Entity

Time filter

Source Type


Lundin R.,Swedish Institute of Space Physics
Space Science Reviews | Year: 2011

Solar wind forcing of Mars and Venus results in outflow and escape of ionospheric ions. Observations show that the replenishment of ionospheric ions starts in the dayside at low altitudes (≈300-800 km), ions moving at a low velocity (5-10 km/s) in the direction of the external/ magnetosheath flow. At high altitudes, in the inner magnetosheath and in the central tail, ions may be accelerated up to keV energies. However, the dominating energization and outflow process, applicable for the inner magnetosphere of Mars and Venus, leads to outflow at energies ≈5-20 eV. The aim of this overview is to analyze ion acceleration processes associated with the outflow and escape of ionospheric ions from Mars and Venus. Qualitatively, ion acceleration may be divided in two categories: (a) Modest ion acceleration, leading to bulk outflow and/or return flow (circulation). (b) Acceleration to well over escape velocity, up into the keV range. In the first category we find a processes denoted "planetary wind", the result of e.g. ambipolar diffusion, wave enhanced planetary wind, and mass-loaded ion pickup. In the second category we find ion pickup, current sheet acceleration, wave acceleration, and parallel electric fields, the latter above Martian crustal magnetic field regions. Both categories involve mass loading. Highly mass-loaded ion energization may lead to a low-velocity bulk flow-A consequence of energy and momentum conservation. It is therefore not self-evident what group, or what processes are connected with the low-energy outflow of ionospheric ions from Mars. Experimental and theoretical findings on ionospheric ion acceleration and outflow from Mars and Venus are discussed in this report. © 2011 Springer Science+Business Media B.V. Source


Graham D.B.,Swedish Institute of Space Physics | Graham D.B.,University of Sydney | Cairns I.H.,University of Sydney
Physical Review Letters | Year: 2013

Localized Langmuir waves are commonly observed in space plasmas and are a potential source of radio waves. Using electric field data from STEREO, it is shown that these localized Langmuir waves are eigenmodes of density wells estimated independently. An analytic model is developed for the eigenmode frequencies. The inferred depths and widths of the density wells typically only allow the zeroth-order Langmuir eigenmode to form, explaining the preponderance of single-peaked waveforms. More complicated waveforms are shown to be consistent with single eigenmode solutions of more complicated density profiles. The inferred depth of the density well increases with Langmuir wave intensity, consistent with the ponderomotive force but not wave packet collapse. © 2013 American Physical Society. Source


Nordblad E.,Swedish Institute of Space Physics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

By applying geometrical optics (GO) to each plane-wave component of a nonparaxial electromagnetic (em) Bessel beam carrying spin and orbital angular momentum (SAM and OAM), we calculate the shift of the beam centroid during propagation in a weakly inhomogeneous, isotropic medium. Apart from recovering the transverse spin and orbital Hall shifts expected from paraxial theory, the nonparaxial treatment reveals additional shifts in both the transverse and lateral directions. When the propagation is close to perpendicular to the refractive index gradient, these shifts should be significant also for nearly paraxial beams. Suggestions are given for an experimental verification of the results. © 2012 American Physical Society. Source


Wintoft P.,Swedish Institute of Space Physics
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2011

The sunspot number (SSN), 10.7cm radio flux (F 10.7), MgII index, and SOHO/SEM EUV flux have been studied, using wavelet analysis, in order to describe how the first three parameters are related to EUV on scales of days to years. The wavelet transform decomposes the time series into series which captures variability on different temporal scales. The three proxies show weak correlation on time scales of days, thus they are of limited use in space weather when the day-to-day variability is considered. However, the underlying modulation due to the solar rotation and the solar activity cycle is so strong that there is a big influence on the daily values. Both F 10.7 and MgII show a more persistent increase in correlation with scale than SSN and should be the preferred proxies. When a linear regression model is used for SEM/EUV the RMS error is about 26%lower, for the analysed period (1996-2010), for MgII compared to F 10.7. However, when only the long term is considered (scale -1.4yr) the RMS error is 20%larger when MgII is used compared to F 10.7. This is caused by an offset between MgII and SEM that appears around the cycle 23 maximum. This offset is not seen between F 10.7 and SEM. For space weather purposes, although none of the studied proxies works on a daily basis, the MgII index performs the best, but for the longer time scales F 10.7 is the most suitable. © 2011 Elsevier Ltd. Source


Fu H.S.,Swedish Institute of Space Physics | Fu H.S.,Beihang University | Khotyaintsev Y.V.,Swedish Institute of Space Physics | Vaivads A.,Swedish Institute of Space Physics | And 2 more authors.
Nature Physics | Year: 2013

The mechanism that produces energetic electrons during magnetic reconnection is poorly understood. This is a fundamental process responsible for stellar flares, substorms, and disruptions in fusion experiments. Observations in the solar chromosphere an. The Earth's magnetosphere indicate significant electron acceleration during reconnection, whereas in the solar wind, energetic electrons are absent. Here we show that energetic electron acceleration is caused by unsteady reconnection. I. The Earth's magnetosphere an. The solar chromosphere, reconnection is unsteady, so energetic electrons are produced; in the solar wind, reconnection is steady, so energetic electrons are absent. The acceleration mechanism is quasi-adiabatic: betatron and Fermi acceleration in outflow jets are two processes contributing to electron energization during unsteady reconnection. The localized betatron acceleration in the outflow is responsible for at least half of the energy gain fo. The peak observed fluxes. © 2013 Macmillan Publishers Limited. All rights reserved. Source

Discover hidden collaborations