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

  • warm bias of sea surface temperature in Eastern Boundary Current regions a study of effects of horizontal resolution in cesm
    Ocean Dynamics, 2019
    Co-Authors: Bin Wang
    Abstract:

    Warm bias of modeled sea surface temperature (SST) in the Eastern Boundary upwelling systems (EBUS) is a ubiquitous feature in coupled climate models. This paper investigates the causes underlying this warm bias, with a focus on the effect of horizontal resolution in the atmospheric component of coupled models, by using Community Earth System Model (CESM) as an example. By breaking down the energy budget of the upper ocean, we conclude that surface net heat flux and Ekman upwelling process exert a considerable influence (over 80%) on upper ocean temperature of EBUS in CESM. Besides, the problem of underestimation of stratocumulus cloud is not present near the coast, and hence not responsible for this warm bias in CESM. On the contrary, downward shortwave radiation bias is overcompensated by longwave radiation and latent flux bias on the open ocean. Therefore, the insufficient ocean dynamic upwelling is the dominantly cause for SST warm bias. Finer horizontal resolution atmosphere component of CESM enables better representation of low-level coastal jet structure, with stronger and closer alongshore wind stress and curl leading to realistic representation of upwelling process and horizontal water mass transportation. Furthermore, low-level coastal jet is shown to be sensitive to coastal mountain topography, especially in South East Pacific region, through both thermodynamic and dynamic atmospheric processes and oceanic response. This article provides further proof of improving coupled climate models in reducing the SST biases in EBUS regions.

  • Warm bias of sea surface temperature in Eastern Boundary Current regions—a study of effects of horizontal resolution in CESM
    Ocean Dynamics, 2019
    Co-Authors: Bin Wang
    Abstract:

    Warm bias of modeled sea surface temperature (SST) in the Eastern Boundary upwelling systems (EBUS) is a ubiquitous feature in coupled climate models. This paper investigates the causes underlying this warm bias, with a focus on the effect of horizontal resolution in the atmospheric component of coupled models, by using Community Earth System Model (CESM) as an example. By breaking down the energy budget of the upper ocean, we conclude that surface net heat flux and Ekman upwelling process exert a considerable influence (over 80%) on upper ocean temperature of EBUS in CESM. Besides, the problem of underestimation of stratocumulus cloud is not present near the coast, and hence not responsible for this warm bias in CESM. On the contrary, downward shortwave radiation bias is overcompensated by longwave radiation and latent flux bias on the open ocean. Therefore, the insufficient ocean dynamic upwelling is the dominantly cause for SST warm bias. Finer horizontal resolution atmosphere component of CESM enables better representation of low-level coastal jet structure, with stronger and closer alongshore wind stress and curl leading to realistic representation of upwelling process and horizontal water mass transportation. Furthermore, low-level coastal jet is shown to be sensitive to coastal mountain topography, especially in South East Pacific region, through both thermodynamic and dynamic atmospheric processes and oceanic response. This article provides further proof of improving coupled climate models in reducing the SST biases in EBUS regions.

Noah S. Diffenbaugh - One of the best experts on this subject based on the ideXlab platform.

  • Pleistocene water cycle and Eastern Boundary Current processes along the California continental margin
    Paleoceanography, 2010
    Co-Authors: Mitchell W Lyle, Linda E. Heusser, Christina Ravelo, Dyke Andreasen, Annette Olivarez Lyle, Noah S. Diffenbaugh
    Abstract:

    [1] Coastal marine sediments contain mixtures of terrestrial and marine paleoclimate proxies that record how the coastal water cycle has behaved over long time frames. We explore a 600 kyr marine record from ODP Site 1018, located due west of Santa Cruz, California, to identify coastal wet and dry periods and to associate them with oceanographic processes. Wet periods in central California, identified by increased tree pollen relative to pollen from grasslands and scrublands, are found on every major deglaciation in the last 600 kyr. Sea surface temperature (SST) data were collected for the last two deglaciations. Wet periods are associated with a rapid rise in SST off central California. SST gradients along the California margin and changes in biogenic deposition show that wet periods in central California are associated with a weakening of the California Current and weakened coastal upwelling. High carbonate production suggests that there was significant curl-of-wind stress upwelling offshore. We propose that wet periods in central California are associated with a meteorological connection to the tropical Pacific and weakened southward flow in the California Current that shunted temperate Pacific water northward into the Alaska gyre. We do not observe evidence for a south-shifted westerly storm track at the last glacial maximum but find that wet periods are diachronous along the California margin. The wettest period around the Santa Barbara Basin peaked at 16 ka, preceding the wet peak in central and northern California by 4 kyr.

  • Response of large‐scale Eastern Boundary Current forcing in the 21st century
    Geophysical Research Letters, 2005
    Co-Authors: Noah S. Diffenbaugh
    Abstract:

    [1] Greenhouse-induced changes in large-scale atmospheric circulation, particularly the strength, location and variability of the subtropical high pressure centers, could alter the dynamics and ecology of Eastern Boundary Current regions. An unprecedented ensemble of coupled climate model experiments reveals potentially important changes in large-scale Eastern Boundary Current forcing over the next century, including relaxation of the strength and variability of peak-season equatorward wind forcing in all four Eastern Boundary Current regions, and intensification of inter-annual variability of annual maximum sea level pressure in the southern hemisphere subtropical gyres. While these projected changes in large-scale forcing are difficult to distinguish from the multi-model noise, they are of sufficient magnitude to have important dynamical and ecological consequences.

  • response of large scale Eastern Boundary Current forcing in the 21st century
    Geophysical Research Letters, 2005
    Co-Authors: Noah S. Diffenbaugh
    Abstract:

    [1] Greenhouse-induced changes in large-scale atmospheric circulation, particularly the strength, location and variability of the subtropical high pressure centers, could alter the dynamics and ecology of Eastern Boundary Current regions. An unprecedented ensemble of coupled climate model experiments reveals potentially important changes in large-scale Eastern Boundary Current forcing over the next century, including relaxation of the strength and variability of peak-season equatorward wind forcing in all four Eastern Boundary Current regions, and intensification of inter-annual variability of annual maximum sea level pressure in the southern hemisphere subtropical gyres. While these projected changes in large-scale forcing are difficult to distinguish from the multi-model noise, they are of sufficient magnitude to have important dynamical and ecological consequences.

  • Could CO(2)-induced land-cover feedbacks alter near-shore upwelling regimes?
    Proceedings of the National Academy of Sciences of the United States of America, 2003
    Co-Authors: Noah S. Diffenbaugh, Mark A. Snyder, Lisa C. Sloan
    Abstract:

    The response of marine and terrestrial environments to global changes in atmospheric carbon dioxide (CO2) concentrations will likely be governed by both responses to direct environmental forcing and responses to Earth-system feedbacks induced by that forcing. It has been proposed that anthropogenic greenhouse forcing will intensify coastal upwelling in Eastern Boundary Current regions [Bakun, A. (1990) Science 247, 198–201]. Focusing on the California Current, we show that biophysical land-cover–atmosphere feedbacks induced by CO2 radiative forcing enhance the radiative effects of CO2 on land–sea thermal contrast, resulting in changes in Eastern Boundary Current total seasonal upwelling and upwelling seasonality. Specifically, relative to CO2 radiative forcing, land-cover–atmosphere feedbacks lead to a stronger increase in peak- and late-season near-shore upwelling in the northern limb of the California Current and a stronger decrease in peak- and late-season near-shore upwelling in the southern limb. Such changes will impact both marine and terrestrial communities [Bakun, A. (1990) Science 247, 198–201; Soto, C. G. (2001) Rev. Fish Biol. Fish. 11, 181–195; and Agostini, V. N. & Bakun, A. (2002) Fish. Oceanogr. 11, 129–142], and these and other Earth-system feedbacks should be expected to play a substantial role in shaping the response of Eastern Boundary Current regions to CO2 radiative forcing.

Steven J. Bograd - One of the best experts on this subject based on the ideXlab platform.

  • Optimal Environmental Conditions and Anomalous Ecosystem Responses: Constraining Bottom-up Controls of Phytoplankton Biomass in the California Current System
    Scientific reports, 2016
    Co-Authors: Michael G. Jacox, Elliott L. Hazen, Steven J. Bograd
    Abstract:

    In Eastern Boundary Current systems, wind-driven upwelling drives nutrient-rich water to the ocean surface, making these regions among the most productive on Earth. Regulation of productivity by changing wind and/or nutrient conditions can dramatically impact ecosystem functioning, though the mechanisms are not well understood beyond broad-scale relationships. Here, we explore bottom-up controls during the California Current System (CCS) upwelling season by quantifying the dependence of phytoplankton biomass (as indicated by satellite chlorophyll estimates) on two key environmental parameters: subsurface nitrate concentration and surface wind stress. In general, moderate winds and high nitrate concentrations yield maximal biomass near shore, while offshore biomass is positively correlated with subsurface nitrate concentration. However, due to nonlinear interactions between the influences of wind and nitrate, bottom-up control of phytoplankton cannot be described by either one alone, nor by a combined metric such as nitrate flux. We quantify optimal environmental conditions for phytoplankton, defined as the wind/nitrate space that maximizes chlorophyll concentration and present a framework for evaluating ecosystem change relative to environmental drivers. The utility of this framework is demonstrated by (i) elucidating anomalous CCS responses in 1998–1999, 2002 and 2005 and (ii) providing a basis for assessing potential biological impacts of projected climate change.

  • Poleward displacement of coastal upwelling‐favorable winds in the ocean's Eastern Boundary Currents through the 21st century
    Geophysical Research Letters, 2015
    Co-Authors: Ryan R. Rykaczewski, William J. Sydeman, Marisol García-reyes, Bryan Andrew Black, John P. Dunne, Steven J. Bograd
    Abstract:

    Upwelling is critical to the biological production, acidification, and deoxygenation of the ocean's major Eastern Boundary Current ecosystems. A leading conceptual hypothesis projects that the winds that induce coastal upwelling will intensify in response to increased land-sea temperature differences associated with anthropogenic global warming. We examine this hypothesis using an ensemble of coupled, ocean-atmosphere models and find limited evidence for intensification of upwelling-favorable winds or atmospheric pressure gradients in response to increasing land-sea temperature differences. However, our analyses reveal consistent latitudinal and seasonal dependencies of projected changes in wind intensity associated with poleward migration of major atmospheric high-pressure cells. Summertime winds near poleward boundaries of climatological upwelling zones are projected to intensify, while winds near equatorward boundaries are projected to weaken. Developing a better understanding of future changes in upwelling winds is essential to identifying portions of the oceans susceptible to increased hypoxia, ocean acidification, and eutrophication under climate change.

  • Climate change and wind intensification in coastal upwelling ecosystems
    Science (New York N.Y.), 2014
    Co-Authors: William J. Sydeman, Marisol García-reyes, David S. Schoeman, Ryan R. Rykaczewski, Sarah Ann Thompson, Bryan Andrew Black, Steven J. Bograd
    Abstract:

    In 1990, Andrew Bakun proposed that increasing greenhouse gas concentrations would force intensification of upwelling-favorable winds in Eastern Boundary Current systems that contribute substantial services to society. Because there is considerable disagreement about whether contemporary wind trends support Bakun's hypothesis, we performed a meta-analysis of the literature on upwelling-favorable wind intensification. The preponderance of published analyses suggests that winds have intensified in the California, Benguela, and Humboldt upwelling systems and weakened in the Iberian system over time scales ranging up to 60 years; wind change is equivocal in the Canary system. Stronger intensification signals are observed at higher latitudes, consistent with the warming pattern associated with climate change. Overall, reported changes in coastal winds, although subtle and spatially variable, support Bakun's hypothesis of upwelling intensification in Eastern Boundary Current systems.

Michael A. Spall - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear Radiating Instability of a Barotropic Eastern Boundary Current
    Journal of Physical Oceanography, 2013
    Co-Authors: Jinbo Wang, Michael A. Spall, Glenn R. Flierl, Paola Malanotte-rizzoli
    Abstract:

    Linear and nonlinear radiating instabilities of an Eastern Boundary Current are studied using a barotropic quasigeostrophic model in an idealized meridional channel. The Eastern Boundary Current is meridionally uniform and produces unstable modes in which long waves are most able to radiate. These long radiating modes are easily suppressed by friction because of their small growth rates. However, the long radiating modescanovercomefrictionbynonlinear energyinputtransferredfromthemoreunstabletrappedmodeand play an important role in the energy budget of the Boundary Current system. The nonlinearly powered long radiating modes take away part of the perturbation energy from the instability origin to the ocean interior. The radiated instabilities can generate zonal striations in the ocean interior that are comparable to features observed in the ocean. Subharmonic instability is identified to be responsible for the nonlinear resonance betweentheradiatingandtrappedmodes,butmoregeneralnonlineartriadinteractionsareexpectedtoapply in a highly nonlinear environment.

  • A new mechanism for the generation of quasi‐zonal jets in the ocean
    Geophysical Research Letters, 2012
    Co-Authors: Jinbo Wang, Michael A. Spall, Glenn R. Flierl, Paola Malanotte-rizzoli
    Abstract:

    [1] A simple barotropic quasi-geostrophic model is used to demonstrate that instabilities radiated from an unstable Eastern Boundary Current can generate zonal striations in the ocean interior with realistic wavelengths and amplitudes. Nonlinear transfer of energy from the more unstable trapped modes is important for radiating modes to overcome friction. The dynamics shown here are generic enough to point to the Eastern Boundary Current as a likely source of the observed striations extending from oceanic Eastern boundaries.

  • Radiating Instability of a Meridional Boundary Current
    Journal of Physical Oceanography, 2008
    Co-Authors: Hristina G. Hristova, Joseph Pedlosky, Michael A. Spall
    Abstract:

    Abstract A linear stability analysis of a meridional Boundary Current on the beta plane is presented. The Boundary Current is idealized as a constant-speed meridional jet adjacent to a semi-infinite motionless far field. The far-field region can be situated either on the Eastern or the western side of the jet, representing a western or an Eastern Boundary Current, respectively. It is found that when unstable, the meridional Boundary Current generates temporally growing propagating waves that transport energy away from the locally unstable region toward the neutral far field. This is the so-called radiating instability and is found in both barotropic and two-layer baroclinic configurations. A second but important conclusion concerns the differences in the stability properties of Eastern and western Boundary Currents. An Eastern Boundary Current supports a greater number of radiating modes over a wider range of meridional wavenumbers. It generates waves with amplitude envelopes that decay slowly with distan...

  • Wind- and buoyancy-forced upper ocean circulation in two-strait marginal seas with application to the Japan/East Sea
    Journal of Geophysical Research, 2002
    Co-Authors: Michael A. Spall
    Abstract:

    [1] The wind- and buoyancy-forced upper ocean circulation in a marginal sea connected to the open ocean through two straits is investigated using idealized numerical and analytical models. The study is motivated by the Japan/East Sea (JES) and other marginal seas found along the western North Pacific. It is shown that for anticyclonic wind stress curl and atmospheric cooling in the marginal sea, the inflow transport branches into Eastern and western Boundary Currents, in qualitative agreement with observed branching of the Tsushima Current in the southern JES. The Eastern Boundary Current arises because wind forcing in the open ocean, and a circulation integral around the island that separates the marginal sea from the open ocean, maintains the temperature on the island to be warmer than that found in the interior of the marginal sea. Buoyancy forcing in the marginal sea plays a key role in maintaining the Eastern Boundary Current. The dynamics that control the water mass transformation and downwelling are described and related to the model parameters. The largest heat loss to the atmosphere is found in the Eastern Boundary Current. The exchange rates with the open ocean, downwelling within the marginal sea, and Current structure within the marginal sea predicted by a linear analytic theory compare closely with results from a shallow water numerical model.

Alonso Hernández-guerra - One of the best experts on this subject based on the ideXlab platform.

  • Transport variability in the Lanzarote passage (Eastern Boundary Current of the North Atlantic subtropical Gyre)
    Deep Sea Research Part I: Oceanographic Research Papers, 2003
    Co-Authors: Alonso Hernández-guerra, Eugenio Fraile-nuez, Rafael Borges, F. López-laatzen, Pedro Vélez-belchí, Gregorio Parrilla, Thomas J. Müller
    Abstract:

    Observations from a four-year Current meter mooring at 28°44′N, 13°28′W in the Lanzarote passage are used to describe the transport variability of the Eastern Boundary Current of the North Atlantic Subtropical Gyre. Three different water masses are found in the passage: North Atlantic Central Water in the upper levels (roughly Full-size image (

  • The Eastern Boundary Current system between the Canary Islands and the African Coast
    Deep Sea Research Part II: Topical Studies in Oceanography, 2002
    Co-Authors: M. Knoll, Alonso Hernández-guerra, Thomas J. Müller, Francisco Machín, B. Lenz, F. López Laatzen, Gerold Siedler
    Abstract:

    To study the EasternBoundaryCurrentsystem off Northwest Africa in detail several CTD/ADCP-sections and long-term mooring work were carried out in the channel between Lanzarote and Africa. The observations are compared with a fine-resolution model, which was developed in the framework of the CANIGO project. The water masses, which are observed in this area, are characterised and classified in density ranges. The Current field shows a high spatial and temporal variability with maximum velocities of about 35 cm/s. Seasonal means as well as Currents averaged across the channel are only a few cm/s. In the surface water a steady southward flow in the middle of the channel indicates the CanaryCurrent in this area. During fall a strong northward Current is observed close to the African shelf. Though the CanaryCurrent strengthens during summer and fall due to an increase of the trade winds, the transport in the channel decreases or turns northward during that time due to the enhanced poleward Current at the Eastern side. A northward underCurrent with a mean velocity of +2.3 cm/s is observed at the African slope in 950 m depth. The poleward transport of AAIW increases during fall and a strong influence of relatively fresh AAIW is observed during that time. Most of the observations fit well to the results of the CANIGO model, but the occurrence of MW at the bottom of the channel and the corresponding southward flow cannot be resolved by the model.

  • Water masses, circulation and transport in the Eastern Boundary Current of the North Atlantic subtropical gyre*
    Scientia Marina, 2001
    Co-Authors: Alonso Hernández-guerra, F. López-laatzen, Francisco Machín, Demetrio De Armas, Josep Lluís Pelegrí
    Abstract:

    CTD sections carried out in September 1998 are used to describe the water masses, geostrophic circulation and mass transport in the Easternmost branch of the Canary Current. The surface water mass ( 9 kg s -1 . A tongue of relatively fresh water, consisting of Antarctic Intermediate Water (AAIW), was found approximately in the 600-1100 m depth layer. This tongue was 200 km wide, stretching from the African coast almost to Gran Canaria Island, and transported a net mass of 1.1 x 10 9 kg s -1 northward. This system of Currents is what constitutes the real Eastern Boundary Current of the North Atlantic Subtropical Gyre.

  • Water masses, circulation and transport in the Eastern Boundary Current of the North Atlantic subtropical gyre
    Scientia Marina, 2001
    Co-Authors: Alonso Hernández-guerra, Francisco Machín, Demetrio De Armas, Federico López-laatzen, Josep Lluís Pelegrí
    Abstract:

    Publicación online disponible en: http://www.icm.csic.es/scimar/index.phpCTD sections carried out in September 1998 are used to describe the water masses, geostrophic circulation and mass transport in the Easternmost branch of the Canary Current. The surface water mass (