The influence of tropical basin interactions on the 2020-2022 double-dip La Nina

The recharge oscillator mechanism suggests that a strong El Nino event can trigger a following La Nina event that sometimes lasts for two or even three years through warm water volume preconditioning within the tropical Pacific. However, a prominent and persistent "double-dip" La Nina event appeared in the boreal winters of 2020/2021 and 2021/2022 without any significant El Nino preconditioning. Here we explore the possibility that tropical basin interactions may have initiated and helped to prolong La Nina conditions over the 2-year period 2020-2022. This period was preceded by a strong positive Indian Ocean Dipole (IOD) during the boreal fall of 2019 that gave way to basin-scale warming in the Indian Ocean in early 2020 and a notable tropical Atlantic warming in the boreal winter of 2019/2020. Later, a strong Atlantic Nino developed in the boreal summer of 2021. Using composite analyses to characterize earlier double-dip La Ninas, we argue the unusual sequence of events in 2019-2021 in the Indian and Atlantic Oceans may have energized and sustained the 2020-2022 La Nina event without any significant warm water volume preconditioning within the tropical Pacific.