G. Tsiropoula et al., Association of chromospheric sunspot umbral oscillations and running penumbral waves I. Morphological study, ASTRON ASTR, 355(1), 2000, pp. 375-380
Observations of a sunspot region located near the center of the solar disk
were obtained on October 3, 1994, with the Multichannel Subtractive Double
Pass Spectrograph (MSDP). This instrument, operating in Ha, was installed a
t the focus of the VTT at Tenerife (Canary Islands) and provided Ha intensi
ty profiles at every pixel of the field of view. Reconstruction of the Ha p
rofile allowed the computation of two dimensional intensity and Doppler vel
ocity images at different wavelengths within the line. We analyse a time se
ries of 1 hour and 8 min, obtained with a cadence of 36 sec and investigate
the relation between umbral oscillations and running penumbral waves. The
Doppler velocity as a function of time, along radial cuts through the cente
r of the spot, shows several clear cases where waves that originate inside
the umbra continue to propagate in the penumbra. In one case we were able t
o follow the evolution of an oscillating element for 216 sec, from the inne
r part of the umbra to the penumbra and we describe the propagation charact
eristics. We confirm the close association between sunspot oscillations and
running penumbral waves and suggest that they are probably due to the same
resonator.