نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه مهندسی آبیاری و آبادانی، دانشکده مهندسی و فناوری کشاورزی، پردیس کشاورزی و منابع طبیعی دانشگاه تهران
2 استادیار/گروه مهندسی آبیاری و آبادانی، دانشکده مهندسی و فناوری کشاورزی، پردیس کشاورزی و منابع طبیعی دانشگاه تهران
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
The climate is the result of interactions between the atmosphere and the oceans, manifesting in phenomena such as landslides, extreme events. This study investigates the effects of the Southern Oscillation Index on two key variables: precipitation and relative humidity, across 21 principal synoptic stations in Iran over a 30-year period. Utilizing factor analysis alongside twelve teleconnection indices, this research aims to elucidate the intricate relationships between these climatic factors. Based on the correlation matrix derived from the factor analysis, the eigenvalue magnitudes and the percentage of variance elucidate the extent to which various teleconnection indices influence the simultaneous assessment of atmospheric components. The analysis revealed that the Southern Oscillation Index (SOI) exerts a more pronounced effect compared to other indices. Data were evaluated as three-month averages during the rainfall season, specifically from October to June. Notably, several stations exhibited no significant correlation with the index. The highest correlation was observed at the Shiraz station, with a correlation coefficient of 58%. The climatic characteristics of this region, particularly in its southern areas, represent another significant finding of this research. Although this region is predominantly influenced by the Indian monsoon and Mediterranean currents, the Southern Oscillation Index—resulting from the pressure differences at sea level between Tahiti and Darwin in the eastern and northern Pacific Ocean—also exerts a substantial impact on the precipitation and relative humidity of the area. It is recommended to consider the importance of climate change and one of its manifestations, global warming, in future researches, are considered.
کلیدواژه‌ها [English]
The effects of teleconnection indices encompass a wide range of impacts, including their influence on the biogeochemical processes of vegetation. This involves employing various methodologies to investigate the relationships between precipitation and temperature in relation to these indices. Specific case studies have been conducted regarding precipitation variability across different regions of the country, such as Karaj. Furthermore, the analysis extends to the correlation between winter precipitation and teleconnection indices, the impacts of malaria mosquito pollution and its association with precipitation variables, as well as the El Niño-Southern Oscillation (ENSO) phenomenon and the Southern Oscillation Index (SOI). Additionally, the effects of teleconnections on both spatial and temporal humidity in various areas are examined, including the forecasting of winter precipitation along the Caspian Sea coast, particularly in relation to the SOI.
The values of the Southern Oscillation Index (SOI), averaged on a quarterly basis from October to June for the period 1990-2020, were obtained from the National Oceanic and Atmospheric Administration (NOAA) website (https://www.ncei.noaa.gov/access/monitoring/enso/soi). Additionally, temperature and precipitation data from synoptic stations across the country were sourced from the National Meteorological Organization. The climatic characteristics and specifications of the studied stations are presented in Table 1.
The sources of moisture, the mechanisms of moisture transport, and the factors influencing them across different seasons are critical aspects of precipitation and humidity in various regions of Iran. In this context, the role of teleconnection indices is particularly significant. Additionally, the influence of surrounding seas is undeniable. Among the stations examined, Shiraz exhibited the highest correlation with the Southern Oscillation, with a computed correlation of +58%. Located in southern Iran, Shiraz has a dry and semi-arid climate. Given its proximity to the Pacific Ocean, the effects of the Southern Oscillation are more pronounced in this region. The next station demonstrating the highest percentage of correlation with precipitation and relative humidity is Birjand, situated in northeastern Iran. Despite being predominantly influenced by Siberian cold currents and the Pacific Decadal Oscillation (PDO), the significant impact of the Southern Oscillation places this station second in terms of correlation.
Although the examination of the effects of teleconnection indices on components such as precipitation, temperature, and relative humidity significantly impacts various sectors, including agriculture, it is essential to acknowledge that this analysis possesses inherent complexities. In some instances, the results may be deemed unreliable due to the intricate nature of the climate and its interactions with the atmosphere and ocean, a phenomenon that is unavoidable given the dynamic nature of these systems.
In this study, the relationship between precipitation and relative humidity with the Southern Oscillation Index (SOI) was investigated. A total of 21 primary synoptic stations from different regions of the country were selected, and the quarterly averages of precipitation and relative humidity, along with the SOI, were analyzed from October to June. The impact of this index was evaluated concerning the occurrences of El Niño and La Niña phenomena at these synoptic stations, revealing that the highest correlation rates were reported from the Shiraz station, located in southern Iran.
In this region, the northern climate is mountainous, while the provincial center, the city of Shiraz, exhibits a Mediterranean to sub-Mediterranean climate. Conversely, its southern area is influenced by Indian monsoon currents, which are more pronounced in years when monsoonal activity exceeds normal levels. Given the extensive climatic diversity across Iran, many teleconnection indices exert direct and indirect effects on regional climates, manifesting even in stations with differing climatic characteristics.
Results varied notably along the western and eastern coasts of the Caspian Sea; for instance, on the eastern coast, particularly in the Golestan region, the correlation between precipitation and relative humidity with the Southern Oscillation was calculated at 38%, with mean squared error (MSE) and root mean squared error (RMSE) values of 58.6% and 88.23 millimeters, respectively. In contrast, the effects of the Southern Oscillation index on the western coast were less than 20%, largely attributed to the predominant influence of the North Atlantic Oscillation on the western Caspian shores compared to the eastern coast.
Data available on request from the author.
The research was supported by the University of Tehran. The authors would like to express their special thanks to the vice chancellor for research affairs. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
The author avoided data fabrication, falsification, plagiarism, and misconduct.
All authors declare that they have no conflict of interest.
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