The Determination of Convective Precipitation Contribution in Tabriz City Based on Instability Indices

The ascending mechanisms of the rainfall in different regions follow different patterns. Thus, understanding these patterns can amplify the level of environmental planning. The main objective of this research is the study of the spatial and temporal characteristics of the rainfall over five millimeters and the determination of convective precipitation contribution in Tabriz city based on upper air data. In this regard, hourly precipitation data of the station in Tabriz during a twenty-six-year period (2005-1980) collected from the Meteorology Organization with the rainfall data choice of more than 5 mm, and their temporal-spatial frequency was examined. With the selection of samples (precipitation of more than 5 mm), Skew-T diagrams of precipitation days were analyzed with instability indices such as CAPE, LI, TT, SI and KI. Annual precipitation data processing in the station in Tabriz showed that in the last decades, precipitation occurrence of more than 5 mm was more. Also, this precipitation has occurred frequently. In a seasonal scale, the maximum event of this precipitation (more than 5 mm) recorded in spring and the least in summer. Reviewed monthly, the maximum precipitation event of more than 5 mm occurred in May and April. Skew-T diagrams and calculation of instability indices showed that the role of convection factor, as the main cause of this type of precipitation, in heat duration precipitation is negligible. The convection factor is the main factor when the convection rate has sufficient intensity and the convection provides necessary instability for precipitation. In general, the convection factor has had the most important roles in the occurrence of precipitation in months of June and May. In total, after reviewing 96 samples of precipitation during warm period, we recognized that the convection factor frequently influences this area only in 20 percentage of the precipitation.