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  • 1
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    Inflating transform matrices to mitigate assimilation errors with robust filtering based ensemble Kalman filters (2016)
    Wiley
    Details
    Publication Date: 2016-07-26
    Description: An error covariance matrix plays an important role in maintaining the statistical property of the ensemble in an ensemble Kalman filter method. However, data assimilation filter divergence may occur from an inaccurate estimate of the covariance matrix. In this study, based on an ensemble time-local H-infinity filter, which inflates the eigenvalues of the analysis error covariance matrix, a new robust ensemble data assimilation method is proposed, referred to as an inflation transform matrix eigenvalues. By design, new filters may be preferred over other traditional ensemble filters, when model performances are not well known, or change unpredictably. The primary aim is to improve the performance of the assimilation system in the framework of the ensemble filtering, according to the minimum/maximum rule of robust filtering. The proposed estimation method is tested using the well-known Lorenz-96 model, in order to investigate how the ensemble time-local H-infinity filter method of the inflation transform matrix impacts the robustness of the assimilation system under selected special conditions, such as the assimilation steps, force parameters, ensemble sizes, and observation information. The experiments show that the proposed inflation transform matrix method displays good robustness to the changes in the system's parameters. Also, when compared with the traditional filtering methods, this robust filtering method is found to improve the assimilation performance.
    Electronic ISSN: 1530-261X
    Topics: Geosciences , Physics
    Published by Wiley on behalf of The Royal Meteorological Society (RMetS).
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  • 2
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    Carbon loss and chemical changes from permafrost collapse in the northern Tibetan Plateau (2016)
    Wiley
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    Publication Date: 2016-06-24
    Description: Permafrost collapse, known as thermokarst, can alter soil properties and carbon emissions. However, little is known regarding the effects of permafrost collapse in upland landscapes on the biogeochemical processes that affect carbon balance. In this study, we measured soil carbon and physiochemical properties at a large thermokarst feature on a hillslope in the northeastern Tibetan Plateau. We categorized surfaces into three different micro-relief patches based on type and extent of collapse (control, drape and exposed areas). Permafrost collapse resulted in substantial decreases of surface soil carbon and nitrogen stocks, with losses of 29.6 ± 5.9% and 26.7 ± 8.8% for carbon and nitrogen, respectively, in the 0-10 cm soil layer. Laboratory incubation experiments indicated that control soil had significantly higher CO 2 production rates than that of drapes. The results from Fourier transform infrared (FTIR) spectroscopy analysis showed that exposed soils accumulated some organic matter due to their low position within the feature, which was accompanied by substantial changes in the chemical structure and characteristics of the soil carbon. Exposed soils had higher hydrocarbon and lignin/phenol backbone content than in control and drape soils in the 0-10 cm layer. This study demonstrates that permafrost collapse can cause abundant carbon and nitrogen loss, potentially from mineralization, leaching, photo-degradation and lateral displacement. These results demonstrate that permafrost collapse redistributes the soil organic matter, changes its chemical characteristics, and leads to losses of organic carbon due to the greenhouse gas emission.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Opposite effects of winter day and night temperature changes on early phenophases (2019)
    Wiley
    In: Ecology
    Details
    Publication Date: 2019
    Description: Abstract Changes in day (maximum temperature, TMAX) and night temperature (minimum temperature, TMIN) in the preseason (e.g. winter and spring) may have opposite effects on early phenophases (e.g., leafing and flowering) due to changing requirements of chilling accumulations (CAC) and heating accumulations (HAC), which could cause advance, delay or no change in early phenophases. However, their relative effects on phenology are largely unexplored, especially on the Tibetan Plateau. Here, observations were performed using a warming and cooling experiment in situ through reciprocal transplantation (2008‐2010) on the Tibetan Plateau. We found that winter TMIN warming significantly delayed mean early phenophases by 8.60 d °C−1, but winter TMAX warming advanced them by 12.06 d °C−1 across six common species. Thus winter mean temperature warming resulted in a net advance of 3.46 d °C−1 in early phenophases. In contrast, winter TMIN cooling, on average, significantly advanced early phenophases by 5.12 d °C−1, but winter TMAX cooling delayed them by 7.40 d °C−1 across six common species, resulting in a net delay of 2.28 d °C−1 for winter mean temperature cooling. The opposing effects of TMAX and TMIN warming on the early phenophases may be mainly caused by decreased CAC due to TMIN warming (5.29 times greater than TMAX) and increased HAC due to TMAX warming (3.25 times greater than TMIN), and similar processes apply to TMAX and TMIN cooling. Therefore, our study provides another insight into why some plant phenophases remain unchanged or delayed under climate change. This article is protected by copyright. All rights reserved.
    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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    Broadband emission and flat optical gain glass containing Ag aggregates for tunable laser (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Spectroscopic properties of Sm3+‐doped borate glass with silver aggregates were investigated, and it was found that the glass presented broad excitation and emission band covering violet‐infrared region. Furthermore, the optical gain coefficients at various wavelengths were measured via an amplified spontaneous emission technique, it was confirmed that the glass displayed flat net optical gain coefficient in almost full visible region. In addition, the fluorescent temperature quenching of the glass was examined, and it was seen that about 50% of room temperature emission intensity was kept when the sample was heated up to 325°C.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Wiley
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  • 5
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    Influence of Monsoon System on α-HCH Fate in Asia: A Model Study from 1948 to 2008 (2013)
    Wiley
    Details
    Publication Date: 2013-03-29
    Description: [1]  Chinese Gridded Pesticide Emission and Residue Model was applied to simulate long-term environmental fate of α -HCH in Asia spanning 1948 to 2008. The simulation identifies the southern Tibetan Plateau and margin of Asian monsoon regime from the northeast area of the Tibetan plateau to the Northeast China as sink areas. This spatial pattern of sink distribution is closely related to the summer monsoon activities in Asia. Wet deposition associated with the summer monsoon (June to August) is responsible for at least half of α -HCH mass entering into the sink areas. After deposition, relatively low temperature and high soil organic matter in the sink areas are favourable for α -HCH detention. Chinese and Indian sources are the major contributors to α -HCH contamination over the monsoon margin and the Tibetan Plateau, driven by the East Asian summer monsoon and South Asian summer monsoon, respectively.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Incorporating root hydraulic redistribution and compensatory water uptake in the Common Land Model: Effects on site-level and global land modeling (2017)
    Wiley
    Details
    Publication Date: 2017-07-02
    Description: Treatment of plant water uptake through the roots remains a significant issue in land surface models. Most current land surface models calculate the root water uptake (RWU) by extracting soil water in different soil layers based on the relative soil water availability and the root fraction of each layer within the rooting zone. This approach is also used as the default in the Common Land Model (CoLM). This approach often significantly underestimates plant transpiration during dry periods. Therefore, more realistic RWU functions are needed in land surface models. In this study, the modified CoLM with root hydraulic redistribution (HR) and compensatory water uptake (CWU) was evaluated against the CoLM with the default approach by comparing the observed and simulated latent and sensible heat fluxes observed from three sites that experience seasonal drought over the measured periods. We found that the CoLM using the default RWU significantly underestimated latent heat fluxes and overestimated the sensible heat fluxes over dry periods, whereas those biases were significantly reduced by the CoLM with HR and CWU functions. We also ran global offline simulations using the revised CoLM to evaluate the performance of these alternative RWU functions on the global scale. Compared with the estimated latent heat fluxes from the FLUXNET-MTE model product, CoLM with HR and CWU functions significantly improved the estimated latent heat fluxes over the Amazon, Southern Africa and Central Asia during their dry seasons. Therefore, we recommend the implementation of HR and CWU in land surface models.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Reexamination and further development of two-stream canopy radiative transfer models for global land modeling (2016)
    Wiley
    Details
    Publication Date: 2016-12-29
    Description: Four representative two-stream canopy radiative transfer models were examined and intercompared using the same configuration. Based on the comparison results, two modifications were introduced to the widely used Dickinson-Sellers model [ Dickinson , 1983; Sellers , 1985] and then incorporated into the Community Land Model (CLM4.5). The modified model was tested against Monte-Carlo simulations and produced significant improvements in the simulated canopy transmittance and albedo values. In direct comparison with MODIS albedo data, the modified model shows good performance over most snow/ice-free vegetated areas, especially for regions that are covered by dense canopy. The modified model shows seasonally dependent behavior mainly in the near-infrared band. Thus, the improvements are not present in all seasons. Large biases are still noticeable in sparsely vegetated areas, in particular for the snow/ice covered regions, that is possibly related to the model, the land surface input data, or even the observations themselves. Further studies focusing on the impact of the seasonal changes in leaf optical properties, the parameterizations for snow/ice covered regions and the case of sparsely vegetated areas, are recommended. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1942-2466
    Topics: Geography , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Spatial Variability of Active Layer Thickness Detected by Ground-Penetrating Radar in the Qilian Mountains, Western China (2017)
    Wiley
    Details
    Publication Date: 2017-02-05
    Description: The active layer plays a key role in geomorphic, hydrologic, and biogeochemical processes in permafrost regions. We conducted a systematic investigation of active layer thickness (ALT) in northeastern Qinghai-Tibetan Plateau using ground-penetrating radar (GPR) with 100 and 200 MHz antennas. We used mechanical probing, pit, and soil temperature profiles for evaluating ALT derived from GPR. The results showed that GPR is competent for detecting ALT and the error was ± 0.08 m at common-mid point co-located sites. Considerable spatial variability of ALT owing to variation in elevation, peat thickness and slope aspect was found. The mean ALT was 1.32 ± 0.29 m with a range from 0.81 to 2.1 m in Eboling Mountain. In Yeniu Gou, mean ALT was 2.72 ± 0.88 m and varied from 1.07 m on the north-facing slope to 4.86 m around the area near the lower boundary of permafrost. ALT in peat decreased with increasing elevation at a rate of −1.31 m/km (Eboling Mountain) and −2.1 m/km (Yeniu Gou), and in mineral soil in Yeniu Gou the rate changed to −4.18 m/km. At the same elevation, ALT on the south-facing slope was about 0.8 m thicker than that on the north-facing slopes, while the difference was only 0.18 m in peat-covered area. Within a 100 m 2 area with a local elevation difference of 0.8 m, ALT varied from 0.68 m to 1.25 m. Both field monitoring and modeling studies on spatial ALT variations require rethinking of the current strategy and comprehensive design.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Lead exposure reduces sperm quality and DNA integrity in mice (2018)
    Wiley
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    Publication Date: 2018-02-16
    Description: Toxicity of lead on male reproductive functions has raised wide public concern as environmental lead contamination remains common worldwide. Conflicting and controversial data are available regarding effects of lead on male fertility. More importantly, our knowledge on effects of lead on sperm DNA integrity is significantly limited. Thus, further studies should focus on this issue. In the current study, adult male mice were exposed to a series of lead acetate concentrations in drinking water for six weeks. Following administration, lead levels in blood, testicles, and epididymis were measured, and potential changes in morphology of testis and epididymis due to lead exposure were identified. We also analyzed sperm parameters, including sperm density, viability, motility, and morphology, to evaluate quality of sperm collected from epididymis. Especially, hypothetical influence of lead on sperm DNA integrity was also evaluated by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling, alkaline comet assay, and sperm chromatin structure assay. Lead exposure possibly exerted no effect on growth of mice because these animals acquired similar body weight gain during the experimental period. However, high lead concentrations (0.5% and 1%) in drinking water affected sperm motility and increased percentage of spermatozoa with abnormal morphology. In groups treated with 0.25%, 0.5%, and 1% lead acetate, percentages of sperm cells showing DNA breaks and chromatin structure damage significantly increased. Altogether, lead exposure not only exhibits adverse effects on sperm physiological parameters, but also impairs DNA structure and integrity. These effects may lead to significant decline in male fertility.
    Print ISSN: 1520-4081
    Electronic ISSN: 1522-7278
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Wiley
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  • 10
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    Limited formation of isoprene epoxydiols–derived secondary organic aerosol (IEPOX-SOA) under NOx-rich environments in Eastern China (2017)
    Wiley
    Details
    Publication Date: 2017-02-15
    Description: Secondary organic aerosol (SOA) derived from isoprene epoxydiols (IEPOX) have potential impacts on regional air quality and climate, yet is poorly characterized under NO x -rich ambient environments. We report the first real-time characterization of IEPOX-derived SOA (IEPOX-SOA) in Eastern China in summer 2013 using comprehensive ambient measurements, along with model analysis. The ratio of IEPOX-SOA to isoprene high-NO x SOA precursors, e.g., methyl vinyl ketone and methacrolein, and the reactive uptake potential of IEPOX were lower than those generally observed in regions with prevailing biogenic emissions, low NO x levels and high particle acidity, elucidating the suppression of IEPOX-SOA formation under NO x -rich environments. IEPOX-SOA showed high potential source regions to the south with large biogenic emissions, illustrating that the interactions between biogenic and anthropogenic emissions might have played an important role in affecting the formation of IEPOX-SOA in polluted environments in Eastern China.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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