Study on the Responses in the Transition Region of Coronal Extreme-ultraviolet Waves

Abstract Coronal extreme-ultraviolet (EUV) waves are globally propagating disturbances in the solar atmosphere. The existence of coronal EUV waves was predicted by chromospheric Moreton–Ramsey waves. It is widely accepted that Moreton–Ramsey waves represent the chromospheric imprints of coronal EUV waves that compress downward during their lateral propagations. Hence, coronal EUV waves should inevitably compress the interlayer between the corona and the chromosphere, the transition region (TR), before reaching the chromosphere. However, the responses in the TR of coronal EUV waves lack enough attention. Here, we focus on the wave signatures in He ii 304 Å for a sample of 640 coronal EUV waves from 2010 to 2021, aiming to establish a “bridge” connecting coronal EUV waves and chromospheric Moreton–Ramsey waves. It is found that ∼14.4% of all coronal EUV waves have TR responses, and ∼34.5% of “disk events” with TR responses have chromospheric imprints. We specifically analyze the wave front characteristics of disk events with TR responses (58). Statistical analysis shows that TR responses for coronal EUV waves have an average speed of 495.58 ± 27.62 km s −1 , an average duration of 488.4 ± 12 s, an average angular width of 71 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 22, and an average intensity enhancement ratio (IER) of 30.39%. Moreover, all TR responses with chromospheric imprints display a greater inclination angle (&gt;50°) and a larger IER (&gt;30%). All the results suggest that TR responses can be indicators of missing Moreton–Ramsey waves and clarify the resolution of the mystery of the rarity of Moreton–Ramsey waves.