379 research outputs found
Validation of Community Models: 2. Development of a Baseline, Using the Wang-Sheeley-Arge Model
This paper is the second in a series providing independent validation of community models of the outer corona and inner heliosphere. Here I present a comprehensive validation of the Wang-Sheeley-Arge (WSA) model. These results will serve as a baseline against which to compare the next generation of comparable forecasting models. The WSA model is used by a number of agencies to predict Solar wind conditions at Earth up to 4 days into the future. Given its importance to both the research and forecasting communities, it is essential that its performance be measured systematically and independently. I offer just such an independent and systematic validation. I report skill scores for the model's predictions of wind speed and interplanetary magnetic field (IMF) polarity for a large set of Carrington rotations. The model was run in all its routinely used configurations. It ingests synoptic line of sight magnetograms. For this study I generated model results for monthly magnetograms from multiple observatories, spanning the Carrington rotation range from 1650 to 2074. I compare the influence of the different magnetogram sources and performance at quiet and active times. I also consider the ability of the WSA model to forecast both sharp transitions in wind speed from slow to fast wind and reversals in the polarity of the radial component of the IMF. These results will serve as a baseline against which to compare future versions of the model as well as the current and future generation of magnetohydrodynamic models under development for forecasting use
Modeling Active Region Evolution - A New LWS TR and T Strategic Capability Model Suite
In 2006 the LWS TR&T Program funded us to develop a strategic capability model of slowly evolving coronal active regions. In this poster we report on the overall design, and status of our new modeling suite. Our design features two coronal field models, a non-linear force free field model and a global 3D MHD code. The suite includes supporting tools and a user friendly GUI which will enable users to query the web for relevant magnetograms, download them, process them to synthesize a sequence of photospheric magnetograms and associated photospheric flow field which can then be applied to drive the coronal model innner boundary, run the coronal models and finally visualize the results
Modeling coronal magnetic field using spherical geometry: cases with several active regions
The magnetic fields in the solar atmosphere structure the plasma, store free
magnetic energy and produce a wide variety of active solar phenomena, like
flare and coronal mass ejections(CMEs). The distribution and strength of
magnetic fields are routinely measured in the solar surface(photosphere).
Therefore, there is considerable interest in accurately modeling the 3D
structure of the coronal magnetic field using photospheric vector magnetograms.
Knowledge of the 3D structure of magnetic field lines also help us to interpret
other coronal observations, e.g., EUV images of the radiating coronal plasma.
Nonlinear force-free field (NLFFF) models are thought to be viable tools for
those task. Usually those models use Cartesian geometry. However, the spherical
nature of the solar surface cannot be neglected when the field of view is
large. In this work, we model the coronal magnetic field above multiple active
regions using NLFFF extrapolation code using vector magnetograph data from the
Synoptic Optical Long-term Investigations of the Sun survey (SOLIS)/ Vector
Spectromagnetograph (VSM) as a boundary conditions. We compare projections of
the resulting magnetic field lines solutions with their respective coronal
EUV-images from the Atmospheric Imaging Assembly (SDO/AIA) observed on October
11, 2011 and November 13, 2012. This study has found that the NLFFF model in
spherical geometry reconstructs the magnetic configurations for several active
regions which agrees with observations. During October 11, 2011 observation,
there are substantial number of trans-equatorial loops carrying electric
current.Comment: 3 Figures, Submitted to Astrophysics and Space Science Journa
Validation of Community Models: Identifying Events in Space Weather Model Timelines
I develop and document a set of procedures which test the quality of predictions of solar wind speed and polarity of the interplanetary magnetic field (IMF) made by coupled models of the ambient solar corona and heliosphere. The Wang-Sheeley-Arge (WSA) model is used to illustrate the application of these validation procedures. I present an algorithm which detects transitions of the solar wind from slow to high speed. I also present an algorithm which processes the measured polarity of the outward directed component of the IMF. This removes high-frequency variations to expose the longer-scale changes that reflect IMF sector changes. I apply these algorithms to WSA model predictions made using a small set of photospheric synoptic magnetograms obtained by the Global Oscillation Network Group as input to the model. The results of this preliminary validation of the WSA model (version 1.6) are summarized
Electron impact polarization expected in solar EUV lines from flaring chromospheres/transition regions
We have evaluated lower bounds on the degree of impact Extreme Ultraviolet/Ultraviolet (EUV/UV) line polarization expected during solar flares. This polarization arises from collisional excitation by energetic electrons with non-Maxwellian velocity distributions. Linear polarization was observed in the S I 1437 A line by the Ultraviolet Spectrometer and Polarimeter/Solar Maximum Mission (UVSP/SMM) during a flare on 15 July 1980. An early interpretation suggested that impact excitation by electrons propagating through the steep temperature gradient of the flaring transition region/high chromosphere produced this polarization. Our calculations show that the observed polarization in this UV line cannot be due to this effect. We find instead that, in some flare models, the energetic electrons can produce an impact polarization of a few percent in EUV neutral helium lines (i.e., lambda lambda 522, 537, and 584 A)
Effects of Spatial Gradients on Electron Runaway Acceleration
The runaway process is known to accelerate electrons in many laboratory plasmas and has been suggested as an acceleration mechanism in some astrophysical plasmas, including solar flares. Current calculations of the electron velocity distributions resulting from the runaway process are greatly restricted because they impose spatial homogeneity on the distribution. We have computed runaway distributions which include consistent development of spatial gradients in the energetic tail. Our solution for the electron velocity distribution is presented as a function of distance along a finite length acceleration region, and is compared with the equivalent distribution for the infinitely long homogenous system (i.e., no spatial gradients), as considered in the existing literature. All these results are for the weak field regime. We also discuss the severe restrictiveness of this weak field assumption
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