Aerosol-Cloud-Lightning Interactions: A Comparative Study of Mountainous and Coastal Environments in Iran

Aerosols play a crucial role in influencing cloud microphysical processes, which subsequently impacts lightning activity by acting as cloud condensation nuclei. These tiny particles, suspended in the atmosphere, affect both the formation and properties of clouds, leading to variations in precipitation patterns and electrical activity. This study aims to deepen our understanding of these complex dynamics by analyzing extensive data sets related to lightning density, which were obtained from the Lightning Imaging Sensor (LIS). In addition to this, we incorporated cloud fraction, cloud-top height, ice cloud optical thickness, aerosol optical depth (AOD) data from the Moderate Resolution Imaging Spectroradiometer (MODIS), and Convective Available Potential Energy (CAPE) data sourced from the European Centre for Medium-Range Weather Forecasts Reanalysis (ERA5). The dataset encompasses the period from 2000 to 2014, focusing on two distinct environmental regions: Region 1 (R1) and Region 2 (R2). R1 is situated between 32.5°N and 34°N and 46°E and 48°E, characterized by mountainous terrain in western Iran. This region experiences three distinct climatic conditions: Mediterranean, cold mountainous, and warm semi-desert. These diverse climatic conditions create a unique environment for studying thunderstorm behavior. In contrast, R2, located between 27.5°N and 29°N and 50°E and 52°E, is predominantly flat, featuring a warm and dry climate in the northern part, which transitions to a humid, warm climate in the southern part. A detailed analysis of monthly variations reveals that lightning activity exhibits a strong correlation with AOD during spring and autumn, which suggests that aerosol loads may enhance thunderstorm development during these periods. However, during winter, this relationship diverges significantly, and in summer, a negative correlation is observed. The suppressed convective storm activity at high AOD values indicates that elevated aerosol levels can inhibit thunderstorm formation, leading to lower lightning occurrence. This finding emphasizes the dual role of aerosols in affecting weather patterns. Furthermore, the annual variation analysis indicates that R1 experiences a higher frequency of electrical activity compared to R2, likely attributed to the prevalence of sand and dust storms in the region. These storms contribute substantial amounts of aerosols to the atmosphere, facilitating cloud formation and electrical discharge. The study finds that AOD correlates moderately positively with lightning activity in both regions, influenced by diverse aerosol sources such as black carbon, dust, sea salt, and sulphate. Additionally, other cloud parameters—including cloud fraction, ice cloud optical thickness, and cloud-top height—demonstrate a consistent positive correlation with lightning density in both R1 and R2. Notably, the correlation between CAPE and lightning density is lower in R2, likely explained by higher humidity levels that stabilize the atmosphere, resulting in decreased occurrences of intense thunderstorms. In conclusion, this analysis underscores the complex interplay between aerosols and lightning activity, revealing significant regional variations driven by geographical and climatic factors. This research enhances our understanding of how atmospheric conditions, particularly in arid and semi-arid areas, influence thunderstorm behavior and lightning frequency. Moreover, future studies could build on these findings to examine their implications for climate modeling and weather prediction, especially in light of changing aerosol concentrations arising from human activities and natural phenomena. As such, this work lays the foundation for further exploration into how aerosol dynamics can inform our understanding of extreme weather patterns and their climatic impacts.