Synoptic analysis of specific humidity anomalies of dry autumns in the northwest of Iran

There are substantial changes in climate elements, particularly precipitation, over time, and understanding these changes provides the knowledge necessary to maximize the efficiency of nature. As part of this study, dry autumns were determined during the statistical period of 1987-2016 by calculating the standard precipitation index using DIC software based on the environmental approach to circulation. Based on the reconstructed NCAR/NCEP data, combined maps of 500 hPa, 700 hPa, and 1000 hPa specific humidity were obtained from the reconstructed data, and Hof-Müller diagrams of 700 and 1000 hPa specific humidity were analyzed. Based on the results of this research, it is apparent that in dry autumns, there are strong positive anomalies on the earth's surface, indicating the weakening of low pressures and the prevention of low pressures from entering. Due to the high altitude rule, there are positive anomalies compared to the long-term average at 500 hectopascals. As a result, lower latitudes' hot, humid climate has not been transferred to the region. Furthermore, the Hof-Muller diagrams at the levels of 700 hPa and 1000 hPa are examined in the dry autumns of the northwest at latitude 38°N and longitude 48°E, indicating an apparent decrease in specific humidity for this level. In 4 cases out of 5 study samples, Sudanese low-pressure systems and Sudanese-Mediterranean systems had a significant impact on injecting moisture into the study area, especially in the southern latitudes (15 to 30°N).