saeed jahanbakhsh; Ali Mohammad Khorshiddoust; Hamid Mirhashemi
Abstract
Introduction Due to their height, geometry and orientation, the mountains affect the atmospheric currents. Therefore, mountains cause the formation, intensification or weakening of many atmospheric phenomena. One of the most obvious of these phenomena is lee cyclogenesis whose formation and evolution ...
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Introduction Due to their height, geometry and orientation, the mountains affect the atmospheric currents. Therefore, mountains cause the formation, intensification or weakening of many atmospheric phenomena. One of the most obvious of these phenomena is lee cyclogenesis whose formation and evolution is subject to interaction between mountains and atmospheric currents. The lee sides of mesoscale or large-scale mountains, such as the Alps, Rocky Mountains, the East Asian mountains and the Andes, are favorable regions of cyclogenesis. This type of cyclogenesis is known as lee cyclogenesis, and can be defined as the formation of a cyclone with strong positive vertical vorticity or an appreciable fall in pressure with a closed circulation formed in the lee of a mountain that then drifts away (Chung. et al, 1976). In this regard, most studies have been made about the lee cyclogenesis of the Alps and the Rocky Mountains. As a result, the general understanding of mechanism of lee cyclogenesis is derived from studies conducted on these two mountains and partially due to the Alpine Experiment (ALPEX) field project held in 1982. In other words, the general framework of the mechanisms that exists today about lee cyclogenesis is based on the results obtained from the study of the Alps and the Rocky Mountains. Methodology The variables used in this study are consists of horizontal wind speed (u and v), vertical wind speed vertical pressure coordinates (w), temperature (T) geopotential pressure levels (z). The data variables used 1 and 0.5 degrees in the horizontal and vertical distance of 50 hPa from 1000 to 200 hPa. The data were extracting from the archival database ECMWF ERA Interim version with six-hour monitoring. Preliminary investigations showed that unstable systems under certain elevation models are located in the middle of the atmosphere in the region of the west, northwest of the west and west to the upstream slopes of the Zagros Mountains. so that the study of middle - level maps showed how the trough and the ridge of such systems has played an important role in determining the direction and movement of these systems towards zagros because it is different in terms of the confluence or diffluence system, curvature and sheer vorticity advection and ageostrophic wind of the trough, and finally the direction in the trough. In general, the conditions prevailing on these systems and the it direction they pass through to the Zagros have an important role in how they interact with the zagros. Therefore, it is necessary to examine how these systems approach to Zagros. For this purpose, this important issue was further investigated using the ageostrophic wind equation. Because the ageostrophic wind indicates the imbalance of geostrophic, and in fact the change of wind both in space and time causes this imbalance of geostrophic and the creation of the ageostrophic wind (Lynch and Cassano 2006, 123). Also used curvature vorticity in the natural coordinates, quasi-geostrophic height tendency equation and divergence of the isallobaric wind. Results and discussion An examination of the maps of the lower atmospheric levels shows that in some cases the cyclones approaching the windward slopes of the Zagros, under the baroclinic wave’s atmosphere, lead to the formation of a secondary rotation in the lee ward Zagros. Therefore, it is necessary to have a primary cyclone on the windward slope of the Zagros Mountains to form the lee cyclone. So the detection of cyclone approaching windward of the Zagros Mountains shows that cyclones which move and even higher than the Mediterranean latitude to the east, would have approached the Zagros in a way that was accompanied by a pattern of confluence ridge - diffluence trough in the middle of the atmosphere. While the cyclones, accompanied by a trough, were moving northward along the path of their eastward before reaching the Zagros in the north east. On the other hand, the cyclons, formed in the Red Sea region or Sudan, were required to reach the Zagros Mountains (the maximum velocity at the base of the trough) or the diffluence trough to approach the zagros. At the same time, the cyclones that were located in the area were under a confluence trough, never moved to the Zagros Mountains. So, according to the latitude of the primary cyclone and how the stack - trough is the level of 500 hpa, the path of the approaching Zagros is different. However, in many cases the nature of the trough and the level of the level of 500 hpa on the path of the eastward movement changes from difflunce to confluence and vice versa, which occurs due to the changing location in the baroclinic wave Conclusion Because The Zagros Mountains create changes in approaching baroclinicity waves causes advent thermal anomaly and consequently cause the occurrence of cyclone, so, such cyclogenesis is interpreted adjust according to the theory modify baroclinicity waves. Because this theory clearly states that mountain lead to lee cyclogenesis by modify baroclinicity. It is worth noting that many of the much complexities of the relationship between the Zagros Mountains and baroclinicity waves that may cause the occurrence of cyclones are a variety of other theories proposed in the literature to be more consistent Atmospheric Sciences. In any case, this study is based on small portions and a special kind of cyclogenesis can be in the Zagros leeward.
Climatology
Ali Mohammad Khrshieddoust; Hamid Mirhashemi; Mousa Nazari
Volume 23, Issue 68 , September 2019, , Pages 71-90
Abstract
Evaporation is one of the important factors in the hydrological cycle and is one of the determinants of energy equilibrium at ground level and water balance, which is required in various areas such as hydrology, hydrology, agriculture, forest management, and management of water resources (Sanei Nejad ...
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Evaporation is one of the important factors in the hydrological cycle and is one of the determinants of energy equilibrium at ground level and water balance, which is required in various areas such as hydrology, hydrology, agriculture, forest management, and management of water resources (Sanei Nejad et al., 2011). In this regard, one of the basic data in designing irrigation and drainage networks is the amount of evaporation power in each region. Because the design of transmission networks, such as drainage or drainage channels, as well as other parts of water design, depends on the amount of water required by the evaporation phenomenon (Jahanbakhsh et al., 1380). In general, evaporation hydrology is generally referred to as the phenomenon of water It simply turns steam into a physical process.
Saeed Jahahnbakhsh Asl; Hamid Mirhashemi; Masoomeh Tadayyon
Volume 19, Issue 51 , April 2015, , Pages 107-125
Abstract
In this study to identify the synoptic patterns causing heavy rainfall in East Azarbaijan province used with Environment- circulation pattern. Thus, beginning with the use of statistical methods limit type with return periods of ten-thousand-year, precipitation index for the 9 synoptic stations and climatology ...
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In this study to identify the synoptic patterns causing heavy rainfall in East Azarbaijan province used with Environment- circulation pattern. Thus, beginning with the use of statistical methods limit type with return periods of ten-thousand-year, precipitation index for the 9 synoptic stations and climatology located at the province was determined and finally 25 days was analyzed as day's high Heavy. The clustering of the 1000 hPa geopotential height level these days, were identified three patterns of spring cyclone, deformation and winter cyclone as the creator of this precipitation patterns. Synoptic analysis of this patterns showed that the low pressure at polar latitudes move to down and troughs on the Mediterranean and the Middle East that it has spread. Next to the tropical high pressure and subsequent ridge are moved to higher latitudes. There are conditions in the planetary patterns, increased temperature and pressure gradient zonal and meridional circulation of establishing Cut-off low and blocking high system is in the region. Research area within the affected system has been up and down simultaneously. Thermodynamic analysis using data from the radio station of Tabriz probe showed that the potential instability in the event of heavy rain on the atmospheric vertical profile has prevailed. In fact, because the study area in this period of low and high latitudes is dominated systems and the systems at different height levels of temperature and humidity differences are great together, a stratification of temperature, moisture in the atmosphere will be created and established conditions of potential instability
