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  • 1
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    Low frequency electromagnetic cyclotron waves in and around magnetic clouds: STEREO observations during 2007−2013 (2017)
    Wiley
    Details
    Publication Date: 2017-05-17
    Description: Wave activities in the solar wind are an important topic and magnetic clouds (MCs) are a common phenomenon in interplanetary space, though waves activities associated with MCs have not been well documented. Based on a survey of 120 MCs observed by STEREO spacecraft during the years 2007−2013, this work studies electromagnetic cyclotron waves (ECWs) near the proton cyclotron frequency in and around MCs. For total 7807 ECW events, 24% of them occurred in the regions within MCs while 76% occurred in the regions around MCs. Statistics indicate that ECWs around MCs have higher frequencies, wider bandwidths, and stronger powers relative to the waves in MCs. More ECWs, on the other hand, tend to be related to a plasma with higher temperature, lower density, and larger velocity. In particular, it is found that there exist positive power-law correlations between plasma betas and the wave frequencies, bandwidths, and powers. The results imply that the plasma beta should play an important role in determining the properties of ECWs, which is consistent with previous theory studies and the recent simulation results.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Zircon U-Pb ages and Hf isotope compositions of migmatites from the North Qinling terrane and their geological implications (2013)
    Wiley
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    Publication Date: 2013-12-18
    Description: Migmatites are predominant in the North Qinling orogen. However, the formation ages of the migmatites are poorly constrained. This paper presents a combined study of CL image, U-Pb age, trace element, and Hf isotope of zircon in migmatites from the North Qinling unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U-Pb ages of c . 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating the protoliths were derived from reworking of Paleoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c . 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c . 455 to 400 Ma. The migmatization was about 50 Ma later than the c . 490 Ma ultra-high pressure metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite-facies metamorphism and the granitic magmatism in the North Qinling unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. Ultra-high pressure rocks were distributed mainly along the northern margin and occasionally in the inner part of the North Qinling unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process. This article is protected by copyright. All rights reserved.
    Print ISSN: 0263-4929
    Electronic ISSN: 1525-1314
    Topics: Geosciences
    Published by Wiley
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  • 3
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    Ecosystem engineering by a gall-forming wasp indirectly suppresses diversity and density of herbivores on oak trees (2016)
    Wiley
    In: Ecology
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    Publication Date: 2016-03-08
    Description: Ecosystem engineers, organisms that modify the physical environment, are generally thought to increase diversity by facilitating species that benefit from engineered habitats. Recent theoretical work, however, suggests that ecosystem engineering could initiate cascades of trophic interactions that shape community structure in unexpected ways, potentially having negative indirect effects on abundance and diversity in components of the community that do not directly interact with the habitat modifications. We tested the indirect effects of a gall-forming wasp on arthropod communities in surrounding unmodified foliage. We experimentally removed all senesced galls from entire trees during winter and sampled the arthropod community on foliage after budburst. Gall removal resulted in 59% greater herbivore density, 26% greater herbivore richness, and 27% greater arthropod density five weeks after budburst. Gall removal also reduced the differences in community composition among trees (i.e., reduced beta diversity), even when accounting for differences in richness. The community inside galls during winter and through the growing season was dominated by jumping spiders (Salticidae; 0.87 ± 0.12 spiders per gall). We suggest that senesced galls provided habitat for spiders, which suppressed herbivorous arthropods and increased beta diversity by facilitating assembly of unusual arthropod communities. Our results demonstrate that the effects of habitat modification by ecosystem engineers can extend beyond merely providing habitat for specialists; the effects can propagate far enough to influence the structure of communities that do not directly interact with habitat modifications.
    Print ISSN: 0012-9658
    Electronic ISSN: 1939-9170
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 4
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    Gross nitrous oxide production drives net nitrous oxide fluxes across a salt marsh landscape (2016)
    Wiley
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    Publication Date: 2016-01-01
    Description: Sea level rise will change inundation regimes in salt marshes, altering redox dynamics that control nitrification—a potential source of the potent greenhouse gas, nitrous oxide (N 2 O)—and denitrification, a major nitrogen (N) loss pathway in coastal ecosystems and both a source and sink of N 2 O. Measurements of net N 2 O fluxes alone yield little insight into the different effects of redox conditions on N 2 O production and consumption. We used in situ measurements of gross N 2 O fluxes across a salt marsh elevation gradient to determine how soil N 2 O emissions in coastal ecosystems may respond to future sea level rise. Soil redox declined as marsh elevation decreased, with lower soil nitrate and higher ferrous iron in the low marsh compared to the mid and high marshes (p 〈 0.001 for both). In addition, soil oxygen concentrations were lower in the low and mid marshes relative to the high marsh (p 〈 0.001). Net N 2 O fluxes differed significantly among marsh zones (p = 0.009), averaging 9.8 ± 5.4 μ g N m −2 h −1 , -2.2 ± 0.9 μ g N m −2 h −1 , and 0.67 ± 0.57 μ g N m −2 h −1 in the low, mid, and high marshes, respectively. Both net N 2 O release and uptake were observed in the low and high marshes, but the mid marsh was consistently a net N 2 O sink. Gross N 2 O production was highest in the low marsh and lowest in the mid marsh (p = 0.02), whereas gross N 2 O consumption did not differ among marsh zones. Thus, variability in gross N 2 O production rates drove the differences in net N 2 O flux among marsh zones. Our results suggest that future studies should focus on elucidating controls on the processes producing, rather than consuming, N 2 O in salt marshes to improve our predictions of changes in net N 2 O fluxes caused by future sea level rise. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 5
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    Experimental shifts in phenology affect fitness, foraging, and parasitism in a native solitary bee (2018)
    Wiley
    In: Ecology
    Details
    Publication Date: 2018
    Description: Abstract Phenological shifts have been observed in a wide range of taxa, but the fitness consequences of these shifts are largely unknown, and we often lack experimental studies to assess their population‐level and evolutionary consequences. Here, we describe an experimental study to determine the fitness consequences of phenological shifts in blue orchard bee (Osmia lignaria) emergence, compare the measured seasonal fitness landscape with observed phenology in the unmanipulated population, and assess seasonal variation in key factors related to reproduction, foraging, and brood parasitism that were expected to affect the shape of the fitness landscape. By tracking individually marked females, we were able to estimate the lifetime fitness impacts of phenological advances and delays. We also measured parasitism risk, floral resource use, and nesting behavior to understand how each varies seasonally, and their combined effects on realized fitness. Survival to nesting decreased non‐monotonically throughout the season, with a 20.4% decline in survival rates between the first and second cohorts. The total reproductive output per maternal bee was 14.9% higher in the second cohort compared to the first, and 161% higher in the second cohort compared to the third. Combining seasonal patterns in survival and reproductive output, experimentally advanced females showed 30.6% higher fitness than bees released at the historic peak. In contrast, the nesting phenology of unmanipulated bees showed nearly equal numbers of nesting attempts in the first two cohorts. Both increased resource availability and reduced parasitism risk favored earlier emergence. These results are consistent with a population experiencing directional selection for earlier emergence, adaptive bet‐hedging, or developmental constraints. Our study offers insight into the fitness consequences of phenological shifts, the mechanisms affecting the fitness consequences of phenological shifts in a community context, and the potential for adaptive responses to climate change.
    Print ISSN: 0012-9658
    Electronic ISSN: 1939-9170
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 6
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    Finding the Normal Direction of Interplanetary Directional Discontinuities‐ A New Scheme (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Directional discontinuities (DDs) are common structures in the interplanetary space. Correctly determining the normal of a DD is important to understand the changes of phase fronts of magnetic fields adjacent to a discontinuity as well as helpful for the applications in many regimes of space physics research. In this work, we propose a new scheme to estimate the normal directions of DDs by finding the smallest standard deviation of normal magnetic fields derived from the cross‐product of magnetic fields on both sides of the discontinuity, based on the idea that the phase fronts of the adjacent magnetic fields are closely parallel to the DD plane. By comparing with the normal direction determined from Cluster multiple spacecraft, we show that our scheme can provide the same accuracy as that from the multi‐spacecraft estimation. Moreover, our scheme gives a consistent result of normal estimations at different Cluster spacecraft. We notice that in some cases, the normal directions derived from the minimum variance analysis (MVA) have large differences from those of multi‐spacecraft method and our scheme implying significant influence of the kinetic effect of particles in the transition region of the discontinuity. A few events of STEREO B observations are further studied to show that our scheme can be applied to DDs in single spacecraft measurements with even small rotation of magnetic fields across the discontinuities. With the help of an accurate normal estimation, we can understand the variations of magnetic field phase fronts in the vicinity of discontinuities.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Interannual controls on oxygen isotope variability in Asian monsoon precipitation and implications for paleoclimate reconstructions (2016)
    Wiley
    Details
    Publication Date: 2016-07-06
    Description: Orbital to millennial scale variations in Asian monsoon speleothem δ 18 O have been widely interpreted as records of monsoon intensity and/or rainfall amount. To assess the influence of these and other mechanisms on higher-frequency δ 18 O variability, we utilize simulations from a spectrally nudged isotope-enabled general circulation model coupled with instrumental climate data to investigate the climatic controls on interannual precipitation δ 18 O (δ 18 O p ) variability at four key cave locations affected by the Asian monsoon: Qunf Cave, Oman; Mawmluh Cave, India; Tham Mai Cave, Laos; and Dongge Cave, China. Comparison with instrumental climate data show that interannual δ 18 O p variations are only weakly related to local precipitation amount at the four sites, and are instead controlled primarily by large-scale monsoon intensity and upstream precipitation over the tropical Indo-Pacific region, which influence the δ 18 O of incoming moisture. Spatial correlations with sea surface temperature and precipitation, composite analyses, and time series analyses show that the El Niño Southern Oscillation (ENSO) also plays a key role in modulating interannual precipitation δ 18 O p variability in the region, especially in northern India and Southeast Asia, with positive δ 18 O p anomalies during El Niño years reflecting increased contribution of high δ 18 O moisture from the nearby Bay of Bengal. Coherent interannual to decadal δ 18 O variations seen in high-resolution proxy records from across the Asian Monsoon region, likely record monsoon intensity and upstream rainout, whereas ENSO related variability is likely to be strongest in records from northern India and Southeast Asia, with the largest anomalies expected when weak monsoons and El Niño occur together.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    A test of a field-based 15N-nitrous oxide pool dilution technique to measure gross N2O production in soil (2011)
    Wiley
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    Publication Date: 2011-06-22
    Description: Soils are both a major source and sink of nitrous oxide (N 2 O), but the proportion of soil N 2 O production released to the atmosphere (termed the N 2 O yield) is poorly constrained due to the difficulty in measuring gross N 2 O production. The quantification of gross N 2 O fluxes would greatly improve our ability to predict N 2 O dynamics across the soil-atmosphere interface. We report a new approach, the 15 N 2 O pool dilution technique, to measure rates of gross N 2 O production and consumption under laboratory and field conditions. In the lab, gross N 2 O production and consumption compared well between the 15 N 2 O pool dilution and acetylene inhibition methods whereas the 15 NO 3 - tracer method measured significantly higher rates. In the field, N 2 O emissions were not significantly affected by increasing chamber headspace concentrations up to 100 ppb 15 N 2 O. The pool dilution model estimates of 14 N 2 O and 15 N 2 O concentrations as well as net N 2 O fluxes fit observed data very well, suggesting that the technique yielded robust estimates of gross N 2 O production. Estimated gross N 2 O consumption rates were underestimated relative to rates calculated as the difference between gross and net N 2 O production rates, possibly due to heterogeneous and/or inadequate tracer diffusion to deeper layers in the soil profile. Gross N 2 O production rates were high, averaging 8.4 ± 3.2 mg N m −2 d −1 , and were most strongly correlated to mineral nitrogen concentrations and denitrifying enzyme activity (R 2 = 0.73). Gross N 2 O production rates varied spatially, with the highest rates in soils with the best drainage and the highest mineral N availability. Estimated and calculated N 2 O consumption rates constrained the average N 2 O yield from 0.70 to 0.84. Our results demonstrate that the 15 N 2 O pool dilution technique can provide well-constrained estimates of N 2 O yields and field rates of gross N 2 O production correlated to soil characteristics, improving our understanding of terrestrial N 2 O dynamics.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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  • 9
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    Modeling the effects of riparian planting strategies on stream temperature: Increasing suitable habitat for endangered Formosan Landlocked Salmon in Shei-Pa National Park, Taiwan (2011)
    Wiley
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    Publication Date: 2011-12-03
    Description: Reducing or stabilizing the stream temperature of ChiChiaWan Creek is a crucial work for Formosan Landlocked Salmon because ChiChiaWan Creek is the only one habitat for this endangered species. Planting trees in the riparian zone would be one of the alternatives. The purpose of this study was to evaluate the effects of several planting strategies on daily maximum stream temperature along the river. The results showed the effective vegetative shading angles should be more than 50° along ChiChiaWan Creek to reduce the direct solar radiation heating effectively. Upstream planting with 70° vegetative shading angle could be the most effective way among all the scenarios. However, this planting strategy could not improve the worst situations in summer because of the large solar elevation angles. The upstream planting in ChiChiaWan Creek was strongly recommended because the canopies could be easier to extend to totally cover the narrow width of river producing the most effective shades. Practicing the upstream planting with 90° vegetative shading angle can increase more than 1 km-long suitable habitats for the endangered Salmon in summer. Alternatively the west-side planting scenario was the second effective way for temperature reduction. Our result provided a useful suggestion for the authorities in charge of saving the Formosan Landlocked Salmon, particularly under the stress of global warming. Copyright © 2011 John Wiley & Sons, Ltd.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 10
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    Analyses of the impact of climate change on water resources components, drought, and wheat yield in semi-arid regions: Example Karkheh River Basin in Iran (2013)
    Wiley
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    Publication Date: 2013-02-22
    Description: Water resources availability in the semi-arid regions of Iran has experienced severe reduction due to increasing water use and lengthening of dry periods. To better manage this resource we investigated the impact of climate change on water resources and wheat yield in the Karkheh River Basin (KRB) in the semi-arid region of Iran. Future climate scenarios for 2020-2040 were generated from the Canadian Global Coupled Model for scenarios A1B, B1 and A2. We constructed a hydrological model of KRB using SWAT to project water resources availability. Blue and green water components were modeled with uncertainty ranges for both historic and future data. SUFI2 was used with parallel processing option to calibrate the model based on river discharge and wheat yield. Furthermore, a newly developed program “critical continuous day calculator” (CCDC) was used to determine the frequency and length of critical periods for precipitation, maximum temperature and soil moisture. We found that in the northern part of KRB freshwater availability will increases from 1716 to 2670 m 3 /capita/year despite an increase of 28% in the population in 2025 in B1 scenario. In the southern part, where much of the agricultural lands are located, the freshwater availability will on the average decrease by 44%. The long term average irrigated wheat yield, however will increase in the south by 1.2% to 21% in different subbasins; but for rainfed wheat, this variation is from -4% to 38%. The results of CCDC showed an increase of up to 25% in both frequency and length of dry periods in south Karkheh, while increasing flood events could be expected in the northern and western parts of the region. In general, there is variability in the impact of climate change in the region where some areas will experience net negative, while other areas experience a net positive impact. Copyright © 2013 John Wiley & Sons, Ltd.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
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