Thunderstorm Days Research Articles

Initial Results of Long-term Continuous Observation of Lightning Discharges by FALMA in Chinese Inland Plateau Region

We started a long-term continuous observation of lightning discharges in the Chinese inland plateau region using a fast antenna lightning mapping array (FALMA). During the first year of observation, 2019, we recorded lightning discharges on 25 days in Yinchuan city, the capital of Ningxia. Most of the lightning discharges appeared to occur in the afternoons of individual thunderstorm days in August. We studied the cloud-to-ground (CG) flash percentages, lightning discharge source spatiotemporal distributions, and preliminary breakdown (PB) process characteristics for the two thunderstorm cases that produced the most frequent lightning flashes in 2019 over a wide area. It was found that (1) CG flashes in these two thunderstorms accounted for 28.4% and 32.5% of total lightning flashes, respectively; (2) most lightning discharge sources in these two thunderstorms occurred at temperatures between 5 and −30 °C, with a peak at around −10 °C; and (3) more than 90% of well-mapped PB processes of intracloud (IC) flashes propagated downward. By overlapping the altitudes and the progression directions of the PB processes on the lightning source spatiotemporal distributions, we inferred that the main negative charge of the two storms observed in Ningxia, China, was at a height of around −15 to −25 °C (7 to 9 km) and the main positive charge was at a height of around 5 to 0 °C (2 to 4 km).

Development of novel hybrid machine learning models for monthly thunderstorm frequency prediction over Bangladesh

Thunderstorm frequency (TSF) prediction with higher accuracy is of great significance under climate extremes for reducing potential damages. However, TSF prediction has received little attention because a thunderstorm event is a combination of intricate and unique weather scenarios with high instability, making it difficult to predict. To close this gap, we proposed two novel hybrid machine learning models through hybridization of data pre-processing ensemble empirical mode decomposition (EEMD) with two state-of-arts models, namely artificial neural network (ANN), support vector machine for TSF prediction at three categories over Bangladesh. We have demarcated the yearly TSF datasets into three categories for the period 1981–2016 recorded at 28 sites; high (March–June), moderate (July–October), and low (November–February) TSF months. The performance of the proposed EEMD-ANN and EEMD-SVM hybrid models was compared with classical ANN, SVM, and autoregressive integrated moving average. EEMD-ANN and EEMD-SVM hybrid models showed 8.02–22.48% higher performance precision in terms of root mean square error compared to other models at high-, moderate-, and low-frequency categories. Eleven out of 21 input parameters were selected based on the random forest variable importance analysis. The sensitivity analysis results showed that each input parameter was positively contributed to building the best model of each category, and thunderstorm days are the most contributing parameters influencing TSF prediction. The proposed hybrid models outperformed the conventional models where EEMD-ANN is the most skillful for high TSF prediction, and EEMD-SVM is for moderate and low TSF prediction. The findings indicate the potential of hybridization of EEMD with the conventional models for improving prediction precision. The hybrid models developed in this work can be adopted for TSF prediction in Bangladesh as well as different parts of the world.

Development of a simple equivalent tornado wind profile for structural design and evaluation

Tornadoes cause damage to buildings and infrastructure. Providing the spatially varying tornado activities or tornado occurrence rate alone does not facilitate the tasks of checking and evaluating structures subjected to the tornado wind velocity hazard. In the present study, the estimation of the quantile of the tornado wind velocity hazard along the height for southern Ontario – a tornado-prone region in Canada – is carried out. For the assessment, a tornado occurrence rate model is developed by considering the reporting bias due to population density and by using the cloud-to-ground lightning flash density and thunderstorm days per year as the explanatory variables. Also, a simple equivalent along height tornado design wind profile for a vertical line-like structure is proposed by considering the bending moment and shear force along the height of the structure. Moreover, the concept of disaggregation analysis is employed to identify the scenario tornado wind profiles. The results indicate that the identified scenario wind profiles could be crudely bounded by using the rectangular wind profile and the power-law wind profile for synoptic winds, which are all hinged at the return period value of the tornado wind velocity at 10 ​m height. • A systematic modeling of tornado occurrence for southern Ontario is presented. • The cloud-to-ground lightning flash density and thunderstorm days are used as explanatory variables. • Tornado wind profile based on quantiles of tornado wind speed is presented. • Simple equivalent tornado design wind profiles are developed or point-like and line like structures.

An Experimental Study on the Variation of Atmospheric Magnetic-Field Intensity Related to Dust, Haze, Rain, Snow, and Thunderstorms

Simultaneous measurements of the vertical magnetic field (VMF), three-dimensional electric field, ambient temperature, ambient relative humidity, particle mass concentration, and three-dimensional velocity are conducted during dust, haze, rain, snow, and thunderstorms. The hourly VMF variation (the rate of VMF increment and time increment with a 1-h time interval) is used to evaluate the disturbance level of the atmospheric magnetic field during the abovementioned weather conditions. There is no significant difference in the hourly VMF variations between hazy days and fair weather. However, the hourly VMF variations on dusty, rainy, snowy, and thunderstorm days differ from those in fair weather, implying that these weather conditions significantly affect the atmospheric magnetic field. On hazy days, although the haze particles are charged, the VMF does not change compared with in fair weather, which suggests that the horizontal electric field generated by haze particles is an irrotational field. On dusty and snowy days, the heterogeneity of the charge distribution forms a rotational horizontal electric field, which can induce the VMF to disturb the atmospheric magnetic field. During rain and thunderstorms, the hourly variation in the VMF is larger than in dust and snow, which can be attributed to the rotational horizontal electric field generated by raindrops and clouds. In addition, the hourly variation in the VMF in thunderstorms is one order of magnitude larger than that during days without thunderstorms, indicating that the VMF induced by the cumulonimbus cloud electric field is more significant than that in other weather conditions.

Tornado wind hazard mapping and equivalent tornado design wind profile for Canada

Tornadoes cause property damage and fatalities. A systematic assessment of tornado wind velocity hazard is presented in the present study for Canada based on reported historical tornado catalogue. For the assessment, the Poisson model, zero-inflated Poisson model, and negative binomial model, as well as the adaptive Gaussian kernel smoothing technique, are used to model tornado occurrence. The modeling takes into account the tornado reporting bias due to population density and uses the cloud-to-ground lightning flash density and the thunderstorm days as the explanatory variables. Statistical analysis results indicate that the negative binomial model is preferable.The tornado wind velocity hazard maps for Canada, in terms of wind velocity at 10 m height above the ground surface and return period T, VT(10), are developed based on an available probabilistic tornado wind field model. Also, a simple equivalent tornado design wind profile is developed based on the return period value of tornado wind speed at different heights. The developed tornado design wind profile only depends on VT(10), which greatly facilitates its potential use for structural design subjected to tornado wind load and its possible implementation in structural design code and standards.

Spatial patterns of long-term trends in thunderstorms in India

Long-term trends in the frequency of thunderstorm days are investigated using fifty years of data recorded by weather observatories throughout India. An attempt has been made to identify whether the trends are spatially cohesive and collocated with regions with maximum of thunderstorm days. This analysis of trends is significant, since most of the weather over India is of convective origin and has devastating impact on life and property. There are three thunderstorm maximum regions (a) northwest Indian Himalayas and adjoining Pakistan, (b) east India and (c) extreme southern parts of peninsular India. The results of the study revealed on a monthly scale, the frequency of thunderstorm days has a consistent spatially cohesive decreasing trend over east central and northeast India, collocated with the intra-annually shifting maximum of thunderstorm activity. The trend is more diffused for the thunderstorm maxima over north and south peninsular India. Comparison with rainfall trends from previous studies indicates that this decreasing trend of thunderstorm days is in phase with decreasing trends in rainfall activity over east central and northeast Indian regions. Detailed analysis indicates that frequency of thunderstorm days over these regions decreased during the latter half of the twentieth century followed by gradually increasing trend. This corresponds to a global warming hiatus and matches similar findings around the world. It seems likely that the decreasing moisture inflow from the surrounding oceans into the Indian subcontinent throughout the year due to weakening of the land-sea thermal gradient is causing a decreasing trend in the convection during this period. Over north and south peninsular India, where circum-global planetary waves play an important role in triggering convection, the strengthening of these waves offsets the effect of the generally decreasing moisture.

Volcanic alert system by lightning detection using the WWLLN - ash cloud monitor

Electrical discharges are observed in many volcanic eruptions and they have often been used as indicators of such eruptions. Volcanic lightning is remarkably similar to those produced during thunderstorms and is called analogous to thunderstorm-like plume lightning. The WWLLN developed a program called “Ash Cloud Monitor” (ACM), in which alerts are issued for possible volcanic eruptions when lightning strokes are detected around a volcano. The ACM tool has demonstrated to be a very effective technique to be aware of volcanic eruptions. However, most of the alerts released by ACM belong to false alarms of volcanic activity, because, in general, the detected lightning is produced by thunderstorms near the volcano.In order to assess and improve the ACM to detect volcanic eruptions, reducing false alert emissions and improving the quick interpretation of them, we develop a web platform called Georayos-VolcanoAr with a new structure and a modified algorithm, with respect to the algorithm used by ACM, for the classification of alerts. The new algorithm considers an alert system with 3 levels: Red - Yellow - Green, with the Red alert being the highest level and decreasing towards Green. The Red alert was assigned to those volcanoes where only recorded lightning within a radius of 20 km or the lightning detected within a radius of 20 km is at least twice as much as that detected up to 100 km from the vent.The study focused on 32 volcanoes located in the Andes, close to the Argentine-Chilean border, and analyzed the results reported by the ACM network in terms of a climatological study of the lightning activity, thunderstorm days and predominant winds in that region. This analysis serves as a basis for a general recognition of the study zone in order to improve the interpretation of the distribution and generation of false alerts; as well as to help decision makers, among others, to have a reference that allows them to issue the warning.

Winter Positive Cloud‐to‐Ground Lightning Flashes Observed by LMA in Japan

Using a lightning mapping array (LMA), we have observed 24 positive cloud‐to‐ground (CG) flashes occurred in three thunderstorm days. These flashes can be apparently grouped into 5 clusters according to their occurrence times. We have obtained the charge structures for both the individual flashes and clusters. It was found that 4 out of 5 clusters of positive CG flashes exhibited either inverter dipolar or tri‐polar charge structures. This result indicates that the high percentage of positive CG flashes in Hokuriku winter thunderstorms originated from the inverted charge structure rather than the various deformations of normal charge structures widely accepted in literatures. The flash positive charge appeared to distribute usually in a layer with its thickness of around 1 km, its horizontal area of more than 100 km2 and its bottom altitude of around 1–2 km above the ground. For each of the flash, we have also obtained its duration, length, duration before the first stroke and convex area. It was found that all flashes with a large peak return stroke current had short durations before their first return strokes. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Spatial Diversity of Cloud-to-Ground Lightning Flashes in the Kujawsko-Pomorskie Voivodeship (Poland), 2002-2019

This research focuses on the spatial diversity of cloud-to-ground (CG) flashes in the Kujawsko-Pomorskie voivodeship (Poland) based on data from the PERUN lightning detection system, 2002-2019. The storm season usually lasts from May to September, with July having the highest number of thunderstorms days and flashes. Thunderstorms most often occur in the afternoon. A generated grid of 5×5-km cells was used to characterise the variables related to CG flashes. In the analysed period 432,925 CG flashes were detected in the voivodeship (24,051 flashes year-1). The highest electrical activity was found in the south-eastern part of the province. In grids with a large water surface, the number of CG flashes was small and increased with distance from the Vistula River. The distribution of atmospheric discharges in major cities of the region (Bydgoszcz, Toruń, Włocławek and Grudziądz) was random. Years with greater electrical storm activity (27,614 discharges in 2017) are interspersed with calmer years (5000-7000 discharges). There were found an upward trend in lightning discharges (of 1681 discharges year-1) during period 2002-2019. To develop maps specifying the number of thunderstorm days, a 1×1-km grid cell was used with a 15-km radius buffer from the bin centre. The annual number of thunderstorm days in the voivodeship fluctuates from 27 to 41 days and increases from north-west to south-east. Consecutive days with a thunderstorm, the most common runs are of three days in a row with a storm. The number of thunderstorm days shows an increasing trend (0.82 days year-1). This trend is related to the increase in air temperature in the storm season (Apr-Sept) reaching (0.04°C/year).

盘州市50年雷暴日数气候变化特征分析

盘州市50年雷暴日数气候变化特征分析

青海省雷暴日数分布及其气候变化趋势

青海省雷暴日数分布及其气候变化趋势

A first assessment of rainfall erosivity synchrony scale at pan-European scale

Soil loss by water erosion is a major land degradation processes that can locally reduce crop productivity and cause off-site negative effects such as siltation, eutrophication of waterways, flooding and terrestrial and aquatic biodiversity loss. The major driver of water erosion is the erosive power of rainfall. Using the detailed erosive events of the Rainfall Erosivity Database at European Scale (REDES), we study the characteristics and patterns of rainfall erosivity in Europe introducing the Rainfall Erosivity Synchrony Scale (Rsync). Rsync expresses the maximum radius in kilometers around a given meteorological station within which at least half of the other meteorological stations in the database also detect an erosive event. In this study we correlate the Rsync and the annual erosivity with annual number of thunderstorm days, convective and large-scale precipitation and multiple geo-morphological features such as topographic position index and terrain ruggedness index. Our analysis shows an inverse relationship between the Rsync and rainfall erosivity values in Europe. Different spatial patterns of synchrony scale are detected in Europe, which enables us to delineate areas where severe soil erosion can simultaneously occur at larger scales, e.g., large sectors of Italy, Spain, Croatia and Slovenia. Furthermore, we observe a tendency of the Rsync to decrease with convective precipitation, annual number of thunderstorm days and increase with the large-scale precipitation. On the contrary, annual rainfall erosivity increases with convective precipitation and annual number of thunderstorm days and decreases with large-scale precipitation.

Analysis of shielding failure flash-over rate of collection lines of wind farms in mountainous areas

Aiming at the current situation of serious economic losses caused by lightning shielding on the collection lines of wind farms in mountainous areas. First, this paper uses the horizontal section location map of the collection line to extract the terrain parameters, Then use the catenary equation to determine the spatial position of the conductor and ground of any section of the collector line along the pitch direction, and obtain the height of the conductor and the ground to the ground. Finally, complete the modeling calculation analysis of the three-dimensional electrical geometry model (EGM) of the entire collection line. The calculation results show that, when the thunderstorm day, the arrangement of the collection line and the structure of the tower are the same, the SFFOR of the collection line of the wind farm in mountainous terrain is 0.487 times/100 km/year, and the plain terrain is 0.167 times/100 km/year, that is, mountainous area is 2.9 times of plain terrain; It is recommended to use double lightning protection poles with small protection angles on the collection lines of wind farms in mountainous areas, or install lightning arresters for poles that are prone to flashover to meet the design requirements of line lightning protection.

Trends and Variabilities of Thunderstorm Days over Bangladesh on the ENSO and IOD Timescales

Thunderstorms (TS) are one of the most devastating atmospheric phenomena, which causes massive damage and adverse losses in various sectors, including agriculture and infrastructure. This study investigates the spatiotemporal variabilities of TS days over Bangladesh and their connection with El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). The TS, ENSO and IOD years’ data for 42 years (1975–2016) are used. The trend in TS days at the spatiotemporal scale is calculated using Mann Kendall and Spearman’s rho test. Results suggest that the trend in TS days is positive for all months except December and January. The significant trends are found for May and June, particularly in the northern and northeastern regions of Bangladesh. In the decadal scale, most of the regions show a significant upward trend in TS days. Results from the Weibull probability distribution model show the highest TS days in the northeastern region. The connection between TS days and ENSO/IOD indicates a decrease in TS activities in Bangladesh during the El Niño and positive IOD years.

Lightning generated electric field over land and sea at Northern Region of Peninsular Malaysia: Measuring Setup

Lightning is the transfer of significant charge between two charged object, it can appear between cloud-to-cloud, cloud-to-air and cloud-to-ground. All lightning activities are correlated with charge movement and therefore, it can be studied using measurement of electrostatic field (slow field changes), radiation field (fast field changes) and magnetic field affiliated with charge movement. The measuring equipment was a parallel flat plate and vertical whip antenna with an analog filter buffer circuit, connected to a digital high speed oscilloscope. In principle, both antenna have a similar measuring operation, with the exclusion of the antennas dimension, mode of transient recoder and the association of circuitry characteristic (decay time constant). This measurement setup are commonly used to perform electric field characterization related to various lightning events such as as preliminary breakdown, stepped leader, return stroke, subsequent return stroke, dart leader, dart-stepped leader, narrow bipolar pulses and cloud activity between strokes, such as regular pulse trains, K and M changes and chaotic pulse trains. The measurement systems are located very close to the sea, with respect in obtaining a perspicuous explaination of lightning propagation effects on sea instead on land. Noise-distorted effects in data captured usually introduce in a noisy environment or when the lightning strike far from the measurement station, thus the data gathered from the measurement need to be filter using MATLAB computer simulation before conducting further analysis. A promising wavelet 1-D technique, then, were used in signal denoising process rather using conventional filtration. In this works, the state of art in measuring vertical component of electric field focalized sea area during the thunderstorm days been demonstrate and explained.

Review article: A comprehensive review of datasets and methodologies employed to produce thunderstorm climatologies

Abstract. Thunderstorm and lightning climatological research is conducted with a view to increasing knowledge about the distribution of thunderstorm-related hazards and to gain an understanding of environmental factors increasing or decreasing their frequency. There are three main methodologies used in the construction of thunderstorm climatologies: thunderstorm frequency, thunderstorm tracking or lightning flash density. These approaches utilise a wide variety of underpinning datasets and employ many different methods ranging from correlations with potential influencing factors and mapping the distribution of thunderstorm day frequencies to tracking individual thunderstorm cell movements. Meanwhile, lightning flash density climatologies are produced using lightning data alone, and these studies therefore follow a more standardised format. Whilst lightning flash density climatologies are primarily concerned with the occurrence of cloud-to-ground lightning, the occurrence of any form of lightning confirms the presence of a thunderstorm and can therefore be used in the compilation of a thunderstorm climatology. Regardless of approach, the choice of analysis method is heavily influenced by the coverage and quality (detection efficiency and location accuracy) of available datasets as well as by the controlling factors which are under investigation. The issues investigated must also reflect the needs of the end-use application to ensure that the results can be used effectively to reduce exposure to hazard, improve forecasting or enhance climatological understanding.

Bio-climatic classification of Iran by multivariate statistical methods

Traditional classification approaches tend to classify climates in terms of one or a few climatic variables given the specific circumstances. However, climate incorporates wide varieties of variables and serves as a cumulative process. In the present research, the number of 197 climatic parameters were selected and evaluated drawing upon data from the Iranian Meteorological Organization at 164 selected stations during the period of 1981 to 2018. After accuracy verification (by statistics of reliable synoptic stations in the area), such parameters were applied to develop a database. Then, upon reviewing of the library documents while considering the effective climatic elements in the formation and distribution of vegetation in different regions of Iran, finally 137 climatic variables were identified, in turn used as input data to perform factor analysis in SPSS software. Such variables greatly affect the climate of each region, and in fact, are determinant factors of the climate in each area. Subsequently, cluster analysis was performed on climatic factors obtained from the factor analysis method. According to the results, throughout the Iran, nine factors of temperature, relative humidity, cold season rainfall, warm-season rainfall, wind speed, semi-cloudy days, thunderstorm and snowy day with eigenvalues greater than one were 29.71, 22.32, 9.58, 7.52, 6.22, 6.80, 4.25, 3.69, 2.22%, respectively and totally accounted for 92.35% of the variance the data. Cluster analysis was an important step in determining the number of homogeneous clusters in this study. For this, the wards method was applied. First, by GIS software, the whole of Iran was divided into two climatic zones, and the climatic factors separating Iran into two zones were identified. Then two areas were divided into three sub-areas and this was continued until the final stage and at each stage, the factors separating the climatic zones were identified. By the final stage, it means stage at which the number of suitable and final zones is obtained. Subsequently, we reached from the climatic zone of 25 to zone of 26, so that all suitable climate zones of Iran were obtained by cluster analysis. While we proceeded from the zoning phase of 26 to 27 and up, it had no effect on climate factors, and no factor was identified as a separating factor of climatic zones. Eventually, based on the multivariate statistical methods, 26 bio-climatic zones for Iran was obtained. Then, the overall vegetation map of Iran was networked by the kriging method and matched to the Iranian map of climatic zones. And exactly the dominant vegetation types were studied and introduced within each climatic zones. Finally, the results of the multivariate statistical method were compared with those of the traditional Pabout method and the weaknesses and strengths of the Pabout method and also multivariate statistical methods used in the bio-climatic zonation of Iran were investigated.

Determining future thunderstorm-prone environments in Southern Ontario by using statistical downscaling to project changes in convective available potential energy (CAPE)

Considering the potential risks associated with thunderstorms, to date, there has been limited analysis on the projection of thunderstorm occurrence trends in Canada. The small spatial and temporal scales of thunderstorms are not resolved in global climate models (GCMs). In this study, the relationship is established between thunderstorm observations from nine weather stations across Southern Ontario, Canada, and daily maximum convective available potential energy (CAPE). The results from the correlation analysis between CAPE and thunderstorm days suggested that the probability of observing a thunderstorm increases as maximum daily CAPE increases. We then utilize the novel approach of applying statistical downscaling (SDSM) to CAPE. After regenerating CAPE over a 30-year reference period (1981–2010) at each weather station, it was determined that the SDSM-modeled CAPE values well compared to observed CAPE values. Future CAPE values up to the end of the current century are then projected using the SDSM models for each station in combination with three GCMs for future climate. The forecast from the downscaling suggested large increases, as much as tripling, in annual mean CAPE, summer mean CAPE, and number of days exceeding a 50% probability and 80% probability of observing a thunderstorm at all weather stations under SRES business-as-usual and RCP 8.5 scenarios for the study period of 2011–2100. All else being equal, this suggests an increase in the number of days with conditions favorable for thunderstorms under a warmer climate.

Time–height variation of winds and turbulence during typical tropical pre-monsoon thunderstorm events observed from high-resolution Doppler wind lidar measurements

High spatiotemporal resolution measurements of horizontal and vertical winds made using a Doppler wind lidar during development and mature stages of few typical tropical thunderstorm events in 2014 over a continental Indian station are used to study the dynamical changes that take place in the lower atmospheric layers close to surface. Results show significant time–height variability in horizontal wind especially 2–3 h before rainfall on ground. The recorded vertical motions on the thunderstorm days showed that during its developing stage, alternating updrafts and downdrafts are prevalent through the entire vertical column of the lower atmosphere with the magnitude of fluctuations being higher compared to those on non-thunderstorm days. Turbulence intensity is high in magnitude during the evolution of intense convection. Alternating layers of convergence and divergence with horizontally time-stratified layers of strong positive and negative wind shear are observed which seem to contribute to strengthening and vertical growth of local convection. Thus, high-resolution time–height variations in horizontal and vertical winds in the lower atmosphere during the life cycle of a tropical thunderstorm provide a better understanding of the atmospheric dynamics associated with it and short-duration heavy precipitation it produces.

Climatological summaries of Thomas Hughes’ meteorological data, for Stroud, UK (1775–1813)

AbstractThomas Hughes (1742–1813) kept a daily diary of weather and geoscience phenomena at Stroud in Gloucestershire, in the southern UK, between 1775 and 1813, following a short period of similar records made nearby from 1771. Data from the diary have previously been used in compiling the Central England Temperature series and to corroborate aurora sightings elsewhere in Europe. Recent historical research now confirms the suspected authorship of the diaries beyond doubt and strongly suggests that the pre‐Stroud records were made in south Gloucestershire. Here, summary tables of monthly data between 1771 and 1813 are presented for thunderstorm days, snow days, rain days, rainfall, surface air pressure and auroral nights. Consistency checks, both between the different measurements contained and with other contemporary measurements, provide confidence in the reliability of the meteorological and geophysical data which spans part of the Dalton Minimum in solar activity.