1,721,054 research outputs found
Can we distinguish canonical El Niño from Modoki?
Get PDFAuthor Posting. © American Geophysical Union, 2013. 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 40 (2013): 5246–5251, doi:10.1002/grl.51007.Following the recent discovery of the “Modoki” El Niño, a proliferation of studies and debates has ensued concerning whether Modoki is dynamically distinct from “Canonical” El Niño, how Modoki impacts and teleconnections differ, and whether Modoki events have been increasing in frequency or amplitude. Three decades of reliable, high temporal-resolution observations of coupled ocean-atmosphere variability in the equatorial Pacific reveal a rich diversity of El Niños. Although central and eastern Pacific sea surface temperature (SST) anomalies appear mechanistically separable in terms of local and remote forcing, their frequent overlap precludes robust classifications. All observed El Niños appear to be a mixture of locally (central Pacific) and remotely forced (eastern Pacific) SST anomalies. Submonthly resolution appears essential for this insight and for the proper dynamical diagnosis of El Niño evolution; thus, the use of long-term monthly reconstructions for classification and trend analysis is strongly cautioned against.2014-04-0
Constraining the Magnitude of Abrupt Changes in Atmospheric Circulation During the Last Glacial Period
Get PDFWater isotopes serve as a useful proxy for past climate conditions at ice core sites and their respective moisture sources. Here we present the application of a novel numerical model to reconstruct absolute surface temperature, condensation temperature, and source-region evaporation temperature for all publicly accessible Greenland ice core records that yield the necessary data. We apply this analysis to the last glacial period, which was punctuated by a series of rapid climate oscillations—records of which are particularly well-defined in Greenland ice cores. Reconstructed moisture source temperatures are deconvolved from paleo- sea surface temperature variability in the Northern Hemisphere Atlantic to derive changes in moisture source latitude during this time. We attribute shifts in moisture source latitude principally to atmospheric variability. We pair this analysis with investigation into other potential forcings on moisture source latitude and find that changes in atmospheric circulation persists as the dominant contributor of variability. Our reconstructions show dynamic shifts in moisture source latitude (up to 20 degrees within a given abrupt climate event), indicative of a significant atmospheric reorganization during the last glaciation. These results provide a framework from which to assess the role of atmospheric circulation during the abrupt climate shifts that marked the last ice age.</p
Characterizing the Three-Dimensional Ocean Circulation within the Galápagos Archipelago
Get PDFThe Galápagos Islands straddle the equator in the eastern Pacific approximately 1000 kilometers west of the South American conƟnent. Deservingly protected in the world’s second largest marine reserve and holding the disƟncƟon of a UNESCO World Heritage Site, the Islands are iconic for their unique and remarkable biodiversity. Situated at the confluence of several tectonic plates, the Islands’ dynamic geological landscape is also unique in the Earth’s oceans. Connecting these two distinctive characteristics are the coastal and subsurface waters of the eastern equatorial Pacific Ocean. The Galápagos sits amidst and briefly interrupts ocean currents that are widely accepted as integral components of the global climate system including its variability such as the El Niño-Southern Oscillation (ENSO). The Archipelago’s location and distinctive bathymetry result in complex hydrodynamics, the full extent and implications of which are yet unknown.
Although the currents of the equatorial Pacific in the open ocean surrounding the Archipelago are generally understood, the nature of their interaction with the Galápagos Islands and the resulting local circulation within the archipelago are not. This study utilizes a high-resolution configuration of the Community Earth System Model (CESM), a fully coupled, global climate model, to investigate characteristics of flow within the Archipelago. A present-day simulation of this model is used to depict surface and subsurface flow under normal and ENSO conditions.
Results show that surface flows in the Galápagos Archipelago are mainly driven by the westward South Equatorial Current. In the subsurface, the Equatorial Undercurrent (EUC) splits at the archipelago's western edge, wrapping around and flowing into the archipelago. During winter and spring, the southern arm of the bifurcated EUC directs archipelago-interior flow, while in summer and fall, the northern EUC dominates. Large eddies circulate within the archipelago, seasonally varying in speed and location. During La Niña events, velociƟes generally increase and enhance circulation. In El Niño conditions, they decrease, reducing nutrient supply to marine ecosystems. In particular, El Niño summers pose risks to the sensitive Galápagos ecologies due to altered conditions. Additional investigation is needed to fully understand how complex hydrodynamics within the Archipelago influences marine life, yet this study adds to scientific knowledge of local circulation via a characterization of flow within the Galápagos Archipelago. </p
Analysis of Two-Dimensional Computational Fluid Dynamic Simulations of Tidal Turbine Arrays and Their Impact on Larval Transport
Get PDFGiven the increasing urgency of solving the climate change crisis, there has been an increase in the discussion and use of various sources of renewable energy. Wind and solar energy have already proven to be viable alternatives to the use of fossil fuels, and ocean energy has recently been receiving more research interest. Due to the predictability of tides, there is significant potential for consistent energy production within the ocean, as opposed to the limitations of wind and solar, but a better understanding of the potential environmental impacts of the associated technologies is required. In this thesis, three two-dimensional computational fluid dynamic simulations were designed to quantify the impact of tidal turbines in the marine environment. Simulated velocities were then analyzed using a Lagrangian particle-tracking model to predict effects of the turbines on marine larval transport due to fluid disruptions generated by the turbines. The modeled larvae do not represent a specific species, but rather any larvae that go through a germination period, during which traveling to a new settlement location is vital. The desired location – a coral reef, for example – was designated within the channel boundaries of the model. The paths of larvae were then analyzed in the channel with no turbines present and with turbines present, showing that there was a decline in the number of larvae that would survive in some combinations of larval release point and turbine configuration. These results represent a step towards understanding how implemented tidal turbines can affect surrounding waters and marine ecosystems.</p
Analysis of Two-Dimensional Computational Fluid Dynamic Simulations of Tidal Turbine Arrays and Their Impact on Larval Transport
Get PDFGiven the increasing urgency of solving the climate change crisis, there has been an increase in the discussion and use of various sources of renewable energy. Wind and solar energy have already proven to be viable alternatives to the use of fossil fuels, and ocean energy has recently been receiving more research interest. Due to the predictability of tides, there is significant potential for consistent energy production within the ocean, as opposed to the limitations of wind and solar, but a better understanding of the potential environmental impacts of the associated technologies is required. In this thesis, three two-dimensional computational fluid dynamic simulations were designed to quantify the impact of tidal turbines in the marine environment. Simulated velocities were then analyzed using a Lagrangian particle-tracking model to predict effects of the turbines on marine larval transport due to fluid disruptions generated by the turbines. The modeled larvae do not represent a specific species, but rather any larvae that go through a germination period, during which traveling to a new settlement location is vital. The desired location – a coral reef, for example – was designated within the channel boundaries of the model. The paths of larvae were then analyzed in the channel with no turbines present and with turbines present, showing that there was a decline in the number of larvae that would survive in some combinations of larval release point and turbine configuration. These results represent a step towards understanding how implemented tidal turbines can affect surrounding waters and marine ecosystems.</p
Characterizing the Three-Dimensional Ocean Circulation within the Galápagos Archipelago
Get PDFThe Galápagos Islands straddle the equator in the eastern Pacific approximately 1000 kilometers west of the South American conƟnent. Deservingly protected in the world’s second largest marine reserve and holding the disƟncƟon of a UNESCO World Heritage Site, the Islands are iconic for their unique and remarkable biodiversity. Situated at the confluence of several tectonic plates, the Islands’ dynamic geological landscape is also unique in the Earth’s oceans. Connecting these two distinctive characteristics are the coastal and subsurface waters of the eastern equatorial Pacific Ocean. The Galápagos sits amidst and briefly interrupts ocean currents that are widely accepted as integral components of the global climate system including its variability such as the El Niño-Southern Oscillation (ENSO). The Archipelago’s location and distinctive bathymetry result in complex hydrodynamics, the full extent and implications of which are yet unknown.
Although the currents of the equatorial Pacific in the open ocean surrounding the Archipelago are generally understood, the nature of their interaction with the Galápagos Islands and the resulting local circulation within the archipelago are not. This study utilizes a high-resolution configuration of the Community Earth System Model (CESM), a fully coupled, global climate model, to investigate characteristics of flow within the Archipelago. A present-day simulation of this model is used to depict surface and subsurface flow under normal and ENSO conditions.
Results show that surface flows in the Galápagos Archipelago are mainly driven by the westward South Equatorial Current. In the subsurface, the Equatorial Undercurrent (EUC) splits at the archipelago's western edge, wrapping around and flowing into the archipelago. During winter and spring, the southern arm of the bifurcated EUC directs archipelago-interior flow, while in summer and fall, the northern EUC dominates. Large eddies circulate within the archipelago, seasonally varying in speed and location. During La Niña events, velociƟes generally increase and enhance circulation. In El Niño conditions, they decrease, reducing nutrient supply to marine ecosystems. In particular, El Niño summers pose risks to the sensitive Galápagos ecologies due to altered conditions. Additional investigation is needed to fully understand how complex hydrodynamics within the Archipelago influences marine life, yet this study adds to scientific knowledge of local circulation via a characterization of flow within the Galápagos Archipelago. </p
Supporting Data: Cloud Height Distributions and the Role of Vertical Mixing in the Tropical Cyclone Eye Derived from Compact Raman Lidar Observations
No full text<p>These five files allow for the recreation of all figures displayed in Murray et al. 2024, which focuses on the variable, convective properties of tropical cyclone eye clouds. "P3_20210927H1_processed.nc" and "P3_20210929H2_processed.nc" both contain compact Raman lidar and in situ observations of the inner core of TC Sam. When combined with the tail Doppler radar files under the format "tdr_combined_sam_...", plots of the tropical cyclone inner core can be created. Finally, "flight_heights_metadata.pkl" is a pickle file that can be read using the Python package Pandas. This file contains information about all eye passes conducted using the compact Raman lidar. Identifiying information, cloud heights, and environmental characteristics are included for all eye passes.</p>
Constraining the Magnitude of Abrupt Changes in Atmospheric Circulation During the Last Glacial Period
Get PDFWater isotopes serve as a useful proxy for past climate conditions at ice core sites and their respective moisture sources. Here we present the application of a novel numerical model to reconstruct absolute surface temperature, condensation temperature, and source-region evaporation temperature for all publicly accessible Greenland ice core records that yield the necessary data. We apply this analysis to the last glacial period, which was punctuated by a series of rapid climate oscillations—records of which are particularly well-defined in Greenland ice cores. Reconstructed moisture source temperatures are deconvolved from paleo- sea surface temperature variability in the Northern Hemisphere Atlantic to derive changes in moisture source latitude during this time. We attribute shifts in moisture source latitude principally to atmospheric variability. We pair this analysis with investigation into other potential forcings on moisture source latitude and find that changes in atmospheric circulation persists as the dominant contributor of variability. Our reconstructions show dynamic shifts in moisture source latitude (up to 20 degrees within a given abrupt climate event), indicative of a significant atmospheric reorganization during the last glaciation. These results provide a framework from which to assess the role of atmospheric circulation during the abrupt climate shifts that marked the last ice age.</p
Oceanography : oxygen and climate dynamics
Get PDFAuthor Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Climate Change 4 (2014): 862-863, doi:10.1038/nclimate2386.Low
oxygen
levels
in
tropical
oceans
shape
marine
ecosystems
and
biogeochemistry
with
climate
change
expected
to
expand
these
regions.
Now,
a
study
indicates
that
regional
dynamics
control
tropical
oxygen
trends,
bucking
projected
global
reductions
in
ocean
oxygen.2015-03-2
Predicting Atlantic seasonal hurricane activity using outgoing longwave radiation over Africa
Get PDFAuthor Posting. © American Geophysical Union, 2016. 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 43 (2016): 7152–7159, doi:10.1002/2016GL069792.Seasonal hurricane activity is a function of the amount of initial disturbances (e.g., easterly waves) and the background environment in which they develop into tropical storms (i.e., the main development region). Focusing on the former, a set of indices based solely upon the meridional structure of satellite-derived outgoing longwave radiation (OLR) over the African continent are shown to be capable of predicting Atlantic seasonal hurricane activity with very high rates of success. Predictions of named storms based on the July OLR field and trained only on the time period prior to the year being predicted yield a success rate of 87%, compared to the success rate of NOAA's August outlooks of 53% over the same period and with the same average uncertainty range (±2). The resulting OLR indices are statistically robust, highly detectable, physically linked to the predictand, and may account for longer-term observed trends.Alfred P. Sloan Foundation;
Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution;
Ocean and Climate Change Institute2017-01-0
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