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  • 1
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    Variability in the South Atlantic Anticyclone and the Atlantic Niño mode (2014)
    AMS (American Meteorological Society)
    In:  Journal of Climate, 27 (21). pp. 8135-8150.
    Details
    Publication Date: 2020-08-04
    Description: Sea surface temperature (SST) anomalies in the eastern equatorial Atlantic are connected to modulations in the strength of the South Atlantic subtropical high-pressure system, referred to as the South Atlantic Anticyclone (SAA). Using ocean and atmosphere reanalysis products we show here that the strength of the SAA from February to May impacts the timing of the cold tongue onset and the intensity of its development in the eastern equatorial Atlantic (EEA) via anomalous tropical wind power. This modulation of the timing and amplitude of the seasonal cold tongue development manifests as anomalous SST events peaking between June and August. The timing and impact of this connection is not completely symmetric for warm and cold events. For cold events, an anomalously strong SAA in February and March leads to positive wind power anomalies from February to June resulting in an early cold tongue onset and subsequent cold SST anomalies in June and July. For warm events the anomalously weak SAA persists until May, generating negative wind power anomalies that lead to a late cold tongue onset as well as a suppression of the cold tongue development and associated warm SST anomalies. Mechanisms by which SAA induced wind power variations south of the equator influence EEA SST are discussed, including ocean adjustment via Rossby and Kelvin wave propagation, meridional advection, and local intraseasonal wind variations
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1175/JCLI-D-14-00202.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Assessing the Twenty-First-Century Shift in ENSO Variability in Terms of the Bjerknes Stability Index* (2014)
    AMS (American Meteorological Society)
    In:  Journal of Climate, 27 (7). pp. 2577-2587.
    Details
    Publication Date: 2014-10-22
    Description: A decadal change in the character of ENSO was observed around year 2000 toward weaker-amplitude, higher-frequency events with an increased occurrence of central Pacific El Niños. Here these changes are assessed in terms of the Bjerknes stability index (BJ index), which is a measure of the growth rate of ENSO-related SST anomalies. The individual terms of the index are calculated from ocean reanalysis products separately for the time periods 1980–99 and 2000–10. The spread between the products is large, but they show a robust weakening of the thermocline feedback due to a reduced thermocline slope response to anomalous zonal wind stress as well as a weakened wind stress response to eastern equatorial Pacific SST anomalies. These changes are consistent with changes in the background state of the tropical Pacific: cooler mean SST in the eastern and central equatorial Pacific results in reduced convection there together with a westward shift in the ascending branch of the Walker circulation. This shift leads to a weakening in the relationship between eastern Pacific SST and longitudinally averaged equatorial zonal wind stress. Also, despite a steeper mean thermocline slope in the more recent period, the thermocline slope response to wind stress anomalies weakened due to a smaller zonal wind fetch that results from ENSO-related wind anomalies being more confined to the western basin. As a result, the total BJ index is more negative, corresponding to a more strongly damped system in the past decade compared to the 1980s and 1990s.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/JCLI-D-13-00438.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    A Comparative Stability Analysis of Atlantic and Pacific Nino Modes (2013)
    American Meteorological Society
    In:  Journal of Climate, 26 (16). pp. 5965-5980.
    Details
    Publication Date: 2020-07-24
    Description: El Niño–Southern Oscillation (ENSO) in the Pacific and the analogous Atlantic Niño mode are generated by processes involving coupled ocean–atmosphere interactions known as the Bjerknes feedback. It has been argued that the Atlantic Niño mode is more strongly damped than ENSO, which is presumed to be closer to neutrally stable. In this study the stability of ENSO and the Atlantic Niño mode is compared via an analysis of the Bjerknes stability index. This index is based on recharge oscillator theory and can be interpreted as the growth rate for coupled modes of ocean–atmosphere variability. Using observational data, an ocean reanalysis product, and output from an ocean general circulation model, the individual terms of the Bjerknes index are calculated for the first time for the Atlantic and then compared to results for the Pacific. Positive thermocline feedbacks in response to wind stress forcing favor anomaly growth in both basins, but they are twice as large in the Pacific compared to the Atlantic. Thermocline feedback is related to the fetch of the zonal winds, which is much greater in the equatorial Pacific than in the equatorial Atlantic due to larger basin size. Negative feedbacks are dominated by thermal damping of sea surface temperature anomalies in both basins. Overall, it is found that both ENSO and the Atlantic Niño mode are damped oscillators, but the Atlantic is more strongly damped than the Pacific primarily because of the weaker thermocline feedback.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/jcli-d-12-00758.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Symmetry of the Atlantic Nino mode (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 44 (2). pp. 965-973.
    Details
    Publication Date: 2020-02-06
    Description: El Niño-Southern Oscillation (ENSO) in the Pacific is asymmetric for warm and cold events with respect to amplitude, spatial patterns and temporal evolution. Here the symmetry of the Atlantic Niño mode, which many previous studies have argued is governed by atmosphere–ocean dynamics similar to those of ENSO, is investigated using two different ocean reanalysis products. Calculation of Bjerknes feedback terms for the Pacific reveals a pronounced asymmetry between warm and cold events, though unlike most previous studies, the largest asymmetry is found in the relationship between eastern Pacific thermocline depth and SST anomalies. For the Atlantic, cold events are effectively mirror images of warm events with Bjerknes feedbacks of similar strength. The analysis supports not only the conclusion that Atlantic Niños are more symmetric than ENSO, but the hypothesis itself that the Bjerknes feedback is operative in the Atlantic given the strength of the relationship between the key variables involved.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2016GL071829
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Enhanced warming over the global subtropical western boundary currents (2012)
    Nature Publishing Group
    In:  Nature Climate Change, 2 . pp. 161-166.
    Details
    Publication Date: 2019-09-23
    Description: Subtropical western boundary currents are warm, fast-flowing currents that form on the western side of ocean basins. They carry warm tropical water to the mid-latitudes and vent large amounts of heat and moisture to the atmosphere along their paths, affecting atmospheric jet streams and mid-latitude storms, as well as ocean carbon uptake1, 2, 3, 4. The possibility that these highly energetic currents might change under greenhouse-gas forcing has raised significant concerns5, 6, 7, but detecting such changes is challenging owing to limited observations. Here, using reconstructed sea surface temperature datasets and century-long ocean and atmosphere reanalysis products, we find that the post-1900 surface ocean warming rate over the path of these currents is two to three times faster than the global mean surface ocean warming rate. The accelerated warming is associated with a synchronous poleward shift and/or intensification of global subtropical western boundary currents in conjunction with a systematic change in winds over both hemispheres. This enhanced warming may reduce the ability of the oceans to absorb anthropogenic carbon dioxide over these regions. However, uncertainties in detection and attribution of these warming trends remain, pointing to a need for a long-term monitoring network of the global western boundary currents and their extensions.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1038/NCLIMATE1353
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    El Nino–Southern Oscillation complexity (2018)
    Nature Research
    Details
    Publication Date: 2024-04-19
    Description: El Niño 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 Niño and cold La Niña conditions, referred to as the El Niño–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.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    PIRATA: A Sustained Observing System for Tropical Atlantic Climate Research and Forecasting (2019)
    AGU (American Geophysical Union) | Wiley
    In:  Earth and Space Science, 6 (4). pp. 577-616.
    Details
    Publication Date: 2022-01-31
    Description: Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) is a multinational program initiated in 1997 in the tropical Atlantic to improve our understanding and ability to predict ocean-atmosphere variability. PIRATA consists of a network of moored buoys providing meteorological and oceanographic data transmitted in real time to address fundamental scientific questions as well as societal needs. The network is maintained through dedicated yearly cruises, which allow for extensive complementary shipboard measurements and provide platforms for deployment of other components of the Tropical Atlantic Observing System. This paper describes network enhancements, scientific accomplishments and successes obtained from the last 10 years of observations, and additional results enabled by cooperation with other national and international programs. Capacity building activities and the role of PIRATA in a future Tropical Atlantic Observing System that is presently being optimized are also described.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1029/2018EA000428
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    The 2nd International Indian Ocean Expedition (IIOE-2): Motivating New Exploration in a Poorly Understood Basin. (2016)
    ASLO
    In:  EPIC3Limnology and Oceanography Bulletin, ASLO, 25(4), pp. 117-124, ISSN: 1539-607X
    Details
    Publication Date: 2017-06-23
    Description: Overview The Indian Ocean remains one of the most poorly sampled and overlooked regions of the world ocean. Today, more than 25% of the world’s population lives in the Indian Ocean region and the population of most Indian Ocean rim nations is increasing rapidly. These increases in population are giving rise to mul- tiple stressors in both coastal and open ocean environments. Combined with warming and acidification due to global climate change, these regional stressors are resulting in loss of biodi- versity in the Indian Ocean and also changes in the phenology and biogeography of many spe- cies. These pressures have given rise to an urgent need to understand and predict changes in the Indian Ocean, but the measurements that are needed to do this are still lacking. In response, SCOR, IOC, and IOGOOS have stimulated a second International Indian Ocean Expedition (IIOE-2). An international Science Plan and an Implementation Strategy for IIOE-2 have been developed, the formulation of national plans is well underway in several countries, and new research initiatives are being motivated. An Early-Career Scientist Network for Indian Ocean Research has self-organized to support the Expedition. The success of IIOE-2 will be gauged not just by how much it advances our understanding of the complex and dynamic Indian Ocean system, but also by how it con- tributes to sustainable development of marine resources, environmental stewardship, ocean and climate forecasting, and training of the next generation of ocean scientists. We encourage ASLO members to get involved.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
    Format: application/pdf
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    PAPER (OA)
  • 9
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    Ocean preconditioning of Cyclone Nargis in the Bay of Bengal : interaction between Rossby waves, surface fresh waters, and sea surface temperatures (2011)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 41 (2011): 1741–1755, doi:10.1175/2011JPO4437.1.
    Description: An in-depth data analysis was conducted to understand the occurrence of a strong sea surface temperature (SST) front in the central Bay of Bengal before the formation of Cyclone Nargis in April 2008. Nargis changed its course after encountering the front and tracked along the front until making landfall. One unique feature of this SST front was its coupling with high sea surface height anomalies (SSHAs), which is unusual for a basin where SST is normally uncorrelated with SSHA. The high SSHAs were associated with downwelling Rossby waves, and the interaction between downwelling and surface fresh waters was a key mechanism to account for the observed SST–SSHA coupling. The near-surface salinity field in the bay is characterized by strong stratification and a pronounced horizontal gradient, with low salinity in the northeast. During the passage of downwelling Rossby waves, freshening of the surface layer was observed when surface velocities were southwestward. Horizontal convergence of freshwater associated with downwelling Rossby waves increased the buoyancy of the upper layer and caused the mixed layer to shoal to within a few meters of the surface. Surface heating trapped in the thin mixed layer caused the fresh layer to warm, whereas the increase in buoyancy from low-salinity waters enhanced the high SSHA associated with Rossby waves. Thus, high SST coincided with high SSHA. The dominant role of salinity in controlling high SSHA suggests that caution should be exercised when computing hurricane heat potential in the bay from SSHA. This situation is different from most tropical oceans, where temperature has the dominant effect on SSHA.
    Description: This work was supported by the NOAA/Office of Climate Observation (OCO) program.
    Keywords: Rossby waves ; Sea surface temperature ; Sea/ocean surface
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 10
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    Ecological impacts of the 2015/16 El Niño in the Central Equatorial Pacific (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 99, Suppl. S (2018): S21-S26, doi:10.1175/BAMS-D-17-0128.1.
    Description: NOAA Coral Reef Conservation Program; National Science Foundation OCE 1537338, OCE 1605365, OCE 1031971
    Repository Name: Woods Hole Open Access Server
    Type: Article
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