Strengthening impacts of spring sea surface temperature in the north tropical Atlantic on Indian Ocean dipole after the mid-1980s

Abstract

It is well known that the Indian Ocean dipole (IOD) is closely related to El Niño-Southern Oscillation (ENSO). In this study, it is found that spring–summer north tropical Atlantic (NTA) sea surface temperature (SST) anomalies can contribute to the development of the IOD since the mid-1980s as well as ENSO. After the mid-1980s, an anticyclonic circulation over the subtropical northeastern Pacific could be excited by cool NTA SST anomalies in spring and summer due to a Gill-type Rossby-wave response. A low-level cyclonic circulation appears in the west Pacific in turn. The anomalous lower-level southwesterlies on the southeastern flank of the cyclonic circulation reduce the climatological wind speed, and thus, warm SST anomalies appear and extend to the central tropical Pacific via the wind-evaporation-SST (WES) feedback. As a result, Walker circulation over the Indo-Pacific region is changed, with anomalous descending in the eastern tropical Indian Ocean and ascending in the central tropical Pacific. The descending branch of anomalous Walker circulation generates surface southeasterly wind anomalies along the coast off Sumatra and lifts the thermocline in the eastern tropical Indian Ocean, which produces a positive IOD event in autumn. Such a cross-basin mechanism is supported by a coupled model experiment with warm SST perturbations over the NTA. In contrast, although cold NTA SST anomalies can induce warm SST anomalies in the eastern equatorial Pacific through interhemispheric meridional circulation before the mid-1980s, the responses in the tropical Indian Ocean are rather weak. In addition, the enhancement in the NTA-IOD relationship after the mid-1980s is suggested to result from the changes in the SST mean state under the context of global warming, which is confirmed by two coupled model experiments with different mean SST backgrounds.

ENSO–IOD Inter‐Basin Connection Is Controlled by the Atlantic Multidecadal Oscillation

“…Accompanying the decadal variation of ENSO related IOD variability, ENSO–IOD relationship shows clear decadal fluctuation, undergoing low‐correlation periods during 1920–1960 and after 1990, and a high‐correlation period from 1960 to 1980. Previous studies have highlighted the importance of decadal climate modes, such as AMO and IPO (Lim et al., 2017; Zhang et al., 2022), we therefore investigate their possible roles in modulating the ENSO–IOD connection. Figure 1a presents the correlation map between the decadal variation of ENSO–IOD relation and SST anomalies based on the ERSST data set.…”

Seasonally-reversed trends in the subtropical Northwestern Pacific linked to asymmetric AMO influences

“…Previous studies have pointed out that global warming can enhance inter-basin interaction between the pantropical (including Pacific) and Northern Atlantic regions, especially after the 1990s 29 , 43 , 44 . Therefore, it is likely that climate change in the Atlantic will become increasingly important for the Pacific climate.…”

North Atlantic oscillation controls multidecadal changes in the North Tropical Atlantic−Pacific connection

“…The NTA warming can force a northward shift of the Atlantic intertropical convergence zone (ITCZ) with a subsequent impact on the frequency of Atlantic extreme hurricanes and precipitation in Northeast Brazil and Sahel 10 – 14 . Beyond the Atlantic sector, the NTA SST can exert pronounced impacts on the western North Pacific (WNP) tropical cyclone genesis 15 , the WNP subtropical High 16 , and the Indian Ocean Dipole 17 . In particular, the NTA SST may conversely play an important role in shaping the evolution of ENSO events and could therefore serve as a potential precursor for ENSO 18 – 22 .…”