No CrossRef data available.
Published online by Cambridge University Press: 03 August 2017
Doppler shifts of the nonsplit line Fe I 7090Å have been measured simultaneously in the sunspot umbra, penumbra and the photosphere using a 100 × 100 diode array. The power in the range 2.5–4.5 mHz is found to decrease from the photosphere towards the umbra. Besides the minimum at the center of the umbra, further power minima occur at the transition region between umbra and penumbra. No significant power is found in the range 5.0–6.0 mHz.