Some aspects of transformations of compositional data and the identification of outliers

The statistical analysis of compositional data is based on determining an appropriate transformation from the simplex to real space. Possible transfonnations and outliers strongly interact: parameters of transformations may be influenced particularly by outliers, and the result of goodness-of-fit tests will reflect their presence. Thus, the identification of outliers in compositional datasets and the selection of an appropriate transformation of the same data, are problems that cannot be separated. A robust method for outlier detection together with the likelihood of transformed data is presented as a first approach to solve those problems when the additive-logratio and multivariate Box-Cox transformations are used. Three examples illustrate the proposed methodology.     

Generation of realistic synthetic catchments to explore fine continental surface processes

Understanding, analysing, and predicting the erosion mechanisms and sedimentary flows produced by catchments plays a key role in environmental conservation and restoration management and policies. Numerical case-testing studies are generally undertaken to analyse the sensitivity of flood and soil erosion processes to the physical characteristics of catchments. Most analyses are conducted on simple virtual catchments with physical characteristics that, unlike real catchments, are perfectly controlled. Virtual catchments generally correspond to V-shaped valley catchments. However, although these catchments are suitable for methodical analysis of the results, they do not provide a realistic representation of the spatial structures of the landscape and field conditions. They can, therefore, lead to potential modelling errors and can make it difficult to extend or generalize their results. Our proposed method bridges the gap between real and traditional virtual catchments by creating realistic virtual catchments with perfectly controllable physical characteristics. Our approach represents a real alternative to traditional test case procedures and provides a new framework for geomorphological and hydrological communities. It combines a field procedural generation approach, geographic information system processing procedures, and the CAESAR-Lisflood landscape evolution model. We illustrate how each of these components acts in the process of generating virtual catchments. Five physical parameters were adjusted and tested for each virtual catchment: drainage density, hypsometric integral, mean slope of the main channel, granulometry, and land use. One of our virtual catchments is compared with a real catchment and a virtual catchment produced by a standard method. This comparison indicates that our approach can produce more realistic virtual catchments than those produced by more traditional methods, while a high degree of controllability is maintained. This new method of generating virtual catchments therefore offers significant research potential to identify the impacts of the physical characteristics of catchments on hydro-sedimentary dynamics and responses.     

Remote sensing of coral reefs and their physical environment

There has been a vast improvement in access to remotely sensed data in just a few recent years. This revolution of information is the result of heavy investment in new technology by governments and industry, rapid developments in computing power and storage, and easy dissemination of data over the internet. Today, remotely sensed data are available to virtually anyone with a desktop computer. Here, we review the status of one of the most popular areas of marine remote sensing research: coral reefs. Previous reviews have focused on the ability of remote sensing to map the structure and habitat composition of coral reefs, but have neglected to consider the physical environment in which reefs occur. We provide a holistic review of what can, might, and cannot be mapped using remote sensing at this time. We cover aspects of reef structure and health but also discuss the diversity of physical environmental data such as temperature, winds, solar radiation and water quality. There have been numerous recent advances in the remote sensing of reefs and we hope that this paper enhances awareness of the diverse data sources available, and helps practitioners identify realistic objectives for remote sensing in coral reef areas.     

Performance assessment of an underwater setting chute to mitigate seabird bycatch in the Hawaii pelagic longline tuna fishery

Mortality in longline fisheries is one of the most critical global threats to some seabird species. Underwater setting technology may offer an effective and commercially viable solution. The underwater setting chute for pelagic longline fisheries releases baited hooks underwater, out of sight and reach of diving seabirds. Results from a study in the Hawaii pelagic longline tuna fishery indicate that the underwater setting chute is the most effective technology tested to date to minimize seabird capture in this fishery. The chute eliminated seabird capture during this short-term trial. During control replicates, the capture rate was 4.24 captures per 1000 hooks and when normalized for albatross abundance, the rate was 0.114 captures per 1000 hooks per albatross. Expressed as contacts per 1000 hooks per albatross, the chute was 95% effective at reducing albatross contacts with fishing gear compared to a control.The chute was practical for use and design and installation improvements are likely possible to make the chute more palatable for uptake by industry. The chute has the added benefit of increasing fishing efficiency. The cost for purchasing and installing the chute would be recouped after only a maximum of two fishing trips. Based on an assessment of bait retention and hook setting interval when using the chute versus setting conventionally, vessels would experience a gain in efficiency of between 14.7% and 29.6% when albatrosses are abundant. Economic incentives are essential to abate global seabird mortality in longline fisheries.     

Regional climate of hazardous convective weather through high-resolution dynamical downscaling

We explore the use of high-resolution dynamical downscaling as a means to simulate the regional climatology and variability of hazardous convective-scale weather. Our basic approach differs from a traditional regional climate model application in that it involves a sequence of daily integrations. We use the weather research and forecasting (WRF) model, with global reanalysis data as initial and boundary conditions. Horizontal grid lengths of 4.25?km allow for explicit representation of deep convective storms and hence a compilation of their occurrence statistics over a large portion of the conterminous United States. The resultant 10-year sequence of WRF model integrations yields precipitation that, despite its positive bias, has a diurnal cycle consistent with observations, and otherwise has a realistic geographical distribution. Similarly, the occurrence frequency of short-duration, potentially flooding rainfall compares well to analyses of hourly rain gauge data. Finally, the climatological distribution of hazardous-thunderstorm occurrence is shown to be represented with some degree of skill through a model proxy that relates rotating convective updraft cores to the presence of hail, damaging surface winds, and tornadoes. The results suggest that the proxy occurrences, when coupled with information on the larger-scale atmosphere, could provide guidance on the reliability of trends in the observed occurrences.     

Atmospheric inversion strength over polar oceans in winter regulated by sea ice

Low-level temperature inversions are a common feature of the wintertime troposphere in the Arctic and Antarctic. Inversion strength plays an important role in regulating atmospheric processes including air pollution, ozone destruction, cloud formation, and negative longwave feedback mechanisms that shape polar climate response to anthropogenic forcing. The Atmospheric Infrared Sounder (AIRS) instrument provides reliable measures of spatial patterns in mean wintertime inversion strength when compared with available radiosonde observations and reanalysis products. Here, we examine the influence of sea ice concentration on inversion strength in the Arctic and Antarctic. Correlation of inversion strength with mean annual sea ice concentration, likely a surrogate for the effective thermal conductivity of the wintertime ice pack, yields strong, linear relationships in the Arctic (r?=?0.88) and Antarctic (r?=?0.86). We find a substantially greater (stronger) linear relationship between sea ice concentration and surface air temperature than with temperature at 850?hPa, lending credence to the idea that sea ice controls inversion strength through modulation of surface heat fluxes. As such, declines in sea ice in either hemisphere may imply weaker mean inversions in the future. Comparison of mean inversion strength in AIRS and global climate models (GCMs) suggests that many GCMs poorly characterize mean inversion strength at high latitudes.     

昆仑断裂带东段滑动速率梯度

欧亚大陆走滑断裂带是否实现对青藏地壳及岩石层的向东挤出,很大程度上取决于断层尾端变形的动力学机制。本文我们利用青藏高原北部昆仑断裂最东段千年尺度的地貌标志物提供一组最新的滑动速率测定结果。该断裂带是印度?亚欧碰撞带产生的最主要走滑断裂带之一,在西藏岩石层向东挤出的模型中扮演着主要的作用。曾有人争论在相当长的长度内该断裂显示出相同的滑动速率。黄河支流上的河流阶地位移以及阶地上物质的14C测年可以控制晚更新世至全新世断层以来的滑动速率。结果显示沿断裂东部约150km滑动速率从>10mm/a～<2mm/a自西向东系统地递减。这些数据向那些认为整条断裂滑动速率保持一致的观点提出质疑,相反揭示出位错的梯度性,这与那些在断层尾端预期的情形是类似的。另外,沿断层的滑动看起来在增厚的高原地壳内部终结,因此沿昆仑断裂的滑动导致的西藏岩石层的挤出都会被断裂尾端周围高原的内部变形所吸收。     

The Flux Tube Tectonics model for coronal heating

An account is presented of the Flux Tube Tectonics model for heating the solar corona, in which a multitude of current sheets are continually forming and dissipating. In addition, a model is summarised for the time-dependent response of the corona to the sudden dissipation of one such current sheet.