Jump conditions for pressure anisotropy and comparison with the Earth's bow shock

International audienceTaking into account the pressure anisotropy in the solar wind, we study the magnetic field and plasma parameters downstream of a fast shock, as functions of upstream parameters and downstream pressure anisotropy. In our theoretical approach, we model two cases: a) the perpendicular shock and b) the oblique shock. We use two threshold conditions of plasma instabilities as additional equations to bound the range of pressure anisotropy. The criterion of the mirror instability is used for pressure anisotropy p \perp /p\parrallel > 1. Analogously, the criterion of the fire-hose instability is taken into account for pressure anisotropy p \perp /p\parrallel < 1. We found that the variations of the parallel pressure, the parallel temperature, and the tangential component of the velocity are most sensitive to the pressure anisotropy downstream of the shock. Finally, we compare our theory with plasma and magnetic field parameters measured by the WIND spacecraft

Jump conditions for pressure anisotropy and comparison with the Earth's bow shock

Taking into account the pressure anisotropy in the solar wind, we study the magnetic field and plasma parameters downstream of a fast shock, as functions of upstream parameters and downstream pressure anisotropy. In our theoretical approach, we model two cases: a) the perpendicular shock and b) the oblique shock. We use two threshold conditions of plasma instabilities as additional equations to bound the range of pressure anisotropy. The criterion of the mirror instability is used for pressure anisotropy p perp /pparrallel > 1. Analogously, the criterion of the fire-hose instability is taken into account for pressure anisotropy p perp /pparrallel < 1. We found that the variations of the parallel pressure, the parallel temperature, and the tangential component of the velocity are most sensitive to the pressure anisotropy downstream of the shock. Finally, we compare our theory with plasma and magnetic field parameters measured by the WIND spacecraft

Tenuous solar winds: Insights on solar wind-magneto sphere interactions

During solar cycle 23 quasi-dropouts of the solar wind (density < 1 cm_3) were observed. These tenuous winds allow us to probe properties of the magnetosphere and its coupling to the solar wind which would otherwise be obscured by the effect of high density. We focus on five areas which provided new insights into the response of geospace to solar wind variations: (i) the magnetospheric magnetic cofiguration; (ii) the polar rain; (iii) dayside flux erosion; (iv) magnetosheath waves; and (v) ring current constants. We find: (i) the geostationary field had dipolar strength and was inclined by £ 5°  to the dipolar direction; (ii) The solar wind strahl, and consequently the polar rain, were intensified; (iii) The depression of the geostationary field (DBGS) due to dayside flux erosion could be measured and was related to IMF BZ by DBGS = 2:8 + 2:3 Bz (nT); (iv) Right-hand electromagnetic ion cyclotron waves were excited alone in the magnetosheath and were generated directly from the temperature anisotropy of the solar wind; (v) Ring and magnetopause currents decreased to asymptotic values of 5 nT and 3 nT, respectively, which are substantially smaller than quiet-time values obtained from statistics.Fil: Farrugia, C. J.. University of New Hampshire; Estados UnidosFil: Gratton, Fausto Tulio Livio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; ArgentinaFil: Jordanova, V. K.. Laboratorio Nacional de Los Álamos; Estados UnidosFil: Matsui, H.. University of New Hampshire; Estados UnidosFil: Muehlbachler, S.. Max-Planck Institut fuer Sonnensystemforschung; AlemaniaFil: Torbert, R.. University of New Hampshire; Estados UnidosFil: Ogilvie, K.. Goddard Space Flight Center; Estados UnidosFil: Singer, H. J.. Space Weather Prediction Center; Estados Unido

Observation of energetic electrons within magnetic islands

Magnetic reconnection is the underlying process that releases impulsively an enormous amount of magnetic energy in solar flares, flares on strongly magnetized neutron stars and substorms in the Earths magnetosphere. Studies of energy release during solar flares, in particular, indicate that up to 50% of the released energy is carried by accelerated 20-100 keV suprathermal electrons. How so many electrons can gain so much energy during reconnection has been a long-standing question. A recent theoretical study suggests that volume-filling contracting magnetic islands formed during reconnection can produce a large number of energetic electrons. Here we report the first evidence of the link between energetic electrons and magnetic islands during reconnection in the Earths magnetosphere. The results indicate that energetic electron fluxes peak at sites of compressed density within islands, which imposes a new constraint on theories of electron acceleration. © 2008 Nature Publishing Group