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111.
Mangrove sediments play a pivotal role in the nutrient biogeochemical processes by behaving as both source and sink for nutrients and other materials. Surface and core sediments were collected from various locations of the Pichavaram mangrove (India) and analyzed for grain size distribution, nutrients and stable N isotope (δ15N) signatures in order to understand the spatial and vertical distribution of nutrients and biogeochemical processes of the C, N, P and S in this ecosystem. Sand is the dominant fraction followed by silt and clay. Spatial distribution of nutrients is controlled by the external and internal loadings, whereas vertical distribution is largely driven by the in situ microbial activities. Interior mangrove sediments contain higher concentrations of organic carbon (OC) than the estuarine sediments reflecting high rates of organic matter retention. Finer fractions of sediment hold ∼60% OC due to high surface area. At some sampling points, moderately high δ15N signatures were observed and this may be because of agricultural runoff and aquaculture effluents. 相似文献
112.
Dalia Bach Kirschbaum Robert Adler Yang Hong Sujay Kumar Christa Peters-Lidard Arthur Lerner-Lam 《Environmental Earth Sciences》2012,66(6):1683-1696
The increasing availability of remotely sensed data offers a new opportunity to address landslide hazard assessment at larger
spatial scales. A prototype global satellite-based landslide hazard algorithm has been developed to identify areas that may
experience landslide activity. This system combines a calculation of static landslide susceptibility with satellite-derived
rainfall estimates and uses a threshold approach to generate a set of ‘nowcasts’ that classify potentially hazardous areas.
A recent evaluation of this algorithm framework found that while this tool represents an important first step in larger-scale
near real-time landslide hazard assessment efforts, it requires several modifications before it can be fully realized as an
operational tool. This study draws upon a prior work’s recommendations to develop a new approach for considering landslide
susceptibility and hazard at the regional scale. This case study calculates a regional susceptibility map using remotely sensed
and in situ information and a database of landslides triggered by Hurricane Mitch in 1998 over four countries in Central America.
The susceptibility map is evaluated with a regional rainfall intensity–duration triggering threshold and results are compared
with the global algorithm framework for the same event. Evaluation of this regional system suggests that this empirically
based approach provides one plausible way to approach some of the data and resolution issues identified in the global assessment.
The presented methodology is straightforward to implement, improves upon the global approach, and allows for results to be
transferable between regions. The results also highlight several remaining challenges, including the empirical nature of the
algorithm framework and adequate information for algorithm validation. Conclusions suggest that integrating additional triggering
factors such as soil moisture may help to improve algorithm performance accuracy. The regional algorithm scenario represents
an important step forward in advancing regional and global-scale landslide hazard assessment. 相似文献
113.
Single, interferometric dual, and quad-polarization mode data were evaluated for the characterization and classification of seven land use classes in an area with shifting cultivation practices located in the Eastern Amazon (Brazil). The Advanced Land-Observing Satellite (ALOS) Phased Array L-band Synthetic Aperture Radar (PALSAR) data were acquired during a six month interval. A clear-sky Landsat-5/TM image acquired at the same period was used as additional ground reference and as ancillary input data in the classification scheme. We evaluated backscattering intensity, polarimetric features, interferometric coherence and texture parameters for classification purposes using support vector machines (SVM) and feature selection. Results showed that the forest classes were characterized by low temporal backscattering intensity variability, low coherence and high entropy. Quad polarization mode performed better than dual and single polarizations but overall accuracies remain low and were affected by precipitation events on the date and prior SAR date acquisition. Misclassifications were reduced by integrating Landsat data and an overall accuracy of 85% was attained. The integration of Landsat to both quad and dual polarization modes showed similarity at the 5% significance level. SVM was not affected by SAR dimensionality and feature selection technique reveals that co-polarized channels as well as SAR derived parameters such as Alpha-Entropy decomposition were important ranked features after Landsat’ near-infrared and green bands. We show that in absence of Landsat data, polarimetric features extracted from quad-polarization L-band increase classification accuracies when compared to single and dual polarization alone. We argue that the joint analysis of SAR and their derived parameters with optical data performs even better and thus encourage the further development of joint techniques under the Reducing Emissions from Deforestation and Degradation (REDD) mechanism. 相似文献
114.
Jean Alberto Mensa Zulema Garraffo Annalisa Griffa Tamay Mehmet Özgökmen Angelique Haza Milena Veneziani 《Ocean Dynamics》2013,63(8):923-941
Frontogenesis and frontal instabilities in the mixed layer are known to be important processes in the formation of submesoscale features. We study the seasonality of such processes in the Gulf Stream (GS) region. To approach this problem, a realistic simulation with the Hybrid Coordinate Ocean Model is integrated for 18 months at two horizontal resolutions: a high-resolution (1/48°) simulation able to resolve part of the submesoscale regime and the full range of mesoscale dynamics, and a coarser resolution (1/12°) case, in which submesoscales are not resolved. Results provide an insight into submesoscale dynamics in the complex GS region. A clear seasonal cycle is observed, with submesoscale features mostly present during winter. The submesoscale field is quantitatively characterized in terms of deviation from geostrophy and 2D dynamics. The limiting and controlling factor in the occurrence of submesoscales appears to be the depth of the mixed layer, which controls the reservoir of available potential energy available at the mesoscale fronts that are present most of the year. Atmospheric forcings are the main energy source behind submesoscale formation, but mostly indirectly through mixed layer deepening. The mixed layer instability scaling suggested in the (Fox-Kemper et al., J Phys Oceanogr 38:1145–1165, 2008) parametrization appears to hold, indicating that the parametrization is appropriate even in this complex and mesoscale dominated area. 相似文献
115.
We present results on the energy balance of the Deep Impact experiment based on analysis of 180 infrared spectra of the ejecta obtained by the Deep Impact spacecraft. We derive an output energy of 16.5 (+9.1/−4.1) GJ. With an input energy of 19.7 GJ, the error bars are large enough so that there may or may not be a balance between the kinetic energy of the impact and that of outflowing materials. Although possible, no other source of energy other than the impactor or the Sun is needed to explain the observations. Most of the energy (85%) goes into the hot plume in the first few seconds, which only represents a very small fraction (<0.01%) of the total ejected mass. The hot plume contains 190 (+263/−71) kg of H2O, 1.6 ± 0.5 kg of CO2, 8.2 (+11.3/3.1) kg of CO (assuming a CO/H2O ratio of 4.3%), 27.9 (+25.0/−8.9) kg of organic material and 255 ± 128 kg of dust, while the ejecta contains ∼107 kg of materials. About 12% of the energy goes into the ejecta (mostly water) and 3% to destroy the impactor. Volatiles species other than H2O (CO2, CO or organic molecules) contribute to <7% of the energy balance. In terms of physical processes, 68% of the energy is used to accelerate grains (kinetic energy), 16% to heat them, 6% to sublimate or melt them and 10% (upper limit) to break and compress dust and/or water ice aggregates into small micron size particles. For the hot plume, we derive a dust/H2O ratio of 1.3 (+1.9/−1.0), a CO2/H2O ratio of 0.008 (+0.009/−0.006), an organics/H2O ratio of 0.15 (+0.29/−0.11) and an organics/dust ratio of 0.11 (+0.30/−0.07). This composition refers to the impact site and is different from that of the bulk nucleus, consistent with the idea of layers of different composition in the nucleus sub-surface. Our results emphasize the importance of laboratory impact experiments to understand the physical processes involved at such a large scale. 相似文献
116.
117.
M. Bala Krishna Prasad Wen Long Xinsheng Zhang Robert J. Wood Raghu Murtugudde 《Aquatic Sciences - Research Across Boundaries》2011,73(3):437-451
Eutrophic depletion of dissolved oxygen (DO) and its consequences for ecosystem dynamics have been a central theme of research,
assessment and management policies for several decades in the Chesapeake Bay. Ongoing forecast efforts predict the extent
of the summer hypoxic/anoxic area due to nutrient loads from the watershed. However, these models neither predict DO levels
nor address the intricate interactions among various ecological processes. The prediction of spatially explicit DO levels
in the Chesapeake Bay can eventually lead to a reliable depiction of the comprehensive ecological structure and functioning,
and can also allow the quantification of the role of nutrient reduction strategies in water quality management. In this paper,
we describe a three dimensional empirical model to predict DO levels in the Chesapeake Bay as a function of water temperature,
salinity and dissolved nutrient concentrations (TDN and TDP). The residual analysis shows that predicted DO values compare
well with observations. Nash–Sutcliffe efficiency (NSE) and root mean square error-observations standard deviation ratio (RSR)
are used to evaluate the performance of the empirical model; the scores demonstrate the usability of model predictions (NSE,
surface layer = 0.82–0.86; middle layer = 0.65–0.82; bottom layer = 0.70–0.82; RSR surface layer = 0.37–0.44; middle layer = 0.43–0.58
and bottom layer = 0.43–0.54). The predicted DO values and other physical outputs from downscaling of regional weather and
climate predictions, or forecasts from hydrodynamic models, can be used to forecast various ecological components. Such forecasts
would be useful for both recreational and commercial users of the Chesapeake Bay. 相似文献
118.
The influence of El Nio-Southern Oscillation (ENSO) on the convectively coupled Kelvin waves over the tropical Pacific is investigated by comparing the Kelvin wave activity in the eastern Pacific (EP) El Nio, central Pacific (CP) El Nio, and La Nia years, respectively, to 30-yr (1982-2011) mean statistics. The convectively coupled Kelvin waves in this study are represented by the two leading modes of empirical orthogonal function (EOF) of 2-25-day band-pass filtered daily outgoing longwave radiation (OLR), with the estimated zonal wavenumber of 3 or 4, period of 8 days, and eastward propagating speed of 17 ms-1 . The most significant impact of ENSO on the Kelvin wave activity is the intensification of the Kelvin waves during the EP El Nios. The impact of La Nia on the reduction of the Kelvin wave intensity is relatively weaker, reflecting the nonlinearity of tropical deep convection and the associated Kelvin waves in response to ENSO sea surface temperature (SST) anomalies. The impact of the CP El Nio on the Kelvin waves is less significant due to relatively weaker SST anomalies and smaller spatial coverage. ENSO may also alter the frequency, wavelength, and phase speed of the Kelvin waves. This study demonstrates that low-frequency ENSO SST anomalies modulate high-frequency tropical disturbances, an example of weather-climate linkage. 相似文献
119.
Hyelim Yoo Zhanqing Li Yu-Tai Hou Steve Lord Fuzhong Weng Howard W. Barker 《Climate Dynamics》2013,41(5-6):1595-1613
The objective of this study is to investigate the quality of clouds simulated by the National Centers for Environmental Prediction global forecast system (GFS) model and to examine the causes for some systematic errors seen in the simulations through use of satellite and ground-based measurements. In general, clouds simulated by the GFS model had similar spatial patterns and seasonal trends as those retrieved from passive and active satellite sensors, but large systematic biases exist for certain cloud regimes especially underestimation of low-level marine stratocumulus clouds in the eastern Pacific and Atlantic oceans. This led to the overestimation (underestimation) of outgoing longwave (shortwave) fluxes at the top-of-atmosphere. While temperature profiles from the GFS model were comparable to those obtained from different observational sources, the GFS model overestimated the relative humidity field in the upper and lower troposphere. The cloud condensed water mixing ratio, which is a key input variable in the current GFS cloud scheme, was largely underestimated due presumably to excessive removal of cloud condensate water through strong turbulent diffusion and/or an improper boundary layer scheme. To circumvent the problem associated with modeled cloud mixing ratios, we tested an alternative cloud parameterization scheme that requires inputs of atmospheric dynamic and thermodynamic variables. Much closer agreements were reached in cloud amounts, especially for marine stratocumulus clouds. We also evaluate the impact of cloud overlap on cloud fraction by applying a linear combination of maximum and random overlap assumptions with a de-correlation length determined from satellite products. Significantly better improvements were found for high-level clouds than for low-level clouds, due to differences in the dominant cloud geometry between these two distinct cloud types. 相似文献
120.
RICHARD G. RICHELS THOMAS F. RUTHERFORD GEOFFREY J. BLANFORD LEON CLARKE 《Climate Policy》2013,13(5):409-428
It is becoming increasingly clear that economically efficient climate policies are unlikely to be implemented in the near term. Therefore an analysis is warranted that considers the implications of certain suboptimal transition policies. This analysis constructs a transition scenario based on realistic assumptions about the current trends in policy-making. The transition is examined in the context of varying assumptions about the stringency of the target and the availability of low- or no-carbon energy technologies in the future. In addition to evaluating the effects of suboptimal policies, the transitional analysis offers new insights about the intrinsic uncertainty regarding both the appropriate stabilization target and technology. 相似文献