arXiv subjects

Kyungeun Choi

Publications and source records attributed to Kyungeun Choi.

2 recordsLinked to original sources

arXiv2026

Measurements on the kinetic physics in streamer dynamics

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.

astro-ph.SR↗

arXiv2026

On flying near the base of a pseudo-streamer

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.

physics.space-ph↗