Dynamics and evolution of an eruptive flare

Abstract

Aims. We study the dynamics and the evolution of a C2.3 two-ribbon flare, developed on 2002 August 11, during the impulsive phase as well as during the long gradual phase. To this end we obtained multiwavelength observations using the CDS spectrometer aboard SOHO, facilities at the National Solar Observatory/Sacramento Peak, and the TRACE and RHESSI spacecrafts. . In one footpoint simultaneous Hα data are also available and we find, at the same time and location, downflows with an inferred velocity between 4 and 10 km s −1 . We also verify that the "instantaneous" momenta of the oppositely directed flows detected in Fe xix and Hα are equal within one order of magnitude. These signatures are in general agreement with the scenario of explosive chromospheric evaporation. Combining RHESSI and CDS data after the coronal upflows have ceased, we prove that, independently from the filling factor, an essential contribution to the density of the post-flare loop system is supplied from evaporated chromospheric material. Finally, we consider the cooling of this loop system, that becomes successively visible in progressively colder signatures during the gradual phase. We show that the observed cooling behaviour can be obtained assuming a coronal filling factor of ≈0.2 to 0.5.

Multi-wavelength fine structure and mass flows in solar microflares

“…The observed flow velocities in comparison with predictions of hydrodynamic simulations were studied by Brosius & Phillips (2004), who report observations of a flare jointly observed by CDS and Yohkoh/BCS suggesting momentum balance between up-and downward flowing material in the impulsive phase. Teriaca et al (2006) find an order of magnitude agreement of the momenta of cospatial, oppositely directed flows in a small two ribbon flare. The combination of flare X-ray spectra and images and CDS Doppler velocities enabled Milligan et al (2006) to demonstrate observations in rough agreement with simulations of explosive chromospheric evaporation.…”

An Observational Overview of Solar Flares

“…Other observations without HXRs have instead used the time derivative of the GOES flux (assuming the Neupert effect) to identify the impulsive phase (Teriaca et al 2006;Del Zanna et al 2006). Spectroscopy from CDS at high time cadence (10 s) of a "flare-like transient" has also been obtained (Brosius & Holman 2007).…”

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

“…Simulations predict that downflows are noticeable only in spectral lines formed below transition region temperatures and that they reach velocities of several tens of km s −1 because of the higher mass and inertia of the chromospheric material (Fisher et al 1985;Allred et al 2005;Reep et al 2015). Observational evidence for the proposed momentum balance during explosive evaporation was found for several events (Zarro et al 1988;Teriaca et al 2006;Milligan et al 2006a). Other observational studies, however, also revealed downflows at coronal temperatures (Milligan & Dennis 2009;Young et al 2013), suggesting that the flaring atmosphere is very dynamic and complex on small spatial scales (e.g., Veronig et al 2010).…”