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 forward and inverse problems in time-distance helioseismology

Abstract: Time-distance helioseismology is a set of tools for peering into the solar interior. In this paper we discuss and provide examples of the steps that go into current high-resolution time-distance helioseismic analyses. These steps include observations (cross covariances, travel times), modeling of the seismic wavefield for a weakly inhomogeneous solar model, and inversion of the travel times. The discussion is framed in the context of studying quiet-Sun flows, although the extension to other solar perturbations is straightforward and analogous. The two-plus-one-dimensional (2+1D) inversion procedure implemented here produces maps of vector flows in the near-surface layers of the photosphere. We examine the flows obtained by compromising, or 'trading off', between different observation times, spatial resolutions, and noise levels. Also studied is the correlation of the flows at different depths and over different time intervals.

Making global map of the solar surface Br from the HMI vector magnetic field observations

Abstract: The Helioseismic Magnetic Imager (HMI) has made full-disk vector magnetic field measurements of the Sun with cadence of 12 minutes. The three-component solar surface magnetic field vector data are from the HMI observations with the data process pipeline modules, VFISV (Very Fast Inversion of the Stokes Vector, Borrero et al., 2011) for Milne-Eddington inversion and the minimum-energy disambiguation algorithm (Metcalf 1994, Leka et al, 2009). The models of the global corona and solar wind, such as the PFSS (potential-field source-surface) model and the MHD simulations, often use the maps of solar surface magnetic field, especially the radial component (Br) as the boundary condition. The HMI observation can provide new Br data for these model. Because of weak magnetic signals at the quiet regions of the Sun, the limb darkening, and geometric effects near solar poles, we need to apply an assumption to make a whole-surface map. In this paper, we tested two assumptions for determining Br at weak-field regions. The coronal structures calculated by the PFSS model with the vector-based Br are compared with those with the magnetogram-based Br and the corona observed by the SDO/AIA (Atmospheric Imaging Assembly). In the tested period, CR 2098, the vector-based Br map gives better agreements than the line-of-sight magnetogram data, though we need further investigation for evaluation.

Direct Numerical Simulation of Isotropic and Stratified Optical Turbulence

Abstract: Direct numerical simulation (DNS) is a technique to computationally generate turbulent velocity and scalar fields based on the first principles of hydrodynamics. DNSs (up to 8192^3 grid points) of isotropic and stratified optical turbulence are presented and discussed.

Filterbanks for Adaptive Transmit Filtering

Abstract: The terrestrial terminals of the MUOS (Mobile User Objective System) satellite communication system transmit and receive in UHF bands near 300 MHz. These bands are used worldwide by a variety of narrowband voice and data systems. The MUOS waveform is not narrowband, however; and can interfere with these systems, possibly causing loss of critical links in host nations, including the US. UHF receivers that have the potential to experience MUOS interference are referred to as victim radios, and the MUOS system is designed to minimize the impact on victim radios by employing an adaptive notch-on-transmit filter Moreover; the MUOS terrestrial radio equipment must adaptively notch its transmit band to match high-interference subbands that are unilaterally notched at the basestation receiver. In this paper, two filterbanks are considered for use in adaptive transmit filtering in MUOS: the DFT filterbank and the modified DFT (mDFT) filterbank. The frequency resolution, achievable notch depth, computational cost, and design flexibility properties of the filterbanks are studied and compared in the context of MUOS adaptive transmit filtering.

A Fixed-point Scheme for the Numerical Construction of Magnetohydrostatic Atmospheres in Three Dimensions

Abstract: Magnetohydrostatic models of the solar atmosphere are often based on idealized analytic solutions because the underlying equations are too difficult to solve in full generality. Numerical approaches, too, are often limited in scope and have tended to focus on the two-dimensional problem. In this article we develop a numerical method for solving the nonlinear magnetohydrostatic equations in three dimensions. Our method is a fixed-point iteration scheme that extends the method of Grad and Rubin (Proc. 2nd Int. Conf. on Peaceful Uses of Atomic Energy 31, 190, 1958) to include a finite gravity force. We apply the method to a test case to demonstrate the method in general and our implementation in code in particular.