On flying near the base of a pseudo-streamer

TL;DR

This study reports the first observation of a large electric field in the plasma rest frame near the base of a pseudo-streamer, revealing complex plasma dynamics and turbulence during a Parker Solar Probe encounter.

Contribution

It provides new insights into electric fields and plasma behavior near pseudo-streamers, highlighting the importance of pressure gradients and turbulence in the region.

Findings

Detected a large electric field of up to 400 mV/m in the plasma frame.

Observed significant plasma turbulence with density fluctuations up to 0.3.

Identified the role of pressure gradients and turbulence in the electric field dynamics.

Abstract

Near the 10 solar radius perihelion of Parker Solar Probe encounter 24, a confined region containing an enhanced plasma density (25,000 per cubic centimeter) and broadband electrostatic waves was encountered. The solar wind velocity (200 kilometers per second) and ion temperature (25 electron Volts) were significantly reduced as compared to their values in the ambient solar wind. Because the polarity of the radial magnetic field did not change sign on the two sides of the crossing and the crossed region contained a double-peaked plasma structure, the spacecraft must have passed near the base of a pseudo-streamer. In the plasma frame, an electric field as large as 400 millivolts per meter was detected during the crossing. This field is not associated with an ExB drift because it is observed in the plasma rest frame. Instead, it is balanced by the Generalized Ohm's Law terms whose current dependent term associated with this electric field was less than 1 milliampere per square meter, corresponding to a drift velocity less than 2.5 kilometers per second. The region also contained a turbulent plasma with density fluctuations as large as 0.3, suggesting that the resistive term in the Generalized Ohm's Law could be significant. In addition, both the density and electric field had non-zero slopes as functions of time, suggesting that the pressure gradient term in the Generalized Ohm's Law also mattered. This large electric field in the plasma rest frame may be the first and largest such field ever reported.