Multi-wavelength observations of 4 homologous global coronal waves
SolarMHDWav
David
Long
Date Submitted
2019-03-14 10:17:04
UCL-MSSL
David M. Long (UCL-MSSL), Jack Jenkins (UCL-MSSL), Gherardo Valori (UCL-MSSL)
Freely-propagating global waves in the solar atmosphere are commonly observed using Extreme UltraViolet passbands (EUV or “EIT waves”), and less regularly in H-alpha (Moreton-Ramsey waves). Despite decades of research, joint observations of EUV and Moreton-Ramsey waves remain rare, complicating efforts to quantify the connection between these phenomena. We present observations of four homologous global waves originating from the same active region between 28-30 March 2014 and observed using both EUV and H-alpha data. Each global EUV wave was observed by the Solar Dynamics Observatory, with the associated Moreton-Ramsey waves identified using the Global Oscillations Network Group (GONG) network. Each global wave exhibits high initial velocity and strong deceleration in each passband studied, with the EUV wave kinematics exceeding those of the Moreton-Ramsey wave. The density compression ratio of each global wave was estimated using both differential emission measure and intensity variation techniques, with both indicating that the observed waves were weakly shocked with a Mach number slightly greater than one. This suggests that, according to current interpretation, the global coronal waves were not strong enough to produce Moreton-Ramsey waves, indicating an alternative explanation for these observations. Instead, we conclude that the evolution of the global waves was restricted by the surrounding coronal magnetic field, in each case producing a downward-angled wavefront propagating towards the north solar pole which perturbed the chromosphere and was observed as a Moreton-Ramsey wave.
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