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Accueil > Recherche > Plasmas Spatiaux > Thématiques scientifiques > Space Weather

Space Weather

The space weather is a recent discipline that focuses on the impact of solar activity on our terrestrial environment. The site of « Space Situational Awareness » of the European Space Agnecy (ESA) gives the following definition : “Space weather refers to the environmental conditions in Earth’s magnetosphere, ionosphere and thermosphere due to the Sun and the solar wind that can influence the functioning and reliability of spaceborne and ground-based systems and services or endanger property or human health.”

  LPP team :

C. Amory-Mazaudier, N. Cornilleau-Wehrlin, D. Fontaine

 some significant publications :

  Solar activity and Sun-Earth relationships :

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Figure 1.
CME - Une grande éjection de masse coronale envoie un nuage de particules dans l’espace le 2 Décembre 2003. Image composite du Soleil où l’on peut voir une image obtenue par EIT superposée à une image obtenue par le coronographe LASCO C2 (avec un disque occulteur rouge), ce qui permet d’observer les détails de la couronne.
Source : site de SOHO

Sun continuously emits radiation over a wide range of wavelengths, from X and gamma rays (respectively less than 1 nm and 1 micron) to radio waves (m, km) with a power peak at the level of visible and near infrared radiations (around micro m). A part of the radiation, particularly UV, is absorbed by the atmosphere and contributes to excite, dissociate and ionize atmospheric atomic and molecular components. In the upper layers of the atmosphere, typically in the thermosphere above 100 km altitude, a region is created that comprises ionized particles in addition to neutral components : it is the ionosphere. In contrast to the inert atmosphere, the ionospheric layer is conductive and thus allows circulation of electric fields and currents.

The sun also emits continuously charged particles, mainly electrons and protons at temperatures of the order of 10 eV, which propagate at supersonic speeds ( 400 m / s) throughout the solar system : it is the solar wind. It does not directly collide with the surface if these objects have an atmosphere (Mars, Venus) and / or a magnetic field (Earth, giant magnetized planets), the thermal and/or magnetic pressure of which is able to balance the solar wind pressure. Their interaction with the solar wind is then responsible for the formation of a shock wave upstream of the planetary obstacle, which helps to slow the solar wind downstream at subsonic speeds and flow around the obstacle. It creates and a global cavity, or magnetosphere, around the planet. The magnetospheric environment is separated from the interplanetary medium by a boundary, the magnetopause, relatively well sealed.

Moreover, the Sun, sporadically, emits energetic protons and ions at energies of the order of tens to hundreds of MeV. These emissions, called solar flares and coronal mass ejections, can reach the Earth’s environment. Solar activity has an eleven years cycle ( last minimum around 2008-2010, last maximum around 2012-2014).

 Space weather

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Figure 2. Effets de la météorologie de l’espace sur l’activité humaine
Source L.J. Lanzerotti, Bell Laboratories

The arrival to the Earth of electromagnetic emissions and solar particles that result from solar activity, in turn the various components of the Earth’s environment are affected, each one differently. Electromagnetic radiations travel at the speed of light and reach the Earth’s environment within 8 minutes after being emitted. The UV radiation, highly variable, acts in particular on heating and ionization of the upper terrestrial atmosphere, the concentration, composition and heating of the ionosphere. These could affect the positioning of the low-altitude satellites, the communications with satellites and in particular GPS communications,...

Solar energetic particles take between ten minutes and a few hours for getting to the terrestrial environment. While they don’t change really the environment itself, they have a significant impact on the electronics of satellites or aircraft flying in polar areas.

Reconfiguration of the magnetic field in the magnetosphere, induced by strong variations in solar wind pressure and/or by coronal mass ejections arrival, can lead to various physical phenomena in the magnetosphere as for example polar auroras. See the sections about it : Acceleration, radiation and turbulence in terrestrial polar regions and magnetospheric substorms. The idea that solar eruptions release plasma clouds which then propagate in the interplanetary medium was proposed by Sidney Chapman in 1929. These structures are called coronal mass ejections. Magnetic clouds are a special case, they are characterized by a well defined magnetic structure. At the Earth, about one third of the observed coronal mass ejections are magnetic clouds, which play a central role in solar-terrestrial relationship, especially because they are the source of the most intense geomagnetic storms. The study of their interaction with the Earth’s environment is also of major interest because it raises more fundamental questions, such as how does the coupling between the solar wind and the magnetosphere work.

The system ionosphere - magnetosphere being strongly coupled via the highly conductive magnetic field lines, magnetospheric disturbances affect the ionosphere and vice versa. Several hours are needed to build up a new circulation of particles and currents in this coupled system. The flow of currents in the ionosphere can become very intense due to solar events and affect communications with law orbiting satellites mainly in the high latitudes (auroral), GPS positioning ... In extreme cases, it generates induced currents inside Earth (telluric currents) that can affect ground facilities as the "pipelines" or high voltage power lines and cause massive power lines outages as happened in Quebec in 1989.

 Questions studied at LPP

- * Study of solar eruptions géoeffectivity, especially of coronal mass ejections (CME). The goal is to analyze the impact of CMEs on the terrestrial environment, based on a set of measures, spaceborn and ground based, all along the Sun-Earth system : the Sun, interplanetary medium (the Lagrange point L1 , about 235 earth radii towards the sun), magnetosheath (especially the role of the orientation of the magnetic field during the passage of a magnetic cloud), Magnetosphere, Ionosphere, Thermosphere.
- * Study of solar events impacts on the ionosphere of middle and low latitudes and more particularly on their effect on GNSS signals (GPS, GLONASS, GALLILEO etc ...) and Earth’s magnetic field .

The forthcoming arrival of the Solar Orbiter. satellite, the team being involved in its instrumentation, complemented by the data of Earth orbit satellites already in operation as MMS, Cluster, THEMIS to which members of the team are also associated, will allow to couple the study solar emissions, with those of the solar wind and the effects on the magnetosphere, with more points of measurements and an instrumentation having a much better temporal resolution than previous studies.

 Links :

  • French data bases :

MEDOC
BASS2000
CDPP


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Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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Directeur de la publication : Pascal Chabert (Directeur)