واکاوی پراکنش و تغییرات زمانی –مکانی توفان‌های تندری در جنوب ایران در سه چرخه خورشیدی اخیر

ABSTRACT
Thunderstorms, one of the most common and characteristic phenomena of convective systems, can cause severe damage and psychological impacts on individuals. In this study, thunderstorm-related codes from synoptic meteorological stations with complete records during each solar cycle were extracted from the dataset of the Iranian Meteorological Organization over a 33-year statistical period, corresponding to solar cycles 22, 23, and 24 (1986–2018). The Inverse Distance Weighting (IDW) interpolation method was applied to illustrate the spatiotemporal variations of thunderstorms. The findings indicate that the frequency of thunderstorm events does not follow a regular pattern across solar cycles 22 to 24, with the highest occurrence observed during cycle 23. Overall, during the 33 years, 1997 recorded the highest number of thunderstorms, while the lowest occurred in 1990. In terms of spatial distribution, during the cold seasons, when Sudanese low-pressure systems are the dominant atmospheric pattern, the highest concentration of thunderstorm events was recorded at Bushehr station, with a decreasing trend toward the east and north. In contrast, the lowest frequencies were observed at Siri Island and Bandar Lengeh stations. The peak occurrences were reported in December and January, particularly at Bushehr during the cold months, whereas during summer, due to the influence of monsoon systems, a notable eastward shift in thunderstorm hotspots was evident, especially at Bandar Abbas, Lar, and Hajjiabad stations.
Extended Abstract
Introduction
Natural hazards claim thousands of lives worldwide each year, with a significant portion of these fatalities attributed to weather-related hazards. Thunderstorms, regional floods, and other severe weather events are examples of such hazards. Thunderstorms are localized, mesoscale weather systems that develop within a limited area of 20 to 50 kilometers and depend on the height of convective clouds. Rainfall associated with thunderstorms and accompanying weather systems, coupled with lightning, are complex and composite atmospheric phenomena. Due to their unique dynamic and structural characteristics, these events typically negatively impact the natural environment, infrastructure, civil structures, transportation systems, and social activities. With its topographic features, large-scale climate systems influencing the region, and access to moisture sources from the southern warm seas, Southern Iran is susceptible to thunderstorm formation. This study uses station data to analyze the spatial variations in thunderstorm frequency over three solar cycles (22, 23, and 24). The relationship between thunderstorm frequency and solar cycles is of particular interest, as variations in solar radiation can influence atmospheric and climatic processes. Analyzing these changes contributes to a better understanding of the temporal and spatial patterns of thunderstorm occurrences and identifying high-risk areas. Moreover, these studies can provide a solid foundation for disaster risk management planning and more accurate weather forecasts in affected regions.
 
Methodology
For this study, data on thunderstorm occurrences was collected from 24-hour observational reports provided by the Iranian Meteorological Organization, covering a long-term period from 1986 to 2018. The study period was specifically selected to align with three 11-year solar cycles (Cycles 22, 23, and 24). This long-term and comprehensive dataset allows for examining the potential impacts of solar cycle variations on thunderstorm occurrence and intensity. Solar Cycle 22 spans from 1986 to 1996, Cycle 23 from 1997 to 2007, and Cycle 24 from 2008 to 2018. Therefore, in addition to analyzing the temporal and spatial variations of thunderstorms within each solar cycle, this research also compares these variations across different cycles. In the next step, the data obtained from the Iranian Meteorological Organization's database was organized and sorted in Excel based on stations and corresponding regions. For more accurate analysis, days with recorded thunderstorm occurrences in 6-hourly observational reports were extracted for each station and month of the year. Subsequently, the frequency of thunderstorm occurrences was calculated for each year within the 33-year study period (1986-2018). The Inverse Distance Weighting (IDW) method was employed to analyze and visualize the spatiotemporal variations of thunderstorms. This analysis was conducted on a monthly average basis for each solar cycle. In this phase, thunderstorm data and the stations' geographical coordinates were entered into ArcMap software. Subsequently, using the IDW method, spatial distribution maps of the data were generated, and the resulting outputs were prepared for spatial analysis and the examination of spatiotemporal patterns.
 
Results and discussion
The primary findings of this research can be summarized as follows. In terms of temporal distribution, the frequency of thunderstorm occurrences did not follow a consistent pattern from Solar Cycle 22 to 24. Solar Cycle 23 exhibited the highest frequency of thunderstorms compared to the preceding and succeeding cycles. The analysis of temporal distribution revealed that the highest number of occurrences was reported during the years of Solar Cycle 24, indicating a significant influence of solar activity on this phenomenon. For instance, within this cycle, the peak frequency was recorded in 2009 (the beginning of the cycle), while the lowest was in 2016 (towards the end of the cycle). Overall, during the 33-year study period, the highest number of thunderstorms occurred in 1997 and the lowest in 1990.
In terms of monthly distribution, the highest frequency of thunderstorms was observed in December and January, while the lowest occurred in September. Regarding spatial distribution, the thunderstorm hotspot was located over the Bushehr station during colder months when Sudanese systems dominate. This hotspot exhibited a decreasing trend towards the east and north. Another hotspot was observed over Bandar Abbas and Shiraz stations in February and April. The spatial distribution pattern in the early spring months resembled that of the cold months. However, in the final month of spring and throughout summer, the spatial pattern of thunderstorm occurrences changed significantly, with hotspots shifting eastward to stations such as Lar and Bandar Abbas. This phenomenon indicates the undeniable impact of topographic conditions on the intensification of incoming systems over the region.
 
Conclusion
Due to their unique dynamic and structural characteristics, thunderstorms cause widespread devastation to the environment, infrastructure, transportation systems, and social activities. Beyond inducing psychological distress among affected populations, these phenomena pose significant challenges to aviation and maritime operations. Neglecting the impacts of thunderstorms can lead to fatal accidents for passengers, pilots, and crew members of both air and sea vessels. With its distinctive topography, influence of large-scale climate systems, and proximity to the warm southern seas, Southern Iran provides a conducive environment for thunderstorm formation. The findings of this study reveal that November experiences the highest frequency of reported thunderstorms in Southern Iran. Bushher Airport meteorological station records the most frequent occurrences during this month and is identified as one of the primary entry points for storm systems from the southwest into the country's coastline. Furthermore, an increase in thunderstorm activity is observed around Bandar Abbas in March. Results indicate that the peak thunderstorm activity in Southern Iran occurs during the autumn season, although significant activity is also recorded in spring. Nevertheless, thunderstorms can occur throughout the year. A detailed analysis of monthly and seasonal frequencies reveals that May, April, June, and October exhibit the highest occurrence rates.
 
Funding
There is no funding support.
 
Authors’ Contribution
All of the authors approved the content of the manuscript and agreed on all aspects of the work.
 
Conflict of Interest
Authors declared no conflict of interest.
 
Acknowledgments
We are grateful to all the scientific consultants of this paper.