS) tornado events during the winter, while bulk wind differences ...

An Objective High-Resolution Hail Climatology of the Contiguous United States

Abstract: The threat of damaging hail from severe thunderstorms affects many communities and industries on a yearly basis, with annual economic losses in excess of $1 billion (U.S. dollars). Past hail climatology has typically relied on the National Oceanic and Atmospheric Administration/National Climatic Data Center’s (NOAA/NCDC) Storm Data publication, which has numerous reporting biases and nonmeteorological artifacts. This research seeks to quantify the spatial and temporal characteristics of contiguous United States (CONUS) hail fall, derived from multiradar multisensor (MRMS) algorithms for several years during the Next-Generation Weather Radar (NEXRAD) era, leveraging the Multiyear Reanalysis of Remotely Sensed Storms (MYRORSS) dataset at NOAA’s National Severe Storms Laboratory (NSSL). The primary MRMS product used in this study is the maximum expected size of hail (MESH). The preliminary climatology includes 42 months of quality controlled and reprocessed MESH grids, which spans the warm seasons fo...

Lightning Related Transient Luminous Events at High Altitude in the Earth’s Atmosphere: Phenomenology, Mechanisms and Effects

Abstract: This paper presents a literature survey on the recent developments related to experimental and modeling studies of transient luminous events (TLEs) in the middle atmosphere termed elves, sprites and jets that are produced in association with thunderstorm activity at tropospheric altitudes. The primary emphasis is placed on publications that appeared in refereed literature starting from year 2008 and up to the present date. The survey covers general phenomenology of TLEs and their relationships to characteristics of individual thunderstorms and lightning, physical mechanisms and modeling of TLEs, past, present and future orbital observations of TLEs, and their chemical, energetic and electric effects on local and global scales.

Relationships between lightning flash rates and radar reflectivity vertical structures in thunderstorms over the tropics and subtropics

Abstract: [1] Relationships between the vertical profile of radar reflectivity and lightning flash rates are investigated using 13 years of Tropical Rainfall Measuring Mission (TRMM) observations during 1998–2010. First the Radar Precipitation Features (RPFs) are defined by grouping raining areas detected by the TRMM Precipitation Radar (PR). Then the characteristics of radar reflectivity and lightning flash rate are calculated in each RPF using PR and Lightning Imaging Sensor (LIS) observations. Using these RPFs, temperatures at 20, 30, and 40 dBZ radar echo tops, used as proxies of the maximum convective intensity of precipitation systems, are examined as indicators of the probability of lightning. Although 30 and 40 dBZ echo top temperatures are better indicators of the probability of lightning than the 20 dBZ echo top temperature, there is a large regional variation in the temperature thresholds, especially between land and ocean. In general, oceanic thunderstorms have higher 20 dBZ echo top and larger horizontal extent than those over land. However, radar reflectivity is more likely to exceed 30 and 40 dBZ at cold temperatures over land than over ocean. The correlations between flash rates and radar echo top temperatures, areas and volumes of radar reflectivity, and ice water contents in the mixed phase region are analyzed using RPFs with at least one flash. In agreement with previous studies, the correlations with the echo top temperatures are low, but the correlations between flash rates and areas and volumes of high radar reflectivity in the mixed phase region are much higher. There is a high correlation between the flash rates and the volumes with radar reflectivity greater than 30, 35, or 40 dBZ in the mixed phase region, but the correlation coefficient varies significantly between thunderstorms over different regions, especially between land and ocean. These results are confirmed by repeating the analysis for regions of the storms defined as convective, thus eliminating the contribution from large areas of stratiform radar echo that have much less lightning.

Urban-induced thunderstorm modification in the Southeast United States

Abstract: This study provides the first climatological synthesis of how urbanization augments warm-season convection among a range of cities in the southeastern U.S. By comparing the location of convection in these cities and adjacent control regions via high-resolution, radar reflectivity and lightning data, we illustrate that demographic and land-use changes feed back to local atmospheric processes that promote thunderstorm formation and persistence. Composite radar data for a 10-year, June–August period are stratified according to specific “medium” and “high” reflectivity thresholds. As surrogates for potentially strong (medium reflectivity) and severe (high reflectivity) thunderstorms, these radar climatologies can be used to determine if cities are inducing more intense events. Results demonstrate positive urban amplification of thunderstorm frequency and intensity for major cities. Mid-sized cities investigated had more subtle urban effects, suggesting that the urban influences on thunderstorm development and strength are muted by land cover and climatological controls. By examining cities of various sizes, as well as rural counterparts, the investigation determined that the degree of urban thunderstorm augmentation corresponds to the geometry of the urban footprint. The research provides a methodological template for continued monitoring of anthropogenically forced and/or modified thunderstorms.

Convective Modes for Significant Severe Thunderstorms in the Contiguous United States. Part III: Tropical Cyclone Tornadoes

Abstract: A gridded, hourly, three-dimensionalenvironmental mesoanalysis databaseat the Storm Prediction Center (SPC), based on objectively analyzed surface observations blended with the Rapid Update Cycle (RUC) model-analysis fields and described in Parts I and II of this series, is applied to a 2003‐11 subset of the SPC tropical cyclone (TC) tornado records. Distributions of environmental convective parameters, derived from SPC hourly mesoanalysis fields that have been related to supercells and tornadoes in the midlatitudes, are evaluated for their pertinence to TC tornado occurrence. The main factor differentiating TC from non-TC tornadoenvironments ismuchgreater deep-troposphericmoisture,associatedwith reducedlapserates,lower CAPE, and smaller and more compressed distributions of parameters derived from CAPE and vertical shear. For weak and strong TC tornado categories (EF0‐EF1 and EF2‐EF3 on the enhanced Fujita scale, respectively), little distinction is evident across most parameters. Radar reflectivity and velocity data also are examined for the same subset of TC tornadoes, in order to determine parent convective modes (e.g., discrete, linear, clustered, supercellular vs nonsupercellular), and the association of those modes with several mesoanalysis parameters. Supercellular TC tornadoes are accompanied by somewhat greater vertical shear than those occurring from other modes. Tornadoes accompanying nonsupercellular radar echoes tend to occur closer to the TC center, where CAPE and shear tend to weaken relative to the outer TC envelope, though there is considerable overlap of their respective radial distributions and environmental parameter spaces.

Source altitudes of terrestrial gamma‐ray flashes produced by lightning leaders

Abstract: [1] Terrestrial gamma-ray flashes (TGFs) are energetic photon bursts observed from satellites and associated with lightning activity. Comparison between calculations based on the model of relativistic runaway electron avalanches (RREA) in large-scale weak electric field in thunderstorms and satellite measurements usually shows that the photon spectrum is consistent with source altitudes around 15 km. However, recent observations have located intra-cloud lightning (IC) discharges responsible for TGFs much deeper in the atmosphere (at altitudes ∼10 km). In the present work, we show that the TGF spectrum as produced by acceleration of electrons in the strong electric field of stepping IC leaders is consistent with the lower altitudes recently discovered. This study reconciles observations and measurements by setting new altitudes for the TGF sources based on mechanism of direct acceleration of electrons in the lightning leader field. Moreover, the photon source beaming geometry is consistently determined from the geometry of electric field lines produced by the lightning leader.

Observation of a gamma-ray flash at ground level in association with a cloud-to-ground lightning return stroke

Abstract: [1] Terrestrial gamma-ray flashes (TGFs) are bright, sub-millisecond bursts of gamma-rays, originating within the Earth's atmosphere. Most TGFs have been detected by spacecraft in low-Earth orbit. Only two TGFs have previously been observed from within our atmosphere: one at ground level and one from an aircraft at 14.1 km. We report on a new TGF-like gamma-ray flash observed at ground level, detected by the 19-station Thunderstorm Energetic Radiation Array (TERA) at the University of Florida/Florida Tech International Center for Lightning Research and Testing (ICLRT). The gamma-ray flash, which had a duration of 52.7 μs, occurred on June 30, 2009 during a natural negative cloud-to-ground lightning return stroke, 191 μs after the start of the stroke. This event is the first definitive association of a gamma-ray flash with natural CG lightning and is among the most direct links to a specific lightning process so far. For this event, 19 gamma-rays were recorded, with the highest energy exceeding 20 MeV. The high-energy radiation exhibited very different behavior from the typical x-ray emission from lightning. Specifically, the gamma-ray flash had a much harder energy spectrum, consistent with relativistic runaway electron avalanche (RREA) multiplication; it did not arrive in sub-microsecond bursts, typical of leader emission from lightning, and it occurred well after the start of the return stroke, which has not been previously observed for the x-ray emission from lightning. Nevertheless, we present evidence that the source region for the gamma ray flash was the same as that for the preceding leader x-ray bursts.

Electromagnetic Atmosphere-Plasma Coupling: The Global Atmospheric Electric Circuit

Abstract: A description is given of the global atmospheric electric circuit operating between the Earth’s surface and the ionosphere. Attention is drawn to the huge range of horizontal and vertical spatial scales, ranging from 10−9 m to 1012 m, concerned with the many important processes at work. A similarly enormous range of time scales is involved from 10−6 s to 109 s, in the physical effects and different phenomena that need to be considered. The current flowing in the global circuit is generated by disturbed weather such as thunderstorms and electrified rain/shower clouds, mostly occurring over the Earth’s land surface. The profile of electrical conductivity up through the atmosphere, determined mainly by galactic cosmic ray ionization, is a crucial parameter of the circuit. Model simulation results on the variation of the ionospheric potential, ∼250 kV positive with respect to the Earth’s potential, following lightning discharges and sprites are summarized. Experimental results comparing global circuit variations with the neutron rate recorded at Climax, Colorado, are then discussed. Within the return (load) part of the circuit in the fair weather regions remote from the generators, charge layers exist on the upper and lower edges of extensive layer clouds; new experimental evidence for these charge layers is also reviewed. Finally, some directions for future research in the subject are suggested.

Comparison between GOES-12 Overshooting-Top Detections, WSR-88D Radar Reflectivity, and Severe Storm Reports

Abstract: Studies have found that convective storms with overshooting-top (OT) signatures in weather satellite imagery are often associated with hazardous weather, such as heavy rainfall, tornadoes, damaging winds, and large hail. An objective satellite-based OT detection product has been developed using 11-mm infrared window (IRW) channel brightness temperatures (BTs) for the upcoming R series of the Geostationary Operational Environmental Satellite (GOES-R) Advanced Baseline Imager. In this study, this method is applied to GOES-12 IRW data and the OT detections are compared with radar data, severe storm reports, and severe weather warnings over the eastern United States. The goals of this study are to 1) improve forecaster understanding of satellite OT signatures relative to commonly available radar products, 2) assess OT detection product accuracy, and 3) evaluate the utility of an OT detection product for diagnosing hazardous convective storms. The coevolution of radar-derived products and satellite OT signatures indicates that an OT often corresponds with the highest radar echo top and reflectivity maximum aloft. Validation of OT detections relative to composite reflectivity indicates an algorithm false-alarm ratio of 16%, with OTs within the coldest IRW BT range (,200 K) being the most accurate. A significant IRW BT minimum typically present with an OT is more often associated with heavy precipitation than a region with a spatially uniform BT. Severe weather was often associated with OT detections during the warm season (April‐September) and over the southern United States. The severe weather to OT relationship increased by 15% when GOES operated in rapid-scan mode, showing the importance of high temporal resolution for observing and detecting rapidly evolving cloud-top features. Comparison of the earliest OT detection associated with a severe weather report showed that 75% of the cases occur before severe weather and that 42% of collocated severeweatherreportshadeitheranOTdetectedbeforeasevereweatherwarningor nowarningissuedat all. The relationships between satellite OT signatures, severe weather, and heavy rainfall shown in this paper suggest that 1) when an OT is detected, the particular storm is likely producing heavy rainfall and/or possibly severe weather; 2) an objective OT detection product can be used to increase situational awareness and forecaster confidence that a given storm is severe; and 3) this product may be particularly useful in regions with insufficient radar coverage.

Strong flux of low-energy neutrons produced by thunderstorms.

Abstract: We report here for the first time about the registration of an extraordinary high flux of low-energy neutrons generated during thunderstorms. The measured neutron count rate enhancements are directly connected with thunderstorm discharges. The low-energy neutron flux value obtained in our work is a challenge for the photonuclear channel of neutron generation in thunderstorm: the estimated value of the needed high-energy γ-ray flux is about 3 orders of magnitude higher than that one observed.

Measurements of Atmospheric Electricity Aloft

Abstract: Measurements of the electrical characteristics of the atmosphere above the surface have been made for over 200 years, from a variety of different platforms, including kites, balloons, rockets and aircraft. From these measurements, a great deal of information about the electrical characteristics of the atmosphere has been gained, assisting our understanding of the global atmospheric electric circuit, thunderstorm electrification and lightning generation mechanisms, discovery of transient luminous events above thunderstorms and many other electrical phenomena. This paper surveys the history of atmospheric electrical measurements aloft, from the earliest manned balloon ascents to current day observations with free balloons and aircraft. Measurements of atmospheric electrical parameters in a range of meteorological conditions are described, including clear air conditions, polluted conditions, non-thunderstorm clouds, and thunderstorm clouds, spanning a range of atmospheric conditions, from fair weather to the most electrically active.

Mesospheric concentric gravity waves generated by multiple convective storms over the North American Great Plain

Abstract: [1] We report on six continuous hours of OH airglow imager observations (at z ∼ 87 km) of convectively generated gravity waves (GWs) near Fort Collins, Colorado, on the evening of 08 September 2005. These GWs appeared as nearly concentric rings, and had epicenters near the locations of deep convection in three thunderstorms in Colorado, Nebraska and South Dakota. Using GOES satellite and weather radar observations, we show that the GWs closely follow the thunderstorms. Using the background wind from a nearby radar, the intrinsic wave parameters and vertical wavelengths are calculated. The temperature perturbations are estimated to be T′/T¯ ∼ 1–3% for GWs with horizontal wavelengths λh∼ 20–40 km and horizontal phase speeds ∼40–60 m/s. The horizontal wavelengths of GWs from a convective cluster decreased in time from 30 to 15 km. We employ convective plume and ray-trace models to simulate the GW-induced OH intensity perturbations from convective plumes, clusters and complexes. We find that the results using the background model wind (radiosonde/TIME-GCM) agree well with the late-time observations, when the images are dominated by southwestward, short-wavelength, high-frequency GWs. These late-time GWs propagate against the background wind, and haveλh ∼ 30–40 km and periods of τ ∼ 20–30 min. The OH intensity perturbations are enhanced because the vertical wavelengths λz increased, T′/T¯ increased, and the vertical velocity perturbations w′ decreased (because the GWs were near their reflection levels). We also find that these short-wavelength GWs were created ∼5 h earlier by an extremely energetic, deep convective plume in South Dakota, thereby showing that small-scale, convective GWs directly link the troposphere and mesopause region.

Thunderstorms and upper troposphere chemistry during the early stages of the 2006 North American Monsoon

Abstract: . To study the meteorology and chemistry that is associated with the early stages of the North American Monsoon, the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is applied for the first time at high resolution (4 km grid spacing, allowing for explicit representation of convection) over a large region (continental US and northern Mexico) for a multi-week (15 July to 7 August 2006) integration. Evaluation of model results shows that WRF-Chem reasonably represents the large-scale meteorology and strong convective storms, but tends to overestimate weak convection. In the upper troposphere, the WRF-Chem model predicts ozone (O3) and carbon monoxide (CO) to within 10–20% of aircraft and sonde measurements. Comparison of UT O3 and CO frequency distributions between WRF-Chem and satellite data indicates that WRF-Chem is lofting CO too frequently from the boundary layer (BL). This excessive lofting should also cause biases in the WRF-Chem ozone frequency distribution; however it agrees well with satellite data suggesting that either the chemical production of O3 in the model is overpredicted or there is too much stratosphere to troposphere transport in the model. Analysis of different geographic regions (West Coast, Rocky Mountains, Central Plains, Midwest, and Gulf Coast) reveals that much of the convective transport occurs in the Rocky Mountains, while much of the UT ozone chemical production occurs over the Gulf Coast and Midwest regions where both CO and volatile organic compounds (VOCs) are abundant in the upper troposphere and promote the production of peroxy radicals. In all regions most of the ozone chemical production occurs within 24 h of the air being lofted from the boundary layer. In addition, analysis of the anticyclone and adjacent air indicates that ozone mixing ratios within the anticyclone region associated with the North American Monsoon and just outside the anticyclone are similar. Increases of O3 within the anticyclone are strongly coincident with entrainment of stratospheric air into the anticyclone, but also are from in situ O3 chemical production. In situ O3 production is up to 17% greater within the anticyclone than just outside the anticyclone when the anticyclone is over the southern US indicating that the enhancement of O3 is most pronounced over regions with abundant VOCs.

Role of the Lower Positive Charge Region (LPCR) in initiation of the Thunderstorm Ground Enhancements (TGEs)

Abstract: Despite the ubiquity of thunderstorms, lightning, and related electrical phenomena, many important electromagnetic processes in our atmosphere are poorly understood; the key questions about the thundercloud electrification and lightning initiation remain unanswered. The bulk information on particle fluxes correlated with thunderstorm can be used to better understand the electrical structure of thunderclouds. Only very specific electric configuration of the lower part of the cloud can support the sustainable acceleration of the electrons. Our analysis is based on the thunderstorm data from the Aragats Mountain in Armenia, 3200 m above sea level Varieties of particle detectors located at Aragats Space Environmental Center are registering neutral and charged particle fluxes correlated with thunderstorms, so-called Thunderstorm Ground Enhancements (TGEs). Simultaneously the electrical mills and lightning detectors are monitoring the near-surface electric field and type of lightning occurrences; weather stations are measuring plenty of meteorological parameters. In the present paper we relate particle fluxes to the electrical structure of thunderclouds, namely, to the origination of the Lower Positive Charged Region (LPCR) below the main negative charged layer in the middle of the thundercloud, and to lightning occurrences. Only after creation of the lower dipole in the thundercloud can the electrons be accelerated and particle flux be directed downward. Maturity of the LPCR is correlated with increasing particle fluxes. Thus, the temporal evolution of TGE gives direct evidence of the maturity of LPCR, its initiation, and its decaying.

Using of artificial clouds of charged water aerosol for investigations of physics of lightning and lightning protection

Abstract: Using of experimental methods for investigation of lightning and lightning protection physics was and is relevant as its help to build or approve the physical and mathematical models of thunderstorm and lightning discharge formation, to check and to analyze detail the possible effectiveness of modern and perspective methods and utilities of lighting protection. Application of artificial strongly charged aerosol clouds opens new possibilities for experimental simulation of the processes in thunderstorm clouds and lightning discharges, significantly approximates the physical simulation of process of object lightning affection to real thunderstorm situation. Paper presents the results of the using of artificial clouds of charged water aerosol for investigations of lightning and lightning protection physics.

Use of dual-polarization signatures in diagnosing tornadic potential

Abstract: Recent research has suggested that the combination of differential reflectivity (ZDR) and specific differential phase (KDP) can be useful in the assessment of low-level wind shear within a thunderstorm, a critical factor in tornado formation. The two main polarimetric signatures indicated for this diagnosis include an arc of ZDR along the right inflow edge of the thunderstorm near or collocated with a large gradient in horizontal reflectivity, ZH, (indicative of regions of preferentially large raindrops) and a region of enhanced KDP located deeper into the forward flank precipitation shield than the ZDR arc (indicating that the smaller drops are preferentially advected farther from the updraft core by the low-level winds). Three severe weather events in North Alabama were examined to assess the utility of these ZDR and KDP signatures in determining the potential for tornadic activity. The cases were: 26 October 2010, when many storms indicated tornadic potential from a standard reflectivity and velocity analysis, but very few storms actually produced tornadoes; 28 February 2011, a broken line event that transitioned from a tornadic to high wind threat; and 27 April 2011, when multiple rounds of tornadic storms, associated with quasi-linear convective systems (QLCS) and supercells, thrashed the Tennessee Valley. All three cases displayed strong evidence of ZDR arcs and horizontal separation of KDP and ZDR during tornadic periods. In addition, non-tornadic storms showed consistent signatures of overlapping dual-pol fields. While some variations remain between supercell, broken line, and QLCS tornadoes, common signatures among all storm types indicate a potentially broad application of this type of signature recognition.

Radar Nowcasting of Total Lightning over the Kennedy Space Center

Abstract: A long-term radar dataset over Melbourne, Florida, was matched with three-dimensional lightning data to optimize radar-derived predictors of total lightning over the Kennedy Space Center (KSC). Four years (2006–09) of summer (June–August) daytime (about 1400–0000 UTC) Weather Surveillance Radar-1988 Doppler data were analyzed. Convective cells were tracked using a modified version of the Storm Cell Identification and Tracking (SCIT) algorithm, and correlated to cloud-to-ground (CG) lightning data from the National Lightning Detection Network (NLDN) and grouped intracloud (IC) flash data from the KSC Lightning Detection and Ranging (LDAR) I and II networks. Reflectivity values at isothermal levels and a vertically integrated ice (VII) product were used to optimize radar-based forecasting of both IC and CG lightning. Results indicate the best reflectivity threshold predictors of CG and IC lightning according to the critical success index (CSI) were 25 dBZ at −20°C and 25 dBZ at −15°C, respectively. ...

Observations of Mergers between Squall Lines and Isolated Supercell Thunderstorms

Abstract: A set of 21 cases in which an isolated supercell merged with a squall line were identified and investigated using analyses from the Rapid Update Cycle (RUC) model, archived data from the Weather Surveillance Radar-1988 Doppler (WSR-88D) network, and severe storm reports. This analysis revealed two primary environments associated with these mergers: a weak synoptic forcing, weak to moderate shear environment (WF) and a strong synoptic forcing, strong shear environment (SF). These environments bear a strong resemblance to those identified for progressive (WF) and serial (SF) derechoes in past studies. Radar reflectivity data revealed a spectrum of storm evolution patterns that generally lead to the merged system organizing as a bow echo. At one extreme, observed exclusively in the WF environment, the entire squall line evolved into a large bow echo following the merger. At the other extreme, observed for several cases in the SF environment, a localized bowing segment developed embedded within the la...

Preliminary lightning observations over Greece

Abstract: [1] The first Precision Lightning Network, monitoring the Cloud-to-Ground (CG) lightning stroke activity over Greece and surrounding waters is operated and maintained by the Hellenic National Meteorological Service. This paper studies the regional (land/water interface), seasonal and diurnal variability of the CG strokes as a function of density, polarity and peak current. Additional investigation uniquely links the CG stroke current to sea surface salinity and cloud electrical capacitance. In brief, this study's major findings area as follows: (1) The seasonal maps of thunder days agree well with the regional climatic convective characteristics of the study area, (2) the CG diurnal variability is consistent with the global lightning activity observations over land and ocean, (3) the maxima of monthly averaged CG counts are located over land and water during typical summer and fall months respectively for both polarities, (4) CG peak currents show a distinct seasonality with larger currents during relatively colder months and smaller currents during summer months, and (5) strong linear trends between −CGs and sea surface salinity; (6) this trend is absent for +CGs data analysis of the employed database relate to the thunderstorm's RC constant and agrees with previous numerical modeling studies.

Cold-Season Thunderstorms in Finland and Their Effect on Aviation Safety

Abstract: A total of 13 commercial airplanes were struck by lightning in October (10 in 1 day) and December (3 on 3 separate days) 2011 in the main Finnish Helsinki–Vantaa airport. The number of lightning-struck airplanes is extremely large, considering the time of year and the small number of flashes by the storms. This paper indicates the characteristics of these cases regarding the synoptic situation as well as their forecasting. There were remarkable differences in the operational models; the high-resolution nonhydrostatic model was superior in predicting the convective nature of the event compared to the coarser-resolution hydrostatic model. The interview of the pilots of the struck airplanes shows that the pilots did not receive detailed information to avoid the situation; also, the lightning strike affected the pilots, even causing temporary loss of sight and hearing. Luckily, no fatalities or severe damage to the airplanes occurred. The most interesting case is 19 October 2011; during this single day, a tot...

Surface Energy and Radiation Budget over a Tropical Station: An Observational Study

Abstract: This study attempts to understand the variations in the radiation and surface energy budget parameters during days of occurrence and non occurrence of convective activity such as thunderstorms at Ranchi (23°25′N, 85°26′E), India using the special experimental data sets obtained during pre-monsoon month of May, 2008. For this purpose five continuous thunderstorm days (TD) of varying intensity, along with three non-thunderstorm days (NTD) preceding the TD are considered. Thunderstorms occurred at site are multi-cellular in nature. Change of wind direction and strong gusty winds are noticed in TD cases. Pre-dominant wind direction is south westerly for the TD; it is northwesterly during NTD. Sudden drop of air temperature and rise of relative humidity and rise/drop in atmospheric pressure is noticed during TD are found to be proportional to the intensity of thunderstorm event. More partitioning of net radiation (QN) is in to latent heat flux (QE) and the contribution of sensible heat flux (QH) and soil heat flux (QG) are same during TD. But in the NTD more partitioning of QN is in to QH followed by QG that of QE. Significant differences in radiation and energy budget components are noticed during TD and NTD events.