The Indian Lightning Location Network (ILLN), established by the Indian Institute of Tropical Meteorology (IITM), provides a comprehensive framework for investigating lightning phenomena, thunderstorm dynamics, and associated nowcasting/forecasting methodologies. ILLN is a ground-based lightning location system operating in VLF/LF/HF radio frequency bands, facilitating effective nationwide lightning mitigation strategies. The detection accuracy of ILLN was thoroughly evaluated using a comprehensive approach, including ground-based observations with electric field mills (EFMs) and C-band polarimetric radar, alongside satellite data from the Global Precipitation Measurement (GPM) mission and the ISS Lightning Imaging Sensor (LIS). The findings reveal that the ILLN exhibits a Relative Detection Efficiency (RDE) of 67.6 % in Pune, 69.4 % in Kohima, and 64.9 % in Rampurhat compared to electric field mill observations, closely aligned during high lightning activity during significant numbers of electric field changes. The average RDE for ILLN with reference to EFM is approximately 60 %, with lower values potentially due to a predominance of intra-cloud (IC) lightning. Lightning flashes detected by ILLN are primarily located within high reflectivity areas detected by GPM and ground radar, concentrated in regions exceeding 30 dBZ. Spatial RDE values concerning ISS ranged from 43 % to 97 %, with quartiles between 55 % and 84 % and median values between 67 % and 85 % across different cases, indicating occasional lower detection of IC lightning by ISS compared to ILLN. Factors such as IC:CG ratios may impact ISSLIS detection, influencing discrepancies in the spatial pattern between ILLN and ISS over Northwest and Eastern regions. Despite minor regional differences, the overall alignment between ISS and ILLN lightning detections is close. These findings underscore the challenges and reliability of lightning detection methods, highlighting ILLN's consistent performance across diverse scenarios. The network's robust detection efficiency reinforces its utility for diverse applications, serving as a pivotal data source for esteemed organizations like the India Meteorological Department and national and state disaster management authorities. ILLN's widespread implementation significantly contributes to mitigating the adverse impact of lightning-induced incidents.

Many studies have shown that aerosols can influence microphysical processes inside thunderclouds that could affect charge-generation processes. Cloud to Ground (CG) lightning data from Ground-based observations (IITM-LLN) over the State of Maharashtra, India, from 2014 to 2023, have been analyzed here to study the percentage and physical mechanism associated with the enhancement of catastrophic Positive CG in total CG lightning. Our analysis shows that the average positive CG percentage remains above 25% during the monsoon (July-September) and post-monsoon (October-November). This increased percentage of positive CG is attributed to elevated dust aerosol concentration over the study region during the monsoon and post-monsoon periods. An enormous amount of dust can be seen during the Indian Summer Monsoon (ISM) over the Arabian Desert and neighborhood extending up to the western Indian (Maharashtra) region. Dust aerosol intrusion into the thunderstorm acts as Ice nuclei (IN) as well as Cloud Condensation Nuclei (CCN) and can influence charge separation processes inside the cloud. In recent years, we observed an enhancement of Dust AOT over Maharashtra state, indicating that the increasing trend in Positive CG lightning is closely linked to the transport of desert dust from the Middle East and elevated aerosol content during the post-monsoon season. Here, we propose that these high concentrations of dust aerosols near the cloud base acting as IN produce a high concentration of ice crystals in the lower portion of the cloud, which can form a strong positive charge region in the lower part of the mixed-phase region by non-inductive charging mechanism. This strong positive charge region in the lower portion of the mixed phase region may be responsible for the observed increased percentage of positive CG over the study region.

The impacts of the COVID-19 lockdown on thunderstorm properties, influenced by changes in air quality, were investigated in Northeastern (Kohima, 25.66 degrees N, 94.08 degrees E) and Eastern (Rampurhat, 24.17 degrees N, 87.78 degrees E) India using seven years of ground-based observations. During the lockdown period (LP), Cloud-to-ground (CG) flashes decreased by 67 % and 51 % over Kohima and Rampurhat respectively. Reductions were noted in the number of thunderstorms and various intensity parameters such as duration, flashes per thunderstorm, Peak Flash Rate (PFR), IC: CG ratio, and lightning peak currents. Significant changes in anthropogenic aerosols were observed, with notable reductions in SOS, NOS, and PM,0 levels. Regardless of the specific raindrop formation mechanism in the two regions, higher concentrations of moderate to larger raindrops were observed during LP. Also, the mixedphase region of thunderstorms shows a reduction in water content (both liquid and ice) in the mixed phase and the total column. Daily-scale analysis reveals non-linear associations between pollutant concentrations and CG flashes in both regions, with relative humidity (RH) potentially influencing these relationships. Overall, thunderstorm intensity parameters, mixed-phase processes, and rain DSDs were associated with reduced pollutant concentrations during LP. The similarity of trends in multiple parameters during PLP-LP-ALP aligns with established facts, affirming that reduced pollutants lead to noticeable changes in thunderstorm characteristics. The partial rebound of pollutants and other parameters during ALP remained below pre-lockdown levels, which might suggest the lasting impacts of reduced human activities on atmospheric conditions. Further research is necessary to confirm if these measures could mitigate climatic changes and potentially guide policymakers in addressing such changes.

This study investigates premonsoon (April) thundercloud properties over Northeastern (Kohima, 25.6 degrees N, 94.1 degrees E) and Eastern (Rampurhat, 24.2 degrees N, 87.8 degrees E) India. Thunderclouds were detected using Electric Field Mills (EFM100) and Lightning Detectors (LD-350), while the WRF model was employed to simulate thundercloud properties. Simulations were performed across all 30 days in each region, regardless of actual thundercloud occurrence, to assess the model's accuracy in differentiating thundercloud and non-thundercloud days. The regional variability of cloud-to-ground (CG) flash density was well represented by the model, with higher flash densities in Rampurhat (mean: 39 x 10-4 km- 2 h- 1) compared to Kohima (mean: 31 x 10-4 km- 2 h- 1), consistent with observations. However, the model exhibited a slight overestimation in Kohima and an underestimation in Rampurhat, with spatiotemporal deviations from observations in both regions. Despite this, the simulations effectively captured regional differences in dynamical parameters (vertical velocity, wind shear) and microphysical properties (mixing ratios: qice, qgraupel, qcloud), with Rampurhat showing higher values overall. Six stability indices were evaluated to determine the most reliable indicator for distinguishing thundercloud/nonthundercloud days. In Kohima, the TT index (>= 38 degrees C) was most effective, while in Rampurhat, CAPE (>= 1680 J kg- 1) proved more suitable, suggesting that distinct physical mechanisms drive thundercloud development in these regions. The dichotomous detection results for all 30 days in Kohima (Rampurhat) yielded 14 (21) successful detections, 5 (1) misses, 3 (1) false alarms, and 8 (7) correct rejections. We introduced the Correct Rejection Rate (CRR) to assess the model's performance in detecting non-thundercloud days, which showed better accuracy over Rampurhat than Kohima. The study underscores the heightened complexity of predicting thunderclouds over the hilly terrain of Northeastern India compared to the flatter terrain of Eastern India and offers valuable insights for improving strategies to mitigate lightning hazards.

A detailed study of cloud-to-ground (CG) and intra-cloud (IC) lightning over southern India was conducted using new high-resolution gridded data generated from the IITM Lightning Location Network in southern India (8°–13.6°N and 74.5°–80.5°E) during 2019–2021 period. More than 5.3 million lightning strikes were observed during the period in the region. Peak CG activity is seen in a lightning hotspot located in the midland and foothills of the Western Ghats in Kerala and another CG peak is seen over the Kochi coastal belt (75.8°–76.2°E and 9.7°–10.4°N) in the Lakshadweep Sea. Our study shows that peak lightning currents during the pre-monsoon (March–May) season are mainly positive, whereas most of the currents were negative in the post-monsoon (October–December) season. This shows that the storm charge structures are different in both lightning seasons. Diurnal changes indicate that the lightning in the southern lightning hotspot region is primarily influenced by solar heating and the lightning activity peaking at 15–18 hours (local time). Higher IC activity is associated with pre-monsoon taller tropical cumulonimbus clouds (Cb), and IC activity peaks at altitudes between 10 and 18 km. It is observed that the average lightning activity duration (first to last strike) is 1.8 hours in the lightning hotspot region. Analysis of CG controlling factors shows that, over land regions, strong connections are observed with lightning and thermodynamic parameters like convective available potential energy (CAPE). However, convective inhibition (CIN) shows a weak positive correlation with lightning over oceanic regions. Also, a significant correlation (0.01 level) was observed between sensible heat flux in the lightning hotspot and coastal regions. In addition, aerosol optical depth (AOD) shows a significant correlation with lightning over the central region in southern India.

Lightning studies are highly focused on spatial and temporal variability in various scales but very limited studies are focused on dominant spatial modes of variability. This study intends to identify the possible spatial modes of climate variability of lightning over India during different seasons and relate them to regional and large-scale climate modes. Empirical orthogonal function analysis of lightning has been carried out and the first three orthogonally independent modes are considered in order to retrieve the maximum variance explained by each mode. To understand the role of remote and local teleconnections on the lightning flash rate (LFR) variability, we have analyzed two Pacific Ocean modes (El Nino Southern Oscillation; ENSO, Pacific Decadal Oscillation; PDO) and two Indian Ocean modes (Indian Ocean Dipole; IOD and Bay of Bengal (BOB) meridional Sea Surface Temperature (SST) gradient). First mode is positively correlated with the warm phase of ENSO and PDO whereas second and third modes are negatively correlated with the warm phase of ENSO and PDO during pre-monsoon, post-monsoon and winter. Reverse is true for the monsoon season due to the shift in walker cell caused by the changes in the location of the heat sources and sinks. A strong positive correlation of IOD and BOB meridional SST gradient with first mode, suggests the vital role of nearby Indian Ocean in explaining the typical lightning flashes over India due to the enhanced zonal and meridional circulation, thereby moisture supply to the Indian subcontinent. The impact of Nino-3.4, IOD and BOB meridional SST gradient on lightning over India further suggest the role of SST in local and remote influence on lightning variability through the distribution and transport of heat and moisture.

The impact of a severe dust storm that originated over the Arabian Peninsula (AP) and travelled to the Indian subcontinent during 20-26 January 2022 is examined. According to the event's synoptic analysis, the Gulf of Oman, adjacent areas of Oman and Iran had strong mid-lower tropospheric westerlies because of the configuration of north-south cyclonic and anticyclonic circulation patterns generated by a sizable north-south pressure gradient. A strong westerly wind component continued down to surface level and brought large quantities of dust from the desert region of the Middle East to the Indian subcontinent. Overall, 90% of the monitoring locations over the Indian subcontinent (mostly the western region) exceeded the national tolerable level of 100 mu g m(-3) (PM10), with peaks as high as 650 mu g m(-3). Changes in optical and physical properties of aerosols varied in accordance with the dust loading, in which absorption aerosol optical depth denotes a 10% increase in absorbing aerosols. Due to the excessive cooling effect, the near-surface air temperature dropped by -6 degrees C from its daily climatology over a sizable zone of high aerosol loading. Additionally, the dust storm prolonged the winter's harshness by lowering temperatures (from pre-dust days) in some of the most severely afflicted areas to 10-12 degrees C. Changes in wind patterns at mid- and low levels have resulted in a temperature inversion (similar to 2.5 km), which prevented trapped dust particles from being diluted, which in turn increased the likelihood of a more significant decline in air quality and affecting human health/wealth.

Lightning is known for its meteorological importance and associated hazard potential. It is known that the polarity of cloud-to-ground flash (CG) can act as a prognosis of the storm's characteristics. Ground-based observation of lightning over the Indian region suggests that during the break period in the summer monsoon seasons, CG lightning of positive polarity increases dramatically relative to the pre-monsoon days. Here we propose that for thunderstorms forming in the wet season, the non-inductive charge separation happens in the presence of larger mean cloud liquid water in the mixed phase region of the storms. This facilitates the positive charging of graupel particles, thereby producing a large amount of positive CG lightning on these days. This observation is found to be consistent with the laboratory results of Takahashi (1978). The implication of these results has been discussed from the perspective of hazard mitigation associated with positive lightning over India.

Association of lightning with Lifting Condensation Level (LCL), Equilibrium Level (EL), K Index, and humidity at 850 mb and 200 mb in 2019 and 2020 over National Capital Region (Delhi) (Lat: 27°N -29°N, Lon: 76°E-78°E) is investigated using in-situ observation data. Study shows high lightning activity during low LCL, and vice versa. This high lighting and low LCL is associated with high relative humidity at 850 mb, and high "K" index. Low LCL and high relative humidity (low dew point depression) at 850 mb helps in generating super cell thunderstorms with spinning/tornado updraft. It is seen that asymmetric LCL height and relative humidity at 850 mb is the prime causes for uneven seasonal lightning in 2019 and 2020 over the region, despite more or less same seasonal aerosol and relative humidity. Anvil clouds behave uneven with time, despite, unanimous cloud top glaciation.

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 flasheskm(-2)year(-1)) and the other over northeastern parts of India (>40 flasheskm(-2)year(-1)). The pre-monsoon (March-May) (0.176 flasheskm(-2)year(-1)) and monsoon (June-September) (0.159 flasheskm(-2)year(-1)) lightning trends are the largest contributors in explaining the annual trend of 0.099 flasheskm(-2)year(-1). All seasons have shown more or less positive trends while post-monsoon (October-December) has shown a negative trend (-0.013 flasheskm(-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.

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 degrees-22 degrees N, 72.5 degrees-81 degrees 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 flasheskm-2 year-1 from 2000 to 2013 (LIS/OTD) and -0.14 M flashesyear-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. The enhanced Indian Ocean warming potentially weakens the land-sea thermal contrast and the horizontal pressure gradient, thereby reducing the wind speed. The decreasing trend in wind speed affects moisture transport over land, which has caused a falling trend in lighting activity in western India. image

The research probes into the seven agro climatic zones in Tamil Nadu which are highly vulnerable to lightning strikes, as well as the human fatalities caused by Cloud to Ground lightning. The purpose of the study is to find out the vulnerable hotspots and diurnal climatology of the Cloud to Ground lightning strikes during the northeast monsoon, southwest monsoon, and summer seasons. Heat maps are used for the lightning strikes using ArcGIS software and the diurnal climatology was performed by interpolating the data from the lightning location network into a 3-hour resolution. In vulnerability analysis, Northeastern zone is more prone to lightning during Southwest and Northeast Monsoon. On the other hand, High rainfall zone and Hilly zone are vulnerable to lightning in summer season. The Northeast monsoon has the highest lightning frequency ratio, followed by the summer. The maximum rate of strikes occurred between 10-15 hrs IST and showed a peak range between 10:00 to 12:00 hrs IST. A labor-intensive agricultural economy is linked to higher rates of lightning-related deaths and injuries. The results of this research could be useful in developing lightning climatology for the future climatic condition for Tamil Nadu.

Present work addressed the variability of lightning flash count and persistence of Convective Available Potential energy (CAPE) during onset-withdrawal and active-break phases of Indian southwest monsoon (ISM) over central India region for the period 2014–2019. We have observed that higher lightning activity is during the prior to onset phase (June) period as well withdrawal phase (September–October) of Indian southwest monsoon season. During the break phase (mid-monsoon months, July and August), the monsoon trough shifts northwards; as a result, lightning activity does not cease totally and some lightning activity is still observed over study region. It is noticed that position of monsoon trough play an important role in the lightning activity and CAPE. The analysis clearly suggests high CAPE is a necessary condition for formation of thunderstorms during ISM period (June to September). From the station based CAPE data, it is seen that lightning activity is higher at a station Nagpur (close to the monsoon trough region) compared to a station Hyderabad (far away from monsoon trough). Further, the monsoon trough region remains conditionally unstable which generates lightning producing storms over the study region during monsoon season. Observations suggest that when monsoon trough is strong, entrainment of cold and dry air in the lower level from north of monsoon trough interact with warm and moist air from south of monsoon trough and can make the atmosphere conditionally unstable that helps in formation of thunderstorms over the study region during ISM.

Abstract 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 f0.61. 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.

Lightning strikes are a well-known danger, and are a leading cause of accidental fatality worldwide. Unfortunately, lightning hazards seldom make headlines in international media coverage because of their infrequency and the low number of casualties each incidence. According to readings from the TRMM LIS lightning sensor, thunderstorms are more common in the tropics while being extremely rare in the polar regions. To improve the precision of lightning forecasts, we develop a technique similar to LightNet's, with one key modification. We didn't just base our model off the results of preliminary numerical simulations; we also factored in the observed fields' time-dependent development. The effectiveness of the lightning forecast rose dramatically once this adjustment was made. The model was tested in a case study during a thunderstorm. Using lightning parameterization in the WRF model simulation, we compared the simulated fields. As the first of its type, this research has the potential to set the bar for how regional lightning predictions are conducted in the future because of its data-driven approach. In addition, we have built a cloud-based lightning forecast system based on Google Earth Engine. With this setup, lightning forecasts over West India may be made in real time, giving critically important information for the area.

A study of the radar characteristics of thunderclouds in India for the monsoon and post-monsoon seasons was carried out, separately for the cloud-to-ground and cloud-to-cloud discharges. It is shown that almost all the considered characteristics (cloud top height, precipitation flux and precipitation rate, maximum radar reflectivity, etc.) increase during the post-monsoon period. A feature of monsoon clouds is low electrical activity, which is confirmed by the results of the study. The characteristics of clouds during the transition to the thunderstorm stage are considered, the most significant of them are identified.

Six cases of dust storms that occurred over the northwestern and northern parts of India have been studied here to understand the effect of dust on the lightning characteristics of these storms. Satellite pictures show high dust content on all six storm days, and ground station data show that visibility was reduced to less than 500 m. Lightning data observed by the lightning detection network indicate that these six cases of convective dust storms produced more than 30 percent of positive CG lightning in the total CG lighting, which is considered to be very high compared to ordinary thunderstorms. Further, analysis indicates that the current carried by positive lightning is much higher than negative lightning. In some cases, the lightning flash rate reached more than 200 flashes per min (fpm). Observation shows that all these thunderstorms were accompanied by dust, and hence, incursion of the abundance of dust particles into the cloud was likely to be very high. Many earlier observations have suggested that aerosols can affect thunderstorms' microphysical (such as vertical distribution of the hydrometers) and electrical characteristics. With the abundance of dust particles in the cloud and increased positive CG discharges, it has been proposed that increased dust particles can modify the vertical distribution of ice particles inside a thundercloud and affect the lightning flash rate as well as polarity.

Association of lightning with winds over Tibetan Plateau (TP) is examined by analyzing lightning data during the period 1999–2013. The study reveals that nearly 92% lightning activity occurred during April to September is associated with the wind circulation, especially cyclonic circulation. Nearly 58% of lightning is found to happen during May (18.6%), June (19.29%), and July (19.56%). Less vertical wind shear (less than 10 m/s) and high CAPE (more than 400 J/kg) are found to be associated with lightning. Analysis shows that negative correlation exists between wind shear and lightning. Results reveal that high wind shear tends to restrict the growth of convection, resulting in lightning. On annual scale, there exist negative correlation between lightning and wind shear and insignificant correlation between lightning and CAPE for April-September. However, a new relationship is established when CAPE and shear are taken together, and a strong positive correlation is found between lightning and CAPE per shear (CAPE/shear). Hence, we propose that for better understanding on lightning over Tibetan Plateau, it would be much more useful to consider CAPE/shear rather than CAPE or wind shear alone.

Three major sequential widespread dust events were experienced in the northern parts of India in May 2018. A significant impact of these pre-monsoon dust storms on the aerosol characteristics over the Indian National capital region (NCR) has been studied using remotely sensed ceilometer and ground-based measurements at Indira Gandhi International airport, New Delhi, India. The results show that after each dust activity, the significant inclusion of dust aerosols loaded in the free troposphere. Consequently, the direct impact on the lower atmospheric parameters like increase in daily average temperature (by 4–5 K), stepped up (stepped down) diurnal cycles of longwave fluxes (shortwave fluxes), has been recorded within 15 days of dust span. Mainly, the adverse meteorological and radiation features noticed before the first dust storm (DS1), which pinpoints the sudden dust intrusion over NCR, Delhi. However, this dust storm has extensively impacted on the atmospheric vertical dust loading, surface boundary layer mechanisms, and socioeconomic way. Therefore, the detailed analysis of vertical dust distribution and its interaction with mid-tropospheric processes has been carried by using the vertical normalized attenuated backscatter coefficients accompanying the radiosonde observation. The aloft floating dust layer up to 3–4 km has been noticed even after shallow rainfall and persisted at almost the same height for the next 34 h due to low-level clouds. Meanwhile, the sub-dust layer below 1 km is formed due to local activity, which also sustains for a long time.