Chromospheric Evaporation in an M1.8 Flare Observed by the Extreme-ultraviolet Imaging Spectrometer on Hinode

TL;DR

This study reports detailed spectroscopic observations of chromospheric evaporation during an M1.8 solar flare, revealing multi-temperature plasma flows, isothermal sources, and possible reconnection-related downflows, enhancing understanding of flare dynamics.

Contribution

It provides the first comprehensive spectroscopic analysis of chromospheric evaporation in a complex flare using Hinode/EIS data, highlighting multi-temperature flow patterns and potential reconnection signatures.

Findings

150-200 km/s upflows in hot flare ions

Cooler ions show complex behavior with some upflows

Evidence of downward shock possibly related to reconnection

Abstract

We discuss observations of chromospheric evaporation for a complex flare that occurred on 9 March 2012 near 03:30 UT obtained from the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. This was a multiple event with a strong energy input that reached the M1.8 class when observed by EIS. EIS obtained a full-CCD spectrum of the flare. Chromospheric evaporation characterized by 150-200 km/s upflows was observed in multiple locations in multi-million degree spectral lines of flare ions such as Fe XXII, Fe XXIII, and Fe XXIV, with simultaneous 20-60 km/s upflows in million degree coronal lines from ions such as Fe XII - Fe XVI. The behavior of cooler, transition region ions such as O VI, Fe VIII, He II, and Fe X is more complex, but upflows were also observed in Fe VIII and Fe X lines. At a point close to strong energy input in space and time, the flare ions Fe XXII, Fe XXIII, and Fe XXIV reveal an isothermal source with a temperature close to 14 MK and no strong blueshifted components. At this location there is a strong downflow in cooler active region lines from ions such as Fe XIII and Fe XIV. We speculate that this downflow may be evidence of the downward shock produced by reconnection in the current sheet seen in MHD simulations. A sunquake also occurred near this location.