Measurements on the kinetic physics in streamer dynamics

Abstract

A major goal of solar physics is understanding the transition of the medium from the closed-loop magnetic configuration of the corona to the open structure of the heliospheric current sheet. The evolution of solar wind streamers, an essential component of this transition, has been observed in-situ for the first time by measuring a pass through a streamer stalk at 11.7 solar radii. A plasma rest frame DC electric field, reaching an amplitude of 400 mV/m, was observed as the magnetic field changed from +1100 nT to -1100 nT. This electric field violates the frozen in condition so it must be understood via the non-MHD Hall term of the Generalized Ohm's Law. Two plasma regimes containing the large electric field were observed. In the first regime, the magnetic field was large, the ion beta was small (~0.1), the ratio of the ion skin depth to ion gyroradius was large (>10), and the current of ~0.3 mA/m2 was carried by electrons. In the second regime, the magnetic field was small, the ion beta was large (~10), the ion skin depth was equal to the ion gyroradius, and the ~10 mA/m2 current was carried by the ions. Also, measurements during 15 such crossings showed that the plasma flow speed inside the current sheets exceeded that outside six times and the 326 km/sec average speed inside the current sheets exceeded the 266 km/sec outside. Such findings challenge the traditional consensus that streamers are the source of the "slow" solar wind.