Volume 5, Issue 1 (6-2018)                   Jsaeh 2018, 5(1): 97-112 | Back to browse issues page

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Ghavidel Y. Climatic geography of Tropical Cyclone hazards Affective on the southern coasts of Iran. Jsaeh. 2018; 5 (1) :97-112
URL: http://jsaeh.khu.ac.ir/article-1-2576-en.html
1- , ghavidel@modares.ac.ir
Abstract:   (353 Views)
Climatic geography of Tropical Cyclone hazards Affective on the southern coasts of Iran
The occurrence of any climatic fringes, including annual tropical storms, leave irreparable risks in its dominated areas. Understanding these events and knowledge of the time of their occurrence can be helpful in managing the unexpected incidents caused by them. Tropical cyclones are important natural turbulent processes in tropical and middle ecosystems in a number of regions of the world. Among the dynamic conditions of the atmosphere for the formation of tropical storms, there are three basic conditions: 1. The vertical wind shear should be limited between the 850 to 200 mb and the wind speed between these levels should be less than 10 meters per second. Such a situation allows the formation of a straight column, without breaking, to initiate tropical storms. 2- The formation state of tropical storms should be such that at least it is five degrees of latitude distant from the equator. Such conditions provide the minimum of Coriolis force to provide the tropical cyclic rotation along with other fundamental and apparent forces of the atmosphere and they occur following the pressure forces, Coriolis and centrifugal forces, cyclostrophic winds, and cyclic circulation in the center of the low pressure. 3- The presence of turbulence or discordance with vorticity and the convergence in the lower troposphere, or the anticyclone rotation and divergence in the upper levels of the atmosphere before the onset of activity, and the formation of tidal disturbances. Tropical storms are created by the presence of various dynamic and thermodynamic factors such as sea surface temperature and moisture content (thermodynamic properties), and flow and vertical winding functions (dynamic characteristics).
The parameters studied in this study for the dynamic and thermodynamic analysis of the tropical rotation of 1948 generally included the mean sea level pressure, geopotential heights, zonal and meridional components of wind, convection available potential energy, convective stabilization index, vertical velocity, relative vorticity, Sea surface temperature, humidity, and cloud cover levels which are drawn from the European Center for Medium Forecast Scale (ECMWF) with spatial resolution of 0.75 applying GRADS software. The study of combinational maps of 500 milligrams of geopotential heights and vorticity advection on the first day of the cyclone (1948/06/05) indicates the presence of a very strong low-altitude center with seven closed curves on the Arabian Sea. The most inner curve of this low-altitude center has the lowest elevation with 5650 geopotential meters height and the maximum vorticity advection and downright negative velocity of 10 and 0.5 Pascal to seconds, respectively. The above-mentioned Jetstream map with a maximum speed of 16 m / s, which covers the east of the center of the altitude, contributes to the greater divergence of this system. The formation of a very strong negative eddy in the 500-mb equilibrium also indicates intense instability at the site of the tropical cyclone and is actually a factor in the formation and reinforcement of such cyclones .The above-mentioned low altitude continues its cyclonic rotation at the level of 850 mb with two closed curves, and the maximum vorticity advection and downright negative velocity of 16 and 0.6 Pascal to second, respectively, due to the presence of lower level radar with a maximum speed of 20 m / s on the south side and similarly, in the south-east, it continued to circulate more rapidly at a rate higher than 500 mb, which results in the formation of the first pressure packet with a central
pressure of 997.5 mb on the sea surface. The high amount of specific humidity of 850 mb from the start of cyclone activity (12 g / kg), and the increase in this parameter in the next days of activity reaches 14 g / kg and also 4.5 g / kg at 500 millimeter equilibrium point to the high humidity at the location of the low-pressure center and the optimum conditions for the extraction of heavy rainfall in the eye wall of cyclone. Cloud cover maps also indicate a climber air density of up to 500 mb and the formation of a cloud at different levels of the atmosphere at the site of the formation of tropical rotation. The results show that the formation of the lower Jetstream, along with the tropical cyclone event (from 05 to 08 of 1948) affecting the southern coast of Iran, has been able to create severe air mass divergences in the left half of the nucleus and following this mechanism and the relationship between this velocity nucleus and the lower levels of the atmosphere and the sea level in the vertical direction, with the convergence of the mass, has been accompanied with the reduction of density and, finally, the reduction of pressure and the formation of turbulence, as the first ring for the development of tropical cyclones; therefore, the altitude of 850 mb and jet stream located at this elevation affected by the high-rise phenomenon on the western shores of the ocean (sometimes in the east of Madagascar) is considered as one of the most effective dynamic factors for the birth and development of this tropical cyclone on the southern coast of Iran. The tropical cyclone was formed from June 5 to June 8, 1948, at approximately 16 degrees north and 60 degrees east on the Arabian Sea. And, in general, the interaction between high pressure tongues on Saudi Arabia, Tibet and Iran, and the tropical cyclones has prepared the conditions for the activity and displacement of the tropical rotation. Previous studies of tropical storms have considered other synthetic systems, such as cyclones over Europe, and the integration of cyclones on the Mediterranean and Oman, as well as the displacement of the axis of tropical cyclones at middle and upper levels of the atmosphere affective in the escalation and displacement of the storm. It is also believed that the southern coast of Iran is also effective, and in general, less attention is paid to the causes of the development of the storm.
Key words:Tropical Cyclone, dynamic and thermodynamic analysis, low level jet stream, Thermodynamic parameters, Southern coast of Iran
Full-Text [PDF 2083 kb]   (192 Downloads)    
Type of Study: Research | Subject: Special
Received: 2016/11/21 | Accepted: 2018/06/12 | Published: 2018/06/13

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