Synoptic Analysis and Identification of Hail Flow Days in Western Iran (Case Study: Zab Basin, West Azerbaijan)

Introduction
Hail is considered as one of the most important atmospheric hazards as a consequence of a thunderstorm having harmful effects on the environment every year. Hailstorms usually occur from the clouds of cumulonimbus and are often thunderstorms and generally accompanied by thunderstorms, especially in spring. In general, hail is the product of intense convection found in a thunderstorm. To analyze and predict the mechanisms of each climatic phenomenon, one needs to have a detailed understanding of the main components of its climatic systems.
Since hail in the Zab basin annually causes significant damages, especially in agriculture and livestock, the aim of this study is to investigate the synoptic patterns of hail in the Zab basin in order to reduce the damaging effects. The climatic phenomenon is on different parts.   The Zab Minor catchment in northwestern and northwest part of Kurdistan Province, southwestern Iran,  consists of Piranshahr, Sardasht and Baneh counties.
Material and methods
In this study, an environmental circulation approach was used to identify the circulation patterns of the days associated with hail in the west of the country. In this study, the code of days associated with the hail of Sardasht, Piranshahr and Baneh synoptic stations (with the longest statistical period between provincial stations) was obtained from the establishment (1992) up to year 2016 from the Meteorological Organization of Iran and then according to the code. The intensity of days associated with the hail event was identified during the study period. To identify large-scale synoptic patterns of day-event hail phenomena, hectopascal altitude and sea-level pressure data from open NCEP / NCAR analysis data on daytime events ranging from 0 ° C to 120 ° C and 0 ° C to 90 ° N They were prepared. Also, to determine the moisture flux of hail event days, Schulz and Benacus moisture flux equation was used.
Results and discussion
The purpose of this study is to establish an appropriate classification of atmospheric patterns in relation to hail events and the climatic characteristics that cause them in the Zab Basin. Using the NCEP / NCAR Center data, it is possible to analyze synoptically and identify the circulation patterns that coincide with these events. Cluster analysis of sea level pressure and geopotential height data revealed three weak, moderate and severe circulation patterns associated with hail precipitation. Finally, in order to identify the most important systems, intra-group correlation was performed between each cluster, and the day that had the highest correlation with other days in one cluster was selected as the representative day of the circulation pattern of the cluster and the basis of this study was analyzed.
Conclusion
In the study of the synoptic patterns of hail precipitation according to the obtained results, the model best justified the hail precipitation is presented for the Zab basin. In the first model, with low hail precipitation, we observed a contrast between warm and humid low-pressure Sudan systems and high-pressure European cold tabs on the study area.
In the second pattern at sea level with the formation of a low pressure center on Iraq, this low pressure is reinforced by the development of warm and humid air through the Sudanese system and the formation of a high-pressure belt across the northern Iranian strip, which, with its rotation and rotation, drives cold air. The study area has provided conditions for frontalisation in the area.
In the third model, Sudan's low sea level is strengthened so that its tongues stretch to the northwest and northwest Iran, which inject hot and humid air and create convergence conditions over the study area. The Siberian high pressure on the north of Iran is also at its peak, and its tabs and motions cause very cold air to fall over the study area, and in this case the very cold northern and warm southern humid conditions make for the front. The region created instability due to the specual circumstances.
Previous research on hail precipitation or only the role of Sudanese high or low pressure northern Sudan in hail precipitation events has shown that hail precipitation in western Iran necessitates confrontation of air masses. The cold north is warm and humid south and the strongest hailstorms occurred when these air masses penetrated the study area at peak times and created conditions for overburden and instability with the help of high-level currents. They cause severe vertical motions in the atmosphere and, as a result, hail over the region.