Correlation between NAO index and the occurrence of ARs in Iran

Atmospheric rivers are one of the atmospheric phenomena that generate heavy rainfall and can lead to significant human and financial losses.Understanding the synoptic mechanisms of water vapor flux and atmospheric river formation in the country's atmosphere, as well as revealing the interaction between the NAO (North Atlantic Oscillation) zonal component and the creation and intensification of this atmospheric phenomenon, can greatly improve the predictability of torrential rainfall events.The main goal of this research is to investigate the atmospheric river phenomenon in the Iranian atmosphere and its relationship with the phases of the NAO phenomenon.In this regard, data on the zonal and meridional components of wind, specific humidity, and NAO anomalies were obtained from the NOAA database during the statistical period of 1944-2019.The results showed that during the study period, atmospheric rivers have shifted in terms of longitude and latitude, moving toward the southern half of Iran.A high correlation was observed between the NAO index and meridional flows at levels above 600 hectopascals.Additionally, a sigma value of 0.2101 indicated a strong correlation with the NAO in the area where atmospheric rivers enter the Iranian atmosphere.High-pressure centers play an important role in directing atmospheric rivers.These rivers cannot pass through high-pressure centers and typically exhibit meridional curvature at the outer borders of these centers in the Northern Hemisphere, resulting in southwest and northeast orientations.The primary moisture source for atmospheric rivers entering Iran is the Atlantic Ocean, which is further enhanced by water bodies such as the Red Sea, the Sea of Oman, the Indian Ocean, and the Persian Gulf.