A multiscale framework for the origin and variability of the South Pacific Convergence Zone

Matthews, Adrian J.

doi:10.1002/qj.1870

Cited by 78 publications

(97 citation statements)

References 46 publications

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“…The Solomon Islands are positioned within the confluence of SPCZ rainfall (Folland et al, 2002;Vincent, 1994;Widlansky et al, 2010), the rising limb of the PWC and Hadley circulation (Matthews, 2011;Takahashi and Battisti, 2007), and the Western Pacific Warm Pool (WPWP; Rayner et al, 2003). Ocean waters surrounding the Solomon Islands have mean annual SSTs greater than 28 • C, a SST that is often used as a criteria for the boundary of the WPWP (Cravatte et al, 2009;Rayner et al, 2003).…”

Section: Modern Climate Setting In the Solomon Islandsmentioning

confidence: 99%

“…For the sunspot number record, the first PC (52 % variance at 12 years) and second PC (33 % variance at 10 years), again averaging to 11 years, are used to create a sunspot RC. The most recent three peaks of sunspot activity used by Matthews (2011) and Meehl et al (2009) to hypothesize a response in SPCZ precipitation to changing sunspot numbers are marked by vertical dashed lines. (e) illustrates the volcanic aerosol optical depth (AOD) proxy reconstruction of global volcanic activity from Crowley and Unterman (2012).…”

Section: Pdv In the Instrumental And Stalagmite Recordsmentioning

confidence: 99%

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Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries

et al. 2014

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Abstract. Modern Pacific decadal variability (PDV) has global impacts; hence records of PDV from the preinstrumental period are needed to better inform models that are used to project future climate variability. We focus here on reconstructing rainfall in the western tropical Pacific (Solomon Islands; ∼ 9.5 • S, ∼ 160 • E), a region directly influenced by PDV, using cave deposits (stalagmite). A relationship is developed between δ 18 O variations in the stalagmite and local rainfall amount to produce a 600 yr record of rainfall variability from the South Pacific Convergence Zone (SPCZ). We present evidence for large (∼ 1.5 m), abrupt, and periodic changes in total annual rainfall amount on decadal to multidecadal timescales since 1423 ± 5 CE (Common Era) in the Solomon Islands. The timing of the decadal changes in rainfall inferred from the 20th-century portion of the stalagmite δ 18 O record coincides with previously identified decadal shifts in PDV-related Pacific ocean-atmosphere behavior (Clement et al., 2011;Deser et al., 2004). The Solomons record of PDV is not associated with variations in external forcings, but rather results from internal climate variability. The 600 yr Solomon Islands stalagmite δ 18 O record indicates that decadal oscillations in rainfall are a persistent characteristic of SPCZ-related climate variability.

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Section: Modern Climate Setting In the Solomon Islandsmentioning

confidence: 99%

Section: Pdv In the Instrumental And Stalagmite Recordsmentioning

confidence: 99%

Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries

et al. 2014

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“…Pacific warm pool in a southeastward direction towards the Southern Hemisphere mid-latitudes [2][3][4] ( Supplementary Fig. S1) and delivers considerable amounts of rainfall to South Pacific islands during austral summer 1,5,6 (December-February: DJF), which we focus on in the analyses presented here.…”

Section: T He Observed Spcz (Ref 1) Extends From the Tropical Westernmentioning

confidence: 99%

Changes in South Pacific rainfall bands in a warming climate

et al. 2012

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The South Pacific Convergence Zone (SPCZ) is the largest rainband in the Southern Hemisphere and provides most of the rainfall to southwest Pacific island nations. In spite of various modelling efforts, it remains uncertain how the SPCZ will respond to greenhouse warming. Using a hierarchy of climate models we show that the uncertainty of SPCZ rainfall projections in present-generation climate models can be explained as a result of two competing mechanisms. Higher tropical sea surface temperatures lead to an overall increase of atmospheric moisture and rainfall whereas weaker sea surface temperature gradients dynamically shift the SPCZ northeastward and promote summer drying in areas of the southwest Pacific. On the basis of a multi-model ensemble of 76 greenhouse warming experiments and for moderate tropical warming of 1-2 • C we estimate a 6% decrease of SPCZ rainfall with a multi-model uncertainty exceeding ±20%. For stronger tropical warming exceeding 3 • C, a tendency for a wetter SPCZ region is identified. Supplementary Fig. S1) and delivers considerable amounts of rainfall to South Pacific islands during austral summer 1,5,6 (December-February: DJF), which we focus on in the analyses presented here. The seasonal march of this ∼8,000-10,000-km-long rainband is largely controlled by the seasonal cycle of the underlying sea surface temperature (SST) field, with air-sea interactions playing a key role 7 .On interannual timescales the southwest Pacific is strongly affected by the El Niño/Southern Oscillation 6,8,9 (ENSO). During El Niño conditions, as a result of the reduced meridional SST gradients, the SPCZ and associated maximum rainfall typically shift northeastward 8 while islands to the southwest often experience drying. An opposite, southwestward, shift in rainfall accompanies La Niña events. The SPCZ response to ENSO-related changes in SST gradients can be understood to a large extent in terms of a combination of equatorial Kelvin and Rossby wave dynamics 10 , convective nonlinearities 11 and boundary layer processes 12 . Recent climate modelling work provides evidence for an increase in extreme zonally oriented SPCZ events associated with strong El Niño events during the twenty-first century 13 . However, there remains much uncertainty on how ENSO will respond to greenhouse warming 14,15 and how the projected increased occurrence of zonal SPCZ events is related to slower basic-state changes.Whereas state-of-the-art coupled general circulation models (CGCMs) consistently simulate an enhanced equatorial warming [16][17][18][19][20] in response to increasing greenhouse-gas concentrations (Fig. 1a,c), the present twenty-first-century projections of SPCZ rainfall remain highly uncertain 21 Fig. 1), one finds that the ensemble mean rainfall response to intensified equatorial warming and reduced off-equatorial South Pacific warming (Fig. 1a) is characterized by a large rainfall increase in the equatorial Pacific, slightly more rainfall (5%) in the northwestern area of the climatological SPCZ and a drying o...

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“…1 and 2a,b). The SPCZ is responsible for a large fraction of the precipitation occurring across the South Pacific, particularly in austral summer [December-February (DJF)], while intense convective heating in the SPCZ generates and modifies Rossby waves, giving the SPCZ a global influence (Brown et al 2011;Matthews 2012). From a societal perspective, the inhabitants of South Pacific island nations are dependent on SPCZ rainfall; deviations from a typical year can result in substantial drought or flooding throughout the region (Murphy et al 2014).…”

Section: Introductionmentioning

confidence: 99%

The Role of Tropical–Extratropical Interaction and Synoptic Variability in Maintaining the South Pacific Convergence Zone in CMIP5 Models

et al. 2015

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The South Pacific convergence zone (SPCZ) is simulated as too zonal a feature in the current generation of climate models, including those in phase 5 of the Coupled Model Intercomparison Project (CMIP5). This zonal bias induces errors in tropical convective heating, with subsequent effects on global circulation. The SPCZ structure, particularly in the subtropics, is governed by the tropical-extratropical interaction between transient synoptic systems and the mean background state. In this study, analysis of synoptic variability in the simulated subtropical SPCZ reveals that the basic mechanism of tropical-extratropical interaction is generally well simulated, with storms approaching the SPCZ along comparable trajectories to observations. However, there is a broad spread in mean precipitation and its variability across the CMIP5 ensemble. Intermodel spread appears to relate to a biased background state in which the synoptic waves propagate. In particular, the region of mean negative zonal stretching deformation or ''storm graveyard'' in the upper troposphere is displaced in CMIP5 models to the northeast of its position in reanalysis data, albeit with pronounced ('258) intermodel longitudinal spread. Precipitation along the eastern edge of the SPCZ shifts in accordance with a storm graveyard shift, and in general models with stronger storm graveyards show higher precipitation variability. Building on prior SPCZ research, it is suggested that SPCZs simulated by CMIP5 models are not simply too zonal; rather, in models the subtropical SPCZ manifests a diagonal tilt similar to observations while SST biases force an overly zonal tropical SPCZ, resulting in a more discontinuous SPCZ than observed.

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A multiscale framework for the origin and variability of the South Pacific Convergence Zone

Cited by 78 publications

References 46 publications

Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries

Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries

Changes in South Pacific rainfall bands in a warming climate

The Role of Tropical–Extratropical Interaction and Synoptic Variability in Maintaining the South Pacific Convergence Zone in CMIP5 Models

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