The Roll of Subtropical Jet-Stream on Daily Precipitation more than 10mm in Zayanderood basin

Zayanderood basin is one of the major internal river basins in the central Iran, where the only permanent river, Zayanderood River, flows. Fluctuations in rainfall in recent years have affected different areas of Iran. Because of the dependence of the provinces of Isfahan, Yazd, and Kerman on water resources of this basin, changes and fluctuations in precipitation within this basin have had many social and economic consequences along with bad outcomes in terms of regional, national and international dimensions. aimed to identify the synoptic patterns of precipitation of more than 10 mm as an effective kind of rainfall to provide water supply and understand the origin and characteristics of precipitation patterns that would contribute to more rainfall. This would lead to a better planning process that could facilitate the optimal utilization of water resources in this basin. The research method is an inductive and synoptic method of environmental circulation. The daily rainfall data obtained from synoptic, climatological and rain gauge stations in the watershed basin within the period of 1987-2011 were collected. The days during which at least two stations had more than 10mm of rainfall were recorded and extracted and then the daily precipitation in the basin stations was grouped. Finally, the days mounted to 266. The data file maps of geopotential heights at 1000, 500 and 300mb levels and orbital wind (U-wind) data from http://www.cru.uea.ac.uk/data site were extracted. After storing the data within the time period mentioned, the data was taken and sorted and processed by Excel software using writing macros. For the purpose of getting the weather patterns, the S method along with Synoptic and Principal Components Analysis (PCA) without rotation was used for classification. As the last step, cluster analysis with Ward method was carried out on factor loadings extracted and 266 days were classified into 4 groups. The Ward method was used for the determination of the clusters and the Squared Euclidean Distance was used to determine the distance between clusters. Based on the results of principal component analysis, 266 days in a year were summarized in 9 factors. The first factor alone would explain 38.1 percent variation in the data and a total of 3 factors could explain 86.1 percent variation in the data. Therefore, by dividing the days into four groups, the maximum correlation within any groups and the highest diffraction between groups were obtained. Thus, these four patterns of rainfall were found to cause river basin rainfall of more than 10mm.Pattern. 1 Dept trough Siberian - Eastern Mediterranean Sea: Survival of geopotential height maps at 500mb load in pattern 1 showed a curved trough in Northern- East, Southern West, which had been stuck on the Black Sea and East Mediterranean. According to this model, Zayanderood basin was located in the Eastern side of the trough. This process led to the ascent of air over Zayanderood basin and the occurrence of rainfall in the region. Pattern. 2: Mediterranean pattern: This model could explain (21.4%) conditions in the upper, middle and ground surface levels of the atmosphere for the occurrence of precipitation of more than ten millimeters in Zayanderood basin. In other words, the typical pattern of occurrence of this precipitation belonged to the Mediterranean pattern. In this model, the core speeds of Jetstream with little curving to north-east was located between the Red Sea and Persian Gulf lied towards the center-left output of Jet stream axis, thereby influencing air advection ascent on the East axis of Western wind wave. Pattern. 3. Red Sea - Blok Sea trough pattern: Average holding position of trough on this model was on the Red Sea and the average holding position of Jetstream was located between the Black Sea and the Persian Gulf on the Arabian Peninsula. Adaptation of the left output to axis Jetstream on air advection ascent in the East-West axis wind led to increased instability of waves and heavy precipitation in this model. The most typical pattern was the Sudanese form in this pattern. Pattern 4: Trough of Turkey – Red Sea: In the map with the height of 500mb, we observed that a trough was located on the Turkey – Red Sea in the West of Iran. This was converted to the stack in the more northern latitudes of Russia. The transition region from the trough to stack was located in the North West of Caspian Sea. A very low core speed at the level of 200mb was obvious above this area. The role of subtropical jet-Stream on daily precipitation of more than 10mm more than ten millimeters that affected the water supply in Zayanderood basin were analyzed in order to come to a good understanding of the effective systems of this precipitation. By using Factor Component Analysis and hierarchical clustering techniques, day’s maps with precipitation of more than ten millimeters were classified in to four patterns in Zayanderood basin. On the other hand, the core position of subtropical Jet-stream in the creation of ten millimeters rainfall was very effective in Zayanderood basin. This was especially the case when Subtropical jet stream core speed composite with the core speed of the polar front Jet-stream was found to have more influence on the creation of an effective rainfall. All models, as determined by means of maps, showed that overlaying of the left output of subtropical jet stream core on the upwelling of westerly winds wave in the left position of trough was very effective in increasing positive vortices and intensifying instability and therefore, the resulting rainfall. Our review also revealed that compliance of the trough axis with the mid-latitude trough in the Western Iran was more important in enhancing and creating instability and precipitation occurrence in comparison to the adaptation level of 500mb of synoptic conditions with the surface pressure.