Thunderstorm Observations Research Articles

An Evaluation of Thunderstorm Observations in Southern Ontario Using Automated Lightning Detection Data

AbstractHigh-impact weather events, such as thunderstorms and their associated hazards, are aspects of a changing climate that are likely to have an adverse effect on society. Southern Ontario is Canada’s most populated region as well as the region of Canada that receives the most thunderstorms. Before completing climatological studies of thunderstorms in southern Ontario, it is important to determine whether historical thunderstorm data are reliable. Archived thunderstorm data are available from eight 24-h-staffed weather stations across southern Ontario. The data may be subject to observer bias. This study compared the manual observations of thunderstorms with automated data from the Canadian Lightning Detection Network. It was found that the data that are based on the manual observations are reliable enough that any significant trends in thunderstorm occurrence over time should be apparent. Because of the small-scale nature of thunderstorms, however, the data may only be valid for small distances (up to 10 km) around each weather station. A diurnal bias was also discovered, with manual thunderstorm observations being slightly better at night.

Relationship between human observations of thunderstorms and the PERUN lightning detection network in Poland

Research presents an overview on thunderstorm occurrence in Poland and focuses mainly on the relationship between human observations of thunderstorms (SYNOP daily summaries) and instrumental lightning detection data (PERUN network) in the timeframe between 2002 and 2013. The total of 4,952,203 cloud-to-ground flashes (2082days with thunderstorms) derived from the PERUN lightning database, and 12,419 daily thunderstorm SYNOP reports from 44 meteorological stations (1417days with thunderstorms) are compared. Within the use of two different computational methods, we define the threshold value of the human average observational thunderstorm detection range within a meteorological station. Results indicate that the average of this value ranges from 16.9km (Delta computational method) to 18.3km (threat score computational method). Given the limitations of both methods, we believe that the average of these two (17.5km) may be the most reliable estimate that expresses how lightning is perceived by humans. Large differences in observational range values between some of the stations (e.g. from 12km in Bielsko-Biała to 24km in Łeba) indicate that thunderstorm measurements performed by humans are not homogeneous and are prone to errors. We estimate that an average increase/decrease of observational range by approximately 1km results in 1 additional/redundant day in the average annual number of thunderstorm days in the climatological sense. Results indicate that already existing thunderstorm climatology papers that are based on SYNOP thunderstorm reports may present presumably not entirely reliable results and overestimate or underestimate values from the real distribution.

Ten minutes continuous recording lightning using broadband VHF interferometer

A continuous recording system for digital signals associated with lightning discharge is designed to enhance lightning discharge processes understanding. The original VHF interferometer occasionally misses small amplitude impulses, and this disadvantage causes imperfect imaging of lightning progressions, especially positive breakdowns. To overcome this difficulty, the method of phase difference standard deviation of frequency components is applied. Numerical simulations and winter thunderstorm observations are presented to show and evaluate the capability of the new system.

Thunderstorm Observation by Radar (ThOR): An Algorithm to Develop a Climatology of Thunderstorms

AbstractThe Thunderstorm Observation by Radar (ThOR) algorithm is an objective and tunable Lagrangian approach to cataloging thunderstorms. ThOR uses observations from multiple sensors (principally multisite surveillance radar data and cloud-to-ground lightning) along with established techniques for fusing multisite radar data and identifying spatially coherent regions of radar reflectivity (clusters) that are subsequently tracked using a new tracking scheme. The main innovation of the tracking algorithm is that, by operating offline, the full data record is available, not just previous cluster positions, so all possible combinations of object sequences can be developed using all observed object positions. In contrast to Eulerian methods reliant on thunder reports, ThOR is capable of cataloging nearly every thunderstorm that occurs over regional-scale and continental United States (CONUS)-scale domains, thereby enabling analysis of internal properties and trends of thunderstorms.ThOR is verified against 166 manually analyzed cluster tracks and is also verified using descriptive statistics applied to a large (~35 000 tracks) sample. Verification also relied on a benchmark tracking algorithm that provides context for the verification statistics. ThOR tracks are shown to match the manual tracks slightly better than the benchmark tracks. Moreover, the descriptive statistics of the ThOR tracks are nearly identical to those of the manual tracks, suggesting good agreement. When the descriptive statistics were applied to the ~35 000-track dataset, ThOR tracking produces longer (statistically significant), straighter, and more coherent tracks than those of the benchmark algorithm. Qualitative assessment of ThOR performance is enabled through application to a multiday thunderstorm event and comparison to the behavior of the Storm Cell Identification and Tracking (SCIT) algorithm.

Evaluation of the stability indices for the thunderstorm forecasting in the region of Belgrade, Serbia

The pre-convective atmosphere over Serbia during the ten-year period (2001–2010) was investigated using the radiosonde data from one meteorological station and the thunderstorm observations from thirteen SYNOP meteorological stations. In order to verify their ability to forecast a thunderstorm, several stability indices were examined. Rank sum scores (RSSs) were used to segregate indices and parameters which can differentiate between a thunderstorm and no-thunderstorm event. The following indices had the best RSS values: Lifted index (LI), K index (KI), Showalter index (SI), Boyden index (BI), Total totals (TT), dew-point temperature and mixing ratio. The threshold value test was used in order to determine the appropriate threshold values for these variables. The threshold with the best skill scores was chosen as the optimal. The thresholds were validated in two ways: through the control data set, and comparing the calculated indices thresholds with the values of indices for a randomly chosen day with an observed thunderstorm. The index with the highest skill for thunderstorm forecasting was LI, and then SI, KI and TT. The BI had the poorest skill scores.

Multifrequency Radar Observations Collected in Southern France during HyMeX-SOP1

Abstract The radar network deployed in southern France during the first special observing period (SOP 1) of the Hydrological Cycle in the Mediterranean Experiment (HyMeX) was designed to precisely document the 3D structure of moist upstream flow impinging on complex terrain as a function of time, height, and along-barrier distance, and surface rainfall patterns associated with orographic precipitation events. This deployment represents one of the most ambitious field experiments yet, endeavoring to collect high-quality observations of thunderstorms and precipitation systems developing over and in the vicinity of a major mountain chain. Radar observations collected during HyMeX represent a valuable, and potentially unique, dataset that will be used to improve our knowledge of physical processes at play within coastal orographic heavy precipitating systems and to develop, and evaluate, novel radar-based products for research and operational activities. This article provides a concise description of this radar network and discusses innovative research ideas based upon preliminary analyses of radar observations collected during this field project with emphasis on the synergetic use of dual-polarimetric radar measurements collected at multiple frequencies.

Thunderstorms and thunderstorm precipitations in southern Poland

Abstract This paper addresses spatial and temporal variability in the occurrence of thunderstorms and related precipitation in southern Poland between 1951 and 2010. The analysis was based on thunderstorm observations and daily precipitation totals (broken down into the few ranges) from 15 meteorological stations. It was found that precipitation accompanied an overwhelming majority of thunderstorms. The most frequent range of thunderstorm precipitation totals was 0.1–10.0 mm which accounted for 60% of all values while precipitation higher than 20.0 mm accounted only for ca. 8%. During the study period, long-term change in the number of days with thunderstorm precipitation within a certain range displayed no clear-cut trends. Exceptions included: 1) an increase in the number of days with thunderstorm precipitation in the lowest range of totals (0.1–10.0 mm) at Katowice, Tarnów, Rzeszów and Lesko and decrease at Mt. Kasprowy Wierch, 2) an increase in the range 10.1–20.0 mm at Zakopane and 20.1–30.0 mm at Opole, 3) a decrease of the top range (more than 30.0 mm) at Mt. Śnieżka. It was found that the heaviest thunderstorm precipitation events, i.e. totalling more than 30 mm, and those events that covered all or most of the study area, occurred at the time of air advection from the southern or eastern sectors and a passage of atmospheric fronts.

Thunderstorm occurrence and characteristics in Central Europe under different synoptic conditions

The occurrence and characteristics of thunderstorms in Central Europe are examined in relation to the predominant synoptic conditions as derived from an automatic classification of synoptic patterns. Lightning strokes measured by a lightning detection network, human thunderstorm observations at weather stations and convective cells derived from radar reflectivity are used. The analysis reveals conditions favourable for thunderstorm development and highlights regions affected under different flow regimes. Additionally, the cell-based analysis shows that different synoptic conditions are typically associated with specific cell characteristics, such as the direction and speed of movement or cell sizes and severity. These relationships can be explained meaningfully via a description of the synoptic-meteorological characteristics of each of the standard weather patterns. As such these results may support a better understanding of thunderstorm formation as well as improve forecasters' situational awareness.

Comparison of thunderstorm hours registered by the lightning detection network and human observers in Estonia, 2006–2011

Relationships between the lightning detection network data and human-reported thunderstorms were studied in Estonia during the period of 2006–2011. Estonia is located in northeastern Europe between 57.5° to 59.5° N and 21° to 28.5° E. Numbers of thunderstorm days (TD) and thunderstorm hours (TH) reported by 61 volunteer observers and six meteorological stations were compared to the data of the lightning detection network. Results indicated that the flash data within 9.0 km from the sites of volunteer observers should be used in order to derive TD numbers equal to human observations. Larger radius of 14.7 km was found on the basis of six meteorological stations with probably better quality of thunderstorm observations. Due to data quality issues, the daily and monthly numbers of THs reported by individual observers explained only 12–39 % of variations in the flash counts within 40 km of their observing sites. In contrast, the average TH data of all observers successfully explained 75–86 % of variations in daily and monthly flash counts within 40 km of the observation sites. The main advantage of using the average data of many human observers seems to be that in case of a dense network, the neighboring observers tend to compensate for each other’s errors. In general, intense storms close to observing sites were found to be most successfully reported by human observers. The most important conclusion of the study is that although human observations of thunderstorms and automatic lightning observations are very different methods, they generally give similar results.

An example of the comparison of middle troposphere instability indices in the prognostic model with the thunderstorm activity data

Presented is a review of thunderstorm forecast methods based on atmospheric instability indices. Described are the main potential sources of thunderstorm observations. Obtained are the estimates of the accutacy of the WWLLN global network that registers lightnings. Compared are the Meteosat-9 infrared images of convective clouds, the model maps of cloudiness, and some instability indices computed using the WRF-ARW model.

Surface mesoscale features associated with leading convective line-trailing stratiform squall lines over the Gangetic West Bengal

In this paper an attempt is made to identify the mesoscale features in surface pressure pattern, if any, associated with thunderstorm over the Gangetic West Bengal region in India. The study was conducted over Kharagpur and the adjoining area in the Gangetic West Bengal, frequently affected by thunderstorms during the pre-monsoon seasons of April–May. Observations recorded at 50 m instrumented micro-meteorological tower and upper air sounding at Kharagpur under nationally coordinated Severe Thunderstorm Observations and Regional Modeling (STORM) Programme are used to study the variation in surface pressure, wind speed and direction, temperature and relative humidity associated with the squall lines with trailing stratiform precipitation region. In the surface pressure variation, pre-squall mesolow, mesohigh and wake low are identified with the passage of the squall line at Kharagpur. It is observed that in the squall line with trailing stratiform precipitation shield, the mesohigh is associated with convective line and wake low exists at the rear of the storms. The position of the mesohigh is typically found in the vicinity of the heavy rain directly beneath the downdraft. The mesohigh seems to be initiated by the cooling due to evaporation of precipitation in the downdraft and intensified due to the non-hydrostatic effect because of the rainfall directly beneath the downdraft. It is also observed that the passage of trailing edges of the stratiform precipitation coincided with the wake low. Upper air sounding shows mid-tropospheric cooling and lower tropospheric warming. It may be possible due to the dominance of evaporative cooling in the mid-levels and dynamically forced descending motion leading to adiabatic warming in the low levels which may lead to the formation of the wake low.

The SAARC STORM: A Coordinated Field Experiment on Severe Thunderstorm Observations and Regional Modeling over the South Asian Region

This article describes a unique field experiment on Severe Thunderstorm Observations and Regional Modeling (STORM) jointly undertaken by eight South Asian countries. Several pilot field experiments have been conducted so far, and the results are analyzed. The field experiments will continue through 2016. The STORM program was originally conceived for understanding the severe thunderstorms known as nor'westers that affect West Bengal and the northeastern parts of India during the pre-monsoon season. The nor'westers cause loss of human lives and damage to properties worth millions of dollars annually. Since the neighboring South Asian countries are also affected by thunderstorms, the STORM program is expanded to cover the South Asian countries under the South Asian Association for Regional Cooperation (SAARC). It covers all the SAARC countries (Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka) in three phases. Some of the science plans (monitoring the life cycle of nor'westers/severe thunderstorms and their three-dimensional structure) designed to understand the interrelationship among dynamics, cloud microphysics, and electrical properties in the thunderstorm environment are new to severe weather research. This paper describes the general setting of the field experiment and discusses preliminary results based on the pilot field data. Typical lengths and the intensity of squall lines, the speed of movements, and cloud-top temperatures and their heights are discussed based on the pilot field data. The SAARC STORM program will complement the Severe Weather Forecast Demonstration Project (SWFDP) of the WMO. It should also generate large-scale interest for fueling research among the scientific community and broaden the perspectives of operational meteorologists and researchers.

Increases in thunderstorm activity and relationships with air pollution in southeast China

This study analyzes 15 years of Tropical Rainfall Measuring Mission (TRMM) satellite data, together with surface observations of thunderstorms and visibility, to study trends and relationships between aerosols and thunderstorms in southeast China. TRMM data used are from the lightning imaging sensor (LIS) and the precipitation radar (PR). Surface data are human-observed thunderstorm occurrence and visibility for the period of 1990–2012 at 70 plain stations and 4 mountain stations. Thunderstorm and lightning activities, as well as PR echo top heights, have all increased significantly over the region during the period under study, while regional mean visibility has decreased greatly at the plain stations. The daily rainfall amount during thunderstorm days has increased significantly, but rainfall without thunderstorms has no trend during this period. In comparison, the four mountain weather stations at elevations greater than 1100 m showed little trend in the number of thunderstorm days during the period of 1990–2012. The ratio of the number of thunderstorm days between plain and mountain stations has increased significantly. The distinct trends seen between plain and mountain stations may originate from large differences in aerosol concentration between the plain and mountain regions. The accumulation of pollution aerosols in the plain region likely invigorates thunderstorms, whereas a lesser, or no, impact on intense convection is found over high-altitude regions.

Empirical Examination of the Factors Regulating Thunderstorm Initiation

Abstract Initiation is the part of the convective life cycle that is currently least understood and least well forecast. The inability to properly forecast the timing and/or location of deep convection initiation degrades forecast skill, especially during the warm season. To gain insight into what atmospheric parameters distinguish areas where storms initiate from areas where they do not initiate, over 55 000 thunderstorm initiation points over the central United States from 2005 to 2007 are found and a number of thermodynamic and kinematic parameters are computed from 20-km Rapid Update Cycle (RUC)-2 data. In addition to the initiation points, data are also collected at nearby locations where thunderstorms did not initiate (null points) for comparison. Thunderstorm identification and tracking are done using several tools within the Warning Decision Support Services–Integrated Information (WDSS-II) package and a thunderstorm tracking algorithm called Thunderstorm Observation by Radar (ThOR). The parameters being examined are intended to represent the four main factors governing the behavior of convection: buoyancy, dilution, lift, and inhibition. Statistical analysis of the data shows that there is no threshold of any single parameter that is consistently able to discriminate between initiation and noninitiation. However, case-by-case comparison of the values showed that lift is most often the factor that distinguishes the thunderstorm initiation environment from other areas.

Automated thunderstorm tracking: utilization of three-dimensional lightning and radar data

Abstract. This paper presents a new hybrid method for automated thunderstorm observation by tracking and monitoring of electrically charged cells (ec-TRAM). The developed algorithm combines information about intense ground precipitation derived from low-level radar-reflectivity scans with three-dimensionally resolved lightning data, which are provided by the European VLF/LF lightning detection network LINET. Based on the already existing automated radar tracker rad-TRAM (Kober and Tafferner, 2009), the new method li-TRAM identifies and tracks electrically active regions in thunderclouds using lightning data only. The algorithm ec-TRAM uses the output of the two autonomously operating routines rad-TRAM and li-TRAM in order to assess, track, and monitor a more comprehensive picture of thunderstorms. The main motivation of this work is to assess the benefit of three-dimensionally resolved total lightning (TL) information for thunderstorm tracking and monitoring. The focus is laid on the temporal development whereby TL is characterized by an effective in-cloud (IC) and cloud-to-ground (CG) event discrimination. It is found that the algorithms li-TRAM and ec-TRAM are both feasible methods for thunderstorm monitoring with potential for nowcasting. The tracking performance of li-TRAM turns out to be comparable to that of rad-TRAM, a result that strongly encourages utilization of lightning data as independent data source for thunderstorm tracking. It is found that lightning data allow an accurate and close monitoring of storm regions with intense internal dynamics as soon as convection induces electrical activity. A case study shows that the current short-term storm dynamics are clearly reflected in the amount of strokes, change of stroke rates and IC/CG ratio. The hybrid method ec-TRAM outperforms rad-TRAM and li-TRAM regarding reliability and continuous assessment of storm tracks especially in more complexly developing storms, where the use of discharge information contributes to more detailed information about storm stage and storm evolution.

In search of discernible infrasound emitted by numerically simulated tornadoes

The comprehensive observational study of Bedard (2005) provisionally found that the infrasound of a tornado is discernible from the infrasound of generic cloud processes in a convective storm. This paper discusses an attempt to corroborate the reported observations of distinct tornado infrasound with numerical simulations. Specifically, this paper investigates the infrasound of an ordinary tornado in a numerical experiment with the Regional Atmospheric Modeling System, customized to simulate acoustic phenomena. The simulation has no explicit parameterization of microphysical cloud processes, but creates an unsteady tornado of moderate strength by constant thermal forcing in a rotational environment. Despite strong fluctuations in the lower corner flow and upper outflow regions, a surprisingly low level of infrasound is radiated by the vortex. Infrasonic pressure waves in the 0.1Hz frequency regime are less intense than those which could be generated by core-scale vortex Rossby (VR) waves of modest amplitude in similar vortices. Higher frequency infrasound is at least an order of magnitude weaker than expected based on infrasonic observations of tornadic thunderstorms. Suppression of VR waves (and their infrasound) is explained by the gradual decay of axial vorticity with increasing radius from the center of the vortex core. Such non-Rankine wind-structure is known to enable the rapid damping of VR waves by inviscid mechanisms, including resonant wave-mean flow interaction and “spiral wind-up” of vorticity. Insignificant levels of higher frequency infrasound may be due to oversimplifications in the computational setup, such as the neglect of thermal fluctuations caused by phase transitions of moisture in vigorous cloud turbulence.

Climatology of thunderstorms in the Baltic countries, 1951–2000

This paper provides an overview of the thunderstorm climate of the Baltic countries during the period of 1951–2000. Our study area is in northeastern Europe and encompasses Estonia, Latvia, and Lithuania. Visual thunderstorm observations at 59 weather stations were used as a data source. The mean annual number of thunderstorm days was 12–29.5. The seasonal cycle of thunderstorm hours with a daily step unexpectedly showed two maxima, whereas the monthly numbers of thunderstorm days had one clear mid-latitude specific peak between June and August. The diurnal cycle of thunderstorm hours showed a peak between 1400 and 1800 local time and a minimum between 0400 and 1000 hours local time. The average annual duration of thunderstorm events was 112 min. The average number of thunderstorm events per thunderstorm day was around 1.1–1.2. Our results showed that the thunderstorm climate of the Baltic countries generally resembles that of other mid-latitude study sites.

Organizational modes of squall-type Mesoscale Convective Systems during premonsoon season over eastern India

Premonsoon thunderstorms, locally known as Nor’westers, were studied over the eastern part of India using routine observations and data acquired from STORM (Severe Thunderstorm Observation and Regional Modelling) program during the premonsoon season, i.e., March through May, of 2006–08. Doppler radar image analysis reveals that premonsoon convective activities on many occasions may be described as squall-type linear Mesoscale Convective Systems (MCSs) which are composed of three common organizational modes viz. Trailing Stratiform (TS), Leading Stratiform (LS) and Parallel Stratiform (PS). The most dominant and common mode of organization, in terms of frequency of occurrences, duration, mean speed and inter-conversion among the different modes, is the TS, contributing about 65% of the cases while LS and PS contribute only about 15% and 20% respectively. Examination of pre-storm environments indicates that line-perpendicular and line-parallel storm-relative winds possibly determine the modes of organization. Case studies, one from each class, were also carried out and the observed structures were found to be similar to that observed in warmer mid-latitudes with certain exceptions. Unlike mid-latitude MCSs, convective cells during the premonsoon season initiate over the region with the support of weak synoptic setting and in course of time, organize themselves to become an MCS under favorable mesoscale convective environment. However they are short-lived irrespective of the modes of organization.

Thunderstorm observations by air-shower radio antenna arrays

Relativistic, charged particles present in extensive air showers (EAS) lead to a coherent emission of radio pulses which are measured to identify the shower initiating high-energy cosmic rays. Especially during thunderstorms, there are additional strong electric fields in the atmosphere, which can lead to further multiplication and acceleration of the charged particles and thus have influence on the form and strength of the radio emission. For a reliable energy reconstruction of the primary cosmic ray by means of the measured radio signal it is very important to understand how electric fields affect the radio emission. In addition, lightning strikes are a prominent source of broadband radio emissions that are visible over very long distances. This, on the one hand, causes difficulties in the detection of the much lower signal of the air shower. On the other hand the recorded signals can be used to study features of the lightning development. The detection of cosmic rays via the radio emission and the influence of strong electric fields on this detection technique is investigated with the LOPES experiment in Karlsruhe, Germany. The important question if a lightning is initiated by the high electron density given at the maximum of a high-energy cosmic-ray air shower is also investigated, but could not be answered by LOPES. But, these investigations exhibit the capabilities of EAS radio antenna arrays for lightning studies. We report about the studies of LOPES measured radio signals of air showers taken during thunderstorms and give a short outlook to new measurements dedicated to search for correlations of lightning and cosmic rays.

Lightning and Thunderstorm Observation with High Resolution

A high resolution radar has been newly developed and tested recently in order to observe the fine structure of thunderstorm. Lightning location system which determines the sources of the VHF impulses emitted from lightning also implemented near the radar site. The initial observation shows that a ground flash initiated near 0 degree level just above the thunderstorm core and propagated to the ground along the edges of the thunderstorm, suggesting that the simultaneous observation with lightning and high resolution radar system will be novel tool for lightning research and prediction.