Representation of tropical subseasonal variability of precipitation in global reanalyses     

Daehyun Kim  Myong-In Lee  Dongmin Kim  Siegfried D. Schubert  Duane E. Waliser  Baijun Tian 《Climate Dynamics》2014,43(1-2):517-534

Tropical subseasonal variability of precipitation from five global reanalyses (RAs) is evaluated against Global Precipitation Climatology Project (GPCP) and Tropical Rainfall Measuring Mission (TRMM) observations. The RAs include the three generations of global RAs from the National Center for Environmental Prediction (NCEP), and two other RAs from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC). The analysis includes comparisons of the seasonal means and subseasonal variances of precipitation, and probability densities of rain intensity in selected areas. In addition, the space–time power spectrum was computed to examine the tropical Madden-Julian Oscillation (MJO) and convectively coupled equatorial waves (CCEWs). The modern RAs show significant improvement in their representation of the mean state and subseasonal variability of precipitation when compared to the two older NCEP RAs: patterns of the seasonal mean state and the amplitude of subseasonal variability are more realistic in the modern RAs. However, the probability density of rain intensity in the modern RAs show discrepancies from observations that are similar to what the old RAs have. The modern RAs show higher coherence of CCEWs with observed variability and more realistic eastward propagation of the MJO precipitation. The modern RAs, however, exhibit common systematic deficiencies including: (1) variability of the CCEWs that tends to be either too weak or too strong, (2) limited coherence with observations for waves other than the MJO, and (3) a systematic phase lead or lag for the higher-frequency waves.  相似文献   

Cloud computing and virtualization within the regional climate model and evaluation system     

Chris A. Mattmann  Duane Waliser  Jinwon Kim  Cameron Goodale  Andrew Hart  Paul Ramirez  Dan Crichton  Paul Zimdars  Maziyar Boustani  Kyo Lee  Paul Loikith  Kim Whitehall  Chris Jack  Bruce Hewitson 《Earth Science Informatics》2014,7(1):1-12

The Regional Climate Model Evaluation System (RCMES) facilitates the rapid, flexible inclusion of NASA observations into climate model evaluations. RCMES provides two fundamental components. A database (RCMED) is a scalable point-oriented cloud database used to elastically store remote sensing observations and to make them available using a space time query interface. The analysis toolkit (RCMET) is a Python-based toolkit that can be delivered as a cloud virtual machine, or as an installer package deployed using Python Buildout to users in order to allow for temporal and spatial regridding, metrics calculation (RMSE, bias, PDFs, etc.) and end-user visualization. RCMET is available to users in an “offline”, lone scientist mode based on a virtual machine dynamically constructed with model outputs and observations to evaluate; or on an institution’s computational cluster seated close to the observations and model outputs. We have leveraged RCMES within the content of the Coordinated Regional Downscaling Experiment (CORDEX) project, working with the University of Cape Town and other institutions to compare the model output to NASA remote sensing data; in addition we are also working with the North American Regional Climate Change Assessment Program (NARCCAP). In this paper we explain the contribution of cloud computing to RCMES’s specifically describing studies of various cloud databases we evaluated for RCMED, and virtualization toolkits for RCMET, and their potential strengths in delivering user-created dynamic regional climate model evaluation virtual machines for our users.  相似文献   

NASA Landsat program accomplishments continue to make a difference II     

Kamlesh Lulla  M. Duane Nellis  Brad Rundquist 《国际地球制图》2013,28(5)

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Commentary on “A Rationale for the National Center for Geographic Information and Analysis”     

M. Duane Nellis 《The Professional geographer》1993,45(2):220-222

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Modulation of tropical ocean surface chlorophyll by the Madden–Julian Oscillation     

Daeho Jin  Duane E. Waliser  Charles Jones  Raghu Murtugudde 《Climate Dynamics》2013,40(1-2):39-58

The MJO modulation of sea surface chlorophyll-a (Chl) examined initially by Waliser et al. in Geophys Res Lett, (2005) is revisited with a significantly longer time-series of observations and a more systematic approach to characterizing the possible mechanisms underlying the MJO-Chl relationships. The MJO composite analysis of Chl and lead-lag correlations between Chl and other physical variables reveal regional variability of Chl and corresponding indicative temporal relationships among variables. Along the path of the MJO convection, wind speed—a proxy for oceanic vertical turbulent mixing and corresponding entrainment—is most strongly correlated with Chl when wind leads Chl by a few days. Composite Chl also displays MJO influences away from the path of the MJO convection. The role of wind speed in those regions is generally the same for Chl variability as that along the path of the MJO convection, although Ekman pumping also plays a role in generating Chl variability in limited regions. However, the wind forcing away from the MJO convection path is less coherent, rendering the temporal link relatively weak. Lastly, the potential for bio-physical feedbacks at the MJO time-scale is examined. The correlation analysis provides tantalizing evidence for local bio-feedbacks to the physical MJO system. Plausible hypothesis for Chl to amplify the MJO phase transition is presented though it cannot be affirmed in this study and will be examined and reported in a future modeling study.  相似文献   

Addendum to “Simulating cold season snowpack: Impacts of snow albedo and multi-layer snow physics”: Waliser, D., J. Kim, Y. Xue, Y. Chao, A. Eldering, R. Fovell, A. Hall, Q. Li, K. N. Liou, J. McWilliams, S. Kapnick, R. Vasic, F. De Sale, and Y. Yu (2011), Climatic Change, 109 (Suppl 1):S95–S117, DOI 10.1007/s10584-011-0312-5     

Duane E. Waliser  Bin Guan  Jui-Lin F. Li  Jinwon Kim 《Climatic change》2012,114(2):399-400

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Shrinkage and swelling of coal induced by desorption and sorption of fluids: Theoretical model and interpretation of a field project     

Hema J. Siriwardane  Raj K. Gondle  Duane H. Smith 《International Journal of Coal Geology》2009,77(1-2):188-202

Geologic sequestration in deep unmineable coal seams and enhanced coalbed methane production is a promising choice, economically and environmentally, to reduce anthropogenic gases such as carbon dioxide in the atmosphere. Unmineable coal seams are typically known to adsorb large amounts of carbon dioxide in comparison to the sizeable amounts of sorbed methane, which raises the potential for large scale sequestration projects. During the process of sequestration, carbon dioxide is injected into the coalbed and desorbed methane is produced. The coal matrix is believed to shrink when a gas is desorbed and swell when a gas is sorbed, sometimes causing profound changes in the cleat porosity and permeability of the coal seam. These changes may have significant impact on the reservoir performance. Therefore, it is necessary to understand the combined influence of swelling and shrinkage, and geomechanical properties including elastic modulus, cleat porosity, and permeability of the reservoir.The present paper deals with the influence of swelling and shrinkage on the reservoir performance, and the geomechanical response of the reservoir system during the process of geologic sequestration of carbon dioxide and enhanced coalbed methane production in an actual field project located in northern New Mexico. A three-dimensional swelling and shrinkage model was developed and implemented into an existing reservoir model to understand the influence of geomechanical parameters, as well as swelling and shrinkage properties, on the reservoir performance. Numerical results obtained from the modified simulator were compared to available measured values from that site and previous studies. Results show that swelling and shrinkage, and the combination of geomechanical and operational parameters, have a significant influence on the performance of the reservoir system.  相似文献   

Kīlauea summit overflows: their ages and distribution in the Puna District, Hawai'i     

David A. Clague  Jonathan T. Hagstrum  Duane E. Champion  Melvin H. Beeson 《Bulletin of Volcanology》1999,61(6):363-381

 The tube-fed pāhoehoe lava flows covering much of the northeast flank of Kīlauea Volcano are named the 'Ailā'au flows. Their eruption age, based on published and six new radiocarbon dates, is approximately AD 1445. The flows have distinctive paleomagnetic directions with steep inclinations (40°–50°) and easterly declinations (0°–10°E). The lava was transported ∼40 km from the vent to the coast in long, large-diameter lava tubes; the longest tube (Kazumura Cave) reaches from near the summit to within several kilometers of the coast near Kaloli Point. The estimated volume of the 'Ailā'au flow field is 5.2±0.8 km³, and the eruption that formed it probably lasted for approximately 50 years. Summit overflows from Kīlauea may have been nearly continuous between approximately AD 1290 and 1470, during which time a series of shields formed at and around the summit. The 'Ailā'au shield was either the youngest or the next to youngest in this series of shields. Site-mean paleomagnetic directions for lava flows underlying the 'Ailā'au flows form only six groups. These older pāhoehoe flows range in age from 2750 to <18,000 BP, and the region was inundated by lava flows only three times in the past 5000 years. The known intervals between eruptive events average ∼1600 years and range from ∼1250 years to >2200 years. Lava flows from most of these summit eruptions also reached the coast, but none appears as extensive as the 'Ailā'au flow field. The chemistry of the melts erupted during each of these summit overflow events is remarkably similar, averaging approximately 6.3 wt.% MgO near the coast and 6.8 wt.% MgO near the summit. The present-day caldera probably formed more recently than the eruption that formed the 'Ailā'au flows (estimated termination ca. AD 1470). The earliest explosive eruptions that formed the Keanakāko'i Ash, which is stratigraphically above the 'Ailā'au flows, cannot be older than this age. Received: 10 October 1998 / Accepted: 12 May 1999  相似文献   

Mineralogical approaches to sourcing pipes and figurines from the eastern woodlands,U.S.A.     

Sarah U. Wisseman  Duane M. Moore  Randall E. Hughes  Mary R. Hynes  Thomas E. Emerson 《Geoarchaeology》2002,17(7):689-715

Provenance studies of stone artifacts often rely heavily upon chemical techniques such as neutron activation analysis. However, stone specimens with very similar chemical composition can have different mineralogies (distinctive crystalline structures as well as variations within the same mineral) that are not revealed by multielemental techniques. Because mineralogical techniques are often cheap and usually nondestructive, beginning with mineralogy allows the researcher to gain valuable information and then to be selective about how many samples are submitted for expensive and somewhat destructive chemical analysis, thus conserving both valuable samples and funds. Our University of Illinois team of archaeologists and geologists employs Portable Infrared Mineral Analyzer (PIMA) spectroscopy, X‐ray diffraction (XRD), and Sequential acid dissolution/XRD/Inductively coupled plasma (SAD‐XRD‐ICP) analyses. Two case studies of Hopewellian pipes and Mississippian figurines illustrate this mineralogical approach. The results for both studies identify sources relatively close to the sites where the artifacts were recovered: Sterling, Illinois (rather than Ohio) for the (Hopewell) pipes and Missouri (rather than Arkansas or Oklahoma) for the Cahokia figurines. © 2002 Wiley Periodicals, Inc.  相似文献   

Low temperature (LT) combustion of sediments does not necessarily provide accurate radiocarbon ages for site chronology     

Fiona Brock  Duane G. Froese  Richard G. Roberts 《Quaternary Geochronology》2010,5(6):625-630

Radiocarbon dating of soils and sediments is notoriously problematic for the purposes of dating a specific event due to their heterogeneous mix of multiple organic fractions, each of which may have a different radiocarbon age. Numerous studies have failed to agree on which sedimentary fraction or radiocarbon pre-treatment method, if any, provides the closest agreement between the age of a sedimentary fraction and that of associated plant macrofossils or charcoal. We tested the stepped-combustion method of McGeehin et al. (2001), as well as standard radiocarbon humin and humic extraction techniques, using samples from a chronologically well-constrained perennially-frozen site at Quartz Creek, Yukon Territory, Canada. The ages in closest agreement with associated radiocarbon-dated plant macrofossils and with the overlying Dawson tephra were given by the humic and humin fractions, but even these were still older than the macrofossil ages by up to 4195 ± 260 radiocarbon years. The low temperature (LT) humin method recommended by McGeehin et al. (2001) yielded ages older than the macrofossils by up to nearly 4425 ± 240 radiocarbon years. These fractions, while still providing information on the mobility and potential residence times of carbon in soils and sediments, should not be relied upon to provide consistently accurate site chronologies.  相似文献