2,524 research outputs found
I\u27m Longing For My Own, Dixie Land
https://digitalcommons.library.umaine.edu/mmb-vp/1794/thumbnail.jp
Myths and Misconceptions about the United Nations
In the U.S. Navy, Inspections measure readieness and perfor mance against standard criteria. These evolutions identify problems for correction and provide an opportunity for improvement. They can offer both assessment and prediction, but only when the inspecton understand the criteria and how they influence performance. Analogously, any evaluation of the United Nations, if it is to achieve comparable results, should proceed from a similar foundation-a shared understanding of standard criteria. Let us consider, then, how these familiar practices may be applied to an assessment of the United Nations
Exodus or Entrenchment: The Catholic Dilemma of Duty
Today we must ask ourselves who are the peacemakers? The Second Vatican Council professed, All those who enter the military service in loyalty to their country ... are contributing to the maintenance of peace
LocalâRegional Similarity in Drylands Increases During Multiyear Wet and Dry Periods and in Response to Extreme Events
Climate change is predicted to impact ecosystems through altered precipitation (PPT) regimes. In the Chihuahuan Desert, multiyear wet and dry periods and extreme PPT pulses are the most influential climatic events for vegetation. Vegetation responses are most frequently studied locally, and regional responses are often unclear. We present an approach to quantify correlation of PPT and vegetation responses (as Normalized Difference Vegetation Index [NDVI]) at the Jornada ARSâLTER site (JRN; 550 km2 area) and the surrounding dryland region (from 0 to 500 km distance; 400,000 km2 study area) as a way to understand regional similarity to locally observed patterns. We focused on fluctuating wet and dry years, multiyear wet or dry periods of 3â4 yr, and multiyear wet periods that contained one or more extreme high PPT pulses or extreme low rainfall. In all but extreme high PPT years, JRN PPT was highly correlated... (See article for full abstract)
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A method for merging flow-dependent forecast error statistics from an ensemble with static statistics for use in high resolution variational data assimilation
The background error covariance matrix, B, is often used in variational data assimilation for numerical weather prediction as a static and hence poor approximation to the fully dynamic forecast error covariance matrix, Pf. In this paper the concept of an Ensemble Reduced Rank Kalman Filter (EnRRKF) is outlined.
In the EnRRKF the forecast error statistics in a subspace defined by an ensemble of states forecast by the dynamic model are found. These statistics are merged in a formal way with the static statistics, which apply in the remainder of the space. The combined statistics may then be used in a variational data assimilation setting. It is hoped that the nonlinear error growth of small-scale weather
systems will be accurately captured by the EnRRKF, to produce accurate analyses and ultimately improved forecasts of extreme events
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The âABC modelâ: a non-hydrostatic toy model for use in convective-scale data assimilation investigations
In developing methods for convective-scale data assimilation (DA) it is necessary to consider the full range of motions governed by the compressible Navier-Stokes equations (including non-hydrostatic and ageostrophic flow). These equations describe motion on a wide range of time-scales with non-linear coupling. For the purpose of developing new DA techniques that suit the convective-scale problem it is helpful to use so-called âtoy modelsâ that are easy to run, and contain the same types of motion as the full equation set. Such a model needs to permit hydrostatic and geostrophic balance at large-scales, but to allow imbalance at small-scales, and in particular, it needs to exhibit intermittent convection-like behaviour. Existing âtoy modelsâ are not always sufficient for investigating these issues.
A simplified system of intermediate complexity derived from the Euler equations is presented, which supports dispersive gravity and acoustic modes. In this system the separation of time scales can be greatly reduced by changing the physical parameters. Unlike in existing toy models, this allows the acoustic modes to be treated explicitly, and hence inexpensively. In addition, the non-linear coupling induced by the equation of state is simplified. This means that the gravity and acoustic modes are less coupled than in conventional models. A vertical slice formulation is used which contains only dry dynamics. The model is shown to give physically reasonable results, and convective behaviour is generated by localised compressible effects. This model provides an affordable and flexible framework within which some of the complex issues of convective-scale DA can later be investigated. The model is called the âABC modelâ after the three tunable parameters introduced: A (the pure gravity wave frequency), B (the modulation of the divergent term in the continuity equation), and C (defining the compressibility)
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