Fine structure of the solar chromosphere from infrared He I line observations

Based on He I 10 830 Angstrom triplet observations, we determined the physi cal parameters of the solar chromosphere: thermal and turbulent velocities, excitation temperature, effective kinetic temperature, and number of He at oms at the 2(3)S level. An analysis of spatial variations in these paramete rs provides new information about thin magnetic flux tubes filling the chro mosphere. The observed dependence of filling factor on the depth of the mai n component in the He I 10 830 Angstrom triplet, on heliocentric angle, and on effective temperature lends support to the following model. A partially ionized plasma rises from the photosphere along each magnetic flux tube to the upper chromosphere. Here, the outflow of neutral atoms across magnetic field Lines leads to an ion-neutral separation. The neutrals fill a more e xtended region-a "cloud" near the upper part of the flux tube. In active re gions, we observe the overlapping of He I clouds in the upper chromosphere.