Measurements on the Kinetic Origin of Streamer Dynamics

A fundamental problem of solar physics is understanding the plasma, fields and currents during their transitions with altitude from the closed-loop magnetic environment of the corona to the open structure of the heliospheric current sheet (HCS). While the large-scale dynamics occur in the MHD regime, the coronal physics must involve non-MHD processes that are unobserved in-situ until now. To attack this problem, a perihelion pass through a streamer stalk at 11.7 solar radii has been measured. DC electric fields in the plasma rest frame, reaching magnitudes of 400 mV/m, were observed. They do not result in an ExB drift because that component of the electric field was removed in transforming the data from the spacecraft frame to the plasma rest frame. Instead, these fields are a violation of the frozen-in condition and must be interpreted with the Generalized Ohm’s Law. The most important term in this law depended on the ratio of the ion skin depth to the ion gyroradius. When it was ~ 10, the η J term dominated because of turbulence. When it approached one, J×B /ne, dominated to produce a largely meridional ~ 5 mA/m ² current that supported the forming HCS. In addition, measurements on 15 such crossings showed that the plasma flow speeds inside the current sheets exceeded those outside six times, and the 326 km/sec average speed inside the current sheets exceeded the average speed of 266 km/sec outside the region. Such findings challenge the traditional consensus that streamers are the source of the "slow" solar wind.