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The magnetic field intensity of most celestial bodies and regions of the universe are known; they range from 10/sup -9/ G in the intergalactic plasma to 10/sup 12/ G at the surface of neutron stars. The approach most researchers use to understand this dynamo mechanism is to consider a cosmic plasma with a stationary motion, which leads to an induction problem where the goal is to find stationary states as solutions of the induction equation. This kind of equation is easily solved via a computer. By choosing convective velocity fields, we can simulate convection cells, which in turn help us understand the behavior of the photosphere, the chromosphere, the Sun's convective zone, and laboratory plasmas. We can also investigate the not-well-understood phenomena of reconnection in this way. The PCell program helps visualize the magnetic field's evolution in different convective plasmas. We wrote the program in C (part of the program was translated from Fortran to C); it runs on Linux or Unix.

La misión CLUSTER está destinada a estudiar la magnetosfera de la Tierra y las relaciones Sol-Tierra. Los 4 satélites de esta misión vuelan en una formación de tetraedro enviando datos en los que por primera vez pueden separar efectos temporales de efectos espaciales. Esta formación nos dará un mejor entendimiento de las características macroscópicas y microscópicas en la magnetosfera y el viento solar. Como un ejemplo presentamos los datos obtenidos de la espectrometría de iones durante una tormenta magnética intensa.

XFTRISTAN es una interfaz gráfica para el programa TRISTAN, un código basado en el método PIC (particle in cell) tridimensional. Este código ha sido ampliamente usado para investigar la naturaleza cinética de los procesos de plasmas espaciales que van desde aplicaciones relacionadas con la interacción de viento solar con la tierra hasta la topología de la reconexión magnética. La primera versión del XFTRISTAN provee un camino fácil para la introducción de parámetros de entrada, visualizaciones de campos y partículas, varias herramientas de diagnóstico y generación automática de imágenes. En este artículo presentamos las ventajas y virtudes de nuestra interfaz gráfica y los primeros resultados de las simulaciones.

Short dropouts of the magnetic field intensity have been frequently observed in the solar wind on interplanetary spacecraft. But so far it could not be established whether these are caused by kinetic instabilities or whether they can be described as solitary MHD waves. The multi-satellite observations of the Cluster-mission allow for the first time to measure proton and electron distributions with a sufficient temporal and spatial resolution to tackle this question. We use measurements by the FGM magnetometer, the CIS ion spectrometer, the PEACE electron instrument and the Whisper plasma wave instrument to investigate the role of protons, heavy ions and electrons for the stability of the structures. We also use the 4-satellite observations of the Cluster magnetic field instrument to determine the proper motion of these structures relative to the solar wind. The presence of foreshock waves close to the Earth bowshock strongly limits the event selection. In the current paper we discuss a 10 s linear wave without sufficient particle data resolution and a 4 min wave for which particle distributions are available. The larger wave shows that the stability of the structure might be caused by changes in the thermal electron distributions while proton and alpha distributions are unaffected.