Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Abstract

Aims. We study the response of the solar atmosphere during a GOES M1.6 flare using spectroscopic and imaging observations. In particular, we examine the evolution of the mass flows and electron density together with the energy input derived from hard X-ray (HXR) in the context of chromospheric evaporation.Methods. We analyzed high-cadence sit-and-stare observations acquired with the Hinode/EIS spectrometer in the Fe xiii 202.044 Å (log T = 6.2) and Fe xvi 262.980 Å (log T = 6.4) spectral lines to derive temporal variations of the line intensity, Doppler shifts, and electron density during the flare. We combined these data with HXR measurements acquired with RHESSI to derive the energy input to the lower atmosphere by flare-accelerated electrons.Results. During the flare impulsive phase, we observe no significant flows in the cooler Fe xiii line but strong upflows, up to 80-150 km s −1 , in the hotter Fe xvi line. The largest Doppler shifts observed in the Fe xvi line were co-temporal with the sharp intensity peak. The electron density obtained from a Fe xiii line pair ratio exhibited fast increase (within two minutes) from the pre-flare level of 5.01 × 10 9 cm −3 to 3.16 × 10 10 cm −3 during the flare peak. The nonthermal energy flux density deposited from the coronal acceleration site to the lower atmospheric layers during the flare peak was found to be 1.34 × 10 10 erg s −1 cm −2 for a low-energy cut-off that was estimated to be 16 keV. During the decline flare phase, we found a secondary intensity and density peak of lower amplitude that was preceded by upflows of ∼15 km s −1 that were detected in both lines. The flare was also accompanied by a filament eruption that was partly captured by the EIS observations. We derived Doppler velocities of 250-300 km s −1 for the upflowing filament material. Conclusions. The spectroscopic results for the flare peak are consistent with the scenario of explosive chromospheric evaporation, although a comparatively low value of the nonthermal energy flux density was determined for this phase of the flare. This outcome is discussed in the context of recent hydrodynamic simulations. It provides observational evidence that the response of the atmospheric plasma strongly depends on the properties of the electron beams responsible for the heating, in particular the steepness of the energy distribution. The secondary peak of line intensity and electron density detected during the decline phase is interpreted as a signature of flare loops being filled by expanding hot material that is due to chromospheric evaporation.

Análise De Emissões Solares Métricas Com Lenta Taxa De Deriva Em Frequência Associadas À Evaporação Cromosférica

“…No caso de determinações a partir de observações no ultravioleta, a velocidade estimada tem a mesma ordem de grandeza das velocidades Doppler do material ascendente, entre 250 e 300 km/s, obtidas por Gömöry et al (2016), para fluxo de plasma ascendente registrado durante a fase de declínio de um flare solar analisado e da velocidade aparente dos fluxos ascendentes de 50 a 630 km/s, com valor médio de ~170 km/s, obtidos por Zhang et al (2019), reforçando as considerações de que as emissões métricas associadas a flare, apresentando lenta taxa de deriva, podem representar assinatura do processo de evaporação cromosférica que ocorre em regiões da coroa solar.…”

“…Com o avanço da tecnologia e aprimoramento dos instrumentos de observação solar, principalmente a bordo de satélites, como o Interface Region Imaging Spectrograph (IRIS) e o Extreme-ultraviolet Imaging Spectrometer (EIS), uma série de estudos do fenômeno da evaporação cromosférica tem sido realizada a partir de dados de linhas espectrais no extremo ultravioleta e deslocamento Doppler. Entre esses trabalhos, podem ser citados, Li et al (2019); Li et al, (2015); Gömöry et al (2016); Li et al (2017a); Li et al, (2017b); Brosius e Inglis (2017); Lee et al (2017) e Gupta, Sarkar e Tripathi (2018); Sadykov et al (2019). A evaporação cromosférica também tem sido estudada a partir de imagens e dados do arranjo de telescópios Atmospheric Imaging Assembly (AIA), abordo do Solar Dynamics Observatory (SDO) (ZHANG et al, 2019).…”

“…Existem muitos trabalhos sobre a análise do processo de evaporação/condensação cromosférica usando observações em ultravioleta com alta resolução espacial, espectroscópica e temporal, cujos resultados apresentam, principalmente, desvio para o vermelho nas linhas de emissão (downflow). Gömöry et al (2016) estudaram a resposta da atmosfera solar durante um flare de classe M1.6, usando observações espectroscópicas e de imagens. Em particular, foi examinada a evolução dos fluxos de massa e de densidade eletrônica juntamente com a entrada de energia derivada de observações em raios-X duros, no contexto de evaporação cromosférica.…”

Spectral Diagnostics of Cool Flare Loops Observed by the SST. I. Inversion of the Ca ii 8542 Å and Hβ Lines

“…As most of the flare energy is deposited in the chromosphere, a strong evaporation of the heated plasma occurs (e. g., Neupert 1968;Fisher et al 1985a,b,c;Graham & Cauzzi 2015). A detailed EUV spectroscopic analysis of explosively evaporating plasma following an M1.6-class flare by Gömöry et al (2016) found electron densities up to 3.16 × 10 10 cm −3 at a temperature of 1.56 MK. The evaporation provides an injection of plasma into flare coronal loops (hereafter flare loops) and leads to the formation of bright high-density structures at the apex of the flare loop arcade.…”

Energy Deposition by Energetic Electrons in a Diffusive Collisional Transport Model

“…Knowledge of the energy deposition profile is a key element in determining the response of the solar atmosphere to flare heating (Mariska et al 1989;Allred et al 2015) and hence in interpreting the plethora of observations of Doppler-shifted and -broadened spectral lines (e.g., Antonucci et al 1982;Emslie & Alexander 1987;Doschek 1990;Mariska et al 1993;Bentley et al 1994;Rilee & Doschek 2001;Landi et al 2003;Brosius & Phillips 2004;Li et al 2015a,b;Milligan 2015;Reep et al 2015;Tian et al 2015;Brosius et al 2016;Brosius & Inglis 2017;Gömöry et al 2016;Polito et al 2016;Warren et al 2016;Kontar et al 2017;Li et al 2017) in terms of the velocity differential emission measure (Newton et al 1995) corresponding to candidate energy transport models. In this paper we therefore build on the results of Bian et al (2017) to derive a formula for the energy deposition profile associated with the passage of electrons through a cold target, where diffusion associated with angular scattering is explicitly taken into account.…”