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  • 1
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    What determines the spatial pattern in summer upwelling trends on the U.S. West Coast? (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. 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 117 (2012): C08012, doi:10.1029/2012JC008016.
    Description: Analysis of sea surface temperature (SST) from coastal buoys suggests that the summertime over-shelf water temperature off the U.S. West Coast has been declining during the past 30 years at an average rate of −0.19°C decade−1. This cooling trend manifests itself more strongly off south-central California than off Oregon and northern California. The variability and trend in the upwelling north of off San Francisco are positively correlated with those of the equatorward wind, indicating a role of offshore Ekman transport in the north. In contrast, Ekman pumping associated with wind stress curls better explains the stronger and statistically more significant cooling trend in the south. While the coast-wide variability and trend in SST are strongly correlated with those of large-scale modes of climate variability, they in general fail to explain the southward intensification of the trend in SST and wind stress curl. This result suggests that the local wind stress curl, often topographically forced, may have played a role in the upwelling trend pattern.
    Description: H.S. acknowledges the WHOI supports from the Coastal Research Fund in Support of Scientific Staff, the Penzance Endowed Fund in Support of Assistant Scientists, and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research. K.B. and C.E. acknowledge support by the National Science Foundation through grants OCE-1059632 and OCE 1061434.
    Description: 2013-03-09
    Keywords: Coastal upwelling ; Multidecadal trend ; Wind stress curl
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Response and impact of equatorial ocean dynamics and tropical instability waves in the tropical Atlantic under global warming : a regional coupled downscaling study (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2011. 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 116 (2011): C03026, doi:10.1029/2010JC006670.
    Description: A regional coupled model is used for a dynamic downscaling over the tropical Atlantic based on a global warming simulation carried out with the Geophysical Fluid Dynamics Laboratory CM2.1. The regional coupled model features a realistic representation of equatorial ocean dynamical processes such as the tropical instability waves (TIWs) that are not adequately simulated in many global coupled climate models. The coupled downscaling hence provides a unique opportunity to assess their response and impact in a changing climate. Under global warming, both global and regional models exhibit an increased (decreased) rainfall in the tropical northeast (South) Atlantic. Given this asymmetric change in mean state, the regional model produces the intensified near-surface cross-equatorial southerly wind and zonal currents. The equatorial cold tongue exhibits a reduced surface warming due to the enhanced upwelling. It is mainly associated with the increased vertical velocities driven by cross-equatorial wind, in contrast to the equatorial Pacific, where thermal stratification is suggested to be more important under global warming. The strengthened upwelling and zonal currents in turn amplify the dynamic instability of the equatorial ocean, thereby intensifying TIWs. The increased eddy heat flux significantly warms the equator and counters the effect of enhanced upwelling. Zonal eddy heat flux makes the largest contribution, suggesting a need for sustained monitoring of TIWs with spatially denser observational arrays in the equatorial oceans. Overall, results suggest that eddy heat flux is an important factor that may impact the mean state warming of equatorial oceans, as it does in the current climate.
    Description: H.S. acknowledges the support from the NOAA Climate and Global Change Postdoctoral Fellowship Program and the Penzance Endowed Fund in Support of Assistant Scientists at WHOI. H.S. and S.‐P.X. are thankful for support from NOAA, NSF, and the Japan Agency for Marine‐Earth Science and Technology.
    Keywords: Climate change ; Ocean mesoscale eddy ; Equatorial Atlantic
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Meridional Gulf Stream shifts can influence wintertime variability in the North Atlantic storm track and Greenland blocking. (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(3), (2019):1702-1708. doi:10.1029/2018GL081087.
    Description: After leaving the U.S. East Coast, the northward flowing Gulf Stream (GS) becomes a zonal jet and carries along its frontal characteristics of strong flow and sea surface temperature gradients into the North Atlantic at midlatitudes. The separation location where it leaves the coast is also an anchor point for the wintertime synoptic storm track across North America to continue to develop and head across the ocean. We examine the meridional variability of the separated GS path on interannual to decadal time scales as an agent for similar changes in the storm track and blocking variability at midtroposphere from 1979 to 2012. We find that periods of northerly (southerly) GS path are associated with increased (suppressed) excursions of the synoptic storm track to the northeast over the Labrador Sea and reduced (enhanced) Greenland blocking. In both instances, GS shifts lead those in the midtroposphere by a few months.
    Description: Our research has been conducted with the support of NSF (AGS‐1355339, OCE‐1419235, and OCE‐1242989), NASA (NNX13AM59G), and NOAA CPO Climate Variability and Predictability Program (NA13OAR4310139) grants to the Woods Hole Oceanographic Institution. We also thank three reviewers for their insightful comments on an earlier draft of this manuscript. Quarterly estimates of our Gulf Stream Index are available as a data file in the supporting information.
    Description: 2019-07-29
    Keywords: Gulf Stream path changes ; Wintertime atmospheric storm track ; Greenland blocking ; Intrerannual variability
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Impact of current-wind interaction on vertical processes in the Southern Ocean (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. 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 125(4), (2020): e2020JC016046, doi:10.1029/2020JC016046.
    Description: Momentum input from westerly winds blowing over the Southern Ocean can be modulated by mesoscale surface currents and result in changes in large‐scale ocean circulation. Here, using an eddy‐resolving 1/20 degree ocean model configured near Drake Passage, we evaluate the impact of current‐wind interaction on vertical processes. We find a reduction in momentum input from the wind, reduced eddy kinetic energy, and a modification of Ekman pumping rates. Wind stress curl resulting from current‐wind interaction leads to net upward motion, while the nonlinear Ekman pumping term associated with horizontal gradients of relative vorticity induces net downward motion. The spatially averaged mixed layer depth estimated using a density criteria is shoaled slightly by current‐wind interaction. Current‐wind interaction, on the other hand, enhances the stratification in the thermocline below the mixed layer. Such changes have the potential to alter biogeochemical processes including nutrient supply, biological productivity, and air‐sea carbon dioxide exchange.
    Description: The MITgcm can be obtained online (http://mitgcm.org). The geostrophic current product derived from the sea level anomaly can be downloaded in the Copernicus Marine and Environment Monitoring Service of Ssalto/Duacs gridded “allsat” series and along‐track Sea Level Anomalies, Absolute Dynamic Topographies and Geostrophic velocities over the Global Ocean, Mediterranean Sea, Black Sea, European Seas and Acrtic Ocean areas, in Delayed‐Time and in Near‐Real‐Time. Resources supporting this work were provided by the NASA High‐End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center with the award number SMD‐15‐5752. H. S., J. M., and D. J. M. were supported by the NSF MOBY project (OCE‐1048926 and OCE‐1048897). H. S. acknowledges the support by National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF‐2019R1C1C1003663) and Yonsei University Research Fund of 2018‐22‐0053. D. J. M. also gratefully acknowledges NSF and NASA support, along with the Holger W. Jannasch and Columbus O'Donnell Iselin shared chairs for Excellence in Oceanography. H. Seo acknowledges the support from the ONR (N00014‐17‐1‐2398), NOAA (NA10OAR4310376), and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research at WHOI. We also thank two anonymous referees whose comments significantly improved the presentation of results.
    Description: 2020-09-17
    Keywords: Southern Ocean ; Eddy-wind interaction ; Ekman pumping ; Stratification ; Eddy kinetic energy ; Mixed layer depth
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Substantial sea surface temperature cooling in the Banda Sea associated with the Madden-Julian Oscillation in the boreal winter of 2015 (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-05-27
    Description: 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(6), (2021): e2021JC017226, https://doi.org/10.1029/2021JC017226.
    Description: Substantial (∼2°C) basin averaged sea surface temperature (SST) cooling in the Banda Sea occurred in less than a 14-day period during the 2015 boreal winter Madden-Julian Oscillation (MJO). Such rapid and large cooling associated with the MJO has not been reported at least in the last two decades. Processes that control the substantial cooling during the 2015 MJO event are examined using high-resolution ocean reanalysis and one-dimensional (1-D) ocean model simulations. Previous studies suggest that MJO-induced SST variability in the Banda Sea is primarily controlled by surface heat flux. However, heat budget analysis of the model indicates that entrainment cooling produced by vertical mixing contributes more than surface heat flux for driving the basin-wide SST cooling during the 2015 event. Analysis of the ocean reanalysis further demonstrates that the prominent coastal upwelling around islands in the southern basin occurs near the end of the cooling period. The upwelled cold waters are advected by MJO-induced surface currents to a large area within the Banda Sea, which further maintains the basin-wide cold SST. These results are compared with another MJO-driven substantial cooling event during the boreal winter of 2007 in which the cooling is mostly driven by surface heat flux. Sensitivity experiments, in which initial temperature conditions for the two events are replaced by each other, demonstrate that the elevated thermocline associated with the 2015 strong El Niño is largely responsible for the intensified cooling generated by the vertical mixing with colder subsurface waters.
    Description: This research is supported by NOAA grant NA17OAR4310256. TS and SP are supported by DOD grant W911NF-20-1-0309. TS is also supported by NSF grant OCE-1658218 and NASA grant NNX17AH25G. HS and JS acknowledge the support from NOAA under NA17OAR4310255. HS is also grateful for additional support from ONR (N00014-17-1-2398).
    Description: 2021-11-30
    Keywords: Banda Sea ; sea surface temperature ; Madden-Julian Oscillation (MJO) ; mixed layer processes ; El Niño-Southern Oscillation (ENSO) ; Maritime Continent
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Suppressed pCO(2) in the Southern Ocean due to the interaction between current and wind (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-05-27
    Description: 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(12),(2021): e2021JC017884, https://doi.org/10.1029/2021JC017884.
    Description: The Southern Ocean, an important region for the uptake of anthropogenic carbon dioxide (CO2), features strong surface currents due to substantial mesoscale meanders and eddies. These features interact with the wind and modify the momentum transfer from the atmosphere to the ocean. Although such interactions are known to reduce momentum transfer, their impact on air-sea carbon exchange remains unclear. Using a 1/20° physical-biogeochemical coupled ocean model, we examined the impact of the current-wind interaction on the surface carbon concentration and the air-sea carbon exchange in the Southern Ocean. The current-wind interaction decreased winter partial pressure of CO2 (pCO2) at the ocean surface mainly south of the northern subantarctic front. It also reduced pCO2 in summer, indicating enhanced uptake, but not to the same extent as the winter loss. Consequently, the net outgassing of CO2 was found to be reduced by approximately 17% when including current-wind interaction. These changes stem from the combined effect of vertical mixing and Ekman divergence. A budget analysis of dissolved inorganic carbon (DIC) revealed that a weakening of vertical mixing by current-wind interaction reduces the carbon supply from below, and particularly so in winter. The weaker wind stress additionally lowers the subsurface DIC concentration in summer, which can affect the vertical diffusive flux of carbon in winter. Our study suggests that ignoring current-wind interactions in the Southern Ocean can overestimate winter CO2 outgassing.
    Description: The Southern Ocean, an important region for the uptake of anthropogenic carbon dioxide (CO2), features strong surface currents due to substantial mesoscale meanders and eddies. These features interact with the wind and modify the momentum transfer from the atmosphere to the ocean. Although such interactions are known to reduce momentum transfer, their impact on air-sea carbon exchange remains unclear. Using a 1/20° physical-biogeochemical coupled ocean model, we examined the impact of the current-wind interaction on the surface carbon concentration and the air-sea carbon exchange in the Southern Ocean. The current-wind interaction decreased winter partial pressure of CO2 (pCO2) at the ocean surface mainly south of the northern subantarctic front. It also reduced pCO2 in summer, indicating enhanced uptake, but not to the same extent as the winter loss. Consequently, the net outgassing of CO2 was found to be reduced by approximately 17% when including current-wind interaction. These changes stem from the combined effect of vertical mixing and Ekman divergence. A budget analysis of dissolved inorganic carbon (DIC) revealed that a weakening of vertical mixing by current-wind interaction reduces the carbon supply from below, and particularly so in winter. The weaker wind stress additionally lowers the subsurface DIC concentration in summer, which can affect the vertical diffusive flux of carbon in winter. Our study suggests that ignoring current-wind interactions in the Southern Ocean can overestimate winter CO2 outgassing.
    Description: 2022-05-15
    Keywords: Southern Ocean ; Current-Wind interaction ; CO2 flux ; Air-Sea interaction ; Biogeochemistry ; DIC
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Climate Process Team: improvement of ocean component of NOAA Climate Forecast System relevant to Madden-Julian Oscillation simulations (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Shinoda, T., Pei, S., Wang, W., Fu, J. X., Lien, R.-C., Seo, H., & Soloviev, A. Climate Process Team: improvement of ocean component of NOAA Climate Forecast System relevant to Madden-Julian Oscillation simulations. Journal of Advances in Modeling Earth Systems, 13(12), (2021): e2021MS002658, https://doi.org/10.1029/2021MS002658.
    Description: Given the increasing attention in forecasting weather and climate on the subseasonal time scale in recent years, National Oceanic and Atmospheric Administration (NOAA) announced to support Climate Process Teams (CPTs) which aim to improve the Madden-Julian Oscillation (MJO) prediction by NOAA’s global forecasting models. Our team supported by this CPT program focuses primarily on the improvement of upper ocean mixing parameterization and air-sea fluxes in the NOAA Climate Forecast System (CFS). Major improvement includes the increase of the vertical resolution in the upper ocean and the implementation of General Ocean Turbulence Model (GOTM) in CFS. In addition to existing mixing schemes in GOTM, a newly developed scheme based on observations in the tropical ocean, with further modifications, has been included. A better performance of ocean component is demonstrated through one-dimensional ocean model and ocean general circulation model simulations validated by the comparison with in-situ observations. These include a large sea surface temperature (SST) diurnal cycle during the MJO suppressed phase, intraseasonal SST variations associated with the MJO, ocean response to atmospheric cold pools, and deep cycle turbulence. Impact of the high-vertical resolution of ocean component on CFS simulation of MJO-associated ocean temperature variations is evident. Also, the magnitude of SST changes caused by high-resolution ocean component is sufficient to influence the skill of MJO prediction by CFS.
    Description: This research was supported by NOAA Grant NA15OAR431074. Computing resources were provided partly by the HPC systems at the Texas A&M University (College Station and Corpus Christi) and the Climate Simulation Laboratory at NCAR's Computational and Information Systems Laboratory, sponsored by the National Science Foundation. TS and SP are supported by DOD Grant W911NF-20-1-0309. TS is also supported by NSF Grant OCE-1658218 and NOAA Grant NA17OAR4310256.
    Keywords: Climate Process Team ; NOAA Climate Forecast System ; Madden-Julian Oscillation ; DYNAMO field campaign ; ocean mixing process
    Repository Name: Woods Hole Open Access Server
    Type: Article
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