Modelling Of The Hydrogen Lyman Lines In Solar Flares

Abstract

The hydrogen Lyman lines ( 91.2 nm < lambda < 121.6 nm) are significant contributors to the radiative losses of the solar chromosphere, and 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. But contrary to expectation, no dominant flow direction was observed, with both redshifts and blueshifts present. To understand the formation of the Lyman lines, particularly their Doppler motions, we have used the radiative hydrodynamic code, RADYN, and 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 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 which 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 (SPICE) instrument on Solar Orbiter.

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• Formation Of The Lyman Continuum During Solar Flares
• On the Importance of Ca II Photoionisation by the Hydrogen Lyman Transitions in Solar Flare Models
• Lyman Continuum Observations of Solar Flares Using SDO/EVE
• The Lyman-$\alpha$ Emission in a C1.4 Solar Flare Observed by the Extreme Ultraviolet Imager aboard Solar Orbiter
• Chromospheric Bubbles in Solar Flares
• Solar Flare Heating with Turbulent Suppression of Thermal Conduction