PROJECT TITLE

Effects of the heliosphere breathing due to solar cycle variations as seen in the backscattered solar Lyman-alpha radiation collected by SOHO/SWAN, HST, Voyager 1, Cassini and Galileo spacecraft over the solar cycle

TEAM MEMBERS

(team coordinator) Vlad Izmodenov, Lomonosov Moscow State University, School of Mechanics and Mathematics, Vorobievy Gory, Moscow 119899, Russia; e-mail: izmod@iki.rssi.ru

Eric Quémerais, Service d'Aéronomie du CNRS, BP3, 91371 Verrières le Buisson France (tel) INT+33 1 64 47 43 14 e-mail:eric.Quémerais@aerov.jussieu.fr

Wayne Pryor, Central Arizona College, 8470 N. Overfield Rd., Coolidge, AZ 85228 United States ;wyane_pryor@centalaz.edu

Maciej Bzowski, Space Research Centre PAS, Bartycka 18A, 00-716 Warsaw, Poland; tel (+48-22) 8403 766 ext 308; fax: (+48-22) 8403-131; e-mail: bzowski@cbk.waw.pl

Dimitra Koutroumpa, Service d'Aéronomie du CNRS, BP3, 91371 Verrières le Buisson France (tel) INT+33 1 64 47 43 05 e-mail:dimitra.koutroumpa@aerov.jussieu.fr

Dmitry Alexashov, Institute for Problems in Mechanics, Russian Academy of Sciences, prospekt Vernadskogo 101-1, Moscow 117526, Russia; e-mail: alexash@ipmnet.ru

Abstract

The interplanetary background radiation has been used to study the interplanetary hydrogen distribution since its discovery in the late 1960’s (Thomas and Krassa 1970; Bertaux and Blamont 1970). However, detailed study of interstellar hydrogen distribution in the interplanetary space became possible only very recently due to measurements made simultaneously by several spacecraft (Voyager 1 and 2, SOHO, HST, Ulysses, Galileo and Cassini) and to tremendous achievements in detailed 3D and time dependent modeling of the interstellar atoms in the heliosphere. The SWAN instrument on board of SOHO spacecraft (Bertaux et al., 1995) is able to study the profiles of backscattered Lyman-alpha radiation by using hydrogen absorption cells. The Lyman-alpha profiles were obtained also by the Hubble Space Telescope. The major importance of the profile measurements is that it makes possible to study the velocity distribution function of the interplanetary hydrogen that provides key information on the level of distortion of the hydrogen in the interface region and, therefore, on the properties of the heliospheric interface. Solar-cycle variations of the profiles of backscattered Lyman-alpha measured by SOHO were analyzed recently by Quémerais et al. (A&A, 2006, in press) who showed that the effective line-of-sight velocities and temperatures of interstellar H atoms are changing with time. The changes cannot be explained only by changing the ionization rate in the vicinity of Sun and the radiation pressure. It is required to include the heliospheric interface effects. More particularly, the measured profiles can only be explained by presence of two populations of interstellar H atoms entering into heliosphere through the heliospheric interface. It becomes also more apparent that time-dependent models are also needed to understand radial dependence of the Lyman-alpha intensities as measured by the Voyagers and Pioneer 10 spacecraft.

In the proposed team-project we will explore the effects of the heliosphere breathing due to the solar cycle variations by analyzing backscattered solar Lyman-alpha radiation collected by SOHO/SWAN, Voyager 1, HST, Galileo and Cassini spacecraft over the solar cycle. The analysis will be performed by using state-of-the-art kinetic models of interstellar H atom distributions. The small team proposed for this ISSI-team project includes six scientists whose combined expertise will be sufficient to achieve the main goals of the proposed project. Eric Quémerais and Dimitra Koutroumpa are working on analyses of SOHO/SWAN, HST, and Voyager data. E. Quémerais is also an expert in the radiative transfer modeling that is crucially important to correct interpretation of the data. Wayne Pryor is working on interpretation of the Galileo and Cassini Ly-alpha measurements. Vlad Izmodenov and Dmitry Alexashov are working on the global modeling of the heliospheric interface structure. V. Izmodenov will also serve as a team-coordinator. Maciej Bzowski is known for his 3D time-dependent models of the interstellar H atom distributions in the inner heliosphere that are complimentary to the global heliospheric interface models, and on the heliospheric 3D, time dependent ionization field.

Link to the project Web-page: http://gasdyn-ipm.ipmnet.ru/~ izmod/ISSI/index.html