Multidecadal variability in the transmission of ENSO signals to the Indian Ocean

Shi, Ge; Ribbe, Joachim; Cai, Wenju; Cowan, Tim

doi:10.1029/2007gl029528

Cited by 34 publications

(33 citation statements)

References 19 publications

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“…For both annual and OND totals, recent years show significantly more (fewer) dry (wet) years than expected at random. These results are consistent with previous studies that show a decrease in rainfall over much of southern Africa during this time period (Hare and Mantua, 2000;Mason, 2001;Shi et al, 2007) and highlights specifically the decrease in OND rainfall for the onset of the growing season across the KAZA region. In addition, analyses associated with the major climate modes of ENSO and IOD along with examination of atmospheric processes before and after the late 1970s shift, indicate a change in variability of southern African rainfall, both for the entire region and specifically the KAZA region in north-central southern Africa.…”

Section: Discussionsupporting

confidence: 94%

Inter- and Intra-annual precipitation variability and associated relationships to ENSO and the IOD in southern Africa

et al. 2015

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Precipitation variability at inter-and intra-annual scales may influence land-use management decisions in semi-arid savannas worldwide, and in particular, over the Kavango-Zambezi Transfrontier Conservation Area (KAZA) in southern Africa. Over KAZA, spatiotemporal precipitation variability forced by the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) is important to local and regional-scale decisions for planting, livestock grazing, and wildlife migration patterns. We investigate the annual water year (October-September) and early rainy season [October-November-December (OND)] precipitation patterns during 60 years before and after a 1970s shift in the global ocean-atmosphere system for this region in southern Africa.The coincidence of the number of wet (upper tercile) and dry (lower tercile) years and OND seasons during the various phases of ENSO and IOD are compared prior to (1950-1975) and after (1980-2008 the 1970s climate shift over KAZA. Since the 1970s climate shift, KAZA has been significantly drier and observed fewer wet years and OND seasons. ENSO is the dominant forcing of precipitation differences over southern Africa before and after the 1970s climate shift, with IOD playing a secondary role. However, when ENSO and IOD phases are analysed simultaneously, El Niño and positive IOD events are significantly related to dry periods.The forcing of atmospheric circulation over southern Africa before and after the 1970s climate shift during El Niño and La Niña events is significantly different. Prior to the 1970s climate shift, atmospheric circulation during El Niño (La Niña) favoured strong (weak) precipitation increases (decreases). Afterward the 1970s climate shift, atmospheric circulation during La Niña (El Niño) favoured strong (weak) precipitation decreases (increases). The shifting nature of climate modes, especially ENSO, and respective influence on rainfall variability for southern Africa is important to understand to better inform seasonal climate forecasts to improve operational decision-making for land-use and water management decisions in semi-arid savanna regions.

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Section: Discussionsupporting

confidence: 94%

Inter- and Intra-annual precipitation variability and associated relationships to ENSO and the IOD in southern Africa

et al. 2015

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“…Eastward-propagating anomalies have been shown to characterize strong El Niñ o events such as those observed in 1982/83 and 1997/98 and are generated remotely involving off-equatorial Rossby waves in the discharge and recharge of the equatorial thermocline. Since 1980, in association with a tendency for stronger El Niñ o events, the off-equatorial Rossby waves are involved in the ENSO discharge and recharge process, a process absent in the pre-1980 period (Shi et al 2007). On the other hand, westward-propagating ENSO SST anomalies are generated locally via zonal advection and Ekman pumping forced by anomalous winds.…”

Section: Response To Itf Blocking a Mean Climatementioning

confidence: 99%

The Role of the Indonesian Throughflow on ENSO Dynamics in a Coupled Climate Model

et al. 2011

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The effects of the Indonesian Throughflow (ITF) on ENSO dynamics are studied in a coupled climate model by comparing two simulations, one with an open ITF and the other with a closed ITF. Closing the ITF results in an El Niñ o-like climate state in the Pacific, which is characterized by weakened trade winds, a flatter equatorial thermocline, and weaker equatorial upwelling. A weakened South Equatorial Current allows the western Pacific warm pool to extend eastward, thereby reducing the zonal temperature gradient along the equator. The interdecadal component of the ENSO-like variability collapses, although the interannual variability is maintained. The core region of the ENSO SST anomalies becomes confined farther east. This results from Bjerknes feedback processes that are shifted eastward. This study conducts an analysis utilizing the Bjerknes coupled stability index as formulated by Jin et al. and finds that the relative importance of the thermocline feedback is enhanced in the closed ITF experiment. This indicates a more prominent ENSO thermocline mode, thus explaining the existence of more prevalent eastward-propagating anomalies. A weaker zonal advective feedback due to the reduced mean zonal temperature gradient contributes to the dominance of the thermocline mode. The strength of the thermocline feedback itself is maintained by enhanced coupling between the zonal wind stress and the east-west thermocline slope. However, an increased thermal damping by air-sea heat flux dominates the overall ENSO feedback process.

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“…The shift is contemporaneous to changes in circulation of the North Pacific, and the way in which ENSO events evolve, particularly their interaction with the Indian Ocean [40,41]. This (Figure 4) exhibits considerable inter-annual variability of input to the Okavango, superimposed upon a consistent decline centered on the 1970s.…”

Section: Precipitation Changementioning

confidence: 98%

“…Mean annual depth of precipitation input to the entire Okavango basin, expressed as deviations from the 50-year median (Figure 4a), indicates the major global climate shift in the mid-1970s identified by many researchers [38][39][40][41][42]. The shift is contemporaneous to changes in circulation of the North Pacific, and the way in which ENSO events evolve, particularly their interaction with the Indian Ocean [40,41].…”

Section: Precipitation Changementioning

confidence: 99%

“…Kalahari sands constitute the dominant soils throughout. The inception of a period of reduced precipitation in the late 1970s correlates to a noted shift in global climate and decreased precipitation over much of southern Africa, possibly in connection to a coupling of the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Di-pole [38][39][40][41][42]. Precipitation variability is apparent at three dominant temporal scales; intra-annual, inter-annual and inter-decadal, all of which may well interact in a non-linear fashion.…”

Section: Study Areamentioning

confidence: 99%

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Integrating Dendrochronology, Climate and Satellite Remote Sensing to Better Understand Savanna Landscape Dynamics in the Okavango Delta, Botswana

Southworth

Rigg

Gibbes

et al. 2013

Land

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This research examines the integration and potential uses of linkages between climate dynamics, savanna vegetation and landscape level processes within a highly vulnerable region, both in terms of climate variability and social systems. We explore the combined applications of two time-series methodologies: (1) climate signals detected in tree ring growth, from published literature, chronologies from the International Tree-Ring Data Bank, and minimal preliminary field data; and (2) new primary production (NPP) data of vegetation cover over time derived from remotely sensed analyses. Both time-series are related to the regional patterns of precipitation, the principle driver of plant growth in the area. The approach is temporally and spatially multiscalar and examines the relationships between vegetation cover, type and amount, and precipitation shifts. We review literature linking dendrochronology, climate, and remotely sensed imagery, and, in addition, provide unique preliminary analyses from a dry study site located on the outer limit of the Okavango Delta. The work demonstrates integration across the different data sources, to OPEN ACCESSLand 2013, 2 638 provide a more holistic view of landscape level processes occurring in the last 30-50 years. These results corroborate the water-limited nature of the region and the dominance of precipitation in controlling vegetation growth. We present this integrative analysis of vegetation and climate change, as a prospective approach to facilitate the development of long-term climate/vegetation change records across multiple scales.

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Multidecadal variability in the transmission of ENSO signals to the Indian Ocean

Cited by 34 publications

References 19 publications

Inter- and Intra-annual precipitation variability and associated relationships to ENSO and the IOD in southern Africa

Inter- and Intra-annual precipitation variability and associated relationships to ENSO and the IOD in southern Africa

The Role of the Indonesian Throughflow on ENSO Dynamics in a Coupled Climate Model

Integrating Dendrochronology, Climate and Satellite Remote Sensing to Better Understand Savanna Landscape Dynamics in the Okavango Delta, Botswana

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