INFRARED LINES AS PROBES OF SOLAR MAGNETIC FEATURES .10. HEI 10830-ANGSTROM AS A DIAGNOSTIC OF CHROMOSPHERIC MAGNETIC-FIELDS

The need for a simple but quantitative diagnostic of upper chromospher ic magnetic fields is keenly felt. We develop the He I 10830 Angstrom line as such a diagnostic. An application to observations of an active region allows us to compare the magnetic field in the upper chromosph ere with the field in the underlying photosphere. In general, the magn etic field in the chromosphere is found to be significantly more homog eneous. We find that dB/dz in the umbra of a large sunspot (0.4-0.6 G km(-1)) is similar to other determinations of this quantity over an eq uivalent height range. Also, dB/dz decreases outwards in the spot. Thu s, in the outer penumbra it has dropped to 0.1-0.3 G km(-1) A comparis on of these values with the results of dB/dz measurements in the photo sphere suggests that dB/dz decreases with height. We also find evidenc e for magnetic canopies near sunspots and for the conservation of magn etic flux with height in solar plages when averaged horizontally over a few are s. Observations of complex Stokes V profiles at the neutral line in a sunspot penumbra (crossover effect) suggest that the upper c hromospheric penumbral magnetic field is not fluted to the same extent as the photospheric field. The large line broadening of He I (up to 1 0 km s(-1)) is found to be due to motions which are largely field alig ned.