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Chunzai Wang - One of the best experts on this subject based on the ideXlab platform.

  • atmospheric circulation cElls associated with the El nino southern Oscillation
    Journal of Climate, 2002
    Co-Authors: Chunzai Wang
    Abstract:

    Abstract Atmospheric circulation cElls associated with the El Nino–Southern Oscillation (ENSO) are described and examined using the NCEP–NCAR reanalysis fiEld and the NCEP sea surface temperature (SST) from January 1950 to December 1999. The divergent wind and pressure vertical vElocity are employed for the identification of atmospheric circulation cElls. The warm phase of ENSO shows positive SST anomalies in the equatorial eastern Pacific and along the east coast of Asia and the west coast of North America, and negative SST anomalies in the off-equatorial western Pacific and in the central North Pacific. Associated with this SST anomaly distribution are variations of atmospheric zonal and meridional circulation cElls over the Pacific. The equatorial zonal Walker circulation cEll is weakened, consistent with previous schematic diagrams. The anomalous meridional Hadley circulation cEll in the eastern Pacific shows the air rising in the Tropics, flowing poleward in the upper troposphere, sinking in the subt...

  • a unified oscillator modEl for the El nino southern Oscillation
    Journal of Climate, 2001
    Co-Authors: Chunzai Wang
    Abstract:

    The dElayed oscillator, the western Pacific oscillator, the recharge-discharge oscillator, and the advective- reflective oscillator have been proposed to interpret the oscillatory nature of the El Nino-Southern Oscillation (ENSO). All of these oscillator modEls assume a positive ocean-atmosphere feedback in the equatorial eastern and central Pacific. The dElayed oscillator assumes that the western Pacific is an inactive region and wave reflection at the western boundary provides a negative feedback for the coupled system to oscillate. The western Pacific oscillator emphasizes an active role of the western Pacific in ENSO. The recharge-discharge oscillator argues that discharge and recharge of equatorial heat content cause the coupled system to oscillate. The advective- reflective oscillator emphasizes the importance of zonal advection associated with wave reflection at both the western and eastern boundaries. Motivated by the existence of these different oscillator modEls, a unified oscillator modEl is formulated and derived from the dynamics and thermodynamics of the coupled ocean-atmosphere system. Consistent with ENSO anomaly patterns observed in the tropical Pacific, this oscillator modEl considers sea surface temperature anomalies in the equatorial eastern Pacific, zonal wind stress anomalies in both the equatorial central Pacific and the equatorial western Pacific, and thermocline depth anomalies in the off-equatorial western Pacific. If the western Pacific wind-forced response is neglected, thermocline and zonal wind stress anomalies in the western Pacific are decoupled from the coupled system, and the unified oscillator reduces to the dElayed oscillator. If wave reflection at the western boundary is neglected, the unified oscillator reduces to the western Pacific oscillator. The mathematical form of the recharge-discharge oscillator can also be derived from this unified oscillator. Most of the physics of the advective-reflective oscillator are implicitly included in the unified oscillator, and the negative feedback of wave reflection at the eastern boundary is added to the unified oscillator. With appropriate modEl parameters chosen to be consistent with those of previous oscillator modEls, the unified oscillator modEl oscillates on interannual timescales.

  • western pacific interannual variability associated with the El nino southern Oscillation
    Journal of Geophysical Research, 1999
    Co-Authors: Chunzai Wang, Robert H Weisberg, Jyotika I Virmani
    Abstract:

    Observations of sea surface temperature (SST), sea levEl pressure (SLP), surface wind, and outgoing longwave radiation (OLR) show that the El Nino-Southern Oscillation (ENSO) displays western Pacific anomaly patterns in addition to eastern Pacific anomaly patterns. During the warm phase of ENSO, warm SST and low SLP anomalies in the equatorial eastern Pacific and low OLR anomalies in the equatorial central Pacific are accompanied by cold SST and high SLP anomalies in the off-equatorial western Pacific and high OLR anomalies in the off-equatorial far western Pacific. Also, while the zonal wind anomalies over the equatorial central Pacific are westerly, those over the equatorial far western Pacific are easterly. The nearly out-of-phase behavior between the eastern and western tropical Pacific is also observed during the cold phase of ENSO, but with anomalies of opposite sign. These western Pacific interannual anomaly patterns are robust features of ENSO, independent of data sets. It is argued that equatorial easterly (westerly) wind anomalies over the far western Pacific during the warm (cold) phase of ENSO are initiated by off-equatorial western Pacific cold (warm) SST anomalies, and that these winds are important for the evolution of ENSO. An atmosphere modEl is employed to demonstrate that small off-equatorial western Pacific cold (warm) SST anomalies (compared to those in the east) are sufficient to produce equatorial easterly (westerly) wind anomalies as observed over the far western Pacific. The coupled ocean-atmosphere modEl of Zebiak and Cane is then modified to investigate the evolution of the western Pacific interannual anomaly patterns in a coupled ocean-atmosphere system, by including a meridional structure to the subsurface temperature parameterization in the western Pacific. The modified modEl produces both western and eastern Pacific interannual anomaly patterns.

Kim M. Cobb - One of the best experts on this subject based on the ideXlab platform.

  • El nino southern Oscillation complexity
    Nature, 2018
    Co-Authors: Antonietta Capotondi, Axel Timmermann, Jong-seong Kug, Wenju Cai, Kim M. Cobb
    Abstract:

    El Nino events are characterized by surface warming of the tropical Pacific Ocean and weakening of equatorial trade winds that occur every few years. Such conditions are accompanied by changes in atmospheric and oceanic circulation, affecting global climate, marine and terrestrial ecosystems, fisheries and human activities. The alternation of warm El Nino and cold La Nina conditions, referred to as the El Nino-Southern Oscillation (ENSO), represents the strongest year-to-year fluctuation of the global climate system. Here we provide a synopsis of our current understanding of the spatio-temporal complexity of this important climate mode and its influence on the Earth system.

  • highly variable El nino southern Oscillation throughout the holocene
    Science, 2013
    Co-Authors: Kim M. Cobb, Niko Westphal, Hussein R Sayani, Jordan T Watson, Emanuele Di Lorenzo, Hai Cheng, R L Edwards, Christopher D Charles
    Abstract:

    The El Nino–Southern Oscillation (ENSO) drives large changes in global climate patterns from year to year, yet its sensitivity to continued anthropogenic greenhouse forcing is uncertain. We analyzed fossil coral reconstructions of ENSO spanning the past 7000 years from the Northern Line Islands, located in the center of action for ENSO. The corals document highly variable ENSO activity, with no evidence for a systematic trend in ENSO variance, which is contrary to some modEls that exhibit a response to insolation forcing over this same period. Twentieth-century ENSO variance is significantly higher than average fossil coral ENSO variance but is not unprecedented. Our results suggest that forced changes in ENSO, whether natural or anthropogenic, may be difficult to detect against a background of large internal variability.

  • El nino southern Oscillation and tropical pacific climate during the last millennium
    Nature, 2003
    Co-Authors: Kim M. Cobb, Hai Cheng, Christopher D Charles, Lawrence R Edwards
    Abstract:

    Any assessment of future climate change requires knowledge of the full range of natural variability in the El Nino/Southern Oscillation (ENSO) phenomenon. Here we splice together fossil-coral oxygen isotopic records from Palmyra Island in the tropical Pacific Ocean to provide 30–150-year windows of tropical Pacific climate variability within the last 1,100 years. The records indicate mean climate conditions in the central tropical Pacific ranging from rElativEly cool and dry during the tenth century to increasingly warmer and wetter climate in the twentieth century. But the corals also document a broad range of ENSO behaviour that corrElates poorly with these estimates of mean climate. The most intense ENSO activity within the reconstruction occurred during the mid-seventeenth century. Taken together, the coral data imply that the majority of ENSO variability over the last millennium may have arisen from dynamics internal to the ENSO system itsElf.

Alexander W Tudhope - One of the best experts on this subject based on the ideXlab platform.

  • palaeoclimate reconstructions reveal a strong link between El nino southern Oscillation and tropical pacific mean state
    Nature Communications, 2013
    Co-Authors: Aleksey Sadekov, Raja S Ganeshram, Laetitia Pichevin, Rose Berdin, Erin L Mcclymont, Henry Elderfield, Alexander W Tudhope
    Abstract:

    The El Nino-Southern Oscillation (ENSO) is one of the most important components of the global climate system, but its potential response to an anthropogenic increase in atmospheric CO2 remains largEly unknown. One of the major limitations in ENSO prediction is our poor understanding of the rElationship between ENSO variability and long-term changes in Tropical Pacific oceanography. Here we investigate this rElationship using palaeorecords derived from the geochemistry of planktonic foraminifera. Our results indicate a strong negative corrElation between ENSO variability and zonal gradient of sea-surface temperatures across the Tropical Pacific during the last 22 ky. This strong corrElation implies a mechanistic link that tightly couples zonal sea-surface temperature gradient and ENSO variability during large climate changes and provides a unique insight into potential ENSO evolution in the future by suggesting enhanced ENSO variability under a global warming scenario.

  • variability in the El nino southern Oscillation through a glacial interglacial cycle
    Science, 2001
    Co-Authors: Alexander W Tudhope, Colin P Chilcott, Malcolm T Mcculloch, Edward R Cook, John Chappell, R M Ellam, Janice M Lough, Graham Shimmield
    Abstract:

    The El Nino-Southern Oscillation (ENSO) is the most potent source of interannual climate variability. Uncertainty surrounding the impact of greenhouse warming on ENSO strength and frequency has stimulated efforts to devElop a better understanding of the sensitivity of ENSO to climate change. Here we use annually banded corals from Papua New Guinea to show that ENSO has existed for the past 130,000 years, operating even during "glacial" times of substantially reduced regional and global temperature and changed solar forcing. However, we also find that during the 20th century ENSO has been strong compared with ENSO of previous cool (glacial) and warm (interglacial) times. The observed pattern of change in amplitude may be due to the combined effects of ENSO dampening during cool glacial conditions and ENSO forcing by precessional orbital variations.

  • variability in the El nino southern Oscillation through a glacial interglacial cycle
    Science, 2001
    Co-Authors: Alexander W Tudhope, Colin P Chilcott, Malcolm T Mcculloch, Edward R Cook, John Chappell, R M Ellam, Janice M Lough, David W Lea, Graham Shimmield
    Abstract:

    The El Nino-Southern Oscillation (ENSO) is the most potent source of interannual climate variability. Uncertainty surrounding the impact of greenhouse warming on ENSO strength and frequency has stimulated efforts to devElop a better understanding of the sensitivity of ENSO to climate change. Here we use annually banded corals from Papua New Guinea to show that ENSO has existed for the past 130,000 years, operating even during "glacial" times of substantially reduced regional and global temperature and changed solar forcing. However, we also find that during the 20th century ENSO has been strong compared with ENSO of previous cool (glacial) and warm (interglacial) times. The observed pattern of change in amplitude may be due to the combined effects of ENSO dampening during cool glacial conditions and ENSO forcing by precessional orbital variations.

Ping Chang - One of the best experts on this subject based on the ideXlab platform.

  • pacific meridional mode and El nino southern Oscillation
    Geophysical Research Letters, 2007
    Co-Authors: Ping Chang, Li Zhang, R Saravanan, Daniel J Vimont, John C H Chiang, Howard F Seidel, Michael K Tippett
    Abstract:

    (1) We present intriguing evidence that the majority of El Nino events over the past four decades are preceded by a distinctive sea-surface warming and southwesterly wind anomaly in the vicinity of the Intertropical Convergence Zone (ITCZ) during the boreal spring. This phenomenon, known as the Meridional Mode (MM), is shown to be intrinsic to the thermodynamic coupling between the atmosphere and ocean. The MM effectivEly acts as a conduit through which the extratropical atmosphere influences ENSO. ModEling results further suggest that the MM plays a vital role in the seasonal phase-locking behavior of ENSO. The findings provide a new perspective for understanding the important role of thermodynamic ocean-atmosphere feedback in ENSO and may have profound implications for ENSO prediction, particularly the unresolved issue of the spring predictability barrier. Citation: Chang, P., L. Zhang, R. Saravanan, D. J. Vimont, J. C. H. Chiang, L. Ji, H. SeidEl, and M. K. Tippett (2007), Pacific meridional mode and El Nino—Southern Oscillation, Geophys. Res. Lett., 34, L16608, doi:10.1029/2007GL030302.

  • interaction between tropical atlantic variability and El nino southern Oscillation
    Journal of Climate, 2000
    Co-Authors: R Saravanan, Ping Chang
    Abstract:

    The interaction between tropical Atlantic variability and El Nino-Southern Oscillation (ENSO) is investigated using three ensembles of atmospheric general circulation modEl integrations. The integrations are forced by specifying observed sea surface temperature (SST) variability over a forcing domain. The forcing domain is the global ocean for the first ensemble, limited to the tropical ocean for the second ensemble, and further limited to the tropical Atlantic region for the third ensemble. The ensemble integrations show that extratropical SST anomalies have little impact on tropical variability, but the effect of ENSO is pervasive in the Tropics. Consistent with previous studies, the most significant influence of ENSO is found during the boreal spring season and is associated with an anomalous Walker circulation. Two important aspects of ENSO's influence on tropical Atlantic variability are noted. First, the ENSO signal contributes significantly to the ''dipole'' corrElation structure between tropical Atlantic SST and rainfall in the Nordeste Brazil region. In the absence of the ENSO signal, the corrElations are dominated by SST variability in the southern tropical Atlantic, resulting in less of a dipole structure. Second, the remote influence of ENSO also contributes to positive corrElations between SST anomalies and downward surface heat flux in the tropical Atlantic during the boreal spring season. However, even when ENSO forcing is absent, the modEl integrations provide evidence for a positive surface heat flux feedback in the deep Tropics, which is analyzed in a companion study by Chang et al. The analysis of modEl simulations shows that interannual atmospheric variability in the tropical Pacific-Atlantic system is dominated by the interaction between two distinct sources of tropical heating: (i) an equatorial heat source in the eastern Pacific associated with ENSO and (ii) an off-equatorial heat source associated with SST anomalies near the Caribbean. ModEling this Caribbean heat source accuratEly could be very important for seasonal forecasting in the Central American-Caribbean region.

  • interactions between the seasonal cycle and El nino southern Oscillation in an intermediate coupled ocean atmosphere modEl
    Journal of the Atmospheric Sciences, 1995
    Co-Authors: Ping Chang, Bin Wang, Link Ji, Tim Li
    Abstract:

    Abstract The nonlinear interactions between the seasonal cycle and El Nino-Southern Oscillation (ENSO) in the coupled ocean-atmosphere system are examined using a newly devEloped intermediate coupled ocean-atmosphere modEl. The modEl permits coupling between total sea surface temperature (SST) and total surface winds and thus is able to produce its own seasonal cycle. This coupling approach allows for the examination of full dynamic interactions between the seasonal cycle and interannual Oscillations. Numerical simulations with realistic surface heat fluxes indicate that this modEl is capable of capturing the essential variability of the coupled ocean-atmosphere system on seasonal-to-interannual timescale in the tropical Pacific. ModEl sensitivity experiments were carried out by independently varying the external forcing strength and coupling strength. These experiments reveal a very different behavior of the coupled system with and without the seasonal cycle. In the presence of the seasonal cycle, the co...

Athanasios Koutavas - One of the best experts on this subject based on the ideXlab platform.

  • El nino southern Oscillation extrema in the holocene and last glacial maximum
    Paleoceanography, 2012
    Co-Authors: Athanasios Koutavas, Stephan Joanides
    Abstract:

    [1] The El Nino–Southern Oscillation (ENSO) is the largest engine of interannual climate variability on the planet, yet its past behavior and potential for future change are poorly understood and vigorously contested. Reconstructions of past ENSO are indispensable for testing climate modEls tasked with predicting future ENSO activity in a warming world, but suitable geologic archives are scarce, especially for the last glacial period. Here we reconstruct mean climate and ENSO variability in the Holocene and Last Glacial Maximum (LGM) from oxygen isotopic ratios (δ18O) of individual foraminifera retrieved from deep-sea sediments. Our results document coordinated adjustments of the tropical Pacific/ENSO system between two diametrically opposite states: an “amplified ENSO” state in the LGM associated with a reduced zonal temperature gradient, and a “damped ENSO” state in the Mid-Holocene with enhanced gradient. Orbital precession provided the switch between these states and acted as the dominant external driver of the tropical Pacific/ENSO system in the past 25,000 years. The linked response of the mean state and variability to orbital forcing provides an integrated framework for testing ENSO theory and modEls.

  • mid holocene El nino southern Oscillation enso attenuation revealed by individual foraminifera in eastern tropical pacific sediments
    Geology, 2006
    Co-Authors: Athanasios Koutavas, Peter B Demenocal, George C Olive, Jean Lynchstieglitz
    Abstract:

    Holocene reconstructions of the El Nino–Southern Oscillation (ENSO) provide valuable perspective on its recent evolution and can be important for assessing its future. Optimal assessment of past ENSO variability requires observations from its center of action in the eastern equatorial Pacific, but these are limited due to paucity of high-resolution paleoceanographic archives (e.g., corals). Here we use a new approach to quantify past ENSO variance based on the oxygen isotopic composition (δ 18 O) of individual foraminifera ( Globigerinoides ruber ) from deep-sea sediments in the ENSO source region. Individual G. ruber foraminifera behave as monthly recorders of sea-surface conditions, including ENSO extremes, circumventing the lack of annual resolution in the sediments. Intrapopulation δ 18 O distributions derived with this method from a core near the Galapagos Islands reveal mid-Holocene reductions in variance of 50%, requiring drastic attenuation of the ENSO amplitude. Furthermore, Mg/Ca thermometry indicates that mid- Holocene background conditions were accompanied by a stronger zonal temperature gradient that coincided with a northward- displaced Intertropical Convergence Zone (ITCZ). The results suggest that the position of the ITCZ is an important factor in the low-frequency modulation of ENSO and could influence its future evolution.