نوع مقاله : مقاله پژوهشی
نویسندگان
1 دانشجوی دکتری آب و هواشناسی، گروه جغرافیای طبیعی، دانشکده علوم اجتماعی، دانشگاه محقق اردبیلی، اردبیل، ایران،
2 استاد آب و هواشناسی، گروه جغرافیای طبیعی، دانشکده علوم اجتماعی، دانشگاه محقق اردبیلی، اردبیل، ایران.
3 استادیار مهندسی آب دانشکده کشاورزی، دانشگاه شهرکرد، شهرکرد، ایران.
4 استادیار گروه علوم جوی و اقیانوسی، دانشگاه علوم دریایی امام خمینی (ره) نوشهر، ایران،
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
The MJO is the dominant mode of sub-seasonal variability in tropical and subtropical regions and plays a crucial role in the atmosphere-ocean circulation system. Numerous studies have investigated the effects of the Madden-Julian Oscillation on precipitation and temperature. In Iran, this phenomenon has also attracted attention, and several studies have been conducted to assess its impact on the country's climate variations. However, historical reviews show that the predictive use of this phenomenon has been less emphasized. Moreover, the MJO significantly affects the behavior of cyclones in the region, and the annual phase changes of the MJO have substantial impacts on the distribution, movement tracking, and intensity of cyclones entering Iran. In this study, to examine the cyclogenesis conditions during different phases of the Madden-Julian Oscillation (MJO) in the Mediterranean region during the warm season (March, April, and May), MJO, OLR index data and Mean sea level pressure data from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 section between 1989 and 2020 were utilized. Cyclogenesis characteristics in three aspects—frequency, depth, and cyclone tracking—were analyzed using the Melbourne University Cyclone Detection and Tracking Algorithm. In this analysis, days with MJO occurrences having an amplitude of 0.75 or higher, and phases one through eight where this amplitude was consecutively maintained, were extracted as the study period. Due to the limited number of selected periods based on the mentioned conditions, phases that missed one cycle were also included, resulting in 34 selected periods for the warm season overall. Filters were applied to the extracted data using the Melbourne University algorithm, including: a) Only cyclones located within the defined spatial and temporal boundaries (10-55°E / 10-45°N, during 1989-2020) were considered. b) Cyclones lasting less than 24 hours (four time steps: 00:00, 06:00, 12:00, 18:00) were excluded. c) Cyclones identified over multiple time steps (assigned identical numbers) were reviewed, and only the instance with the lowest recorded pressure was considered. d) The median pressure during selected days of different phases was calculated, with the maximum pressure of 1005.8 hPa for the warm season. The study of OLR indicated that in phases 1, 2 and 7, the most negative OLR anomaly occurred over the Middle East and especially over Iran, which indicates the occurrence of convective currents with cloudiness in different regions of Iran. The study of the characteristics of the cyclones in the region showed that phase 8 with more than 17% has the most and phases 1 and 4 with nearly 9.36% have the lowest cyclogenesis area in the study region. In terms of distribution, out of the 25 cases of minimum pressure in warn season, 17, 6, and 2 cases are related to April, March, and May, respectively. The tracking of the cyclogenesis indicated that in phase 1, most of the cyclogenesis were on the Mediterranean Sea and very few cases were formed in its east. At the same time, in phase 2, along with the formation of cyclones in the eastern Mediterranean, some of them have entered Iran. In phases 3 and 4 in the north and center of Iraq, the cyclones have traveled their path, and in phases 5 and 6, the majority of the cyclones were over the Mediterranean, and in phases 7, they reached their peak, and the majority of the cyclogenesis were in the central to southern regions of Iraq. The formed cyclone in phase 8 over the Mediterranean Sea have a different behavior and at the same time they have traveled longer paths than other cyclones in different phases. The results of examining the cyclogenesis characteristics during the warm season in different phases of the Madden-Julian Oscillation (MJO) over the Mediterranean Sea reveal that the highest negative anomaly of the OLR index occurs in phase 1 of this oscillation, with its primary focus on Iran. The study of cyclogenesis areas indicates that cyclonic activity during the warm period of the year is asymmetrically distributed. In various phases of the MJO, most cyclones during the warm season are concentrated over Iraq and the western and northwestern regions of Iran, while other cyclonic cores form over the southern Persian Gulf and the Arabian Peninsula. The findings from the number of cyclogenesis centers show that out of 25 cases of minimum pressure during the warm season, 17 cases occurred in April, 6 in March, and 2 in May. Cyclone tracking in the region revealed that cyclones formed over the Mediterranean Sea travel longer distances.
کلیدواژه‌ها [English]
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