University of Tehran Press Journal of the Earth and Space Physics 2538-371X 47 4 2022 01 21 Autumn and Winter Extreme Precipitation Events and their Relationship with ENSO, NAO and MJO Phases over the West of Iran Autumn and Winter Extreme Precipitation Events and their Relationship with ENSO, NAO and MJO Phases over the West of Iran 201 218 83549 10.22059/jesphys.2021.316961.1007280 FA Toraj Jamshidi Khezeli Ph.D. Student, Atmospheric Science and Meteorological Research Center (ASMERC), Tehran, Iran Abbas Ranjbar Saadat Abadi Associate Professor, Department of Weather Hazards Warning, Atmospheric Science and Meteorological Research Center (ASMERC), Tehran, Iran Mohammad Ali Nasr-Esfahany Assistant Professor, Department of Water Engineering, Shahrekord University, Shahrekord, Iran Sahar Tajbakhsh Mosalman Assistant Professor, Department of Atmospheric Prospecting, Atmospheric Science and Meteorological Research Center (ASMERC), Tehran, Iran Ali Reza Mohebalhojeh Professor, Department of Space Physics, Institute of Geophysics, University of Tehran, Tehran, Iran Journal Article 2021 01 11 Some extreme precipitations have occurred in Iran in recent years. This paper is devoted to the study of extreme precipitations in the west of Iran, affected by combination of atmospheric pressure patterns in the period of 1987–2016. At first, monthly precipitations for seven synoptic stations of the west of Iran in autumn and winter with positive anomalies greater than 100% were identified. Then, for statistical-dynamical analysis, the El-Nino Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Madden–Julian Oscillation (MJO) indices were used. Results showed that the extreme precipitations had occurred during moderate to strong El-Nino, while MJO was critical and strong, in phases 2 and 8, and NAO was in positive phase. The anomalies of the MJO index in case studies had positive values. The NAO for case studies has entered a positive phase from a strong negative phase a few days before extreme precipitation. Analyzing the relationship between the NAO and the MJO with lagged composites showed when the MJO leads the NAO, significant positive NAOs are found for phases 2, and negative NAOs for phases 8, indicating a significant influence of the MJO on NAO. The synoptic-dynamic analysis showed that three low pressure and one high pressure were the dominant systems that have been effective in producing extreme precipitation. Examination of the moisture fluxes revealed that the main humidity sources of the heavy precipitation were the Arabian Sea due to easterly winds that travel a long distance over the north west of Indian Ocean to the Arabian Sea. Some extreme precipitations have occurred in Iran in recent years. This paper is devoted to the study of extreme precipitations in the west of Iran, affected by combination of atmospheric pressure patterns in the period of 1987–2016. At first, monthly precipitations for seven synoptic stations of the west of Iran in autumn and winter with positive anomalies greater than 100% were identified. Then, for statistical-dynamical analysis, the El-Nino Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Madden–Julian Oscillation (MJO) indices were used. Results showed that the extreme precipitations had occurred during moderate to strong El-Nino, while MJO was critical and strong, in phases 2 and 8, and NAO was in positive phase. The anomalies of the MJO index in case studies had positive values. The NAO for case studies has entered a positive phase from a strong negative phase a few days before extreme precipitation. Analyzing the relationship between the NAO and the MJO with lagged composites showed when the MJO leads the NAO, significant positive NAOs are found for phases 2, and negative NAOs for phases 8, indicating a significant influence of the MJO on NAO. The synoptic-dynamic analysis showed that three low pressure and one high pressure were the dominant systems that have been effective in producing extreme precipitation. Examination of the moisture fluxes revealed that the main humidity sources of the heavy precipitation were the Arabian Sea due to easterly winds that travel a long distance over the north west of Indian Ocean to the Arabian Sea. https://jesphys.ut.ac.ir/article_83549_54cf55f27446b967d8d61f6895f976ce.pdf