Project in operation

  • Scientific leads: J.-A. Sauvaud and B. Lavraud
  • Technical leads: C. Aoustin, A. Fedorov
  • Other involved scientists: A. Opitz, B. Lavraud, P. Louarn, J. Dandouras, C. Jacquey, V. Génot, G. Fruit

Scientific objectives:

  • Soleil_stereo_large
    Mission: The STEREO mission is designed to study solar phenomena, their interplanetary counterparts and their impact on Earth’s environment in an original fashion. It consists of two satellites, one preceding and the other trailing the Earth on its orbit around the Sun. The spacecraft gradually drift away so as to observe the Sun stereoscopically from two vantage points with varying separation. These solar image data are combined to in situ observations and other terrestrial observatories for detailed studies of solar – terrestrial relationships.
  • IRAP Instruments :The two « Solar Wind Electron Analyzers » (SWEA; one by spacecraft), which were produced at CESR, measure the electron distribution functions of the solar wind core and halo, from 1 to 2000 eV with high energy and angular resolutions. The instruments are part of the STEREO/IMPACT instrument suite, under the responsibility of the Space Sciences Laboratory in Berkeley (USA).
  • Launch: The NASA STEREO Mission was successfully launched on October 25, 2006.

Dedicated Websites :

STEREO : first mission to track solar disturbances from the Sun to the Earth

The Solar Terrestrial Relations Observatory (STEREO) NASA mission consists of two spacecraft that slowly drift ahead (ST-A) and behind (ST-B) the Earth on similar orbits around the Sun. STEREO is the first mission to provide a complete set of both in situ and imaging instruments to study solar phenomena from two vantage points (Figure 1).


Fig. 1 : Positions des satellites ST-A et B en Novembre 2007 par rapport au Soleil, la Terre et le satellite ACE (au point de Lagrange L1). Les champs de vue des imageurs HI sont illustrés pour chaque satellite. Notez que les champs de vue de ST-B sont particulièrement adaptés au suivi des perturbations depuis le Soleil jusqu’à la Terre et ST-A

The STEREO Heliospheric Imagers (HI) from the SECCHI instrument package (PI: R. Howard, NASA) permit to track solar disturbances in the inner heliosphere using white light difference imaging techniques. These instruments measure the electron density variations (from Thomson scattering) from the solar corona up to Earth’s orbit. Each spacecraft also comprises a set of in situ plasma instruments, including the IMPACT suite (PI: J. Luhmann, UC Berkeley). This suite comprises the Solar Wind Electron Analyzers (SWEA) that have been designed and built at CESR (under responsibility of J.-A. Sauvaud, CESR). These are dedicated to the in situ detection of the interplanetary counterpart of solar disturbances.


Figure 2: Images HI provenant de ST-B et A au moment de l’impact d’une perturbation solaire au niveau de la Terre et ST-A. Les panneaux du bas montrent les observations in situ à la Terre (de haut en bas : la densité du plasma, l’intensité, l’azimut et la latitude du vecteur champ magnétique, et la vitesse du plasma).

Using combined data from imaging and in situ instruments, it has for the first time been possible to track solar disturbances all the way from the Sun to Earth. In the case shown in Figure 2 a solar coronal mass ejection could be ideally tracked in ST-B images. At the time shown in Figure 2, the disturbance has already propagated a significant distance and is just about to hit Earth (e.g., ACE spacecraft) and the ST-A spacecraft. In the lower panels of Figure 2, the in situ measurements at Earth show that the solar disturbance indeed impacted Earth at the time predicted from HI images, and that the disturbance was embedded in a structure with enhanced density at both its leading and trailing edges. Such unprecedented capability to track solar disturbances all the way from the Sun to the Earth allows space physicists to perform both fundamental science studies (e.g., propagation and in situ interaction of disturbances) and real-time monitoring of space weather at Earth.

IRAP Contacts (alphabetical order):

Benoit Lavraud, Philippe Louarn, Andrea Opitz, Alexis Rouillard, Jean-André Sauvaud.

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