Past,present and future of a meandering river in the Bolivian Amazon basin     

Kattia Rubi Arnez Ferrel  Jonathan Mark Nelson  Yasuyuki Shimizu  Tomoko Kyuka 《地球表面变化过程与地形》2021,46(4):715-727

Field observations on small rivers of the Amazon basin are less common due to their remote location and difficult accessibility. Here we show, through remote sensing analysis and field works, the planform evolution and riverbed topography of a small river located in the upper foreland Amazon basin, the Ichilo River. By tracking planform changes over 30 years, we identified the factors that control meander migration rates in the Ichilo River: cutoffs, climate and human interventions. The data suggest that neck cutoffs are the main controls in the Ichilo River, with an annual density of 0.022 cutoffs/km. In addition, climate controls have been identified in the form of high-precipitation events that may have promoted cutoffs, an increase in meander migration rate and channel widening. The width distribution of the Ichilo River is well represented by general extreme value and inverse Gaussian distributions. The spatiotemporal variability of meandering migration rates in the Ichilo River is analysed in two locations where neck cutoffs are expected. Analysing the distance across the neck in these two points, we predict the occurrence of a new cutoff. The combined methodology of bathymetric surveys and structure from motion photogrammetry shows us the Ichilo riverbed topography and banks at high resolution, where two scour holes were identified. Finally, we discuss the impact of planform changes of the Ichilo River on communities that are established along its riverbanks.  相似文献   

Spatial and temporal aspects of the lake effect on the southern shore of Lake Superior   总被引：1，自引：0，他引：1  

Kenneth M. Hinkel  Frederick E. Nelson 《Theoretical and Applied Climatology》2012,109(3-4):415-428

A climate-monitoring network was implemented in a large private preserve along the southern shore of Lake Superior. The network uses a dense sampling design to assess the spatial and temporal influence of a large, cold body of water on adjacent terrestrial surfaces. Based on a 3-year record, near-shore sites are 1–2°C cooler than sites 5?km inland in spring and summer, and 1°C warmer in winter. Near the shore, winds are from the NNW most of the year, and are much stronger in winter. Inland, southwesterly flow is typical and overall wind velocity is lower and more consistent. This decoupling is attributable to the influence of the Huron Mountains, a topographic barrier that restricts the lake effect to a narrow coastal zone. A 2-year record of hourly air temperature measurements from 26–30 sites across the study area demonstrates that the mean daily temperature can differ by as much as 11°C, but the average difference is 2.5–3.0°C.  相似文献   

DXL: a sounding rocket mission for the study of solar wind charge exchange and local hot bubble X-ray emission     

Massimiliano Galeazzi  Meng Chiao  Michael R. Collier  Thomas Cravens  Dimitra Koutroumpa  Kip D. Kuntz  Susan Lepri  Dan McCammon  Frederick S. Porter  Krishna Prasai  Ina Robertson  Steve Snowden  Youaraj Uprety 《Experimental Astronomy》2011,32(2):83-99

The Diffuse X-rays from the Local galaxy (DXL) mission is an approved sounding rocket project with a first launch scheduled around December 2012. Its goal is to identify and separate the X-ray emission generated by solar wind charge exchange from that of the local hot bubble to improve our understanding of both. With 1,000 cm² proportional counters and grasp of about 10 cm² sr both in the 1/4 and 3/4 keV bands, DXL will achieve in a 5-min flight what cannot be achieved by current and future X-ray satellites.  相似文献   

Are there social limits to adaptation to climate change?   总被引：1，自引：0，他引：1  

W. Neil Adger  Suraje Dessai  Marisa Goulden  Mike Hulme  Irene Lorenzoni  Donald R. Nelson  Lars Otto Naess  Johanna Wolf  Anita Wreford 《Climatic change》2009,93(3-4):335-354

While there is a recognised need to adapt to changing climatic conditions, there is an emerging discourse of limits to such adaptation. Limits are traditionally analysed as a set of immutable thresholds in biological, economic or technological parameters. This paper contends that limits to adaptation are endogenous to society and hence contingent on ethics, knowledge, attitudes to risk and culture. We review insights from history, sociology and psychology of risk, economics and political science to develop four propositions concerning limits to adaptation. First, any limits to adaptation depend on the ultimate goals of adaptation underpinned by diverse values. Second, adaptation need not be limited by uncertainty around future foresight of risk. Third, social and individual factors limit adaptation action. Fourth, systematic undervaluation of loss of places and culture disguises real, experienced but subjective limits to adaptation. We conclude that these issues of values and ethics, risk, knowledge and culture construct societal limits to adaptation, but that these limits are mutable.  相似文献   

A Simple Method of Estimating Scalar Fluxes Over Forests   总被引：1，自引：0，他引：1  

Nelson Luis Dias  Jinkyu Hong  Monique Y. Leclerc  T. Andrew Black  Z. Nesic  P. Krishnan 《Boundary-Layer Meteorology》2009,132(3):401-414

A simple aerodynamic-variance method is proposed to fill gaps in continuous CO₂ flux measurements in rainy conditions, when open-path analysers do not function. The method requires turbulent conditions (friction velocity greater than 0.1 ms^–1), and uses measurements of mean wind speed, and standard deviations of temperature and CO₂ concentration fluctuations to complement, and at times replace, eddy-covariance measurements of friction velocity, sensible heat flux and CO₂ flux. Friction velocity is estimated from the mean wind speed with a flux-gradient relationship modified for the roughness sublayer. Since normalised standard deviations do not follow Monin-Obukhov similarity theory in the roughness sublayer, a simple classification scheme according to the scalar turbulence scale was used. This scheme is shown to produce sensible heat and CO₂ flux estimates that are well correlated with the measured values.  相似文献   

Trends in fog frequencies in the Los Angeles Basin   总被引：1，自引：0，他引：1  

M.R. Witiw  Steve LaDochy 《Atmospheric Research》2008,87(3-4):293

Data from throughout the Los Angeles area were examined to determine the horizontal distribution of dense fog (visibility < 400 m) in the region and trends over time. The relationship between the occurrence of dense fog to the phase of two atmosphere–ocean cycles: the Pacific Decadal Oscillation (PDO) measured by the PDO Index and the Southern Oscillation measured by the Southern Oscillation Index (SOI) was investigated. In addition, the influence of the urban heat island and the amount of suspended particulate matter were assessed. For the three stations that had 22 or more years of data, we examined trends and the relation to atmosphere–ocean cycles. Results show a decrease in the occurrence of very low visibilities (< 400 m) at the stations in close proximity to the Pacific Ocean, Los Angeles International Airport (LAX) and Long Beach International Airport (LGB). Occurrence of the frequency of low visibilities at these two locations was also highly correlated with the phase of the PDO. Only a weak, non-statistically significant relationship was seen with the SOI. At Burbank, a reporting station about 30 km from the ocean, no trends were noted, and there was no evidence of a correlation with either the PDO Index or the SOI. In the Los Angeles Central Business District (CBD) when comparing dense fog occurrence in the early 1960s to a similar period in the early 2000s we saw a decrease in dense fog from a mean of 10 h per year to a mean of 3 h per year. Also contributing to the decrease was decreasing particulate pollution and increased urban warming. A downward trend in particulate concentrations coupled with an upward trend in urban temperatures were associated with a decrease in dense fog occurrence at both LAX and LGB. These trends were evident for the period 1966–1997, but appear to have ended by the late 1990s.  相似文献   

Saturn's Titan: Surface change, ammonia, and implications for atmospheric and tectonic activity     

R.M. Nelson  L.W. Kamp  P.G.J. Irwin  M.D. Boryta  R. Jaumann  C. Sotin  D.P. Cruikshank  J.C. Pearl  J. Lunine  G. Bellucci  F. Capaccioni  A. Coradini  G. Filacchione  T.B. McCord  P.D. Nicholson 《Icarus》2009,199(2):429-441

Titan is known to have a young surface. Here we present evidence from the Cassini Visual and Infrared Mapping Spectrometer that it is currently geologically active. We report that changes in the near-infrared reflectance of a 73,000 km² area on Titan (latitude 26° S, longitude 78° W) occurred between July 2004 and March of 2006. The reflectance of the area increased by a factor of two between July 2004 and March-April 2005; it then returned to the July 2004 level by November 2005. By late December 2005 the reflectance had surged upward again, establishing a new maximum. Thereafter, it trended downward for the next three months. Detailed spectrophotometric analyses suggest these changes happen at or very near the surface. The spectral differences between the region and its surroundings rule out changes in the distribution of the ices of reasonably expected materials such as H₂O, CO₂, and CH₄ as possible causes. Remarkably, the change is spectrally consistent with the deposition and removal of NH₃ frost over a water ice substrate. NH₃ has been proposed as a constituent of Titan's interior and has never been reported on the surface. The detection of NH₃ frost on the surface might possibly be explained by episodic effusive events occur which bring juvenile ammonia from the interior to the surface. If so, its decomposition would feed nitrogen to the atmosphere now and in the future. The lateral extent of the region exceeds that of active areas on the Earth (Hawaii) or Io (Loki).  相似文献   

The solar system beyond Neptune,edited by M. A. Barucci,H. Boehnhardt,D. P. Cruikshank,and A. Morbidelli     

Steve Kortenkamp 《Meteoritics & planetary science》2009,44(3):463-464

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The influence of halo assembly on galaxies and galaxy groups     

Tatiana Zapata  Josefa Perez  Nelson Padilla  Patricia Tissera 《Monthly notices of the Royal Astronomical Society》2009,394(4):2229-2237

In this paper, we study the variations of group galaxy properties according to the assembly history in Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) selected groups. Using mock SDSS group catalogues, we find two suitable indicators of group formation time: (i) the isolation of the group, defined as the distance to the nearest neighbour in terms of its virial radius and (ii) the concentration, measured as the group inner density calculated using the fifth nearest bright galaxy to the group centre. Groups within narrow ranges of mass in the mock catalogue show increasing group age with isolation and concentration. However, in the observational data the stellar age, as indicated by the spectral type, only shows a correlation with concentration.
We study groups of similar mass and different assembly history, finding important differences in their galaxy population. Particularly, in high-mass SDSS groups, the number of members, mass-to-light ratios, red galaxy fractions and the magnitude difference between the brightest and second-brightest group galaxies, show different trends as a function of isolation and concentration, even when it is expected that the latter two quantities correlate with group age. Conversely, low-mass SDSS groups appear to be less sensitive to their assembly history.
The correlations detected in the SDSS are not consistent with the trends measured in the mock catalogues. However, discrepancies can be explained in terms of the disagreement found in the age-isolation trends, suggesting that the model might be overestimating the effects of environment. We discuss how the modelling of the cold gas in satellite galaxies could be responsible for this problem. These results can be used to improve our understanding of the evolution of galaxies in high-density environments.  相似文献   

The Morpheus ultramodular autonomous underwater vehicle     

Smith  S.M. An  P.E. Holappa  K. Whitney  J. Burns  A. Nelson  K. Heatzig  E. Kempfe  O. Kronen  D. Pantelakis  T. Henderson  E. Font  G. Dunn  R. Dunn  S.E. 《Oceanic Engineering, IEEE Journal of》2001,26(4):453-465

The Advanced Marine Systems Lab at Florida Atlantic University has developed a new ultramodular plastic mini autonomous underwater vehicle (AUV), called the Morpheus, for littoral military and coastal oceanographic sampling, survey, and mapping. The name Morpheus was chosen because the Greek god Morpheus could change shape or "morph." The higher degree of modularity of the Morpheus AUV allows it to "morph" or change its size and components for different applications. This vehicle is composed of modular injection-molded plastic pressure vessels and a cabling system that allow the modules to be rearranged without rewiring bulkheads. The plastic pressure vessels are inexpensive, inherently mass-producible, extremely corrosion-resistant, and have low magnetic signatures. The pressure vessels are small but are sized to fit most standard electronic board standards. The mini AUV can be anywhere from 4 to 10 ft in length, depending on its mission. The vehicle architecture is an adaptation of the Ocean Explorer AUV system and uses an ANSI 709.1 (LonTalk) distributed control network for connecting all sensors and actuator subsystems as smart nodes. The modularity in containers, control, and power makes this vehicle rapidly reconfigurable and easy to repair or upgrade. This paper will present details of the motivation, design, and construction of the new mini AUV. The Morpheus was deployed during the summer of 2000 in field exercises for very shallow and shallow water mine counter measures. Some results from these tests will be presented  相似文献