Objectives

PNST (Programme National Soleil-Terre) is dedicated to analysis of the Sun-Earth system, from generation of the solar magnetic field, flares and coronal mass ejections, until impact on the terrestrial magnetosphere, ionosphere and thermosphere. PNST is operating since 1998. It has been renewed every four years since then. It results from merging of GdRs "Plasmae" and "Solar and Stellar Magnetodynamics" (about 240 researchers). PNST is supported by INSU CNRS, as well as by CNES (France space agency) for activities related to space missions (SOHO, WIND, CLUSTER...).

The main objective of PNST is to coordinate and stimulate research activities of groups working on the Earth's ionized environment and on the Sun's atmosphere. Focus is placed on :

• Analysis of solar magnetism and its effects on the heliosphere, from lower Sun's atmosphere until interplanetary medium : generation of magnetic field, explosive instabilities and dissipation, particle acceleration.
• Analysis of coronal structuring and heating by the magnetic field, as well as coupling between corona and the heliosphere.
• Analysis of the solar wind formation and transport.
• Analysis of solar wind structuring by the interplanetary magnetic field.
• Analysis of energetic particle acceleration and propagation within the heliosphere, as well as related radio emissions.
• Analysis of the interaction of the solar wind with the terrestrial environment, in particular bow shock and boundary layers.
• Analysis of the magnetosphere dynamics, in particular storms and substorms.
• Analysis of the magnetosphere-ionosphere coupling, in particular energy deposition at high latitudes, electron acceleration and wave generation in the auroral zone.
• Analysis of the large-scale circulation of solar wind and ionosphere originating plasmas.
• Coordinated studies of the Sun-Earth connection with applications to space weather.

Physical processes of interest here are those of plasma physics, be it for large scale plasma convection (often treated using an MHD approach) or for small scale phenomena such as magnetic reconnection or charged particle acceleration. Plasmas evolve from collisional state in the lower layers of the solar atmosphere to collisionless in the solar corona, in the solar wind, or in the magnetosphere. In situ measurements and results obtained within PNST field of research are useful for inaccessible astrophysical environments where similar processes are at work. Measurements are collected from a variety of spaceborne and ground-based instruments (radars, spectrometry, spectro-polarimetry, imaging...). These studies also involve a variety of modeling efforts and simulations (MHD, kinetic, hybrid) as well as theroetical works, e.g., on dissipation processes and turbulence.

PNST is connected with PNPS (Programme National de Physique Stellaire) for studies dedicated to solar and stellar magnetism. Indeed, the Sun is not the only magnetized star and polarimetry measurements provided direct evidences of a magnetic field on both cold stars (with surface convection only) and hot stars (fully convective). Studies of the solar magnetism and its effect on atmosphere structuring thus provide information for other Sun-like stars. PNST also is connected with PNP (Programme National de Planétologie) for studies dedicated to interaction of the solar wind with planetary magnetospheres. Finally, the impact of solar activity and irradiance on the near-Earth environment and the neutral atmosphere links PNST activities to those of Programme National de Chimie Atmosphérique (PNCA) et Programme National d'Etude de la Dynamique du Climat (PNEDC).