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

Although "Moreton'' waves have historically been observed in Halpha data, more recently waves have also been observed in chromospheric He I (lambda = 10830 Angstrom) 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 lambda = 195 Angstrom). 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.