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ویژگی ها و اثرهای دورپیوندی ال نینوهای فرین شرق و مرکز اقیانوس آرام و ال نینوی فرین ترکیبی | ||
| پژوهش های جغرافیای طبیعی | ||
| مقاله 5، دوره 52، شماره 1، فروردین 1399، صفحه 65-84 اصل مقاله (2.97 M) | ||
| نوع مقاله: مقاله کامل | ||
| شناسه دیجیتال (DOI): 10.22059/jphgr.2020.284934.1007414 | ||
| نویسندگان | ||
| مونا ذوالقدر شجاعی1؛ امید علیزاده چوبری* 2؛ پرویز ایران نژاد2؛ فرهنگ احمدی گیوی2 | ||
| 1دانشجوی کارشناسی ارشد هواشناسی گروه فیزیک فضا، مؤسسة ژئوفیزیک دانشگاه تهران، تهران، ایران | ||
| 2دانشیار گروه فیزیک فضا، مؤسسة ژئوفیزیک دانشگاه تهران، تهران، ایران | ||
| چکیده | ||
| با استفاده از دادههای میانگین ماهانة ERA-Interim، النینوهای ۱۹۹۷-199۸، ۲۰۰۹-۲۰۱۰، و ۲۰۱۵-201۶، که بهترتیب النینوهای فرین شرق و مرکز اقیانوس آرام و النینوی فرین ترکیبیاند مطالعه شده است. نتایج نشان داد آغاز هر سه النینوی فرین از ماه ژوئیه بوده است؛ درحالیکه تفاوتهای بارزی در زمان از بین رفتن النینوهای ۱۹۹۷-199۸ و ۲۰۱۵-201۶ وجود دارد. در هر سه النینو، بیهنجاریهای مثبت و منفی دمای سطح دریا بهترتیب در مناطق استوایی شرق و غرب اقیانوس آرام تشکیل شدهاند. بیشینة بیهنجاریهای مثبت دمای سطح دریا طی وقوع النینوی ۱۹۹۷-199۸ در مناطق استوایی شرق اقیانوس آرام و در النینوی ۲۰۰۹-۲۰۱۰ در مناطق استوایی مرکز اقیانوس آرام قرار دارند. بیهنجاریهای مثبت دمای سطح دریا در النینوی ۲۰۱۵-201۶ از مرکز تا شرق مناطق استوایی اقیانوس آرام کشیده شدهاند. همچنین، اندازة بیهنجاریهای دمای سطح دریا و فشار تراز دریا در النینوی ۱۹۹۷-199۸ از النینوی ۲۰۰۹-۲۰۱۰ بزرگتر بوده است. در هر سه النینو، بیهنجاریهای مثبت (منفی) ارتفاع ژئوپتانسیلی در تراز 300 هکتوپاسکال در همان مناطقی از اقیانوس آرام حارّهای شکل گرفتهاند که بیهنجاریهای مثبت (منفی) دمای سطح دریا مشاهده میشود. بیهنجاریهای شکلگرفته در ترازهای فوقانی وردسپهر در مناطق حارّهای اقیانوس آرام در طی این سه النینو بر الگوهای جوی مناطق دیگر تأثیر گذاشتهاند. | ||
| کلیدواژه‌ها | ||
| النینو- نوسان جنوبی (انسو)؛ النینوی ترکیبی؛ النینوی شرق اقیانوس آرام؛ النینوی مرکز اقیانوس آرام؛ دورپیونده | ||
| عنوان مقاله [English] | ||
| Characteristics and Teleconnections of the Extreme Eastern and Central Pacific and Mixed El Niños | ||
| نویسندگان [English] | ||
| Mona Zolghadr-Shojaee1؛ Omid Alizadeh Choobari2؛ Parviz Irannejad2؛ Farhang Ahmadi Givi2 | ||
| 1MSc Student of Meteorology, Space Physics Department, Institute of Geophysics, University of Tehran, Tehran, Iran | ||
| 2Associate Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Tehran, Iran | ||
| چکیده [English] | ||
| Introduction The El Niño-Southern Oscillation (ENSO) cycle of alternating warm El Niño and cold La Niña events occurs when the tropical Pacific Ocean and its overlying atmosphere deviated from its natural state for at least several consecutive months (Neelin et al., 1998). The neutral phase of the El Niño-Southern Oscillation is derived by the strong zonally asymmetric state of the equatorial Pacific and is characterized by surface easterly trade winds along the equatorial Pacific, rising motion, deep convection and heavy rainfall over the western equatorial Pacific, westerly winds at upper levels and sinking motion over the eastern equatorial Pacific (Bjerknes, 1969). El Niño is characterized by weak and La Niña by strong zonal SST gradients, accompanied respectively by weakening and strengthening of the trade winds across the equatorial Pacific (McPhaden et al. 2006). As a result, compared to the neutral phase of the El Niño-Southern Oscillation, convective systems intensify in the western tropical Pacific and slightly shift to the west during La Niña events, but shift to the central and eastern tropical Pacific during El Niño events. Since this early recognition of the coupling between the atmosphere and the Pacific Ocean by Bjerknes (1966) and Bjerknes (1969), major advances have beenmade toward a comprehensive understanding of the physics of the El Niño-Southern Oscillation. This is particularly achived through development of complex climatemodels for realistic simulation of the El Niño-Southern Oscillation cycle (Bellenger et al., 2014), and great observational advances that have been made during the international Tropical Ocean-Global Atmosphere (TOGA) program conducted between 1985 and 1994 (McPhaden et al., 1998). El Niño or the warm phase of the El Niño-Southern Oscillation is a quasi-periodic natural phenomenon that occurs in the tropical Pacific Ocean. The El Niño-Southern Oscillation not only influences the climate of nearby regions, but it is the most important natural climate aggent contributing to the interannual climate variability over many regions across the globe, including North America (e.g. Yu et al., 2015; Guo et al., 2017), the Middle East (e.g. Alizadeh-choobari, 2017; Alizaeh-Choobari et al., 2018a, Alizaeh-Choobari et al., 2018b), East Asia (e.g. Feng and Li, 2011), Southeast Asia (e.g. Lee et al., 2017) and the Indian subcontinent (e.g. Kumar et al., 2006). Depending on the location of the maximum sea surface temperature in the eastern or central equatorial Pacific, the eastern Pacific El Niño or the central Pacific El Niño are identified, while a mixed event has also been diagnosed in the eastern and central Pacific El Niño events. Materials and methods In this study, using the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis Interim (ERA-Interim) monthly dataset with a horizontal resolution of 0.75º Í 0.75º, and the Extended Reconstructed Sea Surface Temperature version 5 (ERSSTv5) dataset, we determined the phase of ENSO and the type of El Niño events during the period 1979-2016. In addition, characteristics of the 1997-98 eastern Pacific El Niño, and the 2009-10 central Pacific El Niño and the 2015-16 El Niño are investigated as a mixed event of the eastern and central Pacific El Niño,. Results and discussion The results of this research indicateed that during the period 1979-2016, 1979-80, 1982-83, 1986-87, 1987-88, 1991-92, 1994-95, 1997-98, 2002-03, 2004-05, 2006-07, 2009-10, 2014-15 and 2015-16 have been the years for which three-month running means of the Oceanic Niño Index (ONI) for 5 consecutive periods became greater or equal to 0.5 degree Celcius, indicating the occurrence of El Niño in these years. To determine the eastern and central Pacific El Niños during the period 1979-2016, we used the empirical orthogonal function (EOF) by examining spatial correlation between sea surface temperature anomalies in the equatorial Pacific Ocean and results of the empirical orthogonal function. The 1997-98 and 2015-16 El Niño events are both categorized as extreme El Niño events. The 2009-10 El Niño is weaker than the other two events, but over the last century, it has been the strongest central Pacific El Niño event. Results indicated that the onset of all these three events was in June, while some differences are found between termination of the 1997-98 and 2015-16 El Niños, including different time of dissipation for these events. All these three events have shown characteristics of classic El Niño events, such that anomalous positive and negative sea surface temperature are seen in the eastern and western equatorial Pacific, respectively. Nevertheless, maximum positive sea surface temperature is formed in the eastern equatorial Pacific during the 1997-98 El Niño. This is different from the 2009-10 El Niño events with the maximum sea surface temperature in the central (near the dateline) equatorial Pacific. In fact, maximum positive sea surface temperature anomalies are expanded in the eastern and central equatorial Pacific during the 1997-98 and 2009-10 El Niño events, respectively. However, it extends from central to eastern equatorial Pacific during the 2015-16 El Niño. Intensities of the maximum sea surface temperature anomalies and mean sea level pressure have been greater during the 1997-98 El Niño compared to those during the 2009-10 event, indicating that central Pacific El Niños are generally less intense than eastern Pacific El Niño events. It is shown that positive sea surface temperature anomalies in the 2015-16 El Niño event cover a larger area extending from the central to the eastern equatorial Pacific. It is found that both sea surface temperature and mean sea level pressure anomalies in the equatorial Pacific were larger the 1997-98 eastern Pacific El Niño than those of the 2009-10 central Pacific El Niño. This suggests that the central Pacific El Niño events are generally weaker than the eastern Pacific El Niño events. In all of the three El Niño events, positive (negative) geopotential height anomalies at 300 hPa pressure level in the equatorial Pacific are collocated with positive (negative) sea surface temperature anomalies. Geopotential height anomalies in the upper levels over the tropical Pacific influence weather patterns of other regions. It is discussed that different geopotential height anomalies at upper levels of the equatorial Pacific during the three El Niño events have led to different teleconnections across the globe. For example, temperature anomalies in the Antarctic during the 2009-10 El Niño were opposite to those during the 1997-98 and 2015-16 El Niño events. Conclusion Analysis of the ERA-Interim dataset with the horizontal resolution of 0.75º Í 0.75º for the period 1979-2016 indicated that the eastern, central and mixed El Niño events have generally different characteristics in the equatorial Pacific. As a result, teleconnection patterns of these events across the globe are also found to be different. | ||
| کلیدواژه‌ها [English] | ||
| The El Niño-Southern Oscillation (ENSO), Eastern Pacific El Niño, Central Pacific El Niño, Mixed El Niño, Teleconnections | ||
| مراجع | ||
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