Sunil Dnyandeo Pawar

Thunderstorms drive the separation and redistribution of electric charge, generating intense intracloud and cloud-to-ground lightning and rapidly varying electric fields. Conventional surface electric-field and lightning measurements provide only indirect or localized information on a storm’s three-dimensional electrical structure. Cosmic-ray muons, which penetrate convective cores and are deflected by in-cloud electric fields, offer an independent probe through thunderstorm-induced muon events (TIMEs). Here we investigate a well-defined TIME observed during an intense thunderstorm over southern India on 27 April 2020, using muon measurements from the GRAPES-3 telescope combined with surface electric-field observations, lightning locations, INSAT-3DR infrared brightness temperatures, ERA5 reanalysis and high-resolution WRF simulations. Electrical activity began near 15:30 IST and intensified around 16:00 IST, while intracloud flash counts peaked near 16:30 IST and exceeded 400 flashes per 10 min. ERA5 profiles show mixed-phase condensate increased from 0.026 to 0.283 g kg⁻¹, with liquid water and ice coexisting in the mixed-phase layer. WRF simulations capture the observed development between 15:30 and 17:30 IST and show enhanced graupel and supercooled liquid water during the strongest lightning. These observations indicate that the TIME occurred during rapid convective growth with a well-developed mixed-phase region, supporting the use of muon observations as a complementary diagnostic of thunderstorm electrification.

Thunderstorms and lightning are the deadliest natural disasters in the Indian subcontinent. A better understanding of the regional and seasonal features of thunderstorm occurrences can provide valuable information on mitigating hazards in the region. The study demonstrated an improved method of understanding thunderstorm occurrences and thunder day (TD), an essential climate variable over the Indian region, using the total lightning data sets from the last 5 years. Total lightning data sets are used to find the Lightning flash rate density (FRD) in 0.05° grid resolution. Total lightning data are used to calculate TD, with the condition that a grid is considered to have a TD if it records at least two lightning flashes ensuring that TD corresponds to grids covering an area of approximately 15 km radius. A simultaneous comparison of lightning FRD and TD distribution is done in annual, interannual, seasonal, and monthly time scales spatially and statistically. The results reveal that the maximum TD observes 130–150 days in a year over a few places, including North‐west Himalayan Jammu (Rajori), Southern peninsular Kerala (Kottayam), and north Odisha (Mayurbhanj). The north‐western Himalayan foothills show the maximum TD but not the maximum FRD. The maximum number of TD in the study surpassed all the previous studies made by the station data sets where maximum TD remains in the range of 120–130 days per year. The minimum occurrences of the TD (< 15 days) show over Ladakh, a few parts of Arunachal, and the Kutch Gujarat region. Eastern part of the Indian region observes the most intense and frequent thunderstorms in terms of the number of lightning flash discharges per thunder day.

During the Indian winter, the southerly propagation of cold air at middle and upper altitudes is caused by a trough in westerly jet streams due to the effect of Western Disturbances (WDs). Sometimes, this advection of cold and dry air above near‐surface moist and warm air can make the atmosphere conditionally unstable. Therefore, these WDs are associated with thunderstorm formation and lightning activity over northern India (north of 20° north); however, occasionally, the effect of WDs extends up to the entry point of southern India. The satellite and ground‐based observations of lightning over western India (15.5°–22°N, 72.5°–81°E) over two decades (1997–2023) observed a falling trend of winter lightning at the rate of −0.02 (LIS/OTD), and −0.06 (ILLN) flashes km⁻² year⁻¹, respectively. Our observation suggested that the majority of lightning and thunderstorm activity is primarily initiated by WDs during winter; however, the incursion of moisture from the surrounding oceans also plays a crucial role in producing severe weather and precipitation over the study region. Many researchers and our observations have shown a decreasing trend of WD frequencies and winter precipitation over the Indian region. This paper addresses important aspects of climate change as lightning activity and thunderstorm days decreased steadily over western India, suggesting the falling trend is possibly linked to the weakening and reduced frequency of WDs from 1997 to 2023. While global trends suggest increasing lightning with climate change, this study reveals a decreasing trend in lightning activity, highlighting the uneven regional impacts of climate change.

Lightning originates from electrical discharges driven by the non-inductive charging mechanism within thunderstorms. The charge separation in these regions is governed by the surrounding convective environment, storm dynamics, and microphysical processes, including updraft velocity and ice content, which intensify the storm's electric field. In recent decades, advances in understanding cloud microphysics, charge separation mechanisms, and thundercloud electrical structure have significantly improved lightning forecasting. The selection and tuning of parameterization schemes, particularly for microphysics (MP), cumulus (Cu), and lightning (LP) processes, play a critical role in enhancing model performance and accuracy. This study uses various parameterization schemes to evaluate the performance of the Weather Research and Forecasting (WRF) model in simulating lightning and thunderstorm events. A severe thunderstorm event on May 14, 2022, over eastern India (West Bengal and Jharkhand), which recorded a peak 30-minute flash count of ~8000 flashes observed by the Indian Lightning Location Network (ILLN) was simulated in the WRF model. A total of 57 combinations of MP, Cu, and LP schemes were tested, using three nested domains (27 km, 9 km, 3 km) and analyzed the output of the inner domain (3 km). Seven MP schemes (WSM-6, Goddard, Thompson, Milbrandt, Morrison, WDM-5, WDM-6), two Cu schemes (Kain-Fritsch, Multi Kain-Fritsch), and two LP schemes (LP1: vertical velocity-based; LP2: 20 dBZ reflectivity-based) were assessed. Results show better performance of LP2 over LP1 with higher correlation and lower standard deviation with the observed flash counts. For cumulus parameterization, Kain-Fritsch (KF) turned off for the inner domain, and achieved strong performance (correlation: 0.75–0.95) with lower RMSE and standard deviation. Among MP schemes, Morrison, Goddard, and WDM-6 consistently performed well across different combinations. The best-performing simulations included Goddard (LP2, KF on), Morrison (LP2, KF on), WDM-6 (LP2, KF off), and WDM-5 (LP2, KF on), achieving correlations of 0.94, 0.93, 0.91, and 0.91 with observed flash counts, respectively. This study underscores the WRF model's capability in simulating lightning activity with optimal parameterization combinations, particularly LP2 and KF schemes. These findings provide promising results for real-time lightning forecasting, aiding in mitigating lightning-related hazards.

With future global warming projections, how lightning activity changes in the warmer world is still a debated and challenging question. During the Indian pre‐monsoon season (March–May), land surface heating and moisture availability due to prevailing winds from the neighbouring oceans provide favourable conditions for thunderstorm formation. Based on 24 years of lightning data from 2000 to 2023 detected by Lightning Imaging Sensor/Optical Transient Detector (LIS/OTD) and Indian Lightning Location Network (ILLN), the trend of lightning flashes over western India (15°–22°N, 72.5°–81°E) has been investigated. Our results demonstrate a steady decline in lightning activity during the pre‐monsoon season over western India, which contradicts the previous studies suggesting an increasing lightning trend over the Indian Subcontinent and other parts of the world. Our analysis has shown a falling trend of lightning activity at a rate of −0.066 flashes·km⁻² year⁻¹ from 2000 to 2013 (LIS/OTD) and −0.14 M flashes·year⁻¹ from 2014 to 2023 (ILLN). Our observation and previous research strongly suggested that the pressure difference between the land and the neighbouring oceans during pre‐monsoon and monsoon has been weakening for a long time over the Indian region, and we have found a consistent reduction in wind speed over the study region. Here, we propose that the enhanced Indian Ocean warming potentially weakens the land–sea thermal contrast and, thereby, reduces the horizontal pressure gradient. Further, the decreasing trend in the land–sea horizontal pressure gradient resulted in a declining rate of wind speed over western India, affecting moisture transport over land. Thus, the study emphasizes the impact of the decreased land–sea horizontal pressure gradient on declining lighting activity in western India.

Lightning flash rate data measured by the Tropical Rainfall Measuring Mission (TRMM) for the period 1996–2013 over India are analysed to study the spatial and temporal variation of lightning over India during different seasons. The convective available potential energy (CAPE) and other thermodynamic parameters data for the same period are taken for analysis. This study confirms a systematic increase in lightning flash rate density in India during the last two decades. The annual lightning flash rate density is high along the windward side of the Himalayan foothills with two peaks, one over northwestern parts of India (>50 flashes·km⁻²·year⁻¹) and the other over northeastern parts of India (>40 flashes·km⁻²·year⁻¹). The pre‐monsoon (March–May) (0.176 flasheskm⁻²·year⁻¹) and monsoon (June–September) (0.159 flashes·km⁻²·year⁻¹) lightning trends are the largest contributors in explaining the annual trend of 0.099 flashes·km⁻²·year⁻¹. All seasons have shown more or less positive trends while post‐monsoon (October–December) has shown a negative trend (−0.013 flashes·km⁻²·year⁻¹). The seasonal variations show that the lightning is increasing more over northwest India during the monsoon and northeast India during the pre‐monsoon. To further understand the connection between lightning and climate change, a few thermodynamic or microphysical properties are also analysed. This analysis suggests that the high CAPE values together with thermodynamics and cloud microphysical processes are necessary for organized convection and lightning over this region. Additionally, correlation analysis is adopted to identify the main influencing factors and regions contributing to lightning variability. The increase in lightning activity is found to be due to an increase in CAPE, low‐level moisture content and temperature. The increase in temperature and moisture is attributed to the land use land cover (LULC) changes in India. The impact of the above proxies on lightning varies from region to region and season to season. As several regions are undergoing rapid transformation due to human activity, this study provides insights into the need to understand land use related changes to local and regional lightning activity.

Four years of Indian Institute of Tropical Meteorology lightning location network lightning observation data are used to determine the seasonal and spatial (over different geographical locations) distribution of the ratio of intra‐cloud (IC) lightning to cloud‐to‐ground (CG) lightning in thunderstorms over the Indian subcontinent. The ratio is high (6–10) in the northwestern parts and low (0.5–3.5) in the northeastern parts. No prominent latitudinal variation of the IC to CG ratio exists, but a climatological seasonal variability exists over all regions. In the pre‐monsoon season (March–May), the mean ratio is observed to be 3.81 with a standard deviation of 0.79, and during the monsoon season (June–September), a value of 3.04 with a standard deviation of 0.50. Although convective available potential energy is the regulating factor, little dependency has been found between the ratio of IC to CG lightning (IC:CG ratio) and the total flash rate (f), as well as with cold cloud depths. The ratio is observed to be proportional to the total flash rate as f^0.61. The cold cloud depth is most prominently linked with the regional and seasonal IC:CG ratio. The implication of these observed results has the importance of separating CG lightning flash from total and can be used in numerical models to give a proper prediction of CG lightning in hazard mitigation.

Atmospheric electricity parameters (AEP) measurements from Antarctica predominantly feature either the potential gradient (PG) and/or air‐Earth current (AEC) density. We report for the first time simultaneous measurements of the bipolar ions concentration/conductivity, PG, and AEC density. AEP measurements were carried out at Maitri (70.8°S, 11.8°E) from December 2018 to November 2019. We formulated a few criteria, irrespective of the weather conditions, to select the electrically quiet days and some additional criteria based on the conductivity measurements to discern globally representative data (GRD) from such days. The measurements of the PG and AEC density over the Antarctic plateau demonstrated the diurnal curves similar to the Carnegie pattern, which represents the global thunderstorms and electrified shower clouds (ESCs) occurring on different continents and oceans, we regard the data having such trend as GRD. We found significant variability in the concentration of small bipolar ions/conductivity in the austral summer which in turn affects GRD. However, the concentration of bipolar ions is nearly consistent at ∼250 negative ions cm⁻³ and ∼300 positive ions cm⁻³ in winter and enhances the probability of GRD. Such differences can arise out of the prevalent planetary boundary layer processes in the two seasons. When the PG varied between ∼50 Vm⁻¹ and ∼150 Vm⁻¹ and the maximum range of conductivity variations was ∼0.2 × 10⁻¹⁴ ℧ m⁻¹, the AEPs represented the signatures of the global thunderstorm and ESC activities.