Abstract
Abstract The hydrogen Lyman lines (91.2 nm < λ < 121.6 nm) are significant contributors to the radiative losses of the solar chromosphere, and they are enhanced during flares. We have shown previously that the Lyman lines observed by the Extreme Ultraviolet Variability instrument onboard the Solar Dynamics Observatory exhibit Doppler motions equivalent to speeds on the order of 30 km s−1. However, contrary to expectations, both redshifts and blueshifts were present and no dominant flow direction was observed. To understand the formation of the Lyman lines, particularly their Doppler motions, we have used the radiative hydrodynamic code, RADYN, along with the radiative transfer code, RH, to simulate the evolution of the flaring chromosphere and the response of the Lyman lines during solar flares. We find that upflows in the simulated atmospheres lead to blueshifts in the line cores, which exhibit central reversals. We then model the effects of the instrument on the profiles, using the Extreme Ultraviolet Variability Experiment (EVE) instrument's properties. What may be interpreted as downflows (redshifted emission) in the lines, after they have been convolved with the instrumental line profile, may not necessarily correspond to actual downflows. Dynamic features in the atmosphere can introduce complex features in the line profiles that will not be detected by instruments with the spectral resolution of EVE, but which leave more of a signature at the resolution of the Spectral Investigation of the Coronal Environment instrument onboard the Solar Orbiter.
Highlights
The solar chromosphere emits increased levels of radiation during flares, which can be exceptionally energetic (∼1032 erg) events, initiated by a reconfiguration of the solar magnetic field
We have shown previously that the Lyman lines observed by the Extreme Ultraviolet Variability instrument onboard the Solar Dynamics Observatory exhibit Doppler motions equivalent to speeds on the order of 30 km s−1
We model the effects of the instrument on the profiles, using the Extreme Ultraviolet Variability Experiment (EVE) instruments properties
Summary
The solar chromosphere emits increased levels of radiation during flares, which can be exceptionally energetic (∼1032 erg) events, initiated by a reconfiguration of the solar magnetic field. The extreme ultraviolet (EUV) region is interesting during these events due to its variability, which can be as high as several orders of magnitude This variability, observable in the Ly-α line, directly affects the Earths atmosphere, resulting in detrimental effects on satellites and communication systems (Woods et al 2012; Kretzschmar et al 2013). Flows are typically believed to constitute a high-velocity upflow (“chromospheric evaporation”) detectable in high-temperature species, such as Fe XIX, with an accompanying low-velocity downflow (“chromospheric condensation”) in cooler species such as He II and O V (Fisher 1989; Milligan et al 2006; Taroyan & Bradshaw 2014) Observations of these flows are important in testing flare models, as the speed, direction, and duration of these flows are tied to the transport and deposition of flare energy (Fisher et al 1985; Allred et al 2005). The comparison between these synthetic profiles and those observed by EVE reveals that the loss of detailed features due to instrumental convolution can lead to apparent Doppler shifts that mask the true flow direction of the Lyman lines
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
