The role of InterTropical Convergence Zone (ITCZ) in the development and pattern of Sudanese low-pressure trough expansion in pervasive and severe rainfall in Southern Iran

Document Type : Original Article

Authors

Department of Physical Geography, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

Abstract

Extended abstract
Introduction
Sudanese low-pressure is a system with tropical characteristics. Its precipitation characteristics are very similar to that of tropical systems. This is especially evident in the countries on the southern shores of the Persian Gulf and in the southern and southwestern parts of Iran. Heavy rainfall of this system results in high moisture potential and access to the resources of the warm southern seas. Some researchers believe that the system originated in the northward expansion of the Inter-Tropical Convergence Zone (ITCZ) in the range of 25 to 35° east (in East Africa) and created a thermal nucleus in southern Sudan and Ethiopia (Lashkari, 1996; 2001). The aim of this study is to identify the adaptation of northward expansion of the Sudanese low-pressure trough with the ITCZ northward expansion pattern during pervasive and severe rainfall in the cold season in the southern half of Iran.
Materials and methods
Two categories of data were used for this study. These data included daily precipitation data from the Iranian Meteorological Organization and the ERA interim gridded data which included sea level pressure and the specific humidity of the 700 HP of the ECMWF. Second category data with horizontal resolution of 0.5 × 0.5° during 1997-2017 statistical period were prepared. Subsequently, based on the selected criteria, 86 pervasive and severe rainfall systems were identified. Then, the ITCZ's average monthly position, the central core pattern, the area of the first closed curve, and the expansion of the Sudanese low-pressure trough for all 86 days of rainfall were plotted. In the final step, the position of the ITCZ was identified using a special humidity variable of 700 HP in the tropical region for the systems of each month.
Results and discussion
This study has been examining the degree of adaptation and the role of the ITCZ in the formation, expansion and moisture supply of rainfall by Sudanese systems in three general forms for selected precipitation samples.
Expansion pattern of the Sudanese low-pressure core
During all months, the region between the eastern border of Sudan and Ethiopia is the focus of Sudan's low-pressure core. In November, December, March and April the pattern of distribution of low-pressure cores show very good adaptation with the expansion pattern of the ITCZ. However in January and February, the cores become condensed in the southeastern part of Sudan.
Expansion pattern Sudanese low-pressure first closed curve
The pattern of expansion of Sudanese low-pressure first closed curve shows very good adaptation with the trough pattern of the ITCZ in all months. The adaptation of the ITCZ trough and the pattern of expansion of the low-pressure internal core indicate that it plays a significant role in the strengthening and flowing pattern of Sudanese low-pressure.
Synoptic expansion pattern of Sudanese low-pressure trough axis
In all cases and all months, the extension of the low-pressure trough, especially over the Red Sea and the Bab al-Mandeb Strait, and even part of the Arabian Peninsula is in adaptation with the extension of the ITCZ trough.
Conclusion
During all the months of the rainy season, an ITCZ trough with a southwest-northeast direction extends from the Horn of Africa to northern Yemen. The pattern of expansion of Sudanese low-pressure trough, the pattern of nucleus distribution and the extent of expansion of the first closed curve are fully in adaptation with the monthly pattern of ITCZ expansion. This shows the undeniable role of ITCZ in the formation, expansion and moisture supply of rainfall systems. In January, in all three cases, the number of precipitation systems, the distribution effect area and the penetration depth of the input systems to the southern half of Iran are of primary importance. This could be related to the weaker thermodynamics of the Sudanese system at the beginning of its activity, the weak expansion of ITCZ in the region due to the westward position of the Arabian anticyclone at the beginning of the rainy season and the westward return at the end of the rainy season.

Keywords

Main Subjects

References

References
Persian References:
-Askareh, H., Ghaemi, H. and Rezaei, S., 2016. Review mechanism of expansion and low pressure Red Sea. Geographical Planning of Space Quarterly Journal, v. 6(21), p. 77-90.l
-Fanoodi, M., Omidvar, K. and Mazidi, A., 1396. Investigation of the effect of Sudanese low pressure system on torrential rains in the foothills of Iran. Physical Geography Quarterly, v. 35, p. 74-61.
-Gandomkar, A., 2012. The Crisis Managemet of Flood in Isfahan Using Atmospheric System. Geographical Researches, v. 27(2), p. 115-128.
-Jafari, M. and Lashkari, H., 2021. Synoptic Patterns that Determine the Trajectory of Precipitation Systems of Sudanese Origin. Journal of Spatial Analysis Environmental Hazards, v. 8(1), p. 55-78.
-Javanmard, S., Bodaq Jamali, J. and Asiai, M., 2003. Correlation of Kazakhstan-Oman Sea pressure changes with Iranian rainfall fluctuations. Geographical Research Quarterly, v. 71, p. 150-136.
-Karimi, M., 2007. Analysis of sources of moisture supply in Iranian rainfall. PhD thesis in natural geography, climatology, Faculty of Humanities, Tarbiat Modares University.
-Karimi, M. and Farajzadeh, M., 2011. Moisture Flux and Spatial Temporal Patterns of Moisture Supply Resources in Precipitation of Iran. Journal of Applied Research in Geographical Sciences, v. 19(22), p. 109-127.
-Karimi, M., Khoshakhlagh, F., Bazgir, S. and Jafari, M., 2017. The influence of lower tropospheric circulation of Arabian high pressure on Iran precipitation. Physical Geography Research Quarterly, v. 48(4), p. 569-587.
-Lashkari, H., 1996. Synoptic pattern of heavy rainfall in southern and southwestern Iran. PhD thesis in natural geography, Faculty of Humanities, Tarbiat Modares University.
-Lashkari, H., 2002. Tracking Sudanean Low Systems Entering Iran. Modarres Human Sciences, v. 6(2), p. 133-156.
-Lashkari, H., 2004. The Mechanism of Forming, Deepening and Development of Sudan Low and Its Effect in Precipitation South and South Western of Iran. Geographical Research Quarterly, v. 35(46), p. 1-18.
-Lashkari, H., Matkan, A., Azadi, M. and Mohammadi, Z., 2017. Synoptic Analysis of Arabian Subtropical High Pressure and Subtropical Jet Stream in Shortest Period of Precipitation in South and South West of Iran. Environmental Sciences, v. 14(4), p. 59-74.
-Mohammadi, H., Fattahi, E., Shamsipour, A.A. and Akbari, M., 2012. Dynamic Analysis of Sudan Low- Pressure Systems and Torrents in Southwest of Iran. Journal of Geographical Sciences, v. 12(24), p. 7-24.
-Mohammadi, Z. and Lashkari, H., 2018. Effects of Spatial Movement of Arabia Subtropical High Pressure and Subtropical Jet on Synoptic and Thermodynamic Patterns of Intense Wet Years in the South and South West Iran. Physical Geography Research Quarterly, v. 50(3), p. 491-509.
-Mofidi, A. and Zarrin, A., 2005. The Synoptic Study of Low Pressure Systems of the Sudan in Heavy Falls in Iran, Geographical Research, v. 20(2), p. 113-136.
-Mofidi, A. and Zarrin, A., 2005. Synoptic Analysis of the Nature of Sudan Low Pressure Systems (Case Study: December 2001 Storm), territory, v. 2(6), p. 26-50.
-Parak, F., Roshani, A. and Alijani, B., 2016. Synoptic Investigation of the Role of the Sudanese Low Pressure System during Wet and Drought Years in the Southern Half of Iran. Journal of Geography and Environmental Hazards, v. 4(3), p. 75-90.
 
English References:
-Alpert, P., 2004. A New Seasons Definition Based on Classified Daily Synoptic Systems: An Example for the Eastern Mediterranean: International Journal of Climatology, v. 24, p. 103-1021.
-Chen, B., Lin, X. and Bacmeister, J.T., 2008. Frequency distribution of Daily ITCZ patterns over the western–central Pacific: Journal of Climate, v. 21(17), p. 4207–4222.
-Elfandy, M.G., 1952. Forecasting Thunderstorms in the Red Sea: Bulletin of the American Meteorological Society, v. 33, p. 332-338.
-Elfandy, M.G., 1950a. Effects to Topography and other Factors on the Movement of Lows in the Middle East and Sudan: Bulletin of the American Meteorological Society, v. 31, p. 375-381.
-Farajzadeh, M., Karimi Ahmadabad, M., Ghaemi, H. and Mobasheri, M.R., 2007. Studying the Moisture Flux over West of Iran: A Case Study of January 1 to 7, 1996 Rain Storm: Journal of Applied Sciences, v. 7, p. 3023-3030.
-Jafari, M. and Lashkari, H., 2020. Study of the relationship between the intertropical convergence zone expansion and the precipitation in the southern half of Iran: Journal of Atmospheric and Solar-Terrestrial Physics, v. 210, p. 1-13.
-Hastenrath, S., 1995. Climate Dynamics of the Tropics: nterpretation and Application: Springer Netherlands, Kluwer Acad, Norwell, Mass 8, 488 p.
-Hafez, Y., 2012. Variability of Intertropical Convergence Zone (ITCZ) and Extreme Weather Events: Atmospheric Model Applications, p. 111-136.
-Holloway, C.E. and Neelin, J.D., 2009. Moisture vertical structure, column water vapor, and tropical deep convection: Journal of the Atmospheric Sciences, v. 66(6), p. 1665-1683.
-Johnson, D.H., 1965. African synoptic meteorology: Meteorology and the desert Locus, WMO, Tech. notes, v. 69, p. 48-90.
-Krichak, S.O. and Alpert, P., 1998. Role of large Scale Moist Dynamics in November 1-5,1994, Hazardous Mediterranean Weather: Journal of Geophysical Research, v.103, p. 19453-19468.
-Krichak, S., Alpert, P. and Krishnamurti, T.N., 1997a. Interaction of Topography and Tropospheri Flow–Apossible Generator for the Red Sea Trough: Meteorology and Atmospheric Physics, v. 63, p. 149-158.
-Krichak, S., Alpert, P. and Krishnamurti, T.N., 1997b. Red Sea Trough/Cyclone Development-Numerical Investigation: Meteorology and Atmospheric Physics, v. 63, p. 159-169.
-Lashkari, H. and Jafari, M., 2021a. The role of spatial displacement of Arabian subtropical high pressure in the annual displacement of the ITCZ in East Africa: Theoretical and Applied Climatology, v. 143, p. 1543-1555.
-Lashkari, H. and Jafari, M., 2021b. Annual displacement and appropriate index to determine ITCZ position in East Africa and the Indian Ocean regions: Meteorology and Atmospheric Physics, v. 133, p. 1111-1126.
-Latysheva, I., Belousova, E., Ivanova, A. and Potemkin, V., 2007. Circulation Conditions of the Abnormally Cold Winter of 2005/06 Over Siberia: Conference on Climate Variability and Change 8, San Russian Meteorology Hydrology, v. 32, p. 572-575.
-Lashkari, H. and Mohammadi, Z., 2018. Study on the role of annual movements of Arabian subtropical high pressure in the late start of precipitation in southern and southwestern Iran: Theoretical and Applied Climatology volume, v. 137, p. 2069-2076.
-Mukherjee, P., Sinha, N.  and Chakraborty, S., 2016. Investigating the Dynamical Behavior of the Intertropical Convergence Zone Since the last Glacial Maximum Based on Terrestrial and Marine Sedimentary Records: Quaternary International, p. 1-9.
-Nicholson, S.E., 2018. The ITCZ and the Seasonal Cycle Over Equatorial Africa: American Meteorological Society, p. 337-348.
-Solot, S.B., 1950. General circulation over the Anglo-Egyption Sudan and adjacent regions: Quarterly Journal of the Royal Meteorological Society, v. 31, p. 85-94.
-Waliser, D.E. and Gautier, C., 1993. A satellite-derived climatology of the ITCZ: Journal of Climate, v. 6(11), p. 2162-2174.
 
Researches in Earth Sciences
Volume 12, Issue 3 - Serial Number 47
September 2021
Pages 223-241

Files

Share

How to cite

Statistics