Sea level and dynamic topography in the Western Pacific during 1982-83 El Nino

Pendant le fort El Nino 1982-1983, deux réseaux d'observations océanographiques ont fourni des données continues dans le Pacifique tropical : le réseau de mesure du niveau de la mer créé et maintenu par l'Université d'Hawaii et le réseau XTB - navires marchands du groupe SURTROPAC, Centre ORSTOM de Nouméa - La topographie dynamique mensuelle 0-400 db est calculée le long de la route Nouméa-Japon (20°S-20°N, 150°E-165°E), en utilisant des relations T-S réelles, pour faire ressortir les anomalies interannuelles. Cette topographie est comparée aux valeurs mensuelles du niveau de la mer. Ce très bon accord obtenu entre les variations spatio-temporelles déduites des deux réseaux montre qu'ils se complètent utilement dans la surveillance des anomalies climatiques. (Résumé d'auteur

Multiple causes of interannual sea surface temperature variability in the equatorial Atlantic Ocean

The eastern equatorial Atlantic Ocean is subject to interannual fluctuations of sea surface temperatures, with climatic impacts on the surrounding continents. The dynamic mechanism underlying Atlantic temperature variability is thought to be similar to that of the El Nino/Southern Oscillation (ENSO) in the equatorial Pacific, where air-sea coupling leads to a positive feedback between surface winds in the western basin, sea surface temperature in the eastern basin, and equatorial oceanic heat content. Here we use a suite of observational data, climate reanalysis products, and general circulation model simulations to reassess the factors driving the interannual variability. We show that some of the warm events can not be explained by previously identified equatorial wind stress forcing and ENSO-like dynamics. Instead, these events are driven by a mechanism in which surface wind forcing just north of the equator induces warm ocean temperature anomalies that are subsequently advected toward the equator. We find the surface wind patterns are associated with long-lived subtropical sea surface temperature anomalies and suggest they therefore reflect a link between equatorial and subtropical Atlantic variability

Atmosphere-ocean coupled processes in the Madden-Julian oscillation

The Madden-Julian oscillation (MJO) is a convectively coupled 30-70 day (intraseasonal) tropical atmospheric mode that drives variations in global weather, but which is poorly simulated in most atmospheric general circulation models. Over the past two decades, field campaigns and modeling experiments have suggested that tropical atmosphere-ocean interactions may sustain or amplify the pattern of enhanced and suppressed atmospheric convection that defines the MJO, and encourage its eastward propagation through the Indian and Pacific Oceans. New observations collected during the past decade have advanced our understand of the ocean response to atmospheric MJO forcing and the resulting intraseasonal sea surface temperature (SST) fluctuations. Numerous modeling studies have revealed a considerable impact of the mean state on MJO ocean-atmosphere coupled processes, as well as the importance of resolving the diurnal cycle of atmosphere--upper-ocean interactions. New diagnostic methods provide insight to atmospheric variability and physical processes associated with the MJO, but offer limited insight on the role of ocean feedbacks. Consequently, uncertainty remains concerning the role of the ocean in MJO theory. Our understanding of how atmosphere-ocean coupled processes affect the MJO can be improved by collecting observations in poorly sampled regions of MJO activity, assessing oceanic and atmospheric drivers of surface fluxes, improving the representation of upper-ocean mixing in coupled-model simulations, designing model experiments that minimize mean-state differences, and developing diagnostic tools to evaluate the nature and role of coupled ocean-atmosphere processes over the MJO cycle

Spreading and vertical structure of the Persian Gulf and Red Sea outflows in the Northwestern Indian Ocean

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(4), (2021): e2019JC015983, https://doi.org/10.1029/2019JC015983.In the Indian Ocean, salty water masses from the Persian Gulf and Red Sea are important sources of salt, heat, and nutrients. Across the Arabian Sea, these outflows impact human and biological activities, their thermohaline characteristics and shapes exhibiting important spatial and seasonal variability. The knowledge of the water masses properties is important to validate realistic simulations of the Indian Ocean. A classical approach to study these water masses is to track them on specific isopycnal levels. Nevertheless, their peaking thermohaline characteristics are not always found at a specific density but rather spread over a range. Here, we develop a detection algorithm able to capture the full vertical structure of the outflows, that we applied to a data set of about 126,000 vertical profiles. We are thus able to quantify the changes in their thermohaline signatures and in their vertical structures, characterized here by the intensity of the salinity peaks of the water masses and lateral injection of fresh and salty waters, and describe their spatial variability. Across the northwestern Indian Ocean, the salty outflows undergo several changes, diminishing their thermohaline signatures and peaks and layering. In their early stages in the narrow Gulf of Oman and Aden, the outflows present configurations indicative of diapycnal mixing. In the same regions and along the western edge of the Arabian Sea, these water masses are subject to lateral mixing. All over the Arabian Sea, salt fingering conditions are met for lower layers of the outflows.The authors thank the World Ocean Database (WOD), a collection of scientifically quality-controlled ocean profile data, an NCEI product and an International Oceanographic Data and Information Exchange (IODE) project, funded in partnership with the NOAA OAR Ocean Observing and Monitoring Division

Interannual to Decadal Response of the Indonesian Throughflow Vertical Profile to Indo‐Pacific Forcing

The Indonesian Throughflow (ITF) inflow through the Sulawesi, Maluku, and Halmahera Seas and the ITF outflow into the eastern tropical Indian Ocean, based on reanalysis and model data, are used to investigate the interannual to decadal response of the ITF vertical profile to Indo‐Pacific forcing. The thermocline (upper 300 m) inflow, driven by the North Pacific Ocean, negatively responds to El Niño‐Southern Oscillation (ENSO) with almost no lag; while the thermocline outflow lags by 5–7 months. The sub‐thermocline (300–760 m) inflow, which is influenced by both the North and South Pacific, positively responds to ENSO and Interdecadal Pacific Oscillation (IPO) indices with 13 months lag and displays a long‐term trend tracking the IPO index. Influenced by eastern Indian Ocean variations, the sub‐thermocline outflow positively correlates with the ENSO and IPO indices with about 7–9 months lag, a shorter lag time than the inflow

Experimental forecasts of El Niño

Experimental forecasts of El Niño events occurring since 1970, made with a deterministic model of the coupled ocean-atmosphere system, indicate that El Niño is generally predictable one or two years ahead. A forecast for 1986 is also presented

The Kuroshio Extension : a leading mechanism for the seasonal sea-level variability along the west coast of Japan

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Ocean Dynamics 60 (2010): 667-672, doi:10.1007/s10236-009-0239-9.Sea level changes coherently along the two coasts of Japan on the seasonal time scale. AVISO satellite altimetry data and OFES (OGCM for the Earth Simulator) results indicate that the variation propagates clockwise from Japan's east coast through the Tsushima Strait into the Japan/East Sea (JES) and then northward along the west coast. In this study, we hypothesize and test numerically that the sea level variability along the west coast of Japan is remotely forced by the Kuroshio Extension (KE) off the east coast. Topographic Rossby waves and boundary Kelvin waves facilitate the connection. Our 3-d POM model when forced by observed wind stress reproduces well the seasonal changes in the vicinity of JES. Two additional experiments were conducted to examine the relative roles of remote forcing and local forcing. The sea level variability inside the JES was dramatically reduced when the Tsushima Strait is blocked in one experiment. The removal of the local forcing, in another experiment, has little effect on the JES variability. Both experiments support our hypothesis that the open-ocean forcing, possibly through the KE variability, is the leading forcing mechanism for sea level change along the west coast of Japan.This work was conducted when Chao Ma was a visiting graduate student at WHOI. His visit has been supported by China Scholarship Council and WHOI Academics Office. This study has been supported by WHOI’s Coastal Ocean Institute, the National Basic Research Program of China 2005CB422303 and 2007CB481804), the International Science and Technology Cooperation Program of China (2006DFB21250), the Natural Science Foundation of China (40706006) , and the Ministry of Education’s 111 Project (B07036). Lin was supported by the Program for New Century Excellent Talents in University (NECT-07-0781)

Dissolved Organic Matter in the Upwelling System off Peru: Imprints of Bacterial Activity and Water Mass Characteristics

Microbial degradation of dissolved organic matter (DOM) contributes to the formation and preservation of oxygen minimum zones (OMZs) in the ocean, but information on the spatial distribution and molecular composition of DOM in OMZ regions is scarce. We quantified molecular components of DOM that is, dissolved amino acids (DAA) and dissolved combined carbohydrates (DCCHO), in the upwelling region off Peru. We found the highest concentrations of DCCHO in fully oxygenated surface waters steeply declining at shallow depth. The highest DAA concentrations were observed close to the surface also, but attenuation of DAA concentration over depth was less pronounced. Compositional changes of DCCHO were strongest within more oxygenated waters. Compositional changes of DAA were also evident under suboxic conditions (<5 µmol O2 kg−1) and indicated bacterial peptide degradation. Moreover, specific free amino acids (alanine and threonine) were enhanced within suboxic waters, pointing to a potential production of dissolved organic nitrogen under suboxic conditions. Our results therewith suggest that deoxygenation supports a spatial decoupling of DCCHO and DAA production and degradation dynamics and give new insights to carbon and nitrogen cycling in the OMZ off Peru

Impact of ENSO longitudinal position on teleconnections to the NAO

While significant improvements have been made in understanding how the El Niño–Southern Oscillation (ENSO) impacts both North American and Asian climate, its relationship with the North Atlantic Oscillation (NAO) remains less clear. Observations indicate that ENSO exhibits a highly complex relationship with the NAO-associated atmospheric circulation. One critical contribution to this ambiguous ENSO/NAO relationship originates from ENSO’s diversity in its spatial structure. In general, both eastern (EP) and central Pacific (CP) El Niño events tend to be accompanied by a negative NAO-like atmospheric response. However, for two different types of La Niña the NAO response is almost opposite. Thus, the NAO responses for the CP ENSO are mostly linear, while nonlinear NAO responses dominate for the EP ENSO. These contrasting extra-tropical atmospheric responses are mainly attributed to nonlinear air-sea interactions in the tropical eastern Pacific. The local atmospheric response to the CP ENSO sea surface temperature (SST) anomalies is highly linear since the air-sea action center is located within the Pacific warm pool, characterized by relatively high climatological SSTs. In contrast, the EP ENSO SST anomalies are located in an area of relatively low climatological SSTs in the eastern equatorial Pacific. Here only sufficiently high positive SST anomalies during EP El Niño events are able to overcome the SST threshold for deep convection, while hardly any anomalous convection is associated with EP La Niña SSTs that are below this threshold. This ENSO/NAO relationship has important implications for NAO seasonal prediction and places a higher requirement on models in reproducing the full diversity of ENSO