Estimation of nearshore groundwater discharge and its potential effects on a fringing coral reef     

Blanco AC  Watanabe A  Nadaoka K  Motooka S  Herrera EC  Yamamoto T 《Marine pollution bulletin》2011,62(4):770-785

Radon (²²²Rn) measurements were conducted in Shiraho Reef (Okinawa, Japan) to investigate nearshore submarine groundwater discharge (SGD_nearshore) dynamics. Estimated average groundwater flux was 2-3 cm/h (maximum 7-8 cm/h). End-member radon concentration and gas transfer coefficient were identified as major factors influencing flux estimation accuracy. For the 7-km long reef, SGD_nearshore was 0.39-0.58 m³/s, less than 30% of Todoroki River’s baseflow discharge. SGD_nearshore was spatially and temporally variable, reflecting the strong influence of subsurface geology, tidal pumping, groundwater recharge, and hydraulic gradient. SGD_nearshore elevated nearshore nitrate concentrations (0.8-2.2 mg/l) to half of Todoroki River’s baseflow -N (2-4 mg/L). This increased nearshore Chl-a from 0.5-2 μg/l compared to the typically low Chl-a (<0.1-0.4 μg/l) in the moat. Diatoms and cyanobacteria concentrations exhibited an increasing trend. However, the percentage contributions of diatoms and cyanobacteria significantly decreased and increased, respectively. SGD may significantly induce the proliferation of cyanobacteria in nearshore reef areas.  相似文献   

Modeling Arctic Boundary Layer Cloud Streets at Grey-zone Resolutions     

Hui-Wen LAI  Fuqing ZHANG  Eugene E. CLOTHIAUX  David R. STAUFFER  Brian J. GAUDET  Johannes VERLINDE  Deliang CHEN 《大气科学进展》2020,37(1):42-56

To better understand how model resolution affects the formation of Arctic boundary layer clouds,we investigated the influence of grid spacing on simulating cloud streets that occurred near Utqiaġvik(formerly Barrow),Alaska,on 2 May 2013 and were observed by MODIS(the Moderate Resolution Imaging Spectroradiometer).The Weather Research and Forecasting model was used to simulate the clouds using nested domains with increasingly fine resolution ranging from a horizontal grid spacing of 27 km in the boundary-layer-parameterized mesoscale domain to a grid spacing of 0.111 km in the large-eddy-permitting domain.We investigated the model-simulated mesoscale environment,horizontal and vertical cloud structures,boundary layer stability,and cloud properties,all of which were subsequently used to interpret the observed roll-cloud case.Increasing model resolution led to a transition from a more buoyant boundary layer to a more shear-driven turbulent boundary layer.The clouds were stratiform-like in the mesoscale domain,but as the model resolution increased,roll-like structures,aligned along the wind field,appeared with ever smaller wavelengths.A stronger vertical water vapor gradient occurred above the cloud layers with decreasing grid spacing.With fixed model grid spacing at 0.333 km,changing the model configuration from a boundary layer parameterization to a large-eddy-permitting scheme produced a more shear-driven and less unstable environment,a stronger vertical water vapor gradient below the cloud layers,and the wavelengths of the rolls decreased slightly.In this study,only the large-eddy-permitting simulation with gird spacing of 0.111 km was sufficient to model the observed roll clouds.  相似文献   

A 96-antenna radioheliograph     

Sergey V. Lesovoi Alexander T. Altyntsev Eugene F. Ivanov Alexey V. Gubin 《中国天文和天体物理学报》2014,(7):864-868

Here we briefly present some design approaches for a multifrequency 96-antenna radioheliograph. The configuration of the array antenna, transmission lines and digital receivers is the main focus of this work. The radioheliograph is a T-shaped centrally condensed radiointerferometer operating in the frequency range 4–8 GHz.The justification for the choice of such a configuration is discussed. The signals from antennas are transmitted to a workroom by analog optical links. The dynamic range and phase errors of the microwave-over-optical signal are considered. The signals after downconverting are processed by digital receivers for delay tracking and fringe stopping. The required step of delay tracking and data rates are considered. Two 3-bit data streams(I and Q) are transmitted to a correlator with the transceivers embedded in Field Programmed Gate Array chips and with PCI Express cables.  相似文献   

Quasi-thermal Noise Spectra Measured by a Dipole Antenna in the Upper Hybrid frequency band     

Yury V. Chugunov  Anna Yu. Kazarova  Eugene A. Mareev  Michel Moncuquet  Karine Issautier  Nicole Meyer-Vernet 《Astrophysics and Space Science》2001,277(1-2):313-316

Quasi-thermal noise (QTN) spectroscopy is one of the most effective tools for in situ diagnostics in space plasmas (Meyer-Vernet et al., 1998; Meyer-Vernet and Perche, 1989; Chugunov and Trakhtengerts, 1978). This method produces routine measurements of the bulk electron density and temperature; recently it has been extended to measure the ion bulk speed. Among the advantages of the method its immunity to spacecraft potential and photoelectron perturbations should be noted. Quasi-thermal noise spectroscopy is used particularly on Ulysses and Wind. However for the interpretation of QTN data the calculation of the noise voltage induced on antennas under different conditions is necessary. This question is especially complicated and so far insufficiently studied in magnetized plasmas. In the present paper we calculate the spectrum of the noise voltage induced on a dipole antenna in the upper hybrid frequency range. The computations are adapted to the interpretation of data acquired on the Ulysses and Wind spacecraft. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Radiative backwarming in white-light flares     

Machado  Marcos E.  Emslie  A. Gordon  Avrett  Eugene H. 《Solar physics》1989,124(2):303-317

We examine empirical atmospheric structures that are consistent with enhanced white-light continuum emission in solar flares. This continuum can be produced either by hydrogen bound-free emission in an enhanced region in the upper chromosphere, or by H^- emission in an enhanced region around the temperature minimum. In the former case, weak Paschen jumps in the spectrum will be present, with the spectrum being dominated by a strong Balmer continuum, while in the latter case the spectrum exhibits a weaker, flat enhancement over the entire visible spectrum.We find that when proper account is taken of radiative backwarming processes, the two enhanced atmospheric regions above are not independent, in that irradiation by Balmer continuum photons from the upper chromosphere creates sufficient heating around the temperature minimum to account for the temperature enhancements there. Thus the problem of main phase white-light flare production reduces to one of creating temperature enhancements of order 10⁴ K in the upper chromosphere; radiative backwarming then naturally accounts for the enhancements of order 100 K around the temperature minimum.Heating by electron and proton bombardment, and by XUV irradiation from above, are then considered as candidates for creating the necessary enhancements in the upper chromosphere. We find that electron bombardment can be ruled out, whereas bombardment by protons in the few-MeV energy range is a viable candidate, but one without strong observational support. The XUV irradiation hypothesis is examined by incorporating it self-consistently into the PANDORA radiative transfer algorithm used to construct the empirical model atmospheres; we find that the introduction of XUV radiation, with flux and spectrum appropriate to white-light flare events, does indeed produce sufficient radiative heating in the upper chromosphere to balance the radiative losses associated with the required temperature enhancements.In summary, we find that the radiative coupling of (i) the upper chromosphere and temperature minimum regions (through Balmer continuum photons) and (ii) the transition region and upper chromosphere (through XUV photons) can account for white-light emission in solar flares.Presidential Young Investigator.  相似文献   

On the origin of the seismic anisotropy of the lithosphere     

Eugene V. Artyushkov 《Geophysical Journal International》1984,76(1):173-178

Summary. It is known that flow in the mantle can produce preferred orientation in olivine crystals with seismic anisotropy as a consequence. Flow in the subcrustal lithosphere is unlikely because of the high viscosity. Lenses of high temperature and low-viscosity ( anomalous mantle ) are located under the crust in many tectonically active regions, and viscous flow can easily arise in such material resulting in seismic anisotropy. After cooling, such anomalous mantle acquires high viscosity and becomes incorporated into the lithospheric layer preserving the anisotropy produced by the flows which existed previously. The interaction of the stresses with cracks in the upper crust can be one of the causes of anisotropy in this layer.  相似文献   

Volcanic hazard assessment incorporating expert knowledge: Application to the yucca mountain region, Nevada, USA     

Chih-Hsiang Ho  Eugene I. Smith 《Mathematical Geology》1997,29(5):615-627

Multiple-expert hazard/risk assessments have considerable precedent, particularly in the Yucca Mountain site characterization studies. A certain amount of expert knowledge is needed to interpret the geological data used in a probabilistic data analysis. As may be the situation in science, experts disagree on crucial points. Consequently, lack of consensus in some studies is a sure outcome. In this paper, we present a Bayesian approach to statistical modeling in volcanic hazard assessment for the Yucca Mountain site. Specifically, we show that the expert opinion on the site disruption parameterp is incorporated into the prior distribution, π(p), based on geological information that is available. Moreover, π(p) can combine all available geological information motivated by conflicting but realistic arguments (e.g., simulation, cluster analysis, structural control, ..., etc.). The incorporated uncertainties about the probability of repository disruptionp eventually will be averaged out by taking the expectation over π(p). We use the following priors in the analysis: (1) priors selected for mathematical convenience: Beta (r,s) for (r,s) = (2, 2), (3, 3), (5, 5), (2, 1),(2, 8), (8, 2), and (1, 1);and (2) three priors motivated by expert knowledge. Sensitivity analysis is performed for each prior distribution. Our study concludes that estimated values of hazard based on the priors selected for mathematical simplicity are uniformly higher than those obtained based on the priors motivated by expert knowledge. And, the model using the prior, Beta (8, 2), yields the highest hazard (=2.97 × 10^-2 . The minimum hazard is produced by the “three-expert prior” (i.e., values of p are equally likely for p = 10^-3, 10^-2,and 10^-1 . The estimate of the hazard is 1.39 × 10^-3, which is only about one order of magnitude smaller than the maximum value. The term, “hazard, ” is defined as the probability of at least one disruption of a repository at the Yucca Mountain site by basaltic volcanism for the next 10,000 years.  相似文献   

Sudden death at the end of the Mesozoic     

Cesare Emiliani  Eric B. Kraus  Eugene M. Shoemaker 《Earth and Planetary Science Letters》1981,55(3):317-334

A paleoecological analysis of the fossil record before and after the Cretaceous/Tertiary boundary indicates that the widespread extinctions and biological stresses around the boundary are best explained in terms of a sudden, significant, but short temperature rise. L. Alvarez and co-authors, having found an enrichment in iridium at the same boundary, postulated that it was associated with the impact of an extraterrestrial body. If this body struck the ocean, the water injected into the atmosphere may have led to a transient increase in the global surface temperature. This temperature pulse may have been primarily responsible for the effects observed in the biosphere. The pattern of extinction of higher plant species suggests that splash down occurred in the northern Pacific-Bering Sea area.  相似文献   

CyberConnector: a service-oriented system for automatically tailoring multisource Earth observation data to feed Earth science models     

Ziheng Sun  Liping Di  Haosheng Hao  Xiaoqing Wu  Daniel Q. Tong  Chen Zhang  Cora Virgei  Hui Fang  Eugene Yu  Xicheng Tan  Peng Yue  Li Lin 《Earth Science Informatics》2018,11(1):1-17

Feeding multisource Earth observation (EO) data into Earth science models (ESM) remains a daunting challenge. This paper presents a service-oriented approach as an alternative solution. It uses geospatial web services to process the EO data and geoprocessing workflow for automation. Different from existing approaches, it takes advantage of virtual data products (VDP) to release modelers from intensive data processing. It can directly connect ESMs to public EO sources via Cyberinfrastructure. A prototype called CyberConnector is implemented. CyberConnector supports intuitive building of VDP, automatic execution of workflows and effortless retrieval of model-ready input files. We used it to stream multiple datasets to several ESMs including finite-volume coastal ocean model (FVCOM) and cloud-resolving model (CRM). The results show that CyberConnector can truly benefit modelers on time saving and effort minimizing.  相似文献   

Coral reef recovery in Florida and the Persian Gulf   总被引：1，自引：0，他引：1  

Shinn  Eugene A. 《Environmental Geology》1976,1(4):241-254

Long-term observations and study of coral reef destruction by hurricanes in the Florida Keys show, surprisingly, that although corals are devastated on a grand scale during storms, recovery is rapid. Recovery occurs because of the widespread scattering of live fragments, many of which become growth sites of new colonies. Reef recovery from death by chilling in the Persian Gulf was well under way when last observed, but it is not yet known if the recovery rate was as rapid as recovery from the storm destruction in Florida. Recovery from death by chilling requires settlement of transported coral larvae and a substrate suitable for larval attachment. Such resettlement is subject to the effects of currents, predators, pollution, and competition for substrate. A growth rate of 10 cm per year combined with geometrical progression of branch formation accounts for rapidAcropora cervicornis recovery. Although calculated coral proliferation seems unusually high, it has been confirmed by serial underwater photographs spanning ten years. More precise measurements of growth and branching are needed, along with growth data for other common reef-building corals. Such data would be useful for predicting standing crop of a restocked or transplanted reef.  相似文献