Anti-parallel EUV flows observed along active region filament threads with Hi-C

TL;DR

This study presents high-resolution observations of anti-parallel plasma flows along filament threads in the solar corona, revealing flows previously unobservable due to instrument resolution limits, and suggests such flows are common in filaments.

Contribution

First direct imaging of anti-parallel EUV flows along filament threads at high resolution, providing new insights into filament plasma dynamics.

Findings

Anti-parallel flows observed with velocities of 70-80 km/s.

Resolvable filament thread width estimated at 0.8 arcseconds.

SDO/AIA cannot detect these flows due to lower resolution.

Abstract

Plasma flows within prominences/filaments have been observed for many years and hold valuable clues concerning the mass and energy balance within these structures. Previous observations of these flows primarily come from H-alpha and cool EUV lines (e.g., 304A) where estimates of the size of the prominence threads has been limited by the resolution of the available instrumentation. Evidence of `counter-steaming' flows has previously been inferred from these cool plasma observations but now, for the first time, these flows have been directly imaged along fundamental filament threads within the million degree corona (at 193A). In this work we present observations of an active region filament observed with Hi-C that exhibits anti-parallel flows along adjacent filament threads. Complementary data from SDO/AIA and HMI are presented. The ultra-high spatial and temporal resolution of Hi-C allow the anti-parallel flow velocities to be measured (70-80 km/s) and gives an indication of the resolvable thickness of the individual strands (0.8'' +/- 0.1''). The temperature distribution of the plasma flows was estimated to be log T(K) = 5.45 +/- 0.10 using EM loci analysis. We find that SDO/AIA cannot clearly observe these anti-parallel flows nor measure their velocity or thread width due to its larger pixel size. We suggest that anti-parallel/counter-streaming flows are likely commonplace within all filaments and are currently not observed in EUV due to current instrument spatial resolution.