Analysis of the Polar Vortex Trend in the Northern Hemisphere under Climate Change Conditions

جغرافیا و مخاطرات محیطی

Article 4, Volume 6, Issue 3 - Serial Number 23, January 2018, Pages 181-197   

Document Type: Research Article

DOI: 10.22067/geo.v6i3.62149

Author

Abdolreza Kashki^*

Hakim Sabzevari University

Abstract

1. Introduction
Today, climate change problem is considered as one of the most common scientific subject, even as social and political issues, in fact it is not novelty issue. Principally, because the change and movement are one of the component in macro scale climatic systems, discovering the legitimacy of these systems, which mainly is cyclic, it is can be consider as a tool which can help to predict future behavior of the system. The polar vortex (PV) is defined as a large-scale upper-level cyclonic circulation in the middle and upper troposphere which is centered on the polar region. Measurement undertaken, observational investigation and modeling indicate the oscillation cycles of polar vortex. There are two effective mechanisms for oscillation cycles of polar vortex that could be divided into two categories: internal and external. The internal mechanism is included investigation of oscillation cycles of polar vortex by applying thermal and wavy forcing, which is independent of time and leads to identify the effect of the stratosphere on the troposphere. External mechanism is included investigation of oscillation cycles of polar vortex by applying thermal and wavy forcing, which is depends on time and leads to identify the effect of the troposphere on the stratosphere. Trend changes on the macro scale climatic system, such as polar vortex has a significant role on climate change of the surface. Variability in the atmospheric circulation at the hemispheric-scale can have a direct impact on variations in the surface environmental parameters, such as temperature, precipitation, and pollutant transport. One indicator of the behavior of the hemispheric-scale circulation is the polar vortex. The polar vortex can be used for study the holistic hemispheric-scale sub-tropical circulation because it represents the characteristics of long-wave, upper-level ridge-trough configuration around the entire (northern or southern) hemisphere at a given point in time. The PV is defined as the large-scale upper-level cyclonic circulation in the middle and upper troposphere centered on the polar region. The most fundamental question addressed in this research is whether the northern hemisphere polar vortex (NHPV) exhibits long-term trends in area over the 1948-2007 periods. Therefore, the first part of this study answers the question: How can we characterize the long-term trend of the area of the NHPV? It is hypothesized that the global warming signal would be associated with a reduction in area in the NHPV over time as the cold pool of air over the poles shrinks.
2. Material and Methods
In this research, daily mean data of 500 hPa geopotential height were used from the National Center for Environmental Prediction & National Center of Atmospheric Research (NCEP/NCAR) during the period of 1948 to 2007. Their spatial resolution is 2/5 * 2/5 degree with 36 * 144 pixels. The 500 hPa geopotential height (i.e., constant pressure surface) was selected for analysis for several reasons. First, since the 500 hPa level is in the middle of the atmosphere, it represents characteristics of both the lower and upper atmosphere. Also, most steering of mid-latitude systems occurs at the 500 hPa level and geostrophic flow occurs at this level as well. A specific isohypse(contour) is selected to represent the NHPV for each month in 500 hpa level (table 1).

Table (1): specific isohypse of polar vortex for each month in 500 hpa level
Month Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec
Specific isohypse(gpm) 5460 5460 5520 5580 5640 5700 5700 5760 5640 5580 5520 5460

Choi & et al. (2009)

Monthly polar vortex area is calculated with Grads software. This research utilizes a statistical approach to determine the trend in the northern hemisphere (NH) polar vortex. For comparison of area means, used from Paired-Samples T Test and for the detection of polar vortex area trend used from Kendall's tau trend test in SPSS software. Paired-Samples T Test is one of the statistical parametric tests to compare the mean and variance of the two dependent groups in a region.
3. Results and Discussion
By doing the Kendall tau test in SPSS, it was determined a reduction in the polar vortex area in all months. Polar vortex area has a decreasing trend during May, June, July, August, September and March which is significant at 0.01 level.
The biggest reduction trend is related to August and lowest to December. The results show that the polar vortex during the whole period is declining, but this decline was higher during summer months. The most of decline in the polar vortex area is observed in August that the rate of about 93,000 square kilometers per year. The decline rate has accelerated in the second half of period. Generally, the decline of polar vortex area caused by macro-scale climate change and planetary scale, That certainly global warming and consequently advancement of subtropical high pressure will be one of the components. The results of Paired-Samples Test showed that the mean difference of polar vortex area is negative for all months and this amount represents a reduction in polar vortex area during thirty years of second period compared to the first period.
4. Conclusion
The change in configuration of polar vortex (trough and ridge) and transformation from zonal to meridional as a result of reducing of meridional pressure gradient caused regional climatic anomalies such as the change in the type and amount of precipitation and temperature. Generally, the decline of polar vortex area caused by macro-scale climate change and planetary Scale, that certainly global warming and consequently advancement of subtropical high pressure will be one of the effective components.

Keywords

Polar Vortex; Trend analysis; Climate change; Northern Hemisphere

References

حجازی‌زاده، زهرا؛ 1376. بررسی سینوپتیکی نرمال پرفشار جنب حاره‌. مجله رشد آموزش جغرافیا. شماره 45. 20-25.

علیجانی، بهلول؛ 1378. بررسی سینوپتیک الگوهای سطح 500 هکتوپاسکال خاورمیانه در دوره 1990-1961. مجله نیوار. شماره45-44. 29-7.

علی‌دادی، معصومه؛ 1389. تاوه قطبی و نقش آن در تعیین نوع و مقدار بارش در غرب میانی ایران. پایان نامه کارشناسی ارشد اقلیم‌شناسی. دانشگاه تهران.

مرادی، حمیدرضا و محمد خیراندیش؛ 1379. تاوه قطبی و تطبیق الگوهای سینوپتیکی با شرایط ترسالی و خشکسالی در کشور. اولین کنفرانس ملی بررسی راهکارهای مقابله با کم آبی و خشکسالی. کرمان. دانشگاه باهنر کرمان.

مهدوی، مسعود و طاهرخانی، مهدی؛ 1383. کاربرد آمار در جغرافیا. انتشارات قومس. صفحه 367.

میر رکنی، سید مجید و محب الحجه، علیرضا؛ 1390. تحلیل چرخه‌های نوسان تاوه قطبی در یک مدل آب کم عمق برای پوش‌سپهر با استفاده از فرایافت‌های اویلری. مجلة فیزیک زمین و فضا. دوره 37. شماره 2. صفحه 223-211.

Ahrens, C.D., (1999). Meteorology Today: An introduction to weather, climate and the environment. Pacific Grove, USA: Brooks/ Cole-Thomson Learning.

Angell, J. K. (1998). Contraction of the 300 mbar north circumpolar vortex during 1963– 1997 and its movement into the Eastern Hemisphere, J. Geophysics. Res., 103, 25,887-893.

Angell, J. K.)1992(. Relation between 300-mb north polar vortex and equatorial SST, QBO, and sunspot number and the record contraction of the vortex in 1988– 89, J. Climatology., 5, 22–29.

Angell, J. K.)1997( . Stratospheric warming due to Agung, El Chi chon, and Pinatubo taking into account the quasi-biennial oscillation, J. Geophysics. Res., 102, 979–985.

Burnett, A. W., and A. R. McNicoll, (2000). Inter annual variations in the Southern Hemisphere winter circumpolar vortex: Relationships with the semiannual oscillation, J. Climatology. 13, 991– 999.

Choi, G, Robinson, D. A, and Kwon, Won-Tae. (2009). Recent changes in the northern hemisphere circumpolar vortex. Association of American Geographers, Las Vegas, USA.

Davis, R. E., and S. R. Benkovic, (1994). Spatial and temporal variations of the January circumpolar vortex over the Northern Hemisphere. Int. J.Climatology. 14, 415– 428.

Davis, R. E., and S. R. Benkovic. (1992). Climatological variations in the Northern Hemisphere circumpolar vortex in January. Theor. Appl. Climatology., 46, 63– 74.

Frauenfeld, O. W. and Davis, R. E. (2003). Northern Hemisphere circumpolar vortex trends and climate change implications. Journal Geophysical Research, VOL. 108, NO. D14, 7-13.

Frauenfeld, O. W. and R. E. Davis. (2000). The influence of El Nin˜o-Southern Oscillation events on the Northern Hemisphere 500 hpa circumpolar vortex. Geophysics. Res. Letter., 27, 537–540.

Frauenfeld, O. W., and R. E. Davis. (2002). Mid latitude circulation patterns associated with decadal and inter annual Pacific Ocean variability. Geophysics. Res. Letter., 29(24), 2221.

Levitus, S., J. I. Antonov, T. P. Boyer, and C. Stephens. (2000). Warming of the world ocean. Science, 287, 2225– 2229.

Markham, C. G. (1985). A quick and direct method of estimating mean monthly global temperatures from 500 Mb data. Prof. Geography. 37, 72– 74.

Miller, A. J., D. R. Cayan, T. P. Barnett, N. E. Graham, and J. M. Oberhuber. (1994). The 1976–77 climate shift of the Pacific Ocean. Oceanography, 7, 21– 26.

Minobe, S. (1999). Resonance in bidecadal and pent decadal climate oscillations over the North Pacific: Role in climatic regime shifts. Geophysics. Res. Letter., 26, 855–858.

Rong, P. P. and Waugh, D. W. (2004). Vacillations in a shallow water model of the stratosphere. J. Atmos. Sci. 61, 1174–1185.

Salby, M. and Callaghan, P. (2004) Evidence of the Solar Cycle in the General Circulation of the Stratosphere. J. Climate. 17, 34–46.

Scott, R. K. and Polvani, L. M. (2008) Internal variability of the stratospheric polar vortex. Part II: Time-dependent forcing, J. Atmos. Sci., 65, 2375–2388.

Thompson, D. W. J., and J. M. Wallace. (2001). Annular modes in the extra tropical circulation. part II, Trends, J. Climatology. 13, 1018–1036.

Waugh, D. W. (1993). Subtropical stratospheric mixing linked to disturbances in the polar vortices. Nature, 365, 535–537.

Wrona, K. M. (2005). Long-Term change and variability in northern hemisphere circumpolar vortex. A Thesis, B.S. Northern Illinois University, The Department of Geography and Anthropology, May 2005, 1-104.