Influences of the ENSO and IOD Coupled on the Autumn Rainfall Variations in Northwest Iran

The El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are two important teleconnections that influence precipitation variability in the northwestern districts of Iran. In this research, we investigated the combined impacts of these two phenomena on Iran's northwest autumnal precipitation. Our precipitation data included the monthly values of this variable (Oct-Dec of ۱۹۸۹-۲۰۱۸) for ۲۲ synoptic stations spread in various parts of the study area. The NOAA-based gridded data of precipitation were also used to assess the spatial distribution of precipitation over the desired temporal condition. By utilizing the ENSO and IOD time series, we examined precipitation characteristics during different combinations of these phenomena: where El Niño, La Niña, +IOD, and, –IOD coincided with each other. Our results showed that the simultaneity of El Niño and +IOD increases precipitation up to ۶۰%. Conversely, autumnal droughts were found where La Niña co-occurred with –IOD. Precipitation amounts were statistically different between these two combinations of ENSO and IOD.

Keywords:

Autumn precipitation , ENSO , IOD , combined event , northwest Iran