National Waste & Recycling Association

About: National Waste & Recycling Association is a based out in . It is known for research contribution in the topics: Gravity wave & Stratosphere. The organization has 56 authors who have published 72 publications receiving 3006 citations.

The Imaging Vector Magnetograph at Haleakalā – II. Reconstruction of Stokes Spectra

Abstract: The Imaging Vector Magnetograph (`IVM') at Mees Solar Observatory, Haleakalā, Maui, Hawai`i, is designed to measure the magnetic field vector over an entire solar active region on the Sun. The first step in that process is to correct the raw data for all known systematic effects introduced by the instrument and Earth's atmosphere. We define a functional model of the atmosphere/instrument system and measure the corrections for the degradation introduced by each component of the model. We demonstrate the feasibility of this method and assess the accuracy of the IVM spectra with a direct comparison of the resulting Stokes spectra to a well-described spectropolarimeter.

Composite Life Cycle of Maritime Tropical Mesoscale Convective Systems in Scatterometer and Microwave Satellite Observations

Abstract: This study examines scatterometer-observed surface wind divergence and vorticity, along with precipitable water (PW), across the life cycle of tropical maritime mesoscale convective systems (MCSs) as resolved in 0.5° data. Simple composites were constructed around first appearances of cold (210 K) cloud tops in infrared (IR) data at 3-hourly resolution. Many thousands of such events from the tropical IndoPacific in 2000 were used. Composites of subpopulations were also constructed by subdividing the dataset according to IR event size and duration, as well as by prevailing values of PW and vorticity at a 5° scale. The composite MCS life cycle here spans about a day and covers a few hundred kilometers, with a remarkable sameness across subpopulations. Surface wind convergence and PW buildup lead cold cloud appearance by many hours. Afterward there are many hours of divergence, indicative of downdrafts. Contrary to motivating hypotheses, the strength of this divergence relative to convergence is scarcely different in humid and dry subpopulation composites. Normalized time series of composite vorticity show an evolution that seems consistent with vortex stretching by this convergence–divergence cycle, with peak vorticity near the end of the period of convergence (3 h prior to cold cloud appearance). In rotating conditions, the common 1-day MCS life cycle is superposed on large-scale mean vorticity and convergence, approximately in proportion, which appear to be well scale-separated (covering the whole of the 48-h and 5°–10° averages) and are as strong as or stronger than the MCS signature.

Plumes in rotating convection. Part 1. Ensemble statistics and dynamical balances

Abstract: Atmospheric and oceanic convection often occurs over areas occupied by many localized circulation elements known as plumes. The convective transports therefore may depend not only on the individual elements, but also on the interactions between plumes and the turbulent environment created by other plumes. However, many attempts to understand these plumes focus on individual isolated elements, and the behaviour of an ensemble is not understood. Geophysical convection may be influenced by rotation when the transit time of a convecting element is long compared to an inertial period (for example in deep oceanic convection). Much recent attention has been given to the effect of rotation on individual plumes, but the role of rotation in modifying the behaviour of an ensemble is not fully understood. Here we examine the behaviour of plumes within an ensemble, both with and without rotation, to identify the influence of rotation on ensemble plume dynamics.We identify the coherent structures (plumes) present in numerical solutions of turbulent Rayleigh–Benard convection, a canonical example of a turbulent plume ensemble. We use a conditional sampling compositing technique to extract the typical structure in both non-rotating and rotating solutions. The dynamical balances of these composite plumes are evaluated and compared with entraining plume models. We find many differences between non-rotating and rotating plumes in their transports of mass, buoyancy and momentum. As shown in previous studies, the expansion of the turbulent plume by entrainment of exterior fluid is suppressed by strong rotation. Our most significant new result is quantification of the continuous mixing between the plume and ambient fluid which occurs at high rotation without any net changes in plume volume. This mixing is generated by the plume–plume interactions and acts to reduce the buoyancy anomaly of the plume. By contrast, in the non-rotating case, no such loss of buoyancy by mixing occurs. As a result, the total buoyancy transport by upwardly moving plumes diminishes across the layer in the rotating case, while remaining approximately constant in the non-rotating case. At high values of rotation, the net vertical acceleration is considerably reduced compared to the non-rotating case due to loss of momentum through entrainment and mixing and a decelerating pressure gradient which partially balances the buoyancy-driven acceleration of plumes. As a result of the dilution of buoyancy, the pressure-gradient deceleration and the loss of momentum due to mixing with the environment in the rotating solutions, the conversion of potential energy to kinetic energy is significantly less than that of non-rotating plumes.The combination of efficient lateral mixing and slow vertical movement by the plumes accounts for the unstable mean temperature gradient that occurs in rotating Rayleigh–Benard convection, while the less penetrative convection found at low Rossby number is a consequence of the reduced kinetic energy transport. Within the ensemble of plumes identified by the conditional sampling algorithm, distributions of vertical velocity, buoyancy and vorticity mimic those of the volume as a whole. Plumes cover a small fraction of the total area, yet account for most of the vertical heat flux.

Ocean Ensemble Forecasting, Part I: Ensemble Mediterranean Winds from a Bayesian Hierarchical Model

Abstract: A Bayesian hierarchical model (BHM) is developed to estimate surface vector wind (SVW) fields and associated uncertainties over the Mediterranean Sea. The BHM–SVW incorporates data-stage inputs from analyses and forecasts of the European Centre for Medium-Range Weather Forecasts (ECMWF) and SVW retrievals from the QuikSCAT data record. The process-model stage of the BHM–SVW is based on a Rayleigh friction equation model for surface winds. Dynamical interpretations of posterior distributions of the BHM–SVW parameters are discussed. Ten realizations from the posterior distribution of the BHM–SVW are used to force the data-assimilation step of an experimental ensemble ocean forecast system for the Mediterranean Sea in order to create a set of ensemble initial conditions. The sequential data-assimilation method of the Mediterranean forecast system (MFS) is adapted to the ensemble implementation. Analyses of sample ensemble initial conditions for a single data-assimilation period in MFS are presented to demonstrate the multivariate impact of the BHM–SVW ensemble generation methodology. Ensemble initial-condition spread is quantified by computing standard deviations of ocean state variable fields over the ten ensemble members. The methodological findings in this article are of two kinds. From the perspective of statistical modelling, the process-model development is more closely related to physical balances than in previous work with models for the SVW. From the ocean forecast perspective, the generation of ocean ensemble initial conditions via BHM is shown to be practical for operational implementation in an ensemble ocean forecast system. Phenomenologically, ensemble spread generated via BHM–SVW occurs on ocean mesoscale time- and space-scales, in close association with strong synoptic-scale wind-forcing events. A companion article describes the impacts of the BHM–SVW ensemble method on the ocean forecast in comparisons with more traditional ensemble methods. Copyright © 2011 Royal Meteorological Society

Anisotropy in a stratified shear layer

Abstract: The dynamics and turbulent evolution of a stratified shear layer are explored through direct numerical simulation. Turbulence is instigated through the most unstable asymptotic linear Kelvin-Helmholtz (KH) eigenmode at Richardson number Ri = 0.05 and Reynolds number Re = 2000 (Ri and Re are defined below). The primary 2D KH vortex succumbs to 3D motions in a manner consistent with earlier findings. The shear-layer Reynolds number ReL (defined below) grows to ReL ≈ 2.4 × 104 as the layer expands and small length-scale motions develop. Large- and small-scale anisotropy are examined by comparing 1) spectra for the longitudinal and transverse correlation coefficients, 2) RMS velocity components and 3) velocity and temperature derivatives during the time when turbulence is most intense. The mean shear produces a tendency toward streamwise axisymmetric, as opposed to isotropic, turbulent flow; however, departures from streamwise axisymmetry due to stratification are evident in the dissipation fields (i.e., at small scales).