Fairbanks, AK, United States
Fairbanks, AK, United States

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Cahill C.F.,University of Alaska Fairbanks | Cahill C.F.,Geophysical Institute | Cahill C.F.,Alaska Volcano Observatory | Rinkleff P.G.,Geophysical Institute | And 8 more authors.
Journal of Volcanology and Geothermal Research | Year: 2010

Size and time-resolved aerosol compositional measurements conducted during the 2006 eruption of Augustine Volcano provide quantitative information on the size and concentration of the fine volcanic ash emitted during the eruption and carried and deposited downwind. These data can be used as a starting point to attempt to validate volcanic ash transport models. For the 2006 eruption of Augustine Volcano, an island volcano in south-central Alaska, size and time-resolved aerosol measurements were made using an eight-stage (0.09-0.26, 0.26-0.34, 0.34-0.56, 0.56-0.75, 0.75-1.15, 1.15-2.5, 2.5-5.0, and 5.0-35.0 μm in aerodynamic diameter) Davis Rotating Unit for Monitoring (DRUM) aerosol impactor deployed near ground level in Homer, Alaska, approximately 110 km east-northeast of the volcano. The aerosol samples collected by the DRUM impactor were analyzed for mass and elemental composition every 90 min during a four-week sampling period from January 13 to February 11, 2006, that spanned several explosive episodes during the 2006 eruption. The collected aerosols showed that the size distribution of the volcanic ash fallout changed during this period of eruption. Ash had its highest concentrations in the largest size fraction (5.0-35.0 μm) with no ash present in the less than 1.15 μm size fractions during the short-lived explosive events. In contrast, during the continuous ash emission phase, concentrations of volcanic ash were more significant in the less than 1.15 μm size fractions. Settling velocities dictate that the smaller size particles will transport far from the volcano and, unlike the larger particles, not be retained in the proximal stratigraphic record. These results show that volcanic ash transport and dispersion (VATD) model predictions based on massless tracer particles, such as the predictions from the PUFF VATD model, provide a good first-order approximation of the transport of both large and small volcanic ash particles. Unfortunately, the concentration of particles in different size fractions depends on eruptive style and ash generation processes, so predicting the actual behavior of the ash particles from an eruption requires additional information in real time. © 2010 Elsevier B.V.


Hermann A.J.,University of Washington | Gibson G.A.,University of Alaska Fairbanks | Bond N.A.,University of Washington | Curchitser E.N.,Rutgers University | And 6 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2013

Coupled physical/biological models can be used to downscale global climate change to the ecology of subarctic regions, and to explore the bottom-up and top-down effects of that change on the spatial structure of subarctic ecosystems-for example, the relative dominance of large vs. small zooplankton in relation to ice cover. Here we utilize a multivariate statistical approach to extract the emergent properties of a coupled physical/biological hindcast of the Bering Sea for years 1970-2009, which includes multiple episodes of warming and cooling (e.g. the recent cooling of 2005-2009), and a multidecadal regional forecast of the coupled models, driven by an IPCC global model forecast of 2010-2040. Specifically, we employ multivariate empirical orthogonal function (EOF) analysis to derive the spatial covariance among physical and biological timeseries from our simulations. These are compared with EOFs derived from spatially gridded measurements of the region, collected during multiyear field programs. The model replicates observed relationships among temperature and salinity, as well as the observed inverse correlation between temperature and large crustacean zooplankton on the southeastern Bering Sea shelf. Predicted future warming of the shelf is accompanied by a northward shift in both pelagic and benthic biomass. © 2013 Elsevier Ltd.


Hermann A.J.,University of Washington | Gibson G.A.,University of Alaska Fairbanks | Bond N.A.,University of Washington | Curchitser E.N.,Rutgers University | And 6 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2015

Three global climate simulations from the Intergovernmental Panel on Climate Change Fourth Assessment (AR4) were used as physical forcing to drive a regional model that includes both physical and biological elements of the Bering Sea. Although each downscaled projection indicates a warming of 1-2. °C between 2010 and 2040 on the Bering Sea shelf, the interannual and interdecadal details of this trend vary considerably among the three realizations. In each case, the magnitude of presently observed interannual variability of bottom temperatures and ice cover is found in the models to be maintained out to at least 2040, but with a steadily increasing probability of warm years with less ice on the southern shelf. The overall trends indicate warmer temperatures and the retreat of ice in the southeastern Bering Sea, but continued ice cover in the northeastern Bering Sea. Sensitivity analyses suggest both increasing air temperature and northward wind stress as primary drivers of higher water-column temperatures. Based on currently available models, changes in shortwave radiation are not likely to have a significant role in this warming. Warming trends on the outer shelf may lead to decreased production of large crustacean zooplankton at that location, but could increase such production on the inner shelf. © 2015 Elsevier Ltd.


Gibson G.A.,University of Alaska Fairbanks | Coyle K.O.,University of Alaska Fairbanks | Hedstrom K.,Arctic Region Supercomputing Center | Curchitser E.N.,Rutgers University
Journal of Marine Systems | Year: 2013

The Eastern Bering Sea shelf is divided into distinct hydrographic domains by structural fronts. Despite frontal obstructions to cross-shelf transport, each year large oceanic copepods-primarily Neocalanus spp.-are known to dominate the biomass of the outer-shelf zooplankton communities, and in some years are advected into the middle-shelf domain. Using ROMS (the Regional Ocean Modeling System), coupled with a float tracking model designed to represent ontogenetic vertical migration behavior of Neocalanus, we explored the mechanisms, timing, and location of the transport of oceanic zooplankton onto the eastern Bering Sea shelf from overwintering sources along the Gulf of Alaska and Bering Sea shelf breaks, under a variety of environmental conditions. Our float tracking experiments suggest that the timing of on-shelf transport and the distribution of oceanic zooplankton on the shelf can vary substantially between one year and another. The Bering, Pribilof, and Zhemchug Canyons and Cape Navarin were all regions of elevated on-shelf float transport. Wind direction was the primary factor controlling inter-annual variability in the timing, amount, and location of the on-shelf transport of our Neocalanus floats. Float transport across the northern and southern shelves responded in opposite directions to inter-annual differences in wind forcing: southeasterly wind enhanced on-shelf transport of the Neocalanus floats along the southern shelf but suppressed on-shelf transport over the northern shelf. Conversely, northwesterly wind suppressed on-shelf zooplankton transport onto the southern shelf but promoted enhanced transport around Cape Navarin on the northern shelf. Transport of the Neocalanus floats onto the shelf can be very episodic, reflecting the short duration of winds that promote on-shelf transport. Relatively short (days to weeks) periods of southeasterly wind between March and April significantly impacted the number of floats transported onto the shelf. The relative importance of different source areas to supplying oceanic zooplankton to the Bering Sea shelf does not appear to vary much from year to year. Our model results suggest that the Neocalanus found on the southern shelf most likely originate from overwintering sites in the Alaska Stream or the Eastern Bering Sea shelf break south of the Pribilof Islands, while Neocalanus found on the northern shelf most likely originate from sites north of the Pribilof Islands. © 2013 Elsevier B.V.


Malik M.,George Washington University | Li T.,George Washington University | Sharif U.,George Washington University | Shahid R.,George Washington University | And 2 more authors.
Concurrency Computation Practice and Experience | Year: 2012

SUMMARY Graphical processing units have been gaining rising attention because of their high performance processing capabilities for many scientific and engineering applications. However, programming such highly parallel devices requires adequate programming tools. Many such programming tools have emerged and hold the promise for high levels of performance. Some of such tools may require specialized parallel programming skills, while others attempt to target the domain scientist. The costs versus the benefits out of such tools are often unclear. In this work we examine the use of several of these programming tools such as Compute Unified Device Architecture, Open Compute Language, Portland Group Inc., and MATLAB in developing kernels from the (NAS) NASA Advanced Supercomputing parallel benchmarking suite. The resulting performance as well as the needed programmers' efforts were quantified and used to characterize the productivity of graphical processing units using these different programming paradigms. Copyright © 2011 John Wiley & Sons, Ltd.


Tran T.T.,Arctic Region Supercomputing Center | Newby G.,Arctic Region Supercomputing Center | Molders N.,University of Alaska Fairbanks
Atmospheric Environment | Year: 2011

WRF/Chem simulations were performed using the meteorological conditions of January 2000 and alternatively the emissions of January 1990 and 2000 to examine whether increases in emissions may have caused the increasing trends in observed sulfate-aerosol concentrations at coastal Alaska sites. The analysis focused on six regions in Alaska that are exposed differently to the main emission sources. Meteorological observations at 59 sites and aerosol measurements at three sites showed that WRF/Chem captured the meteorological situation over Alaska well and simulated the aerosol concentrations acceptably. Except for the region adjacent to the Arctic Ocean that is influenced by local SO 2-emissions, Alaska SO 2 and SO 4 2--aerosol distributions are affected by long-range transport of SO 2 from ship emissions and/or emissions in Canada and southern Siberia. Local changes in emissions between 1990 and 2000 are not the main cause for concentrations changes in the six regions. The increases of SO 4 2--aerosols and SO 4 2--in-cloud along the Gulf of Alaska are caused by increased ship or Canadian emissions. The study provides evidence that the increased ship and Canadian emissions during the last decades can cause increases in sulfate aerosols. © 2011 Elsevier Ltd.

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