scholarly journals Circulation Regimes and Low-Frequency Oscillations in the South Pacific Sector

2003 ◽  
Vol 131 (8) ◽  
pp. 1566-1576 ◽  
Author(s):  
Andrew W. Robertson ◽  
Carlos R. Mechoso
Keyword(s):  
Singular Spectrum Analysis ◽  
Low Frequency ◽  
South Pacific ◽  
Stationary Wave ◽  
Gaussian Mixture ◽  
Reanalysis Data ◽  
Oscillatory Behavior ◽  
South American ◽  
The South ◽  
Austral Spring

Abstract The characteristics of subseasonal circulation variability over the South Pacific are examined using 10-day lowpass-filtered 700-hPa geopotential height NCEP–NCAR reanalysis data. The extent to which the variability in each season is characterized by recurrent geographically fixed circulation regimes and/or oscillatory behavior is determined. Two methods of analysis (a K-means cluster analysis and a cross-validated Gaussian mixture model) both indicate three to four geographically fixed circulation regimes in austral fall, winter, and (to some extent) spring. The spatial regime structures are found to be quite similar in each season; they resemble the so-called Pacific–South American (PSA) patterns discussed in previous studies and often referred to as PSA 1 and PSA 2. Oscillatory behavior is investigated using singular spectrum analysis. This identifies a predominantly stationary wave with a period of about 40 days and a spatial structure similar to PSA 1; it is most pronounced in winter and spring and exhibits a noticeable eastward drift as it decays. The power spectrum of variability is otherwise well approximated by a red spectrum, together with enhanced broader-band 15–30-day variability. The results presented herein indicate that low-frequency variability over the South Pacific is not dominated by a propagating wave whose quadrature phases are PSA 1 and PSA 2, as hitherto described. Rather, it is found that the variability is well described by the occurrence of three to four geographically fixed circulation regimes, with a (near) 40-day oscillation that is predominantly stationary in space. The potential subseasonal predictability implied by this duality is discussed. Only during austral spring is a strong correlation found between El Niño and the frequency of occurrence of the circulation regimes.

scholarly journals South Pacific Subtropical High from the late Holocene to the end of the 21st century: insights from climate proxies and general circulation models

2019 ◽  
Author(s):  
Valentina Flores-Aqueveque ◽  
Maisa Rojas ◽  
Catalina Aguirre ◽  
Paola A. Arias ◽  
Charles González
Keyword(s):  
General Circulation ◽  
South Pacific ◽  
General Circulation Models ◽  
Reanalysis Data ◽  
Hadley Cell ◽  
Subtropical High ◽  
South American ◽  
The South ◽  
Paleoclimate Records ◽  
South American Climate

Abstract. The South Pacific Subtropical High (SPSH) is a predominant feature of South American climate. The variability of this high-pressure center induces changes in the intensity of coastal alongshore winds and precipitation, among others, over southwestern South America. In recent decades, a strengthening and expansion of the SPSH have been observed and attributed to the current global warming. These changes have led an intensification of the southerly winds along the coast of northern to central Chile, and a decrease in precipitation from central to southern Chile. Motivated by improving our understanding about the regional impacts of climate change in this part of the Southern Hemisphere, we analyze SPSH changes during the two most extreme climate events of the last millennium: the Little Ice Age (LIA) and the Current Warm Period (CWP: 1970–2000), based on paleoclimate records and CMIP5/PMIP3 model simulations. In order to assess the level of agreement of general circulation models, we also compare them with ERA-Interim reanalysis data for the 1979–2009 period as a complementary analysis. Finally, with the aim of evaluating future SPSH behaviour, we include 21th century projections under a RCP8.5 scenario in our analyses. Our results indicate that during the relative warm (cold) period, the SPSH expands (contracts). Together with this change, alongshore winds intensify (weaken) south (north) of ~ 35º S; also, Southern Westerly Winds become stronger (weaker) and shift southward (northward). Model results generally underestimate reanalysis data. These changes are in good agreement with paleoclimate records, which suggest that these variations could be related to tropical climate dynamics but also to extratropical phenomena. However, although models adequately represent most of the South American climate changes, they fail in representing the Intertropical Convergence Zone - Hadley Cell system dynamics. Climate model projections indicate that changes recently observed will continue during next decades, highlighting the need to establish effective mitigation and adaptation strategies against their environmental and socio-economic impacts.

scholarly journals Linking the atmospheric Pacific-South American mode with oceanic variability and predictability

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Jiale Lou ◽  
Terence J. O’Kane ◽  
Neil J. Holbrook
Keyword(s):  
Climate Variability ◽  
Pacific Decadal Oscillation ◽  
Southern Oscillation ◽  
South Pacific ◽  
Reanalysis Data ◽  
South American ◽  
The South ◽  
Climate Signal ◽  
Pacific Climate Variability ◽  
Oceanic Variability

AbstractWhile Pacific climate variability is largely understood based on El Niño-Southern Oscillation (ENSO), the North Pacific focused Pacific decadal oscillation and the basin-wide interdecadal Pacific oscillation, the role of the South Pacific, including atmospheric drivers and cross-scale interactions, has received less attention. Using reanalysis data and model outputs, here we propose a paradigm for South Pacific climate variability whereby the atmospheric Pacific-South American (PSA) mode acts to excite multiscale spatiotemporal responses in the upper South Pacific Ocean. We find the second mid-troposphere PSA pattern is fundamental to stochastically generate a mid-latitude sea surface temperature quadrupole pattern that represents the optimal precursor for the predictability and evolution of both the South Pacific decadal oscillation and ENSO several seasons in advance. We find that the PSA mode is the key driver of oceanic variability in the South Pacific subtropics that generates a potentially predictable climate signal linked to the tropics.

scholarly journals Decadal Variability in the Large-Scale Sea Surface Height Field of the South Pacific Ocean: Observations and Causes

2006 ◽  
Vol 36 (9) ◽  
pp. 1751-1762 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen
Keyword(s):  
Pacific Ocean ◽  
Rossby Wave ◽  
Large Scale ◽  
South Pacific ◽  
Sea Surface Height ◽  
Sea Surface ◽  
South American ◽  
The South ◽  
South Pacific Ocean ◽  
Spatially Varying

Abstract Large-scale sea surface height (SSH) changes in the extraequatorial South Pacific Ocean are investigated using satellite altimetry data of the past 12 yr. The decadal SSH signals in the 1990s were dominated by an increasing trend in the 30°–50°S band and a decreasing trend in the central South Pacific Ocean poleward of 50°S. In recent years since 2002 there has been a reversal in both of these trends. Spatially varying low-frequency SSH signals are also found in the tropical region of 10°–25°S where the decadal SSH trend is negative in the eastern basin, but positive in the western basin. To clarify the causes for these observed spatially varying SSH signals, a 1½-layer reduced-gravity model that includes the wind-driven baroclinic Rossby wave dynamics and the responses forced by SSH changes along the South American coast was adopted. The model hindcasts the spatially varying decadal trends in the midlatitude and the eastern tropical regions well. Accumulation of the wind-forced SSH anomalies along Rossby wave characteristics is found to be important for both previously reported long-term trends and their reversals in recent years. The boundary forcing associated with the time-varying SSH signals along the South American coast is crucial for understanding the observed SSH signals of all time scales in the eastern tropical South Pacific basin, but it has little impact upon the midlatitude interior SSH signals.

scholarly journals Climatological and Hydrological Observations for the South American Andes: In situ Stations, Satellite, and Reanalysis Data Sets

2020 ◽  
Vol 8 ◽  
Author(s):  
Thomas Condom ◽  
Rodney Martínez ◽  
José Daniel Pabón ◽  
Felipe Costa ◽  
Luis Pineda ◽  
...  
Keyword(s):  
Reanalysis Data ◽  
Data Sets ◽  
South American ◽  
The South

scholarly journals South Pacific Ocean Dipole: A Predictable Mode on Multiseasonal Time Scales

2014 ◽  
Vol 27 (4) ◽  
pp. 1648-1658 ◽  
Author(s):  
Yuanhong Guan ◽  
Jieshun Zhu ◽  
Bohua Huang ◽  
Zeng-Zhen Hu ◽  
James L. Kinter III
Keyword(s):  
Pacific Ocean ◽  
Time Scales ◽  
Southern Oscillation ◽  
Austral Summer ◽  
South Pacific ◽  
The South ◽  
Active Centers ◽  
Austral Spring ◽  
South Pacific Ocean ◽  
South Indian

Abstract Evaluating the climate hindcasts for 1982–2009 from the NCEP CFS Reanalysis and Reforecast (CFSRR) project using the Climate Forecast System, version 2 (CFSv2), this study identifies substantial areas of high prediction skill of the sea surface temperature (SST) in the South Pacific. The skill is the highest in the extratropical oceans on seasonal-to-interannual time scales, and it is only slightly lower than that for the El Niño–Southern Oscillation (ENSO). Two regions with the highest prediction skills in the South Pacific in both the CFSv2 and persistence hindcasts coincide with the active centers of opposite signs in the South Pacific Ocean dipole (SPOD) mode, a seesaw between the subtropical and extratropical SST in the South Pacific with a strong phase locking to austral summer. Interestingly, the CFSv2 prediction exhibits skillful predictions made three seasons ahead, more superior to the persistence forecast, suggesting significant dynamical predictability of the SPOD. An austral “spring predictability barrier” is noted in both the dynamical and persistence hindcasts. An analysis of the observational and model data suggests that the SPOD mode is significantly associated with ENSO, as an oceanic response to the atmospheric planetary wave trains forced by the anomalous atmospheric heating in the western Pacific. Although previous studies have demonstrated that the pattern of subtropical SST dipole is ubiquitous in the Southern Ocean, the SPOD has been least known and studied, compared with its counterparts in the south Indian and Atlantic Oceans. Since the SPOD is the most predictable oceanic mode in the whole Southern Hemisphere, its climate effects for local and remote regions should be further studied.

scholarly journals Low-Frequency Variability of the South Pacific Subtropical Gyre as Seen from Satellite Altimetry and Argo

2015 ◽  
Vol 45 (12) ◽  
pp. 3083-3098 ◽  
Author(s):  
Linlin Zhang ◽  
Tangdong Qu
Keyword(s):  
Thermal Expansion ◽  
Low Frequency ◽  
South Pacific ◽  
Subtropical Gyre ◽  
Sea Surface ◽  
The South ◽  
Argo Data ◽  
Steric Height ◽  
Low Frequency Variability ◽  
Height Increase

AbstractLow-frequency variability of the South Pacific Subtropical Gyre is investigated using satellite altimeter and Argo data. In most of the region studied, both sea surface height and steric height exhibit a linearly increasing trend, with its largest amplitude in the western part of the basin. Analysis of the Argo data reveals that the steric height increase north of 30°S is primarily caused by variations in the upper 500 m, while the steric height increase south of 30°S is determined by variations in the whole depths from the sea surface to 1800 m, with contributions from below 1000 m accounting for about 50% of the total variance. Most of the steric height increase is due to thermal expansion, except below 1000 m where haline contraction is of comparable magnitude with thermal expansion. Correspondingly, the South Pacific Subtropical Gyre has strengthened in the past decade. Within the latitude range between 10° and 35°S, transport of the gyre circulation increased by 20%–30% in the upper 1000 m and by 10%–30% in the deeper layers from 2004 to 2013. Further analysis shows that these variations are closely related to the southern annular mode in the South Pacific.

scholarly journals Austral Spring Southern Hemisphere Circulation and Temperature Changes and Links to the SPCZ

2015 ◽  
Vol 28 (18) ◽  
pp. 7371-7384 ◽  
Author(s):  
Kyle R. Clem ◽  
James A. Renwick
Keyword(s):  
Surface Temperature ◽  
Antarctic Peninsula ◽  
South Pacific ◽  
South Atlantic ◽  
South Pacific Convergence Zone ◽  
Positive Pressure ◽  
West Antarctica ◽  
The South ◽  
Austral Spring ◽  
Sea Ice Concentration

Abstract Significant austral spring trends have previously been observed in West Antarctica and Antarctic Peninsula temperatures and in atmospheric circulation across the southern Pacific and Atlantic. Here, physical mechanisms for the observed trends are investigated through analysis of monthly circulation and temperatures from the ERA-Interim dataset and outgoing longwave radiation (OLR) data. The negative pressure trend over the South Pacific during spring is strongest in September, while the positive pressure trend over the South Atlantic is strongest in October. Pressure trends in November are generally nonsignificant. The authors demonstrate that a significant September trend toward increased convection (reduced OLR) in the poleward portion of the South Pacific convergence zone (SPCZ) is statistically related to Rossby wave–like circulation changes across the southern oceans. The wave response is strongest over the South Pacific in September and propagates eastward to the South Atlantic in October. OLR-related changes are linearly congruent with around half of the observed total changes in circulation during September and October and are consistent with observed trends in South Pacific sea ice concentration and surface temperature over western West Antarctica and the western Antarctic Peninsula. These results suggest SPCZ variability in early spring, especially on the poleward side of the SPCZ, is an important contributor to circulation and surface temperature trends across the South Pacific/Atlantic and West Antarctica.

scholarly journals Project KIWI ONE: Very Low Frequency Acoustic Propagation Measurements in the South Pacific Ocean

1973 ◽  
Vol 53 (1) ◽  
pp. 299-299 ◽  
Author(s):  
D. G. Browing ◽  
W. R. Schumacher ◽  
W. H. Thorp ◽  
R. W. Bannister ◽  
R. N. Denham
Keyword(s):  
Pacific Ocean ◽  
Low Frequency ◽  
South Pacific ◽  
Acoustic Propagation ◽  
The South ◽  
Very Low Frequency ◽  
South Pacific Ocean
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