The Hadley Circulation Regime Change: Combined Effect of the Western Pacific Warming and Increased ENSO Amplitude

2018 ◽  
Vol 31 (23) ◽  
pp. 9739-9751 ◽  
Author(s):  
Yi-Peng Guo ◽  
Zhe-Min Tan
Keyword(s):  
Regime Change ◽  
Southern Oscillation ◽  
Hadley Circulation ◽  
Warming Trend ◽  
Combined Effect ◽  
Western Pacific ◽  
South Pacific Convergence Zone ◽  
Boreal Winter ◽  
Enso Events

The variation in the interannual relationship between the boreal winter Hadley circulation (HC) and El Niño–Southern Oscillation (ENSO) during 1948–2014 is investigated. The interannual variability of the HC is dominated by two principal modes: the equatorial asymmetric mode (AM) and the equatorial symmetric mode (SM). The AM of the HC during ENSO events mainly results from a combined effect of the ENSO sea surface temperature (SST) anomalies and the climatological background SST over the South Pacific convergence zone. Comparatively, the SM shows a steady and statistically significant relationship with ENSO; however, the interannual relationship between the AM and ENSO is strengthened during the mid-1970s, which leads to a HC regime change—that is, the interannual pulse of the HC intensity and its response to ENSO are stronger after the mid-1970s than before. The long-term warming trend of the tropical western Pacific since the 1950s and the increased ENSO amplitude play vital roles in the HC regime change. Although the tropical eastern Pacific also experienced a long-term warming trend, it has little influence on the HC regime change due to the climatologically cold background SST over the cold tongue region.

scholarly journals Seasonal and Secular Variations of Atmospheric 14Co2 Over the Western Pacific Since 1994

Radiocarbon ◽  
2004 ◽  
Vol 46 (2) ◽  
pp. 901-910 ◽  
Author(s):  
H Kitagawa ◽  
Hitoshi Mukai ◽  
Yukihiro Nojiri ◽  
Yasuyuki Shibata ◽  
Toshiyuki Kobayashi ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Southern Oscillation ◽  
Monitoring Program ◽  
Western Pacific ◽  
Environmental Research ◽  
Enso Events ◽  
Global Environmental ◽  
Secular Variations ◽  
The Western Pacific

Air sample collections over the western Pacific have continued since 1992 as a part of Center for Global Environmental Research, National Institute for Environmental Studies (CGER-NIES) global environmental monitoring program. The air samples collected on the Japan-Australia transect made it possible to trace the seasonal and secular 14CO2 variations, as well as an increasing trend of greenhouse gases over the western Pacific. A subset of CO2 samples from latitudes of 10–15°N and 23–28°S were chosen for accelerator mass spectrometry (AMS) 14C analysis using a NIES-TERRA AMS with a 0.3–0.4% precision. These 14CO2 records in maritime air show seasonal variations superimposed on normal exponential decreasing trends with a time constant of about 16 yr. The Δ14C values in the Northern Hemisphere are lower those in the Southern Hemisphere by 3–4 during 1994–2002. The Northern Hemisphere record shows relatively high seasonality (2.3 ± 1.5) as compared with the Southern Hemisphere (1.3 ± 1.2). The maximum values of seasonal cycles appear in late autumn and early winter in the Northern and Southern Hemispheres, respectively. Oscillations of 1–10 yr over the western Pacific are found to correlate possibly with the El Niño/Southern Oscillation (ENSO) events.

Long term population changes of fur seals Arctocephalus gazella and Arctocephalus tropicalis on subantarctic (Crozet) and subtropical (St. Paul and Amsterdam) islands and their possible relationship to El Niño Southern Oscillation

1994 ◽  
Vol 6 (4) ◽  
pp. 473-478 ◽  
Author(s):  
C. Guinet ◽  
P. Jouventin ◽  
J-Y. Georges
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Enso Events ◽  
Fur Seals ◽  
Fur Seal ◽  
Arctocephalus Tropicalis

The population trend over the last decade for subantarctic fur seals (Arctocephalus tropicalis) on Amsterdam and St. Paul islands and on Possession Island (Crozet Archipelago) and Antarctic fur seals (A. gazella) on Possession Island are analysed. At Amsterdam Island, based on pup counts, the subantarctic fur seal population appears to have stabilized after a period of rapid growth. At Possession Island subantarctic fur seal and Antarctic fur seal, with respective annual growth rates of 19.2 and 17.4%, are reaching the maximum growth rate for the genus Arctocephalus. Annual pup censuses at Possession Island since 1978 indicate important variations from year to year with pup production for A. gazella significantly lower the year after an El Niño Southern Oscillation (ENSO) event, but with no such relationship for A. tropicalis. Several other long term demographic studies of seabirds and marine mammals at different breeding locations in the Southern Ocean indicate that the breeding success of several of these predators appears to be widely affected in years which appear to be related to the ENSO events. To clarify this, it is necessary to analyse in more detail the demographic data obtained for the different subantarctic and Antarctic locations where long term monitoring programmes are conducted.

scholarly journals Changes of the Boreal Winter Hadley Circulation in the NCEP–NCAR and ECMWF Reanalyses: A Comparative Study

2007 ◽  
Vol 20 (20) ◽  
pp. 5191-5200 ◽  
Author(s):  
Hua Song ◽  
Minghua Zhang
Keyword(s):  
Radiative Forcing ◽  
Atmospheric Transport ◽  
Vertical Motion ◽  
Hadley Circulation ◽  
Western Pacific ◽  
Boreal Winter ◽  
Tropical Western Pacific ◽  
The Difference ◽  
Upper Level ◽  
Static Energy

Abstract Both the ECMWF and the NCEP–NCAR reanalyses show a strengthening of the atmospheric Hadley circulation in boreal winter over the last 50 years, but the intensification is much stronger in the ECMWF than in the NCEP–NCAR reanalysis. This study focuses on the difference of these trends in the two reanalyses. It is shown that trends in the Hadley circulation in the two reanalyses differ mainly over the tropical western Pacific. This difference is found to be consistent with respective trends of the atmospheric transport of moist static energy, longwave cloud radiative forcing, and upper-level clouds in the two reanalyses. Two independent datasets of upper-level cloud cover and sea level pressure from ship-based measurements are then used to evaluate the reanalyses over the tropical western Pacific. They are found to be more consistent with the trends in the NCEP–NCAR reanalysis than those in the ECMWF reanalysis. The results suggest a weakening of the vertical motion associated with the Hadley circulation in the tropical western Pacific.

scholarly journals Characterization of West African Jet Streams and Their Association to ENSO Events and Rainfall in ERA-Interim 1979–2011

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Churchill Okonkwo ◽  
Belay Demoz ◽  
Sium Tesfai
Keyword(s):  
Decadal Variability ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
West African ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Jet Streams ◽  
Enso Events ◽  
Westerly Jet ◽  
Sahel Region

The interannual variability of West African jet streams and their association with rainfall are reexamined using European Reanalysis ERA-Interim 1979–2011. The objective of the study is to characterize their climatology and role in rainfall variability in western Sahel. Wavelet analysis was used on wind speed data and implications to ENSO were discussed subsequently. Our results show that while the low-level African Westerly Jet (AWJ) correlates well with rainfall south of the equator in boreal winter months, the Tropical Easterly Jet (TEJ) and African Easterly Jet (AEJ) correlate better with rainfall north of the equator in the boreal summer months. Results of interannual-to-decadal variability in 200 mb, 600 mb, and 850 mb of zonal wind reveal that there is enhanced variability in the 2–8 year band. Also, the TEJ, AEJ, and AWJ fluctuations are coupled with variations in southern oscillation. Further analysis suggests a statistically significant association between TEJ and the El Niño events of the 1980s that led to intense drought in the Sahel region of West Africa. The 2007 moderate La Niña shows a statistically significant coherence with the 500 mb, 600 mb, and 850 mb jets. These associations are also phase locked, suggesting that the association may be more than by chance.

scholarly journals ENSO Seasonal Synchronization Theory

2014 ◽  
Vol 27 (14) ◽  
pp. 5285-5310 ◽  
Author(s):  
Karl Stein ◽  
Axel Timmermann ◽  
Niklas Schneider ◽  
Fei-Fei Jin ◽  
Malte F. Stuecker
Keyword(s):  
Annual Cycle ◽  
General Circulation ◽  
Phase Synchronization ◽  
Southern Oscillation ◽  
General Circulation Models ◽  
Boreal Winter ◽  
Nonlinear Frequency ◽  
Coupled Models ◽  
Frequency Locking ◽  
Enso Events

Abstract One of the key characteristics of El Niño–Southern Oscillation (ENSO) is its synchronization to the annual cycle, which manifests in the tendency of ENSO events to peak during boreal winter. Current theory offers two possible mechanisms to account the for ENSO synchronization: frequency locking of ENSO to periodic forcing by the annual cycle, or the effect of the seasonally varying background state of the equatorial Pacific on ENSO’s coupled stability. Using a parametric recharge oscillator (PRO) model of ENSO, the authors test which of these scenarios provides a better explanation of the observed ENSO synchronization. Analytical solutions of the PRO model show that the annual modulation of the growth rate parameter results directly in ENSO’s seasonal variance, amplitude modulation, and 2:1 phase synchronization to the annual cycle. The solutions are shown to be applicable to the long-term behavior of the damped model excited by stochastic noise, which produces synchronization characteristics that agree with the observations and can account for the variety of ENSO synchronization behavior in state-of-the-art coupled general circulation models. The model also predicts spectral peaks at “combination tones” between ENSO and the annual cycle that exist in the observations and many coupled models. In contrast, the nonlinear frequency entrainment scenario predicts the existence of a spectral peak at the biennial frequency corresponding to the observed 2:1 phase synchronization. Such a peak does not exist in the observed ENSO spectrum. Hence, it can be concluded that the seasonal modulation of the coupled stability is responsible for the synchronization of ENSO events to the annual cycle.

The Influence of Atmospheric Convection on the Interaction between the Indian Ocean and ENSO

2017 ◽  
Vol 30 (24) ◽  
pp. 10155-10178 ◽  
Author(s):  
Claudia E. Wieners ◽  
Henk A. Dijkstra ◽  
Will P. M. de Ruijter
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Western Pacific ◽  
Water Volume ◽  
Maritime Continent ◽  
Enso Events ◽  
The Indian Ocean ◽  
The Western Pacific

In recent years it has been proposed that a negative (positive) Indian Ocean dipole (IOD) in boreal autumn favors an El Niño (La Niña) at a lead time of 15 months. Observational analysis suggests that a negative IOD might be accompanied by easterly anomalies over the western Pacific. Such easterlies can enhance the western Pacific warm water volume, thus favoring El Niño development from the following boreal spring onward. However, a Gill-model response to a negative IOD forcing would lead to nearly zero winds over the western Pacific. The authors hypothesize that a negative IOD—or even a cool western Indian Ocean alone—leads to low-level air convergence and hence enhanced convectional heating over the Maritime Continent, which in turn amplifies the wind convergence so as to cause easterly winds over the western Pacific. This hypothesis is tested by coupling an idealized Indian Ocean model and a convective feedback model over the Maritime Continent to the Zebiak–Cane model. It is found that, for a sufficiently strong convection feedback, a negative (positive) IOD indeed forces easterlies (westerlies) over the western Pacific. The contribution from the eastern IOD pole dominates. IOD variability is found to destabilize the El Niño–Southern Oscillation (ENSO) mode, whereas Indian Ocean basinwide warming (IOB) variability dampens ENSO, even in the presence of convection. The influence of the Indian Ocean on the spectral properties of ENSO is dominated by the IOB, while the IOD is a better predictor for individual ENSO events.

scholarly journals On the spatial and temporal variability of ENSO precipitation and drought teleconnection in mainland Southeast Asia

2015 ◽  
Vol 11 (6) ◽  
pp. 5307-5343 ◽  
Author(s):  
T. A. Räsänen ◽  
V. Lindgren ◽  
J. H. A. Guillaume ◽  
B. M. Buckley ◽  
M. Kummu
Keyword(s):  
Southeast Asia ◽  
Southern Oscillation ◽  
Drought Severity ◽  
Spatial And Temporal Variability ◽  
Severe Drought ◽  
Seasonal Evolution ◽  
Enso Events ◽  
Precipitation Anomalies ◽  
Mainland Southeast Asia

Abstract. The variability in the hydroclimate over mainland Southeast Asia is strongly influenced by the El Niño–Southern Oscillation (ENSO) phenomenon, which has been linked to severe drought and floods that profoundly influence human societies and ecosystems alike. However, the spatial characteristics and long-term stationarity of ENSO's influence in the region are not well understood. We thus aim to analyse seasonal evolution and spatial variations in the effect of ENSO on precipitation over the period of 1980–2013, and long-term variation in the ENSO-teleconnection using tree-ring derived Palmer Drought Severity Indices (PDSI) that span from 1650–2004. We found that the majority of the study area is under the influence of ENSO, which has affected the region's hydroclimate over the majority (96 %) of the 355 year study period. Our results further indicate that there is a pattern of seasonal evolution of precipitation anomalies during ENSO. However, considerable variability in the ENSO's influence is revealed: the strength of ENSO's influence was found to vary in time and space, and the different ENSO events resulted in varying precipitation anomalies. Additional research is needed to investigate how this variation in ENSO teleconnection is influenced by other factors, such as the properties of the ENSO events and other ocean and atmospheric phenomena. In general, the high variability we found in ENSO teleconnection combined with limitations of current knowledge, suggests that the adaptation to extremes in hydroclimate in mainland Southeast Asia needs to go beyond "predict-and-control" and recognise both uncertainty and complexity as fundamental principles.

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>

Diverse Influences of ENSO on the East Asian–Western Pacific Winter Climate Tied to Different ENSO Properties in CMIP5 Models

2015 ◽  
Vol 28 (6) ◽  
pp. 2187-2202 ◽  
Author(s):  
Hainan Gong ◽  
Lin Wang ◽  
Wen Chen ◽  
Debashis Nath ◽  
Gang Huang ◽  
...  
Keyword(s):  
Rossby Wave ◽  
Southern Oscillation ◽  
East Asian ◽  
Coupled Model ◽  
Western Pacific ◽  
Cmip5 Models ◽  
Boreal Winter ◽  
Winter Climate ◽  
Climatic Responses ◽  
Longitudinal Extension

Abstract The influence of El Niño–Southern Oscillation (ENSO) on the East Asian–western Pacific (EAWP) climate in boreal winter is investigated in the phase 5 of the Coupled Model Intercomparison Project (CMIP5) model results and then compared to that in the phase 3 (CMIP3) results. In particular, the role played by the differences among models in ENSO properties, including the amplitude and longitudinal extension of ENSO’s sea surface temperature (SST) pattern, is analyzed. Results show that an eastward shrinking of ENSO’s SST pattern leads to quite weak circulation and climatic responses over the EAWP regions in the models. On the contrary, a westward expansion of the SST pattern shifts the anomalous Walker circulation too far west. The resultant precipitation anomalies and lower-tropospheric atmospheric Rossby wave responses both extend unrealistically into the Indian Ocean, and the hemispheric asymmetry of the Rossby wave response is missing. All these features lead to unrealistic climatic impacts of ENSO over the EAWP regions. In contrast to the above two cases, a reasonable longitudinal extension of ENSO’s SST pattern corresponds to better ENSO teleconnections over the EAWP regions. Nevertheless, the atmospheric responses over the western Pacific are still located farther west than observed, implying a common bias of CMIP5 models. In this case, a larger amplitude of ENSO variability to some extent helps to reduce model biases and facilitate better climatic responses to ENSO in the EAWP regions. Compared with CMIP3 models, CMIP5 models perform better in representing ENSO’s impacts on the East Asian winter climate.

scholarly journals Long-Term Variation of the Principal Mode of Boreal Spring Hadley Circulation Linked to SST over the Indo-Pacific Warm Pool

2013 ◽  
Vol 26 (2) ◽  
pp. 532-544 ◽  
Author(s):  
Juan Feng ◽  
Jianping Li ◽  
Fei Xie
Keyword(s):  
Meridional Circulation ◽  
Hadley Circulation ◽  
Warming Trend ◽  
Warm Pool ◽  
Asymmetric Mode ◽  
Principal Mode ◽  
Boreal Spring ◽  
Pacific Warm Pool ◽  
Term Variation

Abstract The variability of the boreal spring [March–May (MAM)] Hadley circulation (HC) is investigated, focusing on the long-term variation of the first principal mode for 1951–2008, which is an equatorially asymmetric mode (AM) with the rising branch located around 10°S. This mode explains about 70% of the variance of the MAM HC and shows an obvious upward trend and thus contributes to the strengthening of the MAM HC. The robust warming trends of sea surface temperature (SST) over the Indo-Pacific warm pool (IPWP) play an essential role in the variations of the MAM HC. When SST over the IPWP is warm, anomalous meridional circulation is induced with descending branches located in regions 30°–20°S and 5°–15°N and rising motion located near 10°S. The anomalous rising south of the equator is due to the inhomogeneous warming of SST over the IPWP. SST within the IPWP in the Southern Hemisphere shows a larger warming trend than that in the Northern Hemisphere. The position of the anomalous convergence associated with SST variations over the IPWP is aligned with the maximum meridional gradient of zonal mean SST, resulting in an equatorially asymmetric meridional circulation. This point is further established in theoretical analyses. However, the meridional SST gradient within the IPWP shows a decreasing trend, suggesting the associated anomalous meridional circulation intensifies, which in turn explains the strengthening of the MAM HC. Under this scenario, the accompanied descent in the regions of 30°–20°S and 5°–15°N is enhanced, implying a frequent drought in these regions during MAM.

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