Microwave Detection of Umbral Oscillation in NOAA Active Region 8156: Diagnostics of Temperature Minimum in Sunspot

Details Microwave Detection of Umbral Oscillation in NOAA Active Region 8156: Diagnostics of Temperature Minimum in Sunspot Microwave Detection of Umbral Oscillation in NOAA Active Region 8156: Diagnostics of Temperature Minimum in Sunspot

Apr 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...550.1113s&link_type=abstract

The Astrophysical Journal, Volume 550, Issue 2, pp. 1113-1118.

Astronomy and Astrophysics

Astronomy

26

Sun: Atmospheric Motions, Sun: Oscillations, Sun: Radio Radiation, Sun: Sunspots

Scientific paper

A radio brightness oscillation of 3 minutes at 17 GHz was detected in a compact radio source associated with a sunspot umbra in the NOAA active region 8156. We interpret the radio brightness oscillation by the density and temperature fluctuations due to upward-traveling acoustic waves through the third harmonic gyroresonance layer (2000 G). SOHO/SUMER observed the same active region close to the time of radio observations by the Nobeyama Radioheliograph. Transition region line observations by SUMER showed both velocity and intensity oscillations with the period of 3 minutes, and the oscillation was interpreted as an upward-traveling acoustic wave. We applied the value of the density and temperature fluctuations deduced from the SUMER experiment to the gyroresonance emission in the transition region and found good agreement with the detected radio brightness oscillation. The origin of the 3 minute oscillation is attributed to the resonant excitation of the cutoff frequency mode of the temperature plateau around the temperature minimum without assuming the chromospheric cavity. We can estimate the temperature of the temperature minimum region in the umbra from the measured frequency.

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