# Spectroscopy and Differential Emission Measure diagnostics of a coronal dimming associated with a fast halo CME

## TL;DR

This study combines spectroscopy and DEM analysis to investigate the plasma dynamics, density changes, and mass loss during a coronal dimming event associated with a fast halo CME, revealing significant plasma outflows and mass transfer processes.

## Contribution

It provides detailed spectroscopic and DEM diagnostics of coronal dimming, highlighting the plasma outflows and density evolution linked to a fast CME, which were not previously characterized in such detail.

## Key findings

- Double component spectra indicate superposition of stationary and fast up-flowing plasma.
- Impulsive density reductions of 40-50% occur within 10 minutes and last for hours.
- Mass loss rate matches the CME mass increase rate, suggesting plasma flows from below.

## Abstract

We study the coronal dimming caused by the fast halo CME (deprojected speed v =1250 km s $^{-1})$ associated with the C3.7 two-ribbon flare on 2012 September 27, using Hinode/EIS spectroscopy and SDO/AIA Differential Emission Measure (DEM) analysis. The event reveals bipolar core dimmings encompassed by hook-shaped flare ribbons located at the ends of the flare-related polarity inversion line, and marking the footpoints of the erupting filament. In coronal emission lines of $\log T \, [{\rm K}] = 5.8-6.3$, distinct double component spectra indicative of the superposition of a stationary and a fast up-flowing plasma component with velocities up to 130 km s$^{-1}$ are observed at regions, which were mapped by the scanning EIS slit close in time of their impulsive dimming onset. The outflowing plasma component is found to be of the same order and even dominant over the stationary one, with electron densities in the upflowing component of $2\times 10^{9}$cm$^{-3}$ at $\log T \, [{\rm K}] = 6.2$. The density evolution in core dimming regions derived from SDO/AIA DEM analysis reveals impulsive reductions by $40 - 50\%$ within $\lesssim$10 min, and remains at these reduced levels for hours. The mass loss rate derived from the EIS spectroscopy in the dimming regions is of the same order than the mass increase rate observed in the associated white light CME ($1 \times 10^{12} {\rm \; g \; s}^{-1}$), indicative that the CME mass increase in the coronagraphic field-of-view results from plasma flows from below and not from material piled-up ahead of the outward moving and expanding CME front.