International Space Science Institute

About: International Space Science Institute is a nonprofit organization based out in Bern, Switzerland. It is known for research contribution in the topics: Solar wind & Comet. The organization has 120 authors who have published 858 publications receiving 25772 citations. The organization is also known as: ISSI.

An ICME observed by Voyager 2 at 58 AU and by Ulysses at 5 AU

Abstract: Between days 175 and 180 (June 24 through 29) of 1999, the PLS instrument on Voyager 2 observed alpha particle enhancements with fractional percentages of alpha to proton number densities exceeding 10%. Ulysses (located at 5.3 AU) observed at least two candidate source features for these enhancements. To identify the correct source structure, a 1D MHD model was used to propagate the Ulysses plasma data to the Voyager radial position (58.2 AU). An ICME-related alpha enhancement observed by Ulysses beginning on day 331 (November 27), 1998 appears to be the correct feature. While a speed jump and cosmic ray decreases were observed by Ulysses in conjunction with this alpha enhancement, the timing of these features differed markedly at Voyager 2. The speed jump arrival-time difference is due to the faster propagation of the shock relative to the rest of the ejecta. It is unclear what mechanism is responsible for the delay in the cosmic ray decrease. Nevertheless, we have demonstrated that alpha enhancement signatures of ICMEs can be used to track these features to heliospheric distances >50 AU.

Spatially dependent heating and ionization in an icme observed by both ace and ulysses

Abstract: The 2005 January 21 interplanetary coronal mass ejection (ICME) observed by multiple spacecraft at L1 was also observed from January 21-February 4 at Ulysses (5.3 AU). Previous studies of this ICME have found evidence suggesting that the flanks of a magnetic cloud like structure associated with this ICME were observed at L1 while a more central cut through the associated magnetic cloud was observed at Ulysses. This event allows us to study spatial variation across the ICME and relate it to the eruption at the Sun. In order to examine the spatial dependence of the heating in this ICME, we present an analysis and comparison of the heavy ion composition observed during the passage of the ICME at L1 and at Ulysses. Using SWICS, we compare the heavy ion composition across the two different observation cuts through the ICME and compare it with predictions for heating during the eruption based on models of the time-dependent ionization balance throughout the event.

Models of Venus atmosphere

Abstract: In the context of an International Space Science Institute (ISSI) working group, we have conducted a project to compare the most recent General Circulation Models (GCMs) of the Venus atmospheric circulation. A common configuration has been decided, with simple physical parametrization for the solar forcing and the boundary layer scheme.

Solar wind from the coronal hole boundaries

Abstract: [1] Recent studies using in situ observations established that the interface between fast and slow wind in interplanetary space has two distinct parts: a smoothly varying boundary layer flow that flanks fast wind from coronal holes and a sharper plasma discontinuity between intermediate and slow solar wind. Other studies using in situ observations and modeling have demonstrated the existence of the sub-Parker spiral structure of the heliospheric magnetic field in which the magnetic connection between fast and slow wind created by foot point motion at the Sun deforms field lines, making them significantly less transverse than the Parker spiral. Here we model the formation of corotating interaction regions, and by including a coronal hole boundary layer (CHBL) and magnetic foot point motion across the coronal hole boundary back at the Sun we explain the detailed, characteristic variations in composition and magnetic field orientation observed in interplanetary space. Our model accomplishes this using only two free parameters, with all other quantities derived directly from solar wind observations. Through the model we trace the observed interplanetary variations back to an intrinsic two-part structure in the source of solar wind at the Sun. These parts are (1) a CHBL that encircles the coronal hole and has a smooth transition in the source properties that produce the fast through intermediate speed (∼600 km s−1) solar wind and (2) a sharp coronal hole discontinuity separating the distinct sources of solar wind with intermediate speeds and temperatures from slow solar wind. This study establishes the connection between the characteristic variations of the solar wind speed, charge state composition, and magnetic field orientation observed in situ near 5 AU with their sources in the two-part structure of coronal hole boundaries back at the Sun.

Model calculations of the planetary ion distribution in the Martian tail

Abstract: Based on a recent model of the Martian atmosphere/exosphere and a model of the magnetic field and solar wind flow around Mars, the distribution of different planetary ion species in the near tail is calculated. Three main regions are identified: 1) “clouds” of pickup ions with distinct mass separation travel along cycloidal trajectories; 2) another group of ions forms a distinct plasma mantle in the magnetosphere; 3) a third population fills up the plasma sheet. Further, the energy of ions in different locations is also analyzed. Finally, comparison of observations made onboard the Phobos-2 spacecraft shows a reasonable agreement with simulation results.