Pacific Meridional Modes without Equatorial Pacific Influence

2021 ◽  
pp. 1-51
Author(s):  
Yu Zhang ◽  
Shiyun Yu ◽  
Dillon J. Amaya ◽  
Yu Kosaka ◽  
Sarah M. Larson ◽  
...  
Keyword(s):  
North Pacific ◽  
Climate Model ◽  
Decadal Variability ◽  
Model Simulation ◽  
Southern Oscillation ◽  
South Pacific ◽  
Tropical Pacific ◽  
South Pacific Convergence Zone ◽  
Convergence Zone ◽  
Atmospheric Teleconnections

AbstractInvestigating Pacific Meridional Modes (PMM) without the influence of tropical Pacific variability is technically difficult if based on observations or fully coupled model simulations due to their overlapping spatial structures. To confront this issue, the present study investigates both North (NPMM) and South PMM (SPMM) in terms of their associated atmospheric forcing and response processes based on a mechanically decoupled climate model simulation. In this experiment, the climatological wind stress is prescribed over the tropical Pacific, which effectively removes dynamically coupled tropical Pacific variability (e.g., the El Niño-Southern Oscillation). Interannual NPMM in this experiment is forced not only by the North Pacific Oscillation, but also by a North Pacific tripole (NPT) pattern of atmospheric internal variability, which primarily forces decadal NPMM variability. Interannual and decadal variability of the SPMM is partly forced by the South Pacific Oscillation. In turn, both interannual and decadal NPMM variability can excite atmospheric teleconnections over the Northern Hemisphere extratropics by influencing the meridional displacement of the climatological intertropical convergence zone throughout the whole year. Similarly, both interannual and decadal SPMM variability can also excite atmospheric teleconnections over the Southern Hemisphere extratropics by extending/shrinking the climatological South Pacific convergence zone in all seasons. Our results highlight a new poleward pathway by which both the NPMM and SPMM feed back to the extratropical climate, in addition to the equatorward influence on tropical Pacific variability.

scholarly journals Subtropical Forcing of Tropical Pacific Climate and Decadal ENSO Modulation

2008 ◽  
Vol 21 (18) ◽  
pp. 4691-4709 ◽  
Author(s):  
Daniela Matei ◽  
Noel Keenlyside ◽  
Mojib Latif ◽  
Johann Jungclaus
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Circulation Model ◽  
South Pacific ◽  
Tropical Pacific ◽  
Ocean Dynamics ◽  
The North ◽  
The North Pacific

Abstract The relative impact of the subtropical North and South Pacific Oceans on the tropical Pacific climate mean state and variability is estimated using an ocean–atmosphere–sea ice coupled general circulation model. Tailored experiments are performed in which the model is forced by idealized sea surface temperature anomalies (SSTAs) in the subtropics of both hemispheres. The main results of this study suggest that subtropical South Pacific climate variations play a dominant role in tropical Pacific decadal variability and in the decadal modulation of El Niño–Southern Oscillation (ENSO). In response to a 2°C warming in the subtropical South Pacific, the equatorial Pacific SST increases by about 0.6°C, approximately 65% larger than the change in the North Pacific experiment. The subtropics affect equatorial SST mainly through atmosphere–mixed layer interactions in the South Pacific experiments; the response is mostly accomplished within a decade. The “oceanic tunnel” dominates in the North Pacific experiments; the response takes at least 100 yr to be accomplished. Similar sensitivity experiments conducted with the stand-alone atmosphere model showed that both air–sea interactions and ocean dynamics are crucial in shaping the tropical climate response. The statistics of ENSO exhibit significant changes in amplitude and frequency in response to a warming/cooling of the subtropical South Pacific: a 2°C warming (cooling) of subtropical South Pacific SST reduces (increases) the interannual standard deviation by about 30% (20%) and shortens (lengthens) the ENSO period. The simulated changes in the equatorial zonal SST gradient are the main contributor to the modulation of ENSO variability. The simulated intensification (weakening) of the annual cycle in response to an enhanced warming (cooling) in subtropical South Pacific partly explains the shifts in frequency, but may also lead to a weaker (stronger) ENSO. The subtropical North Pacific thermal forcing did not change the statistical properties of ENSO as strongly.

scholarly journals The Representation of the South Pacific Convergence Zone in the Twentieth Century Reanalysis

2019 ◽  
Vol 147 (3) ◽  
pp. 841-851 ◽  
Author(s):  
Thomas Harvey ◽  
James A. Renwick ◽  
Andrew M. Lorrey ◽  
Arona Ngari
Keyword(s):  
Twentieth Century ◽  
Southern Oscillation ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Past Century ◽  
Convergence Zone ◽  
The South ◽  
Southwest Pacific ◽  
Surface Observations ◽  
Twentieth Century Reanalysis

Abstract The South Pacific convergence zone (SPCZ) is the largest rainfall feature in the Southern Hemisphere, and is a critical component of the climate for South Pacific island nations and territories. The small size and isolated nature of these islands leaves them vulnerable to short- and long-term changes in the position of the SPCZ. Its position and strength is strongly modulated by El Niño–Southern Oscillation (ENSO), leading to large interannual variability in rainfall across the southwest Pacific including seasonal droughts and pluvials. Currently much of the analysis about SPCZ activity has been restricted to the satellite observation period starting in 1979. Here, the representation of the SPCZ in the Twentieth Century Reanalysis (20CR), which is a three-dimensional atmospheric reconstruction based only on surface observations, is discussed for the period since 1908. The performance of two versions of the 20CR (version 2 and version 2c) in the satellite era is compared with other reanalyses and climate observation products. The 20CR performs well in the satellite era. Extra surface observations spanning the SPCZ region from the longitude of the Cook Islands has improved the representation of the SPCZ during 1908–57 between 20CRv2 and 20CRv2c. The well-established relationship with ENSO is observed in both the representation of mean SPCZ position and intensity, and this relationship remains consistent through the entire 1908–2011 period. This suggests that the ENSO–SPCZ relationship has remained similar over the course of the past century, and gives further evidence that 20CRv2c performs well back to 1908 over the southwest Pacific region.

Tracking the South Pacific convergence zone variability and recent acidification reconstructed from tropical corals

2021 ◽  
Author(s):  
Sara Todorović ◽  
Henry C. Wu ◽  
Braddock Linsley ◽  
Delphine Dissard ◽  
Henning Kuhnert ◽  
...  
Keyword(s):  
Southern Oscillation ◽  
Global Climate ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Convergence Zone ◽  
Climatic Fluctuations ◽  
Ph Variation ◽  
Enso Events ◽  
Strong Trend ◽  
Tropical Oceans

<p>Massive tropical corals represent one of the most important natural archives of modern climate change. Coral based reconstructions give us the possibility to extend the instrumental oceanographic records and observe hydrographic variability on seasonal to interdecadal scales in tropical oceans. South Pacific convergence zone (SPCZ) variability, Interdecadal Pacific Oscillation (IPO) and El Niño-Southern Oscillation (ENSO) events are major drivers of global climate and may exert control on regional CO<sub>2</sub> absorption, outgassing and pH variability.</p><p><em>Porites</em> sp. corals from Tonga and Rotuma (Fijian dependency) are being analyzed for multi-proxy (e.g. Sr/Ca, δ<sup>18</sup>O, δ<sup>13</sup>C, δ<sup>11</sup>B, B/Ca) reconstructions of sea surface temperature and salinity (SST, SSS) and carbonate chemistry, on a monthly to annual resolution. Preliminary data of the Rotuma <em>Porites</em> sp. coral shows δ<sup>18</sup>O has been decreasing by 0.004 ‰ per year at the end of the 20th century, suggesting freshening and/or warming of the surface water. In the same period, we observe a δ<sup>13</sup>C decrease of 0.017 ‰ per year in-line with the anthropogenic CO<sub>2</sub> driven Suess effect. Initial results of the δ<sup>11</sup>B Tonga <em>Porites</em> sp. show high interannual variability, and a strong trend of decrease of -0.0626 ‰ per year in the last five decades of the record (1949-2004) suggesting acidification. The results are in agreement with published coral-based reconstructions from the region.</p><p>When completed, the new records will facilitate exploring the effects of modern anthropogenic influence on ocean carbonate system and pH variation, and the relationship between them and interannual and decadal-interdecadal climatic fluctuations.</p>

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

2014 ◽  
Vol 10 (4) ◽  
pp. 1319-1332 ◽  
Author(s):  
C. R. Maupin ◽  
J. W. Partin ◽  
C.-C. Shen ◽  
T. M. Quinn ◽  
K. Lin ◽  
...  
Keyword(s):  
Climate Variability ◽  
Decadal Variability ◽  
Solomon Islands ◽  
Rainfall Variability ◽  
South Pacific ◽  
Rainfall Amount ◽  
South Pacific Convergence Zone ◽  
Annual Rainfall ◽  
Convergence Zone ◽  
Decadal Scale

Abstract. Modern Pacific decadal variability (PDV) has global impacts; hence records of PDV from the pre-instrumental 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 δ18O 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 δ18O 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 δ18O record indicates that decadal oscillations in rainfall are a persistent characteristic of SPCZ-related climate variability.

scholarly journals The South Pacific Convergence Zone as Depicted in Reanalysis and Satellite Products

2021 ◽  
Author(s):  
◽  
Harvey Thomas Luke
Keyword(s):  
Twentieth Century ◽  
Southern Oscillation ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Past Century ◽  
Enso Cycle ◽  
Convergence Zone ◽  
The South ◽  
Southwest Pacific ◽  
Extended Analysis

<p>The South Pacific Convergence Zone (SPCZ) is the largest rainfall feature in the Southern Hemisphere, and is a critical component of the climate of Southwest Pacific Island nations. The small size and isolated nature of these islands leaves them vulnerable to short and long term changes in the position of the SPCZ. Its location and strength is strongly modulated by the El Niño-Southern Oscillation (ENSO) cycle and the Inter-decadal Pacific Oscillation (IPO), leading to large inter-annual and decadal variability in rainfall across the Southwest Pacific. Much of the analysis on the SPCZ has been restricted to the modern period, more specifically the “satellite era”, starting in 1979. Here, the representation of the SPCZ in the Twentieth Century Reanalysis (20CR) product, which reconstructs the three-dimensional state of the atmosphere based only on surface observations is discussed. The performance of two versions of the 20CR (versions 2 and 2c) in the satellite era is tested via inter-comparison with other reanalysis and observational satellite products, before using 20CR version 2c (20CRv2c) to perform extended analysis back to the early twentieth century. This study demonstrates that 20CR performs well in the satellite era, and is considered suitable for extended analysis. It is established that extra data added in the SPCZ region between 20CR versions 2 and 2c has improved the representation of the SPCZ during 1908-1958. Well-established relationships between ENSO and the IPO with the SPCZ are shown to be present through the entire 1908-2011 period, although it is suggested that the physical link between the IPO and the SPCZ has changed between the first and second half of the twentieth century. Finally, evidence of a southward trend of the SPCZ over the past century is presented, potentially due to an expansion of the tropics as a result of climate change.</p>

A 1300-year reconstruction of the South Pacific Convergence Zone using a Pacific-wide tree-ring network

2020 ◽  
Author(s):  
Philippa Higgins ◽  
Jonathan Palmer ◽  
Christian Turney ◽  
Martin Andersen ◽  
Edward Cook
Keyword(s):  
Tree Ring ◽  
General Circulation ◽  
Southern Oscillation ◽  
South Pacific ◽  
Ice Age ◽  
South Pacific Convergence Zone ◽  
Convergence Zone ◽  
Pacific Island ◽  
The South ◽  
Island Communities

&lt;p&gt;The South Pacific Convergence Zone (SPCZ) is the largest driver of precipitation variability over South Pacific island communities during the austral warm season influencing the severity and duration of drought and the frequency of tropical cyclones. The SPCZ is known to exhibit variability on a range of timescales, from intra-seasonal to multidecadal variations, modulated by the Interdecadal Pacific Oscillation (IPO). Despite its climatic and societal importance, determining the causes of low frequency variability in the SPCZ has been hampered by the short instrumental data record, with most comprehensive analyses since the satellite era. Here we report the first paleoclimate reconstruction of the SPCZ, allowing climate variability in the South Pacific region to be explored back to 700 CE. Our 1300-year reconstruction of the SPCZI (South Pacific Convergence Zone Index; the difference between mean sea level pressure between Apia, Samoa and Suva, Fiji) is based on a trans-Pacific network of precisely dated tree-ring proxies. Capturing SPCZ teleconnections from both sides of the Pacific has produced a robust, unbiased reconstruction with excellent reconstruction skill over the entire period. El Ni&amp;#241;o-Southern Oscillation periodicities (&amp;#8764;3-7 years) are pervasive throughout the SPCZI reconstruction. Multidecadal periodicities wax and wane, apparently coinciding with the timing of the Medieval Climate Anomaly (c. 1000-1200 CE) and Little Ice Age (1300-1700 CE). We discuss some of the drivers of SPCZI variability including global dimming events. Our reconstruction helps improve our understanding of past hydroclimatic behaviour in the southwest Pacific and can be used to validate general circulation model projections for Pacific Island communities in the twenty-first century.&lt;/p&gt;

scholarly journals A Coupled Air–Sea Response Mechanism to Solar Forcing in the Pacific Region

2008 ◽  
Vol 21 (12) ◽  
pp. 2883-2897 ◽  
Author(s):  
Gerald A. Meehl ◽  
Julie M. Arblaster ◽  
Grant Branstator ◽  
Harry van Loon
Keyword(s):  
Climate Model ◽  
Tropical Pacific ◽  
South Pacific Convergence Zone ◽  
Convergence Zone ◽  
Pacific Region ◽  
Solar Forcing ◽  
Coupled Models ◽  
The Pacific ◽  
Precipitation Regimes ◽  
The Tropical Pacific

Abstract The 11-yr solar cycle [decadal solar oscillation (DSO)] at its peaks strengthens the climatological precipitation maxima in the tropical Pacific during northern winter. Results from two global coupled climate model ensemble simulations of twentieth-century climate that include anthropogenic (greenhouse gases, ozone, and sulfate aerosols, as well as black carbon aerosols in one of the models) and natural (volcano and solar) forcings agree with observations in the Pacific region, though the amplitude of the response in the models is about half the magnitude of the observations. These models have poorly resolved stratospheres and no 11-yr ozone variations, so the mechanism depends almost entirely on the increased solar forcing at peaks in the DSO acting on the ocean surface in clear sky areas of the equatorial and subtropical Pacific. Mainly due to geometrical considerations and cloud feedbacks, this solar forcing can be nearly an order of magnitude greater in those regions than the globally averaged solar forcing. The mechanism involves the increased solar forcing at the surface being manifested by increased latent heat flux and evaporation. The resulting moisture is carried to the convergence zones by the trade winds, thereby strengthening the intertropical convergence zone (ITCZ) and the South Pacific convergence zone (SPCZ). Once these precipitation regimes begin to intensify, an amplifying set of coupled feedbacks similar to that in cold events (or La Niña events) occurs. There is a strengthening of the trades and greater upwelling of colder water that extends the equatorial cold tongue farther west and reduces precipitation across the equatorial Pacific, while increasing precipitation even more in the ITCZ and SPCZ. Experiments with the atmosphere component from one of the coupled models are performed in which heating anomalies similar to those observed during DSO peaks are specified in the tropical Pacific. The result is an anomalous Rossby wave response in the atmosphere and consequent positive sea level pressure (SLP) anomalies in the North Pacific extending to western North America. These patterns match features that occur during DSO peak years in observations and the coupled models.

scholarly journals The South Pacific Convergence Zone as Depicted in Reanalysis and Satellite Products

2021 ◽  
Author(s):  
◽  
Harvey Thomas Luke
Keyword(s):  
Twentieth Century ◽  
Southern Oscillation ◽  
South Pacific ◽  
South Pacific Convergence Zone ◽  
Past Century ◽  
Enso Cycle ◽  
Convergence Zone ◽  
The South ◽  
Southwest Pacific ◽  
Extended Analysis

<p>The South Pacific Convergence Zone (SPCZ) is the largest rainfall feature in the Southern Hemisphere, and is a critical component of the climate of Southwest Pacific Island nations. The small size and isolated nature of these islands leaves them vulnerable to short and long term changes in the position of the SPCZ. Its location and strength is strongly modulated by the El Niño-Southern Oscillation (ENSO) cycle and the Inter-decadal Pacific Oscillation (IPO), leading to large inter-annual and decadal variability in rainfall across the Southwest Pacific. Much of the analysis on the SPCZ has been restricted to the modern period, more specifically the “satellite era”, starting in 1979. Here, the representation of the SPCZ in the Twentieth Century Reanalysis (20CR) product, which reconstructs the three-dimensional state of the atmosphere based only on surface observations is discussed. The performance of two versions of the 20CR (versions 2 and 2c) in the satellite era is tested via inter-comparison with other reanalysis and observational satellite products, before using 20CR version 2c (20CRv2c) to perform extended analysis back to the early twentieth century. This study demonstrates that 20CR performs well in the satellite era, and is considered suitable for extended analysis. It is established that extra data added in the SPCZ region between 20CR versions 2 and 2c has improved the representation of the SPCZ during 1908-1958. Well-established relationships between ENSO and the IPO with the SPCZ are shown to be present through the entire 1908-2011 period, although it is suggested that the physical link between the IPO and the SPCZ has changed between the first and second half of the twentieth century. Finally, evidence of a southward trend of the SPCZ over the past century is presented, potentially due to an expansion of the tropics as a result of climate change.</p>

scholarly journals Role of Stochastic Atmospheric Forcing from the South and North Pacific in Tropical Pacific Decadal Variability

2019 ◽  
Vol 32 (13) ◽  
pp. 4013-4038 ◽  
Author(s):  
Tianyi Sun ◽  
Yuko M. Okumura
Keyword(s):  
North Pacific ◽  
Large Scale ◽  
Decadal Variability ◽  
South Pacific ◽  
Tropical Pacific ◽  
Ocean Dynamics ◽  
The South ◽  
Pacific Decadal Variability ◽  
Sst Anomalies ◽  
The Tropical Pacific

Abstract Stochastic variability of internal atmospheric modes, known as teleconnection patterns, drives large-scale patterns of low-frequency SST variability in the extratropics. To investigate how the decadal component of this stochastically driven variability in the South and North Pacific affects the tropical Pacific and contributes to the observed basinwide pattern of decadal variability, a suite of climate model experiments was conducted. In these experiments, the models are forced with constant surface heat flux anomalies associated with the decadal component of the dominant atmospheric modes, particularly the Pacific–South American (PSA) and North Pacific Oscillation (NPO) patterns. Both the PSA and NPO modes induce basinwide SST anomalies in the tropical Pacific and beyond that resemble the observed interdecadal Pacific oscillation. The subtropical SST anomalies forced by the PSA and NPO modes propagate to the equatorial Pacific mainly through the wind–evaporation–SST feedback. This atmospheric bridge is stronger from the South Pacific than the North Pacific due to the northward displacement of the intertropical convergence zone and the associated northward advection of momentum anomalies. The equatorial ocean dynamics is also more strongly influenced by atmospheric circulation changes induced by the PSA mode than the NPO mode. In the PSA experiment, persistent and zonally coherent wind stress curl anomalies over the South Pacific affect the zonal mean depth of the equatorial thermocline and weaken the equatorial SST anomalies resulting from the atmospheric bridge. This oceanic adjustment serves as a delayed negative feedback and may be important for setting the time scales of tropical Pacific decadal variability.

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