Chromospheric waves observed in the He I spectral line (λ = 10830 Å): A closer look

Although "Moreton" waves have historically been observed in Ha data, more recently waves have also been observed in chromospheric He I (λ = 10830 Å) images. In a previous study, we found that chromospheric waves observed in He I data (from the Mauna Loa Solar Observatory) in two events (occurring on 2000 November 25 and 2001 January 20) are cospatial with the corresponding coronal waves observed by EIT (Fe XII λ = 195 Å). In an effort to better understand the nature of chromospheric waves, we focus on these two wave events observed in He I in which two interesting phenomena occur: the waves are visible in the He I velocity data, and multiple waves are observed for each event. We suggest that the velocity signal is a result of slow-mode wave compression followed by a slow-mode wave rarefaction propagating downward from the corona into the upper chromosphere. We also suggest that the observed multiple waves indicate that more than one driving mechanism may be involved.