Temporal variations in the frequency of thunderstorm days in Tabriz and its relationship with sunspots frequency and global atmospheric Co2 concentration

In this study, using various statistical methods such as trend analysis, Mann–Kendall (MK) test and Morlet Wavelet Analysis (MWA), the Frequency of Thunderstorm Days (FTD) and its relationship with Sunspots Frequency (SF) and Global Atmospheric Carbon Dioxide Concentration (GACDC) in the 68-year statistical period of 1951–2018 in Tabriz Synoptic Station has been studied. In terms of distribution and temporal concentration, the highest incidence of Thunderstorm Days (TD) is concentrated in the months of May and June and the lowest in the cold months of the year, i.e. January, February and December, with spring having the highest and winter having the lowest FTD. The analysis of the trend of FTD in the study area showed that except for the trends of January, February, June and December, which have no clear and significant trend, other months, especially April, have an upward and significant trend and the seasonal trend of FTD in Tabriz increase significantly in all seasons, especially in the peak of spring; Also, in the annual time scale, a significant upward trend was observed. Decadal changes in the FTD show a sharp increase in the occurrence of TD in Tabriz, especially in the second decade of the twenty-first century. The results of MWA showed that the FTD, like sunspots, has a periodic cycle in its emergence and occurrence. Based on the results of cross-wavelet analysis, there is a strong negative and anti-phased relationship between SF and the FTD in Tabriz. Also, according to the results of MWA, no significant relationship between the GACDC and the FTD in Tabriz has been found.