Activity of the Southern Annular Mode during 2015–2016 El Niño event and its impact on Southern Hemisphere climate anomalies

Vera, Carolina; Osman, Marisol

doi:10.1002/joc.5419

Cited by 32 publications

(23 citation statements)

References 16 publications

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“…The similar classification accuracies found in 2013 and 2016 provide the first evidence that otolith morphological differences among zones were not sensitive to the El Niño event, which dominated the oceanographic conditions during 2014-16 in the Southern Hemisphere (Vera and Osman 2018). This finding suggests the absence of a generalised movement and mixing of schools in a southward direction, which could be expected as a result of movement of warm water masses from north to south.…”

Section: Population Structure and Spatial Segregation Of Anchovetasupporting

confidence: 61%

Ontogenetic and intraspecific variability in otolith shape of anchoveta (Engraulis ringens) used to identify demographic units in the Pacific Southeast off Chile

Cerna

Saavedra-Nievas

Plaza-Pasten

et al. 2019

Mar. Freshwater Res.

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The phenotypical variability in otolith shape of anchoveta (Engraulis ringens) was analysed in three zones (I, II and III) from north to south along the Chilean coast, using juvenile and adult fish. Generalised additive models were used to analyse shape indices and canonical discriminant analysis was used to analyse elliptical Fourier harmonics. The form factor and ellipticity indices varied significantly among the three zones, whereas roundness, circularity and rectangularity indices only showed differences between Zones I and III. Fourier reconstructed outlines for five ontogenetic stages suggested important differences among sampling zones, which were larger for sampling Zone III, where, at the same fish length, otoliths were smaller than those sampled in Zones I and II, at least at the pre-recruit stage. Elliptical Fourier descriptors showed significant differences among the three units, with a total percentage of correct classifications for juveniles of 89 and 74% for raw data and cross-validated cases respectively, compared with >85 and ~65% respectively for adult fish. The results support the hypothesis that juveniles and adults of anchoveta have remained segregated throughout their entire, or at least a fraction of, their life cycle, mainly between the extreme northward and southward zones.

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Section: Population Structure and Spatial Segregation Of Anchovetasupporting

confidence: 61%

Ontogenetic and intraspecific variability in otolith shape of anchoveta (Engraulis ringens) used to identify demographic units in the Pacific Southeast off Chile

Cerna

Saavedra-Nievas

Plaza-Pasten

et al. 2019

Mar. Freshwater Res.

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“…Byrne et al (2017) attempted this separation in observations via a regression-based approach and concluded that the stratospheric pathway was dominant. More recent work by Vera and Osman (2018), who showed that the "failed" zonally symmetric response to the large El Niño of 2015/2016 was consistent with an exceptionally strong SPV, also supports this conclusion.…”

Section: 1029/2018jd030173mentioning

confidence: 65%

Subseasonal‐to‐Seasonal Predictability of the Southern Hemisphere Eddy‐Driven Jet During Austral Spring and Early Summer

2019

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Several recent studies have suggested that the stratosphere can be a source of subseasonal‐to‐seasonal predictability of Southern Hemisphere circulation during the austral spring and early summer seasons, through its influence on the zonal‐mean eddy‐driven jet. We exploit the large sample size afforded by the hindcasts from the European Centre for Medium‐Range Weather Forecasts Integrated Forecast System to address a number of unanswered questions. It is shown that the picture of coherent seasonal variability of the coupled stratosphere‐troposphere system apparent from the reanalysis record during the spring/early summer period is robust to sampling uncertainty and that there is evidence of nonlinearity in the case of the most extreme variations. The effect of El Niño–Southern Oscillation on the eddy‐driven jet during this time of year is found to occur via the stratosphere, with no evidence of a direct tropospheric pathway. A simple two‐state statistical model of the stratospheric vortex is introduced to estimate the subseasonal‐to‐seasonal predictability associated with shifts of the seasonal cycle in the Southern Hemisphere extratropical atmosphere. This simple model, along with a more general model, is subsequently used to interpret skill scores associated with hindcasts made using the full seasonal forecast system. Together, the results provide evidence of tropospheric predictability on subseasonal‐to‐seasonal timescales during this time of year from at least as early as 1 August and show no evidence of a “signal‐to‐noise paradox” between the hindcasts and the reanalysis.

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“…Results here show a strong SAM influence together with an expansion of the semi-permanent subtropical anticyclones in the South Atlantic and South Indian Oceans as key factors for a poleward deviation of moisture corridors, and consequently for the regional drying trend which culminated in the 'Day Zero' water crisis. In fact, Vera and Osman (2018) have shown a decoupling of a previously strong link between El Niño and the negative phase of SAM since 2015. Given that the subtropical anticyclones are expected to expand further poleward under climate change (despite disparate observational-based rates of expansion-e.g.…”

Section: Discussion and Summarymentioning

confidence: 99%

The ‘Day Zero’ Cape Town drought and the poleward migration of moisture corridors

Sousa

Blamey

Reason

et al. 2018

Environ. Res. Lett.

120

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Since 2015 the greater Cape Town area (∼3.7 million people) has been experiencing the worst drought of the last century. The combined effect of this prolonged dry period with an ever-growing demand for water culminated in the widely publicized 'Day Zero' water crisis. Here we show how: (i) consecutive significant decreases in rainfall during the last three winters led to the current water crisis; (ii) the 2015-2017 record breaking drought was driven by a poleward shift of the Southern Hemisphere moisture corridor; (iii) a displacement of the jet-stream and South Atlantic storm-track has imposed significantly drier conditions to this region. Decreasing local rainfall trends are consistent with an expansion of the semi-permanent South Atlantic high pressure, and reflected in the prevalence of the positive phase of the Southern Annular Mode. Large-scale forcing mechanisms reveal the intensification and migration of subtropical anticyclones towards the mid-latitudes, highlighting the link between these circulation responses and the record warm years during 2015-2017 at the global scale.

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Activity of the Southern Annular Mode during 2015–2016 El Niño event and its impact on Southern Hemisphere climate anomalies

Cited by 32 publications

References 16 publications

Ontogenetic and intraspecific variability in otolith shape of anchoveta (Engraulis ringens) used to identify demographic units in the Pacific Southeast off Chile

Ontogenetic and intraspecific variability in otolith shape of anchoveta (Engraulis ringens) used to identify demographic units in the Pacific Southeast off Chile

Subseasonal‐to‐Seasonal Predictability of the Southern Hemisphere Eddy‐Driven Jet During Austral Spring and Early Summer

The ‘Day Zero’ Cape Town drought and the poleward migration of moisture corridors

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