AUTHOR=Li Zhi , Xu Zecheng , Zheng Yunxia , Fang Yue 

TITLE=Air sea conditions facilitate a transformation of the positive Indian Ocean Dipole with distinct east pole characteristics into an extreme event

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1106130

DOI=10.3389/fmars.2023.1106130

ISSN=2296-7745

ABSTRACT=The Indian Ocean Dipole (IOD) is one of the dominant interannual variabilities in the Indian Ocean (IO), and the extreme IOD, in particular, has dramatic effects on the weather, agriculture and ecosystem around the IO. Therefore, extreme IOD formation has been a worldwide research focus. Among 13 positive IOD (PIOD) events, 2 type-east and 2 type-comparable PIODs developed into extreme events during the 1960-2020 period. This investigation focuses on the cause of the formation of the type-east extreme PIOD, as previous studies have discussed the origin of the type-comparable extreme PIOD. Composite analysis shows that as an entity, the strong East-Asian and Australian monsoon (EAAM) may result in an evident easterly wind anomaly around the Indonesian region of the Marine Continent during May-August of the years when type-east PIODs occurred. The easterly wind anomaly associated with the EAAM is stronger in the extreme IOD group, whereas it is relatively weak in the regular group. The difference in the easterly wind anomaly between the extreme and regular groups could result in a vertical-motion anomaly by enhancing the anomalous westward current. The stronger vertical motion upwells the deep-layer cold water, resulting in a more distinct difference in the vertical-temperature gradient. All these situations promote the transformation of the type-east PIODs that occurred in 1961 and 1994 into extreme events and are indicative of the importance of vertical advection terms in the formation of type-east extreme PIODs. This study reveals the cause of the formation of type-east extreme PIODs, which will be helpful for understanding IOD diversity.