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R. A. Shine (LMSAL)
Denied the radiative splendor of the rest of the solar surface, sunspots seem to be compensated with more vigorous oscillations above their dark interiors. The observational properties of these oscillations will be reviewed along with some possibilities for employing them to study sunspot structure. The most obvious of these phenomena are the umbral oscillations and penumbral running waves seen in the chromosphere. Discovered in the late 1960's, umbral oscillations exhibit well documented non-linear behavior leading to shocks and umbral flashes in the upper chromosphere and transition region. Periods are typically 150 - 180s and are thought to be driven by photospheric motions. Running penumbral waves, best seen in H alpha or Na I D Dopplergrams, have periods near 250s and move outward in the penumbra with horizontal velocities from 10 - 25 km/s. Observations with the SMM/UVSP instrument showed that sunspot oscillations extended into the transition region and recent results from the CDS and SUMER instruments on SOHO show this in much more detail. The TRACE satellite has shown that coronal EUV loops (Fe IX 171Åand Fe X 195Å) originating in sunspots exhibit prominent intensity oscillations wherever they overlay the photospheric penumbra or umbra. Loops not associated with sunspots occasionally show similar oscillations but most do not. Some recent coordinated TRACE and H alpha observations (from the SVST on La Palma) will be presented to establish the relationships between the chromospheric and coronal oscillations.
This work is supported by the TRACE and SOI/MDI projects at LMSAL and Stanford (contract NAS5-38099 and grant NAG5-3077).
The author(s) of this abstract have provided an email address for comments about the abstract: shine@lmsal.com