Role of wave–mean flow interaction in sun–climate connections: Historical overview and some new interpretations and results     

Terrence R. Nathan  John R. Albers  Eugene C. Cordero 《Journal of Atmospheric and Solar》2011,73(11-12):1594-1605

Quasi-decadal variations in solar irradiance – termed the 11-year solar cycle (SC) – have been linked to variations in a variety of atmospheric circulation features, including the polar vortex, the Brewer–Dobson circulation, and the quasi-biennial oscillation. These features share an underlying commonality: they are all rooted in wave–mean flow interaction. The purpose of this paper is to provide a historical overview of the connection between the SC and wave–mean flow interaction and to propose a more complete theoretical framework for solar modulated wave–mean flow interaction that includes both zonal-mean and zonally asymmetric ozone as intermediaries for communicating variations in solar spectral irradiance to the climate system. We solve a quasi-geostrophic model using the WKB formalism to highlight the physics connecting the SC to planetary wave-drag. Numerical results show the importance of the zonally asymmetric ozone field in mediating the effects of solar variability to the wave-driven circulation in the middle atmosphere.  相似文献   

Geochronology and geochemistry of the Wunugetushan porphyry Cu–Mo deposit in NE china,and their geological significance     

Zhiguang Chen  Lianchang Zhang  Bo Wan  Huaying Wu  Nathan Cleven 《Ore Geology Reviews》2011,43(1):92-105

The Wunugetushan porphyry Cu–Mo deposit is located in the Manzhouli district of NE China, on the southern margin of the Mesozoic Mongol–Okhotsk Orogenic Belt. Concentric rings of hydrothermal alteration and Cu–Mo mineralization surround an Early–Middle Jurassic monzogranitic porphyry. The Cu–Mo mineralization is clearly related to the quartz–potassic and quartz–sericite alteration. Molybdenite Re–Os and groundmass ⁴⁰Ar/³⁹Ar of the host porphyry dates indicate that the ore-formation and porphyry-emplacement occurred at 177.6 ± 4.5 Ma and 179.0 ± 1.9 Ma, respectively. Geochemically, the host porphyry of the deposit is characterized by strong LREE/HREE fractionation, enrichment in LILE, Ba, Rb, U, Th and Pb, and depletion of HFSE, Nb, Ta, Ti and HREE. The Sr–Nd–Pb isotopic compositions of the porphyry display an varied initial (⁸⁷Sr/⁸⁶Sr)_i ratio, a positive ε_Nd(t) values and high ²⁰⁶Pb/²⁰⁴Pb_t, ²⁰⁷Pb/²⁰⁴Pb_t and ²⁰⁸Pb/²⁰⁴Pb_t ratios. These data indicate that the magmatic source of the host porphyry comprised two end-members: lithospheric mantle metasomatized by fluids derived from the subducted slab; and continental crust. We infer that the primitive magma of the host porphyry was derived from crust–mantle transition zone. Based on regional geology and geochemistry of the host porphyry, the Wunugetushan deposit is suggested to form in a continental collision environment after closure of the Mongol–Okhotsk Ocean.  相似文献   

Commentary: scale,rent, and symbolic capital: political economy and emerging rural landscapes     

Nathan F. Sayre 《GeoJournal》2011,76(4):437-439

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Community variations in population exposure to near-field tsunami hazards as a function of pedestrian travel time to safety   总被引：4，自引：3，他引：1  

Nathan J. Wood  Mathew C. Schmidtlein 《Natural Hazards》2013,65(3):1603-1628

Efforts to characterize population exposure to near-field tsunami threats typically focus on quantifying the number and type of people in tsunami-hazard zones. To develop and prioritize effective risk-reduction strategies, emergency managers also need information on the potential for successful evacuations and how this evacuation potential varies among communities. To improve efforts to properly characterize and differentiate near-field tsunami threats among multiple communities, we assess community variations in population exposure to tsunamis as a function of pedestrian travel time to safety. We focus our efforts on the multiple coastal communities in Grays Harbor and Pacific Counties (State of Washington, USA), where a substantial resident and visitor population is threatened by near-field tsunamis related to a potential Cascadia subduction zone earthquake. Anisotropic, path distance modeling is conducted to estimate travel times to safety, and results are merged with various population data, including residents, employees, public venues, and dependent-care facilities. Results suggest that there is substantial variability among communities in the number of people that may have insufficient time to evacuate. Successful evacuations may be possible in some communities assuming slow walking speeds, are plausible in others if travel speeds are increased, and are unlikely in another set of communities given the large distances and short time horizon. Emergency managers can use these results to prioritize the location and determine the most appropriate type of tsunami risk-reduction strategies, such as education and training in areas where evacuations are plausible and vertical-evacuation structures in areas where they are not.  相似文献   

Review: Regional groundwater flow modeling in heavily irrigated basins of selected states in the western United States   总被引：1，自引：1，他引：0  

Nathan R. Rossman  Vitaly A. Zlotnik 《Hydrogeology Journal》2013,21(6):1173-1192

Water resources in agriculture-dominated basins of the arid western United States are stressed due to long-term impacts from pumping. A review of 88 regional groundwater-flow modeling applications from seven intensively irrigated western states (Arizona, California, Colorado, Idaho, Kansas, Nebraska and Texas) was conducted to provide hydrogeologists, modelers, water managers, and decision makers insight about past modeling studies that will aid future model development. Groundwater models were classified into three types: resource evaluation models (39 %), which quantify water budgets and act as preliminary models intended to be updated later, or constitute re-calibrations of older models; management/planning models (55 %), used to explore and identify management plans based on the response of the groundwater system to water-development or climate scenarios, sometimes under water-use constraints; and water rights models (7 %), used to make water administration decisions based on model output and to quantify water shortages incurred by water users or climate changes. Results for 27 model characteristics are summarized by state and model type, and important comparisons and contrasts are highlighted. Consideration of modeling uncertainty and the management focus toward sustainability, adaptive management and resilience are discussed, and future modeling recommendations, in light of the reviewed models and other published works, are presented.  相似文献   

A Typology of Catalyst Events for Collaborative Watershed Management in the United States     

Linda Stalker Prokopy  Nathan Mullendore  Kathryn Brasier  Kristin Floress 《社会与自然资源》2014,27(11):1177-1191

While much has been written about the benefits of collaborative watershed management to address nonpoint source pollution and other water quality concerns in the United States, few scholars have addressed the catalytic nature of events that generate these collective action responses. Further, because equivalent catalyst events in different communities do not always lead to collective action, it is critical to understand the interaction between a community's baseline conditions and the catalyst events that lead to collective action. This article presents a conceptual framework that illustrates the relationship between baseline conditions and events that lead to collective action. In this article a theoretical typology of catalyst events is presented that includes both intentional and nonintentional types of events. Understanding these types of catalyst events can help water quality advocates create and/or seize opportunities to nurture a collective action. This article concludes with a call for future research into catalyst events.  相似文献   

Shifting sands on Mars: insights from tropical intra‐crater dunes     

Paul E. Geissler  Nicholas W. Stantzos  Nathan T. Bridges  Mary C. Bourke  Simone Silvestro  Lori K. Fenton 《地球表面变化过程与地形》2013,38(4):407-412

Evidence for sand motion is found in repeated observations of sand dunes at three sites in the Martian tropics by the High Resolution Imaging Science Experiment on Mars Reconnaissance Orbiter. An eroding outcrop of layered sediments is identified as a possible source of the sand in Pasteur crater. Ancient layered sediments in Becquerel crater are actively being carved into flutes and yardangs by the blowing sands. Dunes in an un‐named crater in Meridiani near the Mars Exploration Rover Opportunity landing site advanced as much as 50 cm over an interval of one Martian year. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Radiocarbon ages for the timing of debris avalanches at Mombacho Volcano, Nicaragua     

Nathan D. Stansell 《Bulletin of Volcanology》2013,75(1):1-4

Radiocarbon-dated lake sediments provide minimum-limiting ages for two major debris avalanches originating from Mombacho Volcano in Nicaragua. A basal age from Lake El Gancho indicates that the northeast debris avalanche (Las Isletas) occurred sometime before ～140 to 345 A.D. Basal ages from Lakes Blanca and Verde indicate that the southern (El Crater) debris avalanche occurred sometime before ～270 to 650 A.D. Both events therefore occurred in the space of a few centuries, yet there is strong evidence that the mechanisms varied for destabilization of each flank. Possibly, the influence of a developing hydrothermal system lead first to deeper structural failure in the substrata to produce the Las Isletas sector collapse, progressing to higher level destabilization within the edifice and the El Crater collapse.  相似文献   

Surface and subsurface water contributions to streamflow from a mesoscale watershed in complex mountain terrain          下载免费PDF全文

Qinghuan Zhang  John F. Knowles  Rebecca T. Barnes  Rory M. Cowie  Nathan Rock  Mark W. Williams 《水文研究》2018,32(7):954-967

An understanding of surface and subsurface water contributions to streamflow is essential for accurate predictions of water supply from mountain watersheds that often serve as water towers for downstream communities. As such, this study used the end‐member mixing analysis technique to investigate source water contributions and hydrologic flow paths of the 264 km² Boulder Creek Watershed, which drains the Colorado Front Range, USA. Four conservative hydrochemical tracers were used to describe this watershed as a 3 end‐member system, and tracer concentration reconstruction suggested that the application of end‐member mixing analysis was robust. On average from 2009 to 2011, snowmelt and rainwater from the subalpine zone and groundwater sampled from the upper montane zone contributed 54%, 22%, and 24% of the annual streamflow, respectively. These values demonstrate increased rainwater and decreased snow water contributions to streamflow relative to area‐weighted mean values derived from previous work at the headwater scale. Young water (2.3 ± 0.8 months) fractions of streamflow decreased from 18–22% in the alpine catchment to 8–10% in the lower elevation catchments and the watershed outlet with implications for subsurface storage and hydrological connectivity. These results contribute to a process‐based understanding of the seasonal source water composition of a mesoscale watershed that can be used to extrapolate headwater streamflow generation predictions to larger spatial scales.  相似文献   

The impact of ditch blocking on fluvial carbon export from a UK blanket bog          下载免费PDF全文

Christopher D. Evans  Michael Peacock  Sophie M. Green  Joseph Holden  Pippa J. Chapman  Inma Lebron  Nathan Callaghan  Richard Grayson  Andrew J. Baird 《水文研究》2018,32(13):2141-2154

We investigated the effects of ditch blocking on fluvial carbon concentrations and fluxes at a 5‐year, replicated, control‐intervention field experiment on a blanket peatland in North Wales, UK. The site was hydrologically instrumented, and run‐off via open and blocked ditches was analysed for dissolved organic carbon (DOC), particulate organic carbon, dissolved carbon dioxide, and dissolved methane. DOC was also analysed in peat porewater and overland flow. The hillslope experiment was embedded within a paired control‐intervention catchment study, with 3 years of preblocking and 6 years of postblocking data. Results from the hillslope showed large reductions in discharge via blocked ditches, with water partly redirected into hillslope surface and subsurface flows, and partly into remaining open ditches. We observed no impacts of ditch blocking on DOC, particulate organic carbon, dissolved carbon dioxide or methane in ditch waters, DOC in porewaters or overland flow, or stream water DOC at the paired catchment scale. Similar DOC concentrations in ditch water, overland flow, and porewater suggest that diverting flow from the ditch network to surface or subsurface flow had a limited impact on concentrations or fluxes of DOC entering the stream network. The subdued response of fluvial carbon to ditch blocking in our study may be attributable to the relatively low susceptibility of blanket peatlands to drainage, or to physical alterations of the peat since drainage. We conclude that ditch blocking cannot be always be expected to deliver reductions in fluvial carbon loss, or improvements in the quality of drinking water supplies.  相似文献