A Wall‐Like Sharp Downward Branch of the Walker Circulation Above the Western Indian Ocean

Kohyama, Tsubasa; Suematsu, Tamaki; Miura, Hiroaki; Takasuka, Daisuke

doi:10.1029/2021jd034650

Cited by 2 publications

(1 citation statement)

References 61 publications

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“…A negative IOD event often tends to be associated with La Niña via the Walker Circulation despite some exceptions (Behera et al, 2006(Behera et al, , 2008Luo et al, 2010). The modified Walker Circulation could influence East African climate via atmospheric convergence/divergence (King & Washington, 2021;Kohyama et al, 2021;Zhao & Cook, 2021). The combination of the 2021 negative IOD and the La Niña-like state in the tropical Pacific was also successfully predicted by SINTEX-F (Figure S2 in Supporting Information S1).…”

Section: Resultsmentioning

confidence: 78%

On the Predictability of the Extreme Drought in East Africa During the Short Rains Season

Doi

Behera

Yamagata

2022

Geophysical Research Letters

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Many parts of East Africa experienced extremely dry conditions during the short rains season (October-December) of 2021 (Figure 1a.), and suffered severe food insecurity outcomes afterward (Famine Early Warning Systems Network at https://fews.net/east-africa/, (e.g., Funk, 2020)). Regarding the time series of East African rainfall anomalies within 10°S-10°N; 30°E−45°E (hereafter, East African rainfall (EAR) index, e.g., Lu et al., 2018) during October-December, the 2021 drought reached the level that is comparable to the extreme drought events in 1996, 1998, 2005, and 2016 in the past 40 years (Figure 2a). Such devastating droughts in East Africa always lead to unsafe drinking water, food insecurity, and possible resurgence of infectious diseases (e.g., Azage et al., 2017;Doi, Nonaka, & Behera, 2020). Thus, successful prediction of such an extreme drought at least a few months ahead may contribute to reducing the socio-economic losses by taking necessary mitigation measures. In general, climate models are better at predicting dry extremes than wet extremes (Slater et al., 2019). Therefore, predictions of the drought in East Africa may serve as an optimal test-bed for a study on managing risk with seasonal climate forecasts. Such a research stream is critically important because extreme impacts due to natural climate variability are becoming more serious under the ongoing global warming (e.g., Charles et al., 2012).It is known that major sources of seasonal climate predictability are generally rooted in the tropical sea surface temperature (SST) anomalies and their possible teleconnection patterns (Bjerknes, 1966(Bjerknes, , 1969. Some previous works showed two potential sources of seasonal predictability of East Africa drought; ENSO (Philander, 1989) and the Indian Ocean Dipole (IOD) (Saji et al., 1999). Hastenrath et al. (1993 considered that the short rains increase/decrease were related to El Niño/La Niña possibly via atmospheric teleconnections. However, after the discovery of the IOD (Saji et al., 1999), it is now known that the impacts of the IOD on rainfall variability in East Africa are overwhelming as compared to those of ENSO (

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Section: Resultsmentioning

confidence: 78%

On the Predictability of the Extreme Drought in East Africa During the Short Rains Season

Doi

Behera

Yamagata

2022

Geophysical Research Letters

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Diversity of MJO Initiation Regions and Processes

Wang

2022

Journal of Climate

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The diversity of the Madden–Julian oscillation (MJO) initiation (i.e., initial onset of active convection before moving eastward) regions was explored using a clustering method. Regions favorable for MJO initiations are grouped into four longitude zones: the Atlantic and Africa (AA), the Indian Ocean (IO), the Maritime Continent (MC), and the western Pacific (WP). The region-dependent dominant initiation mechanisms are explored using a composite procedure. The AA initiation is attributed to a circumnavigating process associated with a preceding MJO. As upper-tropospheric westerly anomalies move into the AA region, the associated descending motion leads to suppressed convection over the IO, which further triggers convection onset to its west through anomalous westward moisture advection. The IO initiation arises from the downstream forcing of a preceding suppressed phase of MJO. A delayed air–sea interaction process also plays a role. The MC initiation is triggered by a westward-propagating dry equatorial Rossby wave in the Pacific. The low-level poleward flows associated with the anticyclonic Rossby wave gyres advect high mean moisture, promoting the convection onset over the MC. The WP initiation is triggered by a preceding suppressed phase of MJO that moves eastward, in a way similar to the downstream scenario in the IO. The AA initiation is usually associated with a La Niña–like background sea surface temperature pattern, which favors the decoupling of upper-tropospheric westerly anomalies from the preceding MJO. The MC and WP initiations are more frequent during El Niño, as the relevant meridional moisture gradient is sharper and the eastern Pacific is moister.

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A Wall‐Like Sharp Downward Branch of the Walker Circulation Above the Western Indian Ocean

Cited by 2 publications

References 61 publications

On the Predictability of the Extreme Drought in East Africa During the Short Rains Season

On the Predictability of the Extreme Drought in East Africa During the Short Rains Season

Diversity of MJO Initiation Regions and Processes

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