3D nonlinear wave heating of coronal loops

The heating of solar coronal loops by the resonant absorption or phase-mixing of incident wave energy is investigated in the framework of 3D nonlinear magnetohydrodynamics (MHD) by means of numerical simulations.     

Dynamics of Coronal Loop Oscillations Recent Improvements and Computational Aspects

We will discuss the observed, heavily damped transversal oscillations of coronal loops. These oscillations are often modeled as transversal kink oscillations in a cylinder. Several features are added to the classical cylindrical model. In our models we include loop curvature, longitudinal density stratification, and highly inhomogeneous radial density profiles. In this paper, we will first give an overview of recently obtained results, both analytically and numerically. After that, we shed a light on the computational aspects of the modeling process. In particular, we will focus on the parallellization of the numerical codes.     

Velocity Shear Induced Phenomena in Solar Atmosphere

We present a brief overview of the probable velocity-shear induced phenomena in solar plasma flows. Shear-driven MHD wave oscillations may be the needed mechanism for the generation of solar Alfvén waves, for the transmission of fast waves through the transition region, and for the acceleration of the solar wind. This revised version was published online in June 2006 with corrections to the Cover Date.     

A polytropic model for the solar wind

The solar wind fills the heliosphere and is the background medium in which coronal mass ejections propagate. A realistic modelling of the solar wind is therefore essential for space weather research and for reliable predictions. Although the solar wind is highly anisotropic, magnetohydrodynamic (MHD) models are able to reproduce the global, average solar wind characteristics rather well. The modern computer power makes it possible to perform full three dimensional (3D) simulations in domains extending beyond the Earth’s orbit, to include observationally driven boundary conditions, and to implement even more realistic physics in the equations. In general, MHD models for the solar wind often make use of additional source and sink terms in order to mimic the observed solar wind parameters and/or they hide the not-explicitly modelled physical processes in a reduced or variable adiabatic index. Even the models that try to take as much as possible physics into account, still need additional source terms and fine tuning of the parameters in order to produce realistic results. In this paper we present a new and simple polytropic model for the solar wind, incorporating data from the ACE spacecraft to set the model parameters. This approach allows to reproduce the different types of solar wind, where the simulated plasma variables are in good correspondence with the observed solar wind plasma near 1 AU.     

Why should the latitude of the observer be considered when modeling gradual proton events? An insight using the concept of cobpoint

The shape of flux profiles of gradual solar energetic particle (SEP) events depends on several not well-understood factors, such as the strength of the associated shock, the relative position of the observer in space with respect to the traveling shock, the existence of a background seed particle population, the interplanetary conditions for particle transport, as well as the particle energy. Here, we focus on two of these factors: the influence of the shock strength and the relative position of the observer. We performed a 3D simulation of the propagation of a coronal/interplanetary CME-driven shock in the framework of ideal MHD modeling. We analyze the passage of this shock by nine spacecraft located at ∼0.4 AU (Mercury’s orbit) and at different longitudes and latitudes. We study the evolution of the plasma conditions in the shock front region magnetically connected to each spacecraft, that is the region of the shock front scanned by the “cobpoint” (Heras et al., 1995), as the shock propagates away from the Sun. Particularly, we discuss the influence of the latitude of the observer on the injection rate of shock-accelerated particles and, hence, on the resulting proton flux profiles to be detected by each spacecraft.     

Modelling of Solar Wind, CME Initiation and CME Propagation

Simulations of coronal mass ejections (CMEs) evolving in the interplanetary (IP) space from the Sun up to 1 AU are performed in the framework of ideal magnetohydrodynamics (MHD) by the means of a finite-volume, explicit solver. The aim is to quantify the effect of the background solar wind and of the CME initiation parameters, such as the initial magnetic polarity, on the evolution and on the geo-effectiveness of CMEs. First, three different solar wind models are reconstructed using the same numerical grid and the same numerical scheme. Then, different CME initiation models are considered: Magnetic foot point shearing and magnetic flux emergence. For the fast CME evolution studies, a very simple CME model is considered: A high-density and high-pressure magnetized plasma blob is superposed on a background steady state solar wind model with an initial velocity and launch direction. The simulations show that the initial magnetic polarity substantially affects the IP evolution of the CMEs influencing the propagation velocity, the shape, the trajectory (and thus, the geo-effectiveness).     

A Survey of Field-Aligned Mach Number and Plasma Beta in the Solar Wind

We have surveyed solar wind plasma beta and field-aligned Alfvénic Mach number using Ulysses and Wind data. We show the characteristic timescale and occurrence frequency of ‘magnetically dominated’ solar wind, whose interaction with a planetary magnetosphere may produce a bow shock with multiple shock fronts. We discuss radial, latitudinal, and solar cycle effects. This revised version was published online in August 2006 with corrections to the Cover Date.