Predictability of Indian Ocean precipitation and its North Atlantic teleconnections during early winter

Abstract

The Tropical Western-Central Indian Ocean (WCIO) precipitation anomalies play an important role in modulating the anomalous climate conditions in the North Atlantic and European (NAE) region during the early boreal winter (November–December; ND) season. In this study, we analyzed the forcing mechanism and predictability for the early winter tropical WCIO precipitation anomalies and its teleconnections to the North Atlantic region. The two main forcing mechanisms emerging are the autumn Indian Ocean Dipole (IOD) and a direct atmospheric teleconnection from El Niño-Southern Oscillation (ENSO). Since the autumn IOD is partially forced by ENSO, their independent contributions are also investigated. We found the IOD dominates over the ENSO contribution. The ECMWF-SEAS5 seasonal re-forecast reproduces these forcing mechanisms well and shows a substantial prediction skill for early winter WCIO precipitation. Moreover, the North Atlantic response to the positive WCIO phase projects spatially onto the positive North Atlantic Oscillation (NAO) phase through atmospheric teleconnections and leads to warming in central and western Europe. This teleconnection is reproduced by ECMWF-SEAS5, but with weaker amplitude. Moreover, a significant prediction skill for the NAO as well as for the central and western European temperature anomalies is noted, which is mostly induced by the Indian Ocean precipitation anomalies during early winter.

The role of storm‐track dynamics in the intraseasonal variability of the winter ENSO teleconnection to the North Atlantic

“…Whilst most of the literature has focused on the ENSO teleconnection to the North Atlantic in the late winter, recent studies have emphasised the intraseasonal variability of the teleconnection. In the early winter (November-December), the teleconnection is quite different from that in the late winter, with the associated sea-level pressure anomalies closely resembling the "East Atlantic" pattern (EA) rather than the NAO (Ayarzagüena et al, 2018;Geng et al, 2023;King et al, 2018;King et al, 2023;Moron & Gouirand, 2003), as also shown here in Figure 1a; in addition, some studies have highlighted the possible role of the tropical Indian Ocean in modifying the ENSO teleconnection to the North Atlantic in early winter (Abid et al, 2021(Abid et al, , 2023. Previous studies have demonstrated that free-running coupled climate models struggle to reproduce the early-season teleconnection to the North Atlantic (Ayarzagüena et al, 2018;Molteni, 2020).…”

Seasonal variability and predictability of monsoon precipitation in Southern Africa

“…The similarity between ENSO and IOPD is remarkable but not surprising. In a recent study, it was determined that ENSO's influence on boreal winter precipitation variability over some regions is primarily driven by atmospheric diabatic heating anomalies caused by ENSOdriven precipitation variability in the IO because of the strong coupling between IOPD and ENSO at a seasonal scale [17,50]. This is also true in SA, where the direct influence of contemporaneous ENSO forcing on monsoon precipitation becomes insignificant after controlling for the effects of IOPD and IOD (figure 2(b)).…”

Winter precipitation predictability in Central Southwest Asia and its representation in seasonal forecast systems

“…Recent studies suggest that October IOD and contemporaneous ENSO can affect precipitation variability in the western Indian Ocean during early winter. 43 To understand this phenomenon more deeply, we analyze the association of bi-monthly IOPD with the October preconditioning of IOD and ENSO. In October, ENSO and IOD are strongly correlated (ERA5=0.67; MERRA2=0.62).…”

“…As the winter progresses, precipitation in the western Indian Ocean weakens (Figure S12), which correlates more with IOD. 43 Hence, IOD loses its influence over IOPD. On the other hand, ENSO strongly correlates with IOPD and eastern IO precipitation.…”