Observatoire de Paris Institut national de recherche scientifique français Univerité Pierre et Marie Curie Université Paris Diderot - Paris 7

Kinetics of solar wind expansion : simulations and observations

jeudi 23 octobre 2008, par Lorenzo Matteini (LESIA, Observatoire de Paris)

Mardi 28 octobre 2008 à 11h00 , Lieu : salle de conférence du bât. 17

Kinetic physics plays an important role in many space plasmas and the study of microsopic scales is often necessary to correctly understand the macrosopic dynamics of a system. In situ observations of the solar wind plasma show that particle velocity distribution functions are not Maxwellian and depart from the thermodynamical equilibrium. Proton distributions are characterized by the presence of a velocity beam and a temperature anisotropy with respect the ambient magnetic field ; these properties suggest that kinetic processes take place along the solar wind expansion. I will discuss the role of wave-particle and wave-wave interactions in the evolution of the solar wind protons : the effetcs of plasma kinetic instabilities, cyclotron heating and non-linear particle trapping are investigated using a hybrid numerical code which includes the effects of the expansion on the plasma. Simulation results are compared with direct observations of Helios and Ulysses spacecrafts in the distance range 0.3-2.5 AU, providing in reasonable agreement with solar wind data.

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