Scale lengths in quasi-parallel shocks

Examples of an interplanetary and the bow shock illustrate the small relative size of the electrostatic layer relative to the scale of the magnetic fluctuations in quasi-parallel shocks. While both examples are supercritical, the interplanetary example is marginally so, showing a thickness in absolute and convected ion larmor radii units that is thicker (approximately 13 U/omega sub ci) than at the bow shock (approximately omega sub ci). The fluid speed changes abruptly in the quasi-parallel shock on this shorter scale. The increase in electron and ion random energies also is clearly seen on this shorter scale. In the interplanetary example the scale of the electric layer is certainly less than 1/60th that of the up or downstreams magnetic fluctuations. The thickness of the earth's bow shock deceleration layer is dramatically narrower than any domain of upstream waves as controlled by reflected, intermediate, or diffuse ions

An interplanetary shock traced by planetary auroral storms from the Sun to Saturn

A relationship between solar activity and aurorae on Earth was postulated(1,2) long before space probes directly detected plasma propagating outwards from the Sun(3). Violent solar eruption events trigger interplanetary shocks(4) that compress Earth's magnetosphere, leading to increased energetic particle precipitation into the ionosphere and subsequent auroral storms(5,6). Monitoring shocks is now part of the 'Space Weather' forecast programme aimed at predicting solar-activity-related environmental hazards. The outer planets also experience aurorae, and here we report the discovery of a strong transient polar emission on Saturn, tentatively attributed to the passage of an interplanetary shock - and ultimately to a series of solar coronal mass ejection (CME) events. We could trace the shock-triggered events from Earth, where auroral storms were recorded, to Jupiter, where the auroral activity was strongly enhanced, and to Saturn, where it activated the unusual polar source. This establishes that shocks retain their properties and their ability to trigger planetary auroral activity thoughout the Solar System. Our results also reveal differences in the planetary auroral responses on the passing shock, especially in their latitudinal and local time dependences.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62930/1/nature02986.pd

La théorie variation des rayons complexes pour le calcul des vibrations moyennes fréquences

A new approach named the "Variational Theory of Complex Rays" is introduced for computing the vibrations of elastic structures weakly damped in the medium frequency range. Emphasis has been placed here on the most fundamental aspects. The effective quantities (elastic energy, vibration intensity ...) are evaluated after computing a small system of equations which does not derive from a finite element dicretization of the structure. Numerical examples related to plates show the interest and the possibilities ofthe VTRC