خلاصة:
در این پژوهش با استفاده از دادههای باز تحلیلی MERR2، دوره زندگی گرمایش ناگهانی پوشنسپهر نوع اصلی در زمستانهای نیمکره شمالی(از نوامبر تا مارس) در دوره آماری 2020-1979 بررسی شد. این بررسی بر اساس تغییرات میانگین مداری مولفه مداری باد در مدار 60 درجه شمالی و در تراز فشاری ده هکتوپاسکال انجام شده است که بر پایه آن، روز تولد، روز صفر و دورههای رشد، بلوغ، پیری و روز مرگ تعریف شده است. نتایج حاصل از بررسی میانگین مداری دما و مولفه مداری باد نشان داد که در این دوره آماری در نیمکره شمالی، 19 مورد گرمایش اصلی رخ داده است. از بین موارد آشکار شده، بیشترین افزایش میانگین مداری دما به میزان 8/51 کلوین در دوره کوتاه یازده روزه به گرمایش ژانویه 2009 اختصاص دارد که در طول دوره آماری انتخابی در نیمکره شمالی تا کنون چنین افزایشی، ثبت نشده است. نتایج حاصل از تحلیل دوره زندگی گرمایش ناگهانی پوشنسپهرنوع اصلی نشان داد که کوتاهترین و بلندترین دوره رشد به ترتیب با 6 و 37 روز، در موردهای 6 ژانویه 2013 و 23 ژانویه 1987 ثبت شده است. بلندترین دوره بلوغ با 17 روز تداوم، به گرمایش 23 ژانویه 1987 اختصاص دارد. بلندترین دوره پیری در این دوره آماری نیز 26 روز است که به گرمایش 24 ژانویه 2009 مربوط میشود. کوتاهترین و بلندترین طول دوره زندگی نیز در این دوره آماری به ترتیب به گرمایش 1 فوریه 2017 و 23 ژانویه 1987 اختصاص دارد.
Introduction In the Northern Hemisphere, breaking planetary-scale waves propagating up from the troposphere or the excitation of resonant modes can lead to the disruption and deceleration of the climatological westerly circulation of the polar vortex. Associated with this wind deceleration is a dramatic warming. A sudden stratospheric warmings (SSWs) represent large scale perturbations of the polar winter stratosphere, which substantively influence the temperature and circulation of the middle atmosphere and contents of atmospheric species. It occurs mostly in middle and late winter (January and February) and almost exclusively in the Northern Hemisphere (Charlton and Polvani,2007). During an event, the polar stratospheric temperature increases by several tens of degrees within a few days and eventually becomes warmer than that of the mid latitudes, reversing the climatological gradient. At the same time, the prevailing westerly wind rapidly decelerates and becomes easterly (Kim et al.,2017). When minor SSWs events occur, the polar cap temperature suddenly rises and increases by the twenty fifth of Kelvins over period of several days. To classify the major SSWs events in this study, we used a common definition based on the zonal-mean zonal wind at 10hPa and 60N during the boreal winter season (01 December to 31 March). A zonal wind reversal from westerly to easterly indicates a major SSWs event; the first day of the wind reversal is defined as the zero day of the SSWs. To distinguish SSWs from stratospheric final warming, the zero day should appear at least 10 days before the end of March, and the westerly zonal wind should recover before the end of March. The purpose of this study is investigation of life cycle of a major sudden stratospheric warming. Materials and methods In this study we have used the daily mean data from the Modern Era Retrospective Analysis for Research and Applications version 2 (MERRA2) assimilated data. From the MERRA2 data, zonal wind and temperature were obtained at 10hPa from 01 January 1979 to 04 June 2020.The temperature averaged around the polar cap for latitudes north of 60°N. This is a good measure of the overall temperature in the polar vortex. The average east-west (zonal) wind speed for 60°N. This is near the peak of the polar jet maximum. In this study life cycle of major SSWs is defined by dividing it into five periods. Onset (the first day of maximum zonal-mean zonal wind is reduced), growth (from onset day to zero day), maturation (from zero day to minimum zonal-mean zonal wind), decline (from minimum value to decay day) and decay (the first day of the easterly wind reversal to westerly) of typical SSWs. The first day of the wind reversal is defined as the zero day of the SSWs. Results and discussion Investigation of the polar temperature and zonal-mean zonal wind at 10hPa, is detected 19 and 13 major and minor SSWs events, respectively. According to the shows a rapid increase from 201.6K on 12 January to 253.4K on 23 January 2009 (∆T=51.8K). This is the largest increase in the polar temperature per 11-day in the entire MERRA-2 data set starting from January 1979 to June 2020. The result shows the shortest and longest growth periods, with 6 and 37 days, respectively, were recorded in the cases of January 6, 2013 and January 23, 1987. The longest maturation period, with 17 days of continuity, is dedicated to the warming of January 23, 1987. The longest decline period in this statistical period is 26 days, which is related to the warming of January 24, 2009. The shortest and longest life cycle in this statistical period are dedicated to cases on February 1, 2017 and January 23, 1987, respectively. The shortest and longest life cycle periods, with 12 and 66 days, respectively, were recorded from January 22, 2017 to February 02, 2017 and from December 26, 1986 to February 21, 1987, respectively. Conclusion In this study life cycle of 19 major sudden stratospheric warmings is defined by dividing it into five periods. Onset (the first day of maximum zonal-mean zonal wind is reduced), growth (from onset day to zero day), maturation (from zero day to minimum zonal-mean zonal wind), decline (from minimum value to decay day) and decay (the first day of the easterly wind reversal to westerly) of typical SSWs. The first day of the wind reversal is defined as the zero day of the SSWs. The result shows the shortest and longest growth periods, with 6 and 37 days, respectively, were recorded in the cases of January 6, 2013 and January 23, 1987. The longest maturation period, with 17 days of continuity, is dedicated to the warming of January 23, 1987. The longest decline period in this statistical period is 26 days, which is related to the warming of January 24, 2009. The shortest and longest life cycle in this statistical period are dedicated to cases on February 1, 2017 and January 23, 1987, respectively. The shortest and longest life cycle periods, with 12 and 66 days, respectively, were recorded from January 22, 2017 to February 02, 2017 and from December 26, 1986 to February 21, 1987, respectively.
ملخص الجهاز:
نتایج حاصل از بررسی میانگین مداری دما و مؤلفه مداری باد نشان داد که در این دوره آماری در نیمکره شمالی، ١٩ مورد گرمایش ناگهانی پوشن سـپهر نـوع اصـلی رخ داده اسـت .
1 Ageyava at el 2 Major, Minor 3 McInturff 4 Yamazaki at el 5 Rao at el, Butler and Gerber 6 Charlton and Polvani , Butler at el , Kim at el 7 Hengde at el دسته ای از پژوهشگران اثر گرمایش ناگهانی پوشن سپهر نوع اصلی بر جابجایی تاوه قطبی را بررسی کرده انـد (ماننـد کوهن و جونز،٢٠١١)١ و دسته ای دیگر اثر آن را بر تقسیم هسته تاوه به دو هسته مجزا مطالعه کرده انـد (ماننـد وارجـین و کیریشوف ، ٢٠١٩؛ کوی و پاوسون ، ٢٠١٩)٢.
این در حالی است که در زمستان هایی که پوشن سپهر حالت غیربازتـابی دارد، چـون احتمـال 1 Cohen and Jones 2 Vargin and Kiryushov , Coy and Pawson 3 Choy at el 4 Limpasuvan at el انتشار و نفوذ امواج راسبی از وردسپهر به پوشن سپهر زیرین در فاصله عرض جغرافیایی ٩٠-٧٠ درجـه شـمالی بیشـتر است ، پس احتمال رخداد این پدیده نیز بیشتر است به همین دلیل در این شرایط ، در حـدود ٦٢ درصـد از زمسـتان هـا احتمال رخداد گرمایش ناگهانی پوشن سپهر وجود دارد.
(رجوع شود به تصویر صفحه) شکل ٩- تغییرات روزانه میانگین مؤلفه باد مداری (متر بر ثانیه ) در روی مدار ٦٠ درجه شمالی در تراز فشاری ده هکتوپاسکال و دوره زندگی یک گرمایش ناگهانی پوشن سپهر از نوع اصلی در بازه ١٥ دسامبر ١٩٨٦ تا ٢٥ فوریه ١٩٨٧.