High Thunderstorm Activity Research Articles

Exploiting radar polarimetry for nowcasting thunderstorm hazards using deep learning

Abstract. This work presents the importance of polarimetric variables as an additional data source for nowcasting thunderstorm hazards using an existing neural network architecture with recurrent-convolutional layers. The model can be trained to predict different target variables, which enables nowcasting of hail, lightning, and heavy rainfall for lead times up to 60 min with a 5 min resolution, in particular. The exceedance probabilities of Swiss thunderstorm warning thresholds are predicted. This study is based on observations from the Swiss operational radar network, which consists of five operational polarimetric C-band radars. The study area of the Alpine region is topographically complex and has a comparatively very high thunderstorm activity. Different model runs using combinations of single- and dual-polarimetric radar observations and radar quality indices are compared to the reference run using only single-polarimetric observations. Two case studies illustrate the performance difference when using all predictors compared to the reference model. The importance of the predictors is quantified by investigating the final training loss of the model, with skill scores such as critical success index (CSI), precision, recall, precision–recall area under the curve, and the Shapley value. Results indicate that single-polarization radar data are the most important data source. Adding polarimetric observations improves the model performance compared to reference model in term of the training loss for all three target variables. Adding quality indices does so, too. Including both polarimetric variables and quality indices at the same time improves the accuracy of nowcasting heavy precipitation and lightning, with the largest improvement found for heavy precipitation. No improvement could be achieved for nowcasting of the probability of hail in this way.

Thunderstorm detection from GPM IMERG rainfall: Climatology of dynamical and thermodynamical processes over India

AbstractThis study aims to (i) prepare a premonsoon thunderstorms database, (ii) understand the thunderstorm frequency, duration and intensity and (iii) composite analysis of dynamic and thermodynamic processes related to thunderstorms over India. The thunderstorm associated rainfall varies across India. Hence, a percentile‐based approach is implemented with the integrated multi‐satellite retrievals for global precipitation measurement (IMERG) dataset at 0.1° resolution to identify thunderstorms for 2001–2021. The 93rd percentile appears to be better for thunderstorm detection, with a success ratio of 82% (642 events are confirmed out of 786 detected) in eastern India. Further analysis indicated that 84% of the detected thunderstorms in eastern and northeastern India are associated with lightning activity. Based on this long‐term (2001–2021) thunderstorm data, the highest frequency of thunderstorms (40–45 events·year−1) is observed over the western foothills of the Himalayas, the northeast region, and the west coast of Kerala. The thunderstorm duration in the eastern and northeastern regions and the southwest coast of India is mostly 0.5–2.5 h, producing heavy rainfall (>7 mm·h−1) due to more moisture content and stronger updrafts. The composite structure of thermodynamic indices exhibits significant spatial variations over India and can be used to differentiate the regions of high thunderstorm activity. The minimum (maximum) convective available potential energy (convective inhibition) value required for thunderstorm development is not uniform throughout the country. However, the composites of K index and total totals index during thunderstorms are mostly uniform. This study highlights the benefits of IMERG rainfall in thunderstorm detection over India and helps to understand the local forcings and the effect of thunderstorm activity on different sectors like aviation, agriculture and so forth.

Contribution to the study of thunderstorms in the Congo Basin: Analysis of periods with intense activity

Lightning activity, storm structures, meteorological and environmental conditions are analyzed within a large area of Central Africa (25° × 25°) for two periods of one month (March and December) with high thunderstorm activity in 2013. The lightning flashes issued from WorldWide Lightning Location Network (WWLLN) allow to contribute in highlighting some characteristics in agreement with the literature. Some new findings, that can be useful for future storm monitoring thanks to lightning data issued from the Lightning Imager (LI) onboard Meteosat Third Generation (MTG), have been noted and have to be confirmed with more case studies. Thus, a seasonal correlation is found between the daily flash number and the extent of large CAPE values. The lightning flash density exhibits the same location of its maximum, for December and March with about 3 and 2 flashes km−2, respectively. This location is also reported in the literature for the annual activity in the study area. The storm developments often occur in the regions that combine the presence of lakes and mountains. The flash clusters allow to localize the strong convective activity and to follow the displacement of the storm systems when they move. The flash rate density (FRD) is larger in the convective systems well organized, as the typical MCS, during the development of the storms and when several cells merge. The daily cycle shows a lightning flash rate maximum between 14:00 and 15:00 UT that precedes the maximum development of the storm by one hour. It also shows that the storms that occur within the region of the main maximum of lightning activity, are more frequent and produce larger values of FRD.

Probing vertical coupling effects of thunderstorms on lower ionosphere using GNSS data

Thunderstorm is a complex of electrical, optical, and acoustical phenomena that occurs in the troposphere layer and liberates a huge amount of energy, which diffuses the electric field, propagates atmospheric acoustic and gravity waves into the ionosphere, and changes the ionospheric parameters such as the electron density and ionospheric conductivity. In this paper, irregularities in the TEC, the activity of IGW and IAW, influenced by thunderstorm were investigated for July 2017. Our results show a direct relationship between increase in thunderstorm activities and the TEC irregularities. The average of irregularity amplitudes, under severe thunderstorm conditions was 1.3 times larger than calm conditions (non-lightning days). Further, ROTI average on high thunderstorm activity days was obtained 1.25 times larger in value, compared to calm conditions. Furthermore, the average of IGWs maximum amplitudes was 0.23 and 0.12 TECU for high and low thunderstorm activity days, respectively. Our statistical study showed clear effects of intense thunderstorms on the ionosphere, mostly with a roughly 1–2 h delay. It should be noted that solar activity and geomagnetic conditions were the same in all investigated days.

Global Technogenic Day- and Nightglows Detected onboard the Vernov Satellite in the Ultraviolet and Infrared Optical Spectral Ranges

The generation of transient and other optical phenomena in the Earth’s upper atmosphere under the action of electron fluxes and high- and low-frequency electromagnetic waves resulting from electromagnetic fields [1] has been studied onboard the small Vernov spacecraft (solar synchronous orbit, 98° inclination, altitude 640–830 km). On the night side at middle latitudes, the technogenic glow is shown to be observed along the preferential meridians whose distribution corresponds to the longitudes of the most powerful low-frequency radio stations [2]. The geographic distribution of this glow changes abruptly at the boundary between the day and night sides of the satellite orbit; on the day side, such meridians are not identified, while their geographic distribution in longitude is uniform. The boundaries of the geographic distribution of technogenic glow regions on the day side are unstable in latitude, their northern and southern boundaries are shifted at all latitudes from the North Pole to the South Pole. At middle and low latitudes, zones with random geographic coordinates, where the technogenic glow is completely absent, are observed in the distributions of signals along the meridians. When studying the flashes caused by discharges in the atmosphere, we showed that lightning flashes and transient luminous events at nighttime are observed mainly in equatorial regions, which coincide with zones of high thunderstorm activity. At daytime, flashes of light are recorded much more rarely, have a short duration, are observed most often in the Earth’s polar regions, including the winter periods, the power of their emission exceeds considerably the power of similar (in duration) short flashes observed at night.

Generation of Diffuse Jets and Runaway Electron Beams in Air, SF6, and Helium at Low Pressures

Nanosecond discharges in air, SF6, and helium at pressures of units–tens of Torr are studied. Spatial inhomogeneities of diffuse jets and autographs of runaway electron (RAE) beams are recorded in all three gases during a discharge in a nonuniform electric field. It is shown that diffuse jets change their shape and their lengths increase and change from pulse to pulse in the discharge gap as the pressure decreases; further, it is confirmed that the RAE beam amplitude increases as the gas pressure decreases. It is assumed that inhomogeneities observed in the diffuse jets and RAE beams can be associated with transient luminous events in the Earth’s atmosphere that have sizes of tens of kilometers and occur at high altitudes at low pressures under high thunderstorm activity.

Characteristics of the atmospheric electric field and correlation with CO2 at a rural site in southern Balkans

In the current work, 4 years of atmospheric electric field observations at a rural site near Xanthi, Greece, are presented for 2011–2014. The site is situated in an area with very high radon fluxes and high thunderstorm activity. The annual variation is consistent with that at other Northern Hemisphere continental stations, with maxima (minima) occurring during the cold (warm) months. The diurnal variation of the atmospheric electric field both for fair weather (FW) and all weather is found to exhibit a double-peak structure corresponding to local effects and global thunderstorm activity. Comparison with the Carnegie curve shows that nighttime hours and winter months are preferable for observing the Global Electric Circuit at the Xanthi site. Finally, it is shown that atmospheric CO2 measurements can be effectively utilized as a stratification proxy, indicating conditions of potential radon trapping, whereas CO2 was found to anticorrelate with the atmospheric electric field during such conditions.

Spatial and temporal variations of thunderstorm activities over Sri Lanka

Spatial and temporal variation of frequencies of thunderstorms over Sri Lanka using thunder day data is presented. A thunder day is simply a calendar day in which thunder is heard at least once at a given location. Two sets of data were collected and analyzed: annual totals for 10 climatological stations for a period of 50 years and monthly totals for 20 climatological stations for a period of 20 years. The average annual thunder days over Sri Lanka was found to be 76. Among the climatological stations considered, a high number of annual thunder days was recorded in Ratnapura (150 days/year), followed by Colombo (108 days/year) and Bandarawela (106 days/year). It appears that there are no widespread long-term increasing or decreasing trends in thunderstorm frequencies. However, Colombo, the capital of Sri Lanka which has over two million people shows an increasing trend of 0.8 thunder days per year. Although there is a high variability between stations reporting the number of thunder days, the overall pattern within a year is clear. Thunderstorm frequencies are high during two periods: March–May and September–November, which coincide with the first inter-monsoon and second inter-monsoon periods. Compared to the dry zone, the wet zone, especially the southwestern region, has high thunderstorm activity. There is a clear spatial difference in thunderstorm activities during the southwest and northeast monsoon seasons. During both these seasons, enhanced thunderstorm activities are reported on the leeward side of the mountain range. A slight reduction in the thunderstorm activities was found in the high elevation areas of the hill country compared to the surrounding areas. A lightning ground flash density map derived using annual thunder days is also presented.

Effects of thunderstorm activity in power spectra of the electric field in the near-surface atmosphere at Kamchatka

We have performed a spectral analysis of variations in the Ez component of a quasistatic electric field in the atmospheric surface layer in a wide band of internal gravity waves (from 5 min to 3 h) for quiet and seismically active conditions as well as high thunderstorm activity. Observational data of the field for September, 1999 and August–September, 2002, were used. It has been shown that, if there are no thunderstorms or earthquakes, the background spectrum includes oscillations with maxima at periods of T ∼ 1.8 and 1 h, 40, 30, 15, and 10–13 min. Their intensity in the range of periods of 0.5–3.0 h is two or more orders of magnitude higher than the intensity of maxima in the range of 5–30 min. Before earthquakes, with anomalies in diurnal variations of field intensity, there is a tendency of increased background spectrum at maxima noted there. In both ranges of oscillation periods, the spectral intensity increases by one to one and a half orders of magnitude. Under high thunderstorm activity, the variability is higher as compared to the spectra of earthquake precursors by both locations of maxima and their intensity. The intensity of maxima exceeds the maxima on the eve of earthquakes one to one and a half orders of magnitude in the range of periods 0.5–3.0 h and two and more orders of magnitude in the range of periods 5–30 min.

Lightning hazards and risks to humans: some case studies

There are a lot of scientific papers and information on the subject of lightning hazard to human beings—but the numerical risk assessments are rather sparse. This paper presents and discusses some propositions of the numerical risk estimation procedures for the following categories: • A lightning directly strikes a person (the hazard is real in regions of high thunderstorm activity, e.g. in the Mediterranean). • Contact potential and side flash (when a human stays close to conductor leading lightning current). Some examples on calculation results will also be given. The author's approach is to estimate the energy dissipated in a lightning stroke by analysing a circuit model by the physical geometry.

Investigating the possible association between thunderclouds and plasmaspheric ducts

It has been suggested that quasi‐electrostatic electric fields from thunderclouds might produce whistler ducts by driving plasma interchange of geomagnetic flux tubes. Using lightning activity as a proxy for the presence of electrified clouds, the relation between thunderclouds and duct number was investigated through the study of two periods of 10 days, that is from June 13–22, 1993, and August 6–15, 1993. Typical duct numbers observed using NAA transmissions (24.0 kHz, Cutler, Maine) received at Faraday during the nights of June and August 1993 were ∼ 7, while the maximum duct numbers were 9–12. Duct numbers dropped down to zero or near zero during the day. Times of increased duct number could not be clearly associated with increased thunderstorm activity in the duct footprint region. Duct numbers observed on the path from NLK (24.8 kHz, Seattle, Washington) to Dunedin, New Zealand, were also studied, where very low thunderstorm activity levels imply that thundercloud‐driven duct formation should not be significant. The typical nighttime peak was ∼ 5 at about 1000 UT (23 LT). The difference between duct numbers in areas with high thunderstorm activity and quiet areas might be thought to be due to thundercloud duct formation. However, the F region absorption on the NLK footprints at 1000UT (23 LT) in June was found to be equivalent to 0000 UT (20 LT) in June on the NAA duct footprints. The typical number of ducts observable on the NAA path at 0000 UT in June is ≈ 5, very similar to the number observed on NLK at 0930 UT. The results found in this study are consistent with the idea that ionospheric absorption is a significant influence on the number of ducts observed. It does not appear that quasi‐electronstatic fields from thunderclouds play a significant role in the formation of plasmaspheric whistler ducts. The similarity in quiet time midlatitude duct nuumbers at these two different locations suggest a globally consistent duct formation mechanism, such as the interchange of magnetospheric tubes of plasma induced by spatially varying electric fields in the E region.

Induced voltages on buried coaxial cable by direct lightning strokes

AbstractLarge numbers of failures occur in coaxial line repeaters which are located in areas subject to high thunderstorm activity. J. Kemp [3] has calculated the voltage induced in coaxial cables which undergo direct lightning strokes, but it has been found that the failure rate that occurs in actual installations may, in some cases, be as great as 100 times the failure rate calculated by Kemp's method. Transient phenomena are generally calculated by means of transforms using Heaviside's operational method, but in the case of transmission lines, because of the need to employ approximations, very significant errors can be introduced. In particular, many of the buried cables installed in recent years have metallic sheaths which are insulated from the earth and it has become necessary to take this fact into account to arrive at accurate results.Using line constants which take into account the skin effect, the induced voltage is here determined by numerical computation of the inverse Laplace transform and from this the failure rate is computed. The results are in almost perfect agreement with actual conditions. In addition, comparing the results obtained by this method with those obtained by the conventional method, we see that when the metallic sheath is insulated from earth the induced voltage becomes large because the lightning wave flowing into the metallic sheath is not attenuated very much and a high excitation voltage is therefore distributed over a long distance. Since this method permits quite complicated computations, it is expected that its application will facilitate development of suitable lightning protection methods.

Lightning Protection of Wind Turbines

Because many areas of favorable locations for wind turbines coincide with high thunderstorm activity, a lightning protection system for wind turbines is essential to prevent losses due to strikes. Damage can occur to blades, bearings, mechanical linkages, electrical equipment, power interconnections, and electronics. This paper discusses how often a wind turbine may receive a strike, what damages can be expected, and how protection can be provided.

ISS-b experimental results on global distributions of ionospheric parameters and thunderstorm activity

The experimental results obtained from the Ionosphere Sounding Satellite-b (ISS-b) launched in February 1978 are given with particular emphasis on the global distributions of the ionospheric parameters such as the ionospheric critical frequency (foF2), occurrence probability of the spread echoes, nighttime electron temperature and ionic constituents of the ambient plasma, and also of the thunderstorms detected by means of radio technique. The global maps of foF2 are obtained based on the topside sounding experiment, and comparison between the ISS-b results and CCIR model is discussed. The global maps of the occurrence probability of the spread echoes on the topside ionograms are obtained, and longitudinal variability in the occurrence of the equatorial spread echoes is discussed. The global maps of the nighttime electron temperature of the ambient plasma are obtained, and appearance of the temperature troughs near the magnetic equator is discussed. The geomagnetic vs local time distribution characteristics of the ionic constituents, H +, He + and O +, of the ambient plasma are investigated, and winter bulge in the daytime He + density is found. The global maps of the occurrence rate of the thunderstorms are obtained based on the radio noise measurement, and they indicate existence of peculiar regions of high thunderstorm activity.