Iran Meteorology Society (IMS) Journal of Meteorology and Atmospheric Science 2645-7261 4 3 2021 11 22 Effects of Pure and Combined Events of ENSO and IOD Phenomena on Autumn Precipitation Variations in the Northwest Iran Effects of Pure and Combined Events of ENSO and IOD Phenomena on Autumn Precipitation Variations in the Northwest Iran 193 209 161012 10.22034/jmas.2022.350476.1178 FA Mohammadreza Nazari Radsani Master student of Water Science and Engineering Majoring in Agricultural Meteorology، Faculty of Agriculture، Shiraz University 0000-0003-0492-617X Fatemeh Vatanparast PhD student of Climatology، Faculty of Social Sciences، University of Mohaghegh Ardabili 0000-0002-8873-4660 Mohammadjafar Nazemosadat Professor of Water Engineering and Head of Atmospheric and Oceanic Research Center, Faculty of Agriculture, Shiraz University Bromand Salahi Professor of climatology, Faculty of Social Sciences, University of Mohaghegh Ardabili Journal Article 2021 04 18 The El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are coupled oceanic-atmospheric phenomena that appear over the tropical Pacific and Indian Oceans. In this research, the pure impact and interaction of these two phenomena on the autumn precipitation in the Northwest Iran were analyzed for the period 1989-2018. The findings of 850 hPa vector winds anomaly for pure and combined events illustrate many differences with reciprocal phases. Examining the teleconnection effects on 23 synoptic stations in northwest Iran, displayed that ENSO has a greater influence than IOD at autumn precipitation variations. The conquest of pure ENSO events at autumn precipitation in northwest Iran compared with the long-term average in warm and cold phases has increased by 96% and decreased by 37%, respectively. This amount of autumn precipitation fluctuations under the positive and negative phases of IOD have increase by 61% and decrease by 31%. Shifting of pure IOD events from positive to negative phase, 18 stations in this area appeared an increase and five stations showed a decrease for autumn precipitation. When the El Nino phenomenon is accompanied with the positive IOD phase, the rainfall in the whole area has increased up to 60%. Whereas, autumn drought occurred more, when the La Nina periods was simultaneous with negative IOD phases. Also, evaluating autumn precipitation average of the opposite phases in combined events, findings of the Mann-Whitney test significantly display the occurrence of wet and dry durations in autumn. The El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are coupled oceanic-atmospheric phenomena that appear over the tropical Pacific and Indian Oceans. In this research, the pure impact and interaction of these two phenomena on the autumn precipitation in the Northwest Iran were analyzed for the period 1989-2018. The findings of 850 hPa vector winds anomaly for pure and combined events illustrate many differences with reciprocal phases. Examining the teleconnection effects on 23 synoptic stations in northwest Iran, displayed that ENSO has a greater influence than IOD at autumn precipitation variations. The conquest of pure ENSO events at autumn precipitation in northwest Iran compared with the long-term average in warm and cold phases has increased by 96% and decreased by 37%, respectively. This amount of autumn precipitation fluctuations under the positive and negative phases of IOD have increase by 61% and decrease by 31%. Shifting of pure IOD events from positive to negative phase, 18 stations in this area appeared an increase and five stations showed a decrease for autumn precipitation. When the El Nino phenomenon is accompanied with the positive IOD phase, the rainfall in the whole area has increased up to 60%. Whereas, autumn drought occurred more, when the La Nina periods was simultaneous with negative IOD phases. Also, evaluating autumn precipitation average of the opposite phases in combined events, findings of the Mann-Whitney test significantly display the occurrence of wet and dry durations in autumn. https://www.ims-jmas.net/article_161012_a4b822f1ed6eb046fa5aafcf1859aa91.pdf