Interdecadal wind stress variability over the tropical Pacific causes ENSO diversity in an intermediate coupled model

Abstract

The role of interdecadal wind stress variability in the genesis of ENSO diversity is examined by using an intermediate coupled model (ICM) in the tropical Pacific; two types of experiments are performed, one with the original ICM, and the other with interdecadal wind stress (τ 𝑖𝑛𝑡𝑒𝑟𝑑𝑒 ) effect is explicitly represented. The τ 𝑖𝑛𝑡𝑒𝑟𝑑𝑒 component is derived from NCEP/NCAR reanalysis dataset as follows. First, the ensemble empirical mode decomposition (EEMD) is used to extract the interdecadal component of wind stress anomalies on about a 10-40yr timescale. Next, an idealized interdecadal cycle of τ 𝑖𝑛𝑡𝑒𝑟𝑑𝑒 is reconstructed by a principal oscillation pattern (POP) analysis based on the EEMD-extracted interdecadal wind component. A 110-yr model integration is then performed by explicitly incorporating the reconstructed τ 𝑖𝑛𝑡𝑒𝑟𝑑𝑒 cycle into the ICM. Compared with the regular interannual oscillation in the original ICM, the simulated ENSO events become highly irregular with decadal variations in the amplitude and asymmetry when the τ 𝑖𝑛𝑡𝑒𝑟𝑑𝑒 effect is included. Especially, the model reproduces different types of El Niño and La Niña events with different spatial distribution and temporal evolution of SST anomalies, namely Eastern-Pacific (EP) and Central-Pacific (CP) types. Further attribution analyses are performed to understand the modulating effects of τ 𝑖𝑛𝑡𝑒𝑟𝑑𝑒 in the tropical Pacific using the ocean component of the ICM, forced by the added τ 𝑖𝑛𝑡𝑒𝑟𝑑𝑒 effect. Two different roles of the Interdecadal Pacific Oscillation (IPO) in modulating different El Niño and La Niña events are illustrated. On the one hand, the IPO favors for the emergence of the EP type of El Niño and La Niña events, in association with the initial anomaly signals 3 occurring in the eastern equatorial Pacific, which are absent in the original ICM. On the other hand, the IPO tends to shift the El Niño/La Niña events to an CP type, with which the SST anomalies propagate eastward along the equator but cannot extend into the eastern boundary. This simple modeling study highlights the significant contributions of interdecadal wind variability to the genesis of ENSO irregularity and diversity theoretically.

Synergistic Interdecadal Effects of the North Pacific and North Atlantic SST on Precipitation over eastern China as revealed in the ECHAM5 simulations

“…There are still uncertainties in assessing the relative contributions of SST forcing in the North Pacific and North Atlantic to interdecadal variations in precipitation over China from observations. There is a clear need to clarify precipitation responses to SST forcing in the North Pacific or North Atlantic at specific cycles based on model sensitivity experiments (Zhang et al, 2020;Zhang et al, 2022b;Hu et al, 2023). Further efforts aim to demonstrate corresponding dynamic processes and physical mechanisms through the co-varying SST, precipitation and associated atmospheric circulation fields.…”

“…For example, the severe summer drought in Henan Province in 2014 (Wang et al, 2018) and the record-breaking Meiyu event over the Yangtze River basin in 2020 (e.g., Qiao et al, 2021;Zhou et al, 2021) seriously threatened local living conditions. Various studies have highlighted the impacts of multi-timescale sea surface temperature (SST) forcing on precipitation over China through different mechanisms, such as the El Niño-Southern Oscillation (ENSO; Zhi et al, 2012;Chen et al, 2013;Zhang and Gao, 2016;Gao et al, 2022;Hu et al, 2023), Pacific Decadal Oscillation (PDO; Zhang et al, 1998;Zhou et al, 2014;Zhang et al, 2016a), and Atlantic Multidecadal Oscillation (Wang et al, 2009;Si and Ding, 2016;Ding et al, 2020b). Hence, understanding the synergistic evolution between the low-frequency variability in precipitation over China and multi-timescale SST forcing in different oceans is of great significance for improving precipitation prediction, disaster prevention and reduction in China.…”

Interannual Variation in Mainland China’s Atmosphere Clearness Index Associated with El Niño–Southern Oscillation

“…The variation in the atmospheric pressure difference between Australia and Indonesia and that of the eastern South Pacific is called Southern Oscillation [3,4]. ENSO follows irregular periods of two to seven years [5,6], bringing predictable shifts in ocean surface temperature [7] and disrupting the wind [6,[8][9][10][11] and convection [12] patterns across the tropics. These changes have a cascade of global-scale climatic impacts [13][14][15].…”