Anisotropic Turbulence in the Earth's Magnetosheath 
Sunday, 11 February 2018 12:54 
Turbulence is a complex phenomenon with driving mechanisms still not clearly understood in contemporary science. Turbulence naturally appears in astrophysical plasmas, including the solar wind at planetary and interstellar shocks. The shocks in astrophysical plasmas are usually collisionless due to a very low density of the medium and therefore they differ from those observed in ordinary fluids, because they often result from interaction of nonlinear structures. Therefore, investigating the collisionless shocks, and, in fact, weakly collisional plasma is difficult in laboratory conditions. With the plethora of past and currently operating space missions, the solar wind appears as a natural laboratory for investigating these phenomena. Based on plasma measurements from several space probes within the THEMIS mission, W.M. Macek and A. Wawrzaszek, in collaboration with researchers from other Polish and US institutions, showed that the plasma dynamics within the magnetosheath (i.e., behind the Earth's bow shock, when looking from the Sun) is intermittent, and turbulence is strongly anisotropic. In particular, for very strong shock waves (i.e., for flow speeds much larger than the Alfvén speed, which is the speed of sound in a magnetized medium) the fluctuations of plasma parameters in the direction perpendicular to the local ambient magnetic field strongly differ from the normal probability distribution. However, for the direction parallel to the local magnetic field, the plasma is close to equilibrium, with a normal statistics. These results, published in Macek et al., Astrophysical Journal Letters 851:L42,2017, are potentially important for the development of theory of turbulence.

Last Updated on Wednesday, 14 February 2018 13:01 