نوع مقاله : مقاله پژوهشی
نویسندگان
1 دانشجوی دکتری اقلیم شناسی، دانشگاه شهید بهشتی، دانشکده علوم زمین، گروه جغرافیای طبیعی
2 دانشیار دانشگاه شهید بهشتی، دانشکده علوم زمین، گروه جغرافیای طبیعی
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Introduction
The Sudan low pressure is regarded as a system influencing the rainfall during the cold season, in the South and Southwest of Iran. Often in the cold season these systems have crossed Ethiopia, Sudan, and the Red Sea and then on its way entered the country from the south and southwest of Iran and it is causing rain in these areas. According to El-Fandy (1948), the history of recognizing the Sudan low in the Middle East and the Red Sea region goes back to about 80 years ago when Ashbel (1938) first described the eastern Mediterranean rainfall. Ashbel concluded that the rainfall in the area was affected by a system which he called the “Red Sea low pressure”. Based on the evidence, Olfat (1968) was the first one who studied Sudan low in the context of Iran. Olfat refers to low pressures which are formed in northeastern Africa and the Red Sea and then pass Saudi Arabia and the Persian Gulf, and finally, enter Iran and cause rainfall. The purpose of this study is the Investigation of dynamic fluctuations of Sudan low In May rainfall performance over the course of 60 years.
Materials and methods
The study period is from1957 to 2017. May was considered as a symbol of the poor performance of the Sudan low in the south and southwest of Iran (Lashkari & Mohammadi, 2019). The study period with long-term variations was considered from 9.5 to 11 years based on solar cycle. In this regard, the daily precipitation data of 42 stations of the south and southwest of the country were prepared by the Meteorological Organization of Iran. Rainfall days were extracted in May using the daily rainfall data of 42 synoptic stations. For these days, sea level pressure (SLP) and geopotential (hgt) data at 1000 hPa with 2.5 × 2.5◦ spatial resolution were obtained from the dataset of NCEP/NCAR reanalysis project. Additionally, the frame of the reference was provided in 0-100◦ E and 10-55◦ N latitude belt in GrADS software. The visual analysis of high and low altitude cores and geopotential height at 1000 hPa pressure level (El-Fandy, 1950a; Lashkari, 1996; 2002) were considered based on the aim of the study. Accordingly, the approximate locations of activity centers, as well as the range of the formation and displacement of the Sudan system were initially identified based on the location of the formation of low and high-pressure cores. Then, the rainy days due to the Sudan system in May were separated from the precipitation of the other atmospheric systems (i.e., Sudan-Mediterranean and Mediterranean systems). For these days, SLP, hgt, specific humidity, zonal and meridional wind data at the levels of 1000, 850, 700, and 500 hPa with 2.5 × 2.5◦ spatial resolution were obtained from the NCEP/NCAR dataset. Using the GrADS software, the numerical values of these parameters were calculated at synoptic stations with the highest statistical data over six decades. In addition, for the sum of the days of Sudan low rainfall in each decade, the daily composites of the anomalies of these variables were provided from NCEP/NCAR dataset.
Results and discussion
Analysis of sea level pressure changes
Examination of sea level pressure (SLP) revealed that during the first to sixth decades SLP has declined relative to its long-term average in southwestern of Iran (-1 to -3 hPa). But in the south of Iran during the first to second decades, the SLP decreased slightly and remained constant in the third decade and then increased during the fourth to sixth decades (+1 hPa).
Analysis of Geopotential height Changes
Examination of Geopotential height (hgt) changes over the level of 1000hpa to the 500hpa showed that the height of the Sudan low was reduced Compared to its long-term average, during the first decade to the sixth decade in southwest of Iran but the size of its hgt reduction, was reduced from the first decade (-70 m) to in the sixth decade (–30m). The height of the Sudan low was decreased from the first decade to the third decade in the southern part of Iran (-10m to -30m). But the height of the Sudan low was increased during the fourth to sixth decades (+10 to +15 meters).
Analysis of specific humidity Changes
Examine the specific humidity (Shum) values at 1000,850 and 700hpa showed that moisture change was reduced during the first to the second decade in southwestern Iran (about 2 gr/kg), and it was constant with a slight swing from the second decade to the sixth decade (4 gr/kg). In the south of Iran Shum status was accompanied by decreasing and increasing with a swing during the first decade to the third decade and it was almost fixed from the fourth through the sixth decades (2.5-3 gr/kg). Specific humidity values increased to some extent at 850 and 700hPa during the last decade.
Analysis of vector wind and vorticity Changes
Survey of vector wind and vorticity at 850hpa level showed that Sudan Cyclone deployed in northeast Saudi Arabia and the southern coast of the Persian Gulf and on other hands, Anticyclone (Arabian subtropical High Pressure) Stationed on southern Iran. So during the decades of climate, the Barotropic and Baroclinic Atmosphere is ruler on the south and southwest of Iran, respectively.
Conclusion
The purpose of this study was to investigate the performance of a compressive structure, humidity and other dynamic parameters of systems due to Sudan low in May of south and southwest of Iran. The climate decades were regulated by solar cycles over 60 years (1957-2017). The results made it clear that changing the dynamic parameters of Sudan low system has strengthened and weakened in the southwest and south of Iran respectively, over the decades. Also, Investigation of the average of decidedly precipitation rate due to Sudan low showed the values of rainfall in May, increasing in the south and southwest of Iran over the past decades until now in a long historical trend.
Keywords: Sudan low- solar cycle-Anomaly-south and southwest of Iran.
کلیدواژهها [English]
10. Davis, R.E., and S.R., Benkovic, 1992, Climatological variations in the northern hemisphere circumpolar vortex in January. Theoretical and Applied Climatology. No. 46(2-3), pp. 63-73.
11. Dayan, U., B., Ziv, A., Margalit, E., Morin, and D., Sharon, 2001, A severe autumn storm over the Middle-east: synoptic and Mesoscale Convection analysis. Theoretical and Applied Climatology. No. 69(1-2), pp. 103-122.
12. De Vries, A.J., E., Tyrlis, D., Edry, S.O., Krichak, B., Steil, and J., Lelieveld, 2013, Extreme precipitation events in the Middle East: dynamics of the Active Red Sea Trough. JGR Atmospheres. No. 118(13), pp. 7087–7108.
13. De Vries, A.J., S.B., Feldstein, M., Riemer, E., Tyrlis, M., Sprenger, M., Baumgart, M., Fnais, and J., Lelieveld, 2016, Dynamics of tropical–extratropical interactions and extreme precipitation events in Saudi Arabia in autumn, winter and spring. Q J R Meteorol Soc. No. 142(697), pp. 1862–1880.
14. Dunkerton, T.J., and D.P., Delisi, 1986, Evolution of potential vorticity in the winter stratosphere of January February 1979. JGR Atmospheres. No. 91(D1), pp. 1199-1208.
15. El-Fandy, M.G., 1948, the effect of the Sudan monsoon low on the development of thundery conditions in Egypt, Palestine and Syria. Q J R Meteorol Soc. No. 74(319), pp. 31–38.
16. El-Fandy, M. G., 1950a, Effects of Topography and other Factors on the Movement of Lows in the Middle East and Sudan. Bulletin of the American Meteorological Society. No. 31(10), pp. 375-381.
17. El-Fandy, M. G., 1950b, Troughs in the Upper Westerlies and cyclonic developments in the Nile Valley. Q J R Meteorol Soc. No. 76(328), pp. 166-172.
18. El-Fandy, M. G., 1952, Forecasting Thunder-Storms in the Red Sea. Bulletin of the American Meteorological Society. No. 33(8), pp. 332-338.
19. Faraji, E., 1981, Survey the path to low pressure rain systems On Iran and provide patterns of the situation and how they move. M. S. Thesis, Institute of Geophysics, University of Tehran, 210pp.
20. Flohn, H., 1965, Climatic Problems of the Southern Red Sea Area. Geography. No. 19(3), pp. 179–191.
21. Flohn, H., 1987, Climatic Change and Variability in Southern Africa by P. D. Tyson. Bulletin of the American Meteorological Society. No. 68(12), pp. 1574-1575.
22. Ghaemi, H., 1970, Heavy winds of the upper levels And the impact of Indian Ocean water resources on Iran rainfall. Nivar Journal. No. 1, pp. 77-82.
23. Ghaemi, H., H., Asakereh and S.H., Rezaei, 2017, Spectral Analysis of annual average of red sea low pressure during 1951-2010. Geographic Thought. No. 8(15), pp. 139-150.
24. Haggag, M., H., El-Badry, 2013, Mesoscale numerical study of quasi-stationary convective system over Jeddah in November 2009. Atmospheric and Climate Sciences. No. 3(1), pp. 73–86.
25. Haigh, J. D., 1996, the Impact of Solar Variability on Climate. Science. No. 272(5264), pp. 981-984.
26. Harvey, V. L. and M. H., Hitchman, 1996, climatology of the Aleutian High. Journal of the Atmospheric Sciences. 53(4): 2088-2101.
27. Hoyt, D. V., 1979, Variations in sunspot structure and climate. Climatic Change. No. 2(1), pp. 79-92.
28. Johnson, D. H., 1963, African Synoptic Meteorology. Meteorology and the Desert Locust. WMO Tech. Note 69. 48-90pp.
29. Krichak, S. O., J., Barkan, J. S., Breitgand, S., Gualdi and S.B., Feldstein, 2015, the role of the export of tropical moisture into midlatitudes for extreme precipitation events in the Mediterranean region, Theoretical and Applied Climatology, No. 121(3-4), pp. 499-515.
30. Krichak, S. O., J. S., Breitgand, S. B., Feldstein, 2012, a conceptual model for the identification of Active Red Sea Trough synoptic events over the southeastern Mediterranean. Journal of Applied Meteorology and Climatology. No. 51(5), pp. 962–971.
31. Krichak, S.O., M, Tsidulko, and P., Alpert, 2000, November 2, 1994, severe storms in the south-eastern Mediterranean. Atmospheric Research. No. 53(1-3), pp. 45-62.
32. Krichak, S. O., P, Alpert, and T. N., Krishnamurti, 1997a, Interaction of topography and tropospheric flow–A possible Generator for the Red Sea Trough? Meteorology and Atmospheric Physics. No. 63(3-4), pp. 149-158.
33. Krichak, S. O., P., Alpert, and T. N., Krishnamurti, 1997b, Red Sea Trough/cyclone development-Numerical Investigation, Meteorology and Atmospheric Physics. No. 63(3-4), pp. 159-169.
34. Lashkari, H., 1996, Synoptic Pattern of Severe Precipitation in South and Southwest of Iran, Ph.D. Thesis. Tarbiat Modares University.
35. Lashkari, H., 2002, Routing Sudan low pressure systems to Iran. Journal of Humanities. No. 6(2), pp. 133-157.
36. Lashkari, H., 2003, the mechanism of development, strengthening and development of Sudan low center and its role on the southern and southwest of Iran rainfall. Geographical Research Quarterly. No. 35(3), pp.1-18.
37. Lashkari, H., A.A., Matkan, M., Azadi, Z., Mohammadi, 2018, Synoptic patterns lead to premature precipitation in the South and South West of Iran during the period (1979-2015). Geography and planning, No. 22(64), pp. 247-266.
38. Lashkari, H., H., Ghaemi, and F., Parak, 2013, Analysis of the rainfall regime in the south and southwest of the Iran, Journal of Sepehr Geography Information. No, 22(85), pp. 57-63.
39. Lashkari, H., V., khalilian, 2013, Synoptic Analysis of Rainy Zone of Sudan-Mediterranean Merged System on Iran. Scientific-Research Quarterly of Geographical Data (SEPEHR). No. 21(84), pp. 21-34.
40. Lashkari, H., Z., Mohammadi, 2015, the Role of Saudi Arabian Sub-Tropical High Pressure on the Rainfall Systems on South and Southwest Iran. Physical Geography Research Quarterly. No. 1(47), pp. 73-90.
41. Lashkari, H., Z., Mohammadi, 2018, The Role of Topography in Intensifying Precipitation in the South and Southwest of Iran Case Study: December 3, 2015, Journal of Natural Geography, No. 40, pp. 33-17.
42. Markson, R., and M., Muir, 1980, Solar Wind Control of the Earth's Electric Field. Science, No. 208(4447), pp. 979-990.
43. Mashat, A.S., A.M., Awad, 2015, Synoptic characteristics of the primary widespread winter dust patterns over the northern Arabian Peninsula. Air Quality, Atmosphere & Health, No. 9(5), pp. 503-516.
44. Mofidi, A., (2004). Synoptic Climatology of Flooding Origins of the Red Sea Region in the Middle East, Geographical Research, No. 4, pp. 72-93.
45. Mofidi, A., and A., Zarrin, 2006, the synoptic study of low pressure systems of the Sudan in heavy rain falls in Iran. Geographical Research. No. 20 (2), pp.113-136.
46. Mofidi, A., And Zarrin, A., 2006a, An Analysis of the Nature and Structure of High Pressure and Low Pressure Centers (Part I), Development of Geological Education, No. 46, pp. 53-61.
47. Mofidi, A., And Zarrin, A., 2006b, An Analysis of the Nature and Structure of High Pressure and Low Pressure Centers (Part II), Development of Geological Education, No. 47, pp. 54-58.
48. Mohammadi, F., Lashkari, h., 2019, Investigation of precipitation variation of Sudan low pressure during the historical process in southwestern Iran. Natural Geography research. No. 51 (2), pp. 373-387.
49. Mohammadi, H., Akbari, M., Fatahi, A. And Shamsipour, A, 2012, Dynamic Analysis of Sudanese Systems and Heavy Rainfall Occurrence in Southwestern Iran, Geographical Sciences Applied Researchs, No. 24, pp. 7-23.
50. Mohammadi, Z, 2017, Synoptic Analysis of the Role of Arabia Sub-Tropical High-Pressure and Sub-Tropical Jet stream in Droughts and Wetlands, Beginning, End, and Length of Rainfall Period in South and South western of Iran, Ph.D. Thesis. Shahid Beheshti University.
51. Moradi, M., Meshkati, EH, Azadi, M., Bidokhti, AS, 2008, Importance of Equivalent Potential Vorticity in Determining the Trajectory of Sudan Lows, Nivar, No. 68, pp. 52-33.
52. Movaghari, A., M., Khosravi, 2014, Investigation of the Relationship between Sudan Low-pressure System and the Heavy Precipitation Occurred on April 30, 1994 in Kermanshah. Journal of Natural Environmental Hazards, No. 3(4), pp. 61-80.
53. Olfat, A. 1968, Iran's weather in the past year. Nivar Journal. No. 1, pp. 29-31.
54. Pedgley, D.E., 1966a, The Red Sea convergence zone, part A: The horizontal pattern of winds, Weather, No. 21(10), pp. 350-358.
55. Pedgley, D.E., 1966b, The Red sea convergence zone, part B: Vertical Structure, Weather, No. 21(11), pp. 394-406.
56. Pedgley, D.E., and P.M., Symmons, 1968, Weather and the locust surge. Weather, No. 23(12), pp. 484-492.
57. Reid, G.C., 2000, solar variability and the Earth’s climate: Introduction and overview. Space Science Reviews, No. 94, pp. 1-11.
58. Saaroni, H., B., Ziv, A., Bitan, and P., Alpert, 1998, Easterly wind storms over Israel. Theoretical and Applied Climatology. No. 59(1-2), pp. 61–77.
59. Schlegel, K., G., Diendorfer, S., Thern, and M., Schmidt, 2001, Thunderstorms, lightning and solar activity—Middle Europe. Journal of Atmospheric and Solar-Terrestrial Physics. No. 63(16), pp.1705-1713.
60. Solanki, S., 2002, Solar variability and climate change. Astronomy and Geophysics. No. 43(5), pp. 5.9-5.13.
61. Tsiropoula, G., 2003, Signatures of solar activity variability in meteorological parameters. Journal of Atmospheric and Solar-Terrestrial Physics. No. 65(4), pp. 469-482.
62. Tsvieli, Y., A., Zangvil, 2005, Synoptic climatological analysis of wet and dry Red Sea Troughs over Israel. International Journal of Climatology. No. 25(15), pp. 1997–2015.
63. Tsvieli, Y., A., Zangvil, 2007, Synoptic climatological analysis of Red Sea Trough and non-Red Sea Trough rain situations over Israel. Advances in Geosciences. No. 12, pp. (137-143).
64. Yair, Y., C., Price, D., Katzenelson, N., Rosenthal, L., Rubanenko, Y., Ben-Ami, and E., Arnone, 2015, Sprite climatology in the Eastern Mediterranean Region. Atmospheric Research. No. 157, pp. 108-118.
65. Ziv, B., U., Dayan, D., Sharon, 2004, a mid-winter, tropical extreme flood–producing storm in southern Israel: Synoptic scale analysis. Meteorology and Atmospheric Physics. No. 88(1-2), pp. 53-63.
)