Document Type : Research Article
Authors
1
Ph.D. Candidate in Climatology, University of Zanjan, Zanjan, Iran
2
Professor in Climatology, Department of Geography, University of Zanjan, Zanjan, Iran
3
Assistant Professor in Climatology, Department of Geography, University of Zanjan, Zanjan, Iran
10.22067/geoeh.2025.89265.1508
Abstract
Lightning is a significant atmospheric phenomenon characterized by the transfer and discharge of electricity between clouds and the Earth. This phenomenon poses risks to both humans and the environment, necessitating comprehensive examination of its climatological characteristics. This phenomenon, along with the transfer and discharge of electricity between the clouds and the ground, causes strong sound and light. Cloud formation begins at a height above the condensation level. Below the altitude with a temperature of zero degrees, water droplets form and ice crystals form above it. Water drops or ice crystals grow gradually and reach such a size that they finally descend with a speed of about 8 meters per second. If the speed of droplet descent is lower than the speed of cloud ascent, water droplets and ice crystals move up and down in the atmosphere and collide. This process continues until, first, the droplets and crystals become larger, and secondly, the negative electric charge in the droplets and crystals at the bottom of the cloud and the positive charge in the droplets and fine crystals at the top of the cloud condense. This study analyzes various statistical and geostatistical aspects of lightning frequency across Iran from 2000 to 2022, utilizing data from 382 synoptic stations. The investigation includes descriptive statistics, such as the mean and coefficient of variation of lightning events, as well as their correlation with geographic coordinates (latitude and longitude) and altitude. Regression analysis was employed to model these relationships. The findings indicate that the spatial distribution of lightning frequency in Iran operates as a stochastic process, exhibiting significant annual variability. Among the spatial variables considered, longitude and latitude demonstrated a relatively stronger correlation with annual lightning frequency in Iran.
Introduction
Lightning is a natural phenomenon, sometimes accompanied by danger, that takes the lives of more than two thousand people worldwide every year and occurs especially in regions with variable climates. This phenomenon, along with the transfer and discharge of electricity between clouds and the ground, has numerous consequences. This phenomenon has various effects on the environment and humans. For example, lightning can cause fires, financial losses and human lives when it strikes tall objects such as trees and buildings. This phenomenon ranks second among atmospheric hazards in terms of mortality. Lightning on Earth has shown a direct relationship with the Earth's climate, especially under the influence of temporal-spatial variations in solar radiation. The maximum global distribution of lightning occurrence is in the three tropical regions of the Americas, Africa and the oceans. About 78% of the occurrence of this phenomenon occurs between 30 degrees south latitude and 30 degrees north latitude of the Earth. Analysis of satellite data shows that the frequency of lightning is usually higher in tropical regions and areas with a more humid climate. Lightning events in coastal areas account for approximately 70% of all ocean lightning and occur more often on the east coasts of continents than on the west coasts. Therefore, the spatial distribution of lightning shows significant spatial variation. The maximum of lightning often occurs in the morning and afternoon and its minimum at night. The location of lightning occurrence also varies under the influence of different seasons. Monthly changes in lightning show that the highest lightning activity occurs in July. Studies conducted in different parts of the country showed that the phenomenon of lightning occurs with diverse temporal-spatial patterns. The northern regions of Khuzestan Province and the southern regions of Lorestan Province had the highest frequency of lightning, and the central and flat interior regions of the country had the lowest frequency of lightning.
Data and study method
Study area
The study area in this study is the mainland of Iran with an area of about 1648195 square kilometers within the following coordinates.
Data In this study
The frequency of lightning events between 2000 and 2022 was collected from 411 active synoptic stations throughout Iran. After reviewing the lightning data of the existing synoptic stations, a number of stations that did not have sufficient statistics were removed from the study process. After removing the aforementioned stations, 382 stations that had statistical competence were used as the basis for statistical analyses. Figure 1 shows the spatial distribution of these stations. In this study, the frequency of daily lightning events between 01/01/2000 and 12/31/2022 for 382 stations was extracted from the website of the Iranian Meteorological Organization (IRIMO: https://data.irimo.ir/withoutlogin/index.aspx). An examination of the altitudinal distribution of the stations (Table 1) showed that about 56 percent of the stations (212 stations) are located at an altitude of 500 to 2000 meters and about 3 percent of the stations are located in low-altitude areas, i.e. -22 to 0 meters. From an altitude of 2000 meters to high altitude areas (2500 to 3500 meters), the number of stations was reduced, so that there was only one station above an altitude of 3000 meters.
This study was conducted to investigate the long-term (climatic) frequency of lightning and its relationship with geographical coordinates (longitude, latitude) and altitude. To achieve this goal, some descriptive characteristics of lightning (including annual average and coefficient of variation) were first calculated and estimated, and the spatial distribution of these values was presented in maps.
Results and Discussion
General Characteristics
The maximum lightning occurrence occurred in the northwest of Iran. Precipitation in the northwest of Iran is mainly the result of convective activities, mountain ascent, and local fronts. This region also faces stronger temperature and pressure differences resulting from topographic contrasts. The annual average frequency of lightning occurrence in the southern regions of Iran with a hot and humid climate was almost close to the annual average frequency of lightning occurrence in the western regions. The annual average of lightning occurrence at the stations in the north of the country is relatively high. These areas have a temperate and humid climate, which provides favorable conditions for the occurrence of this phenomenon. The average coefficient of variation of the stations was about 25.5%. A coefficient of variation of less than 25.5 indicates an event with a stable average. If this value is more than 25.5, it indicates an irregularity in the occurrence of lightning from year to year and indicates its strong annual differences.
Probability analysis
The highest probability of occurrence corresponds to the high and mountainous areas of the Zagros and Alborz mountain ranges. Among the reasons for the highest probability of occurrence in this area can be attributed to factors such as the mountainous nature of the region, which is the place where numerous weather masses pass, and the inequality in the distribution of solar energy radiation on the sun-exposed slopes, which in turn leads to the formation of instability and the ascent of warm and humid air due to slope convection in some days of the year. The western half of Iran, and especially the northwestern region of Iran, is the place where various air masses, including westerly winds, Mediterranean cyclones, and short waves with them, pass into the country during the cold season, which provides conditions for instability and the occurrence of thunderstorms. After this area, the northern region of Iran also provides conditions for the occurrence of thunderstorms due to its access to the moisture of the Caspian Sea, its considerable altitudes, and the influence of this area on various weather masses, including the western migratory air mass on the one hand and the Siberian high pressure on the other. In addition to the aforementioned geographical areas, scattered areas of star_border.
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