A study on process of thunder and lightning formation in the west of country applying non-parameter samples

In current study, thunderstorm occurrence data taking from 17 synoptic stations with the longest periods (from 1956 to 2005) have been analyzed to identify the associated spatial and temporal changes in the western part of Iran. First, to provide an initial statement of thunderstorm conditions in the study area, average days with thunderstorm have been mapped using ArcGIS software. Then, thunderstorm trends were established using statistical methods, by applying two of well-known non-parametric Mann-Kendall and Sen's Estimator methods. Both estimators demonstrate very excellent performance in the modeling of thunderstorm occurrence over time, regarding the discrete climatic data. Initial results determine that the number of days with thunderstorm is not homogeneous in the region, since the thundery days decrease from the north to the south, showing an increasing trend in seasonal and annual scales. At final stage, some spatial distributions of thundery days with significant trend were mapped in a GIS setting on the subject of seasonal and annual time series.