Impact of Indian Ocean dipole on Pacific blocking frequency during boreal autumn.

The impact of the positive and negative phase of the Indian Ocean dipole (IOD) on the Pacific blocking frequency (PBF) during boreal autumn is investigated based on the ERA5 daily reanalysis data from 1979 to 2021. It is found that the IOD index are characterized by an obvious interannual variation, and the most obvious dipole feature appears in boreal autumn, which is agree with previous studies. Strong 8 positive and 8 negative phases in boreal autumn are selected to further reveal the regulation of different IOD phases on PBF. The results show that the PBF exhibits negative (positive) anomaly in the North Pacific (East Siberia and Central Siberia) during the positive (negative) IOD phase. During the positive (negative) phase, the cold sea surface temperature anomaly (SSTA) in the tropical southeastern (western) Indian Ocean forces teleconnection wave trains, which are likely results of the northeastward propagation of Rossby wave energy. With such a wave train, a geopotential height anomaly of ‘north negative–south positive’ (‘north positive–south negative’) appears around the Bering Strait (Central Siberia) during the positive (negative) phase, which causes negative (positive) PBF anomalies, based on the ERA5 daily reanalysis data and ECHAM4.6 climate model output from 1979 to 2021. [ABSTRACT FROM AUTHOR]