What Have We Learned About Chromospheric Oscillations from HeI 10830Å?

Time series of He I 10830 spectra taken simultaneously with spectra of other chromospheric lines (Ca II 8542 Å and Ca II K) are analyzed to study wave propagation in the solar chromosphere. Rather than providing conclusive answers to some of the long standing questions concerning chromospheric oscillations, the new results derived from the He 10830 line raise new puzzling questions. The spatio-temporal wave pattern deduced from the Doppler displacements of the He line differs significantly from those of the two Ca II lines, while the phase difference between the Doppler displacements of He 10830 and Ca K_3 stays close to zero in the whole frequency range observed. This is difficult to reconcile with the low oscillation amplitude observed in the He 10830 line (RMS≈1100 m/s), which is less than half the velocity amplitude derived from the core displacement of Ca K_3. Another surprising result is that the Ca K ``bright point'' events are only barely visible in the Doppler displacement of the He 10830 line.